Edited by Berah McSwain
SSRL is funded by the Department of Energy, Office of Basic Energy Sciences, under contract DEAC03-76SF00515. The Biotechnology Program is supported by the National Institutes of Health, Biomedical Technology Program, National Center for Research Resources. Further support is provided by the Department of Energy, Office of Biological and Environmental Research.
After 20 exciting and rewarding years as SSRL's director, it is time for me to step down and say good-bye, at least for a while, to those who have helped to make those years so rewarding.
It is good-bye, first of all, to the SSRL staff, faculty and directorate who have forged a superb user facility. They started at a time when there was no corresponding facility in the world to which large numbers of scientists came for short periods, week after week, to carry out experiments in a variety of disciplines. In the context of parasitic SPEAR operation, they created an atmosphere of true "welcome" in addition to providing cutting edge technical and intellectual support.
Continuing on the forefront, they created the wigglers and undulators, which seemed so extreme at their initiation, but have become commonplace now. They drove PEP to lower emittances than have been achieved yet by the third generation sources and introduced the first hard X-ray undulators.
They built an injector system for SPEAR which made it independent of the SLAC 50 GeV linear accelerator. Then, when SPEAR became fully dedicated to synchrotron radiation, they lowered its emittance and made it into an extremely reliable source. Now, they plan to reduce its emittance even further, and increase the stored current, with the SPEAR3 project.
Finally, they pursue the Linac Coherent Light Source (LCLS) project, which will make entirely new science possible.
It is good-bye and thanks, as well, to our colleagues in the other SLAC divisions, who have supported us in these endeavors. Without their foresight in adding a synchrotron radiation port to SPEAR, there would be no SSRL. They helped us, as well, to learn the many skills required to develop and operate a storage-ring based facility. Later, they greeted us cautiously, as we did them, upon the merger of SSRL and SLAC. Since then, there has been increasing cooperation and mutual support.
It is the users, of course, who make it all meaningful. I have watched with joy through the years as you have used SSRL to develop and do important science with:
Last, but not least, I must thank my graduate students and post-docs, for they have kept me alive in science and kept SSRL's scientific capabilities personally meaningful to me. Together, we played a role in the development of EXAFS as a tool for the study of amorphous alloys and then went on to develop wide angle, grazing incidence and small angle anomalous X-ray scattering for the same purpose. You were a constant source of satisfaction and pleasure. I am pleased to have you all as colleagues now.
I step down now with the sense that SSRL has a magnificent future. It is running extremely well. Good science and technology are resulting from its operation. Over the next half-decade, we can expect SPEAR3 to enhance SPEAR's performance markedly. Subsequently, we anticipate that the LCLS will take us into new realms of synchrotron radiation research, with coherent hard X-ray techniques becoming increasingly feasible and time resolved X-ray scattering and spectroscopy studies becoming feasible on the subpicosecond time scale.
As for me, I am excited about the possibility of going to Washington as Associate Director for Science of the Office of Science and Technology Policy. It is an opportunity to work for the health and vitality of all U.S. science and science education within the political system, a prospect I relish. Over the years, I have become an increasingly strong supporter of that system, which works best when people work and speak loudly for the things in which they believe. Thus, I am pleased with the prospect of becoming a more integral part of it.
I hope that all of you who are associated with SSRL will also continue to think and work with a broad view. Over the past few years, we have all seen vividly that SSRL's fate is directly linked to the health of American science. In the years between fiscal 1992 and fiscal year 1996, SSRL had all the technical capabilities to run 9-10 months per year but lacked the funding. The funding came when we combined forces with all of the Department of Energy's facilities to insure that all of them had sufficient funding to operate effectively.
Then, we faced the threat of a major cut in the funding of the Energy Research program of the Department of Energy. That cut would have devastated SSRL and a large faction of American science. Again, by joining forces with the larger scientific community, we were able to convince executive and legislative leaders that such cuts were inappropriate.
As I look to the future, I see an extremely strong synchrotron radiation community with SSRL an integral part. The only threat that this community faces to its continuing vitality and effectiveness is a decline in the health of all American science and technology. Thus, it is natural for me to want to go to Washington "to fight the bigger fight".
At the same time, I look forward to returning to research. With its high quality and full time operations, SSRL offers opportunities to understand amorphous alloys that just were not feasible when I began this directorship. Similarly, LCLS offers the opportunity to obtain detailed understanding about what is happening as materials pass through the glass transition temperature region. It will be delightful, someday, to devote myself to such studies. It was, after all, this research which led me to participate in SSRL's initiation some twenty-five years ago.
The November 4, 1996 to July 31, 1997 user run was a busy time for the User Administration Group. The SSRL user community continues to grow and now boasts users from 36 U.S. states and 20 countries. Over 1100 users from 169 institutions were involved with proposals which received beamtime.
We recently had an opportunity to profile our user community over the past 10 years and found the following user trends:
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Despite an exceptional (95%) beam time delivery rate, beam time demand continues to outpace beam time availability. The overall ratio of beam time requested to beam time available for all beamlines was 1.43. In other words, users requested 43% more time than we were able to provide.
Overall Experience FY97 |
Beam Quality FY97 | |
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I am pleased to report that the majority of the users that arrived on-site to conduct experiments throughout the FY97 user run had a very favorable experience and were pleased with the quality of the beam provided. SSRL asks all proposal spokespersons to complete an End of Run Summary (ERS) form at the conclusion of each experiment. The form serves three purposes: (1) Positive and negative feedback to SSRL staff with the goal of continually improving our support and productivity, (2) a record of beam time received and (3) a source of information for the DOE and the SSRL staff regarding the work performed here. The user comments and staff responses are summarized for the SSRL Users Organization Executive Committee and SSRL management. The ERS database allows us to sort user comments and staff responses in a variety of ways in order to analyze both negative and positive trends.
Your SSRL Users Organization Executive Committee (SSRLUO-EC) is just a click away. The names and addresses of your elected committee members are available on the web. Please feel free to contact committee members with any issues or concerns you feel should be addressed. The SSRLUO serves in an advisory capacity, and communicates general users' needs and concerns to senior SSRL management. David McKay of Stanford University will be taking the helm of the Executive Committee in October. David's area of expertise is protein crystallography. His research focuses on the structure and mechanism of macromolecules, including molecular chaperones involved in the stress response in cells, chaperones involved in RNA function, and structure of catalytic RNA molecules (ribozymes). He will be succeeding David Shuh of Lawrence Berkeley National Laboratory as chairperson.
We would like to welcome aboard Diana Viera who joined us in February 1997. Diana is one of the first friendly faces users meet upon arriving at SSRL. She ensures that all users are issued a current dosimeter and receive the appropriate safety and no-bars training before gaining access to the experimental floor. Diana will also be one of the last faces users see upon departure as she is in addition responsible for distributing and recording the all-important End of Run Summary Form we ask all spokespersons to complete. You may reach Diana at (650) 926-2079 or viera@ssrl.slac.stanford.edu.
Joining the protein crystallography user support team is Daphne Mitchell. Daphne comes to us with a background of training and scheduling experience. She is now coordinating the protein crystallography proposal review process and is responsible for the scheduling of Beamline 1-5. You will be seeing her name quite often on administrative mailings and she is available to answer questions you may have regarding procedures and beam time requests. She can be reached at (650) 926-2154 or by e-mail at DMitchell@ssrl.slac.stanford.edu.
Michelle Steger is still ever-present and ready to assist users in a variety of capacities. Michelle is now handling the X-ray and VUV proposal submittal and review process. New X-ray and VUV proposals are submitted to SSRL twice a year (May 1 and October 1). Proposals are subject to a rigorous review process that begins with an external peer review. It is not uncommon for proposals to be reviewed by 5-7 external reviewers. These peer reviews, and any subsequent spokesperson responses, are collected and presented to the appropriate Proposal Review Panel(s). The panel carefully reviews the information and assigns a numerical rating to each proposal. This thorough but time-consuming process insures a broad representation of reviews.
A summary of User Administration points of contact:
| Beam Time Request Forms | ||
 X-ray & VUV Beamlines
|
M. Steger | |
| Protein Crystallography/MAD
Beamlines |
D. Mitchell | |
| End of Run Summary Forms | D. Viera | |
| Institutional User Agreements | M. Steger | |
| Proposal Submittals Reviews | ||
| X-ray & VUV Proposals
|
M. Steger | |
| Protein Crystallography/MAD
Proposals |
D. Mitchell | |
| Safety/No Bars Talks | D. Viera | |
| Scheduling | ||
| X-ray & VUV Beamlines
|
S. Barrett | |
| Protein Crystallography/MAD
|
M. St. Pierre/D. Mitchell | |
| User Accounts | M. Steger | |
| User Dosimeters | D. Viera | |
| User Support Forms | M. Steger | |
Was your Beam
Time Request Form eaten by the dog (again)? Trying to determine if accelerator
physics is going to interrupt
your beam time assignment? No problem. It's all
available on the SSRL User
Administration www page:
http://ssrl.slac. stanford.edu/user_administration.html
Check out the web page for user forms, user guides, beamline schedules, upcoming workshops and conferences.
In the past two years, the staff increases due to the new facilities initiative; the preparation for the installation of Beamline 11, and other operational needs have resulted in a number of facilities improvements at SSRL. We have added 3200 square feet of office space, approximately 7500 square feet of experimental floor area and enclosed equipment storage, and three additional alcoves. In addition to the construction of the new facilities, the removal of the old injection lines 15 & 16 has created an access to the west side of Building 131 and made available more open space for outdoor temporary storage.
With the anticipation of the increase of staffing in the early part of 1996, SSRL purchased a 40' x 80' modular office building and installed it between Trailer 271 and Trailer 294, just south of the Building 120 parking lot inside the fenced-off research area. Approximately 20 cubic yards of earth were removed to make room for the installation and to preserve vehicular access to the adjacent existing facilities. The new modular building is supported on reinforced concrete pier footings. This new structure contains 17 permanent-partition offices, one handicap-access restroom, light kitchen facilities and a conference room. The installation was completed in July 1996 and occupied immediately. A second turnstile gate was also installed at south end of the new modular office building to provide easier access from Building 137.
The concrete shielding of the entire Quadrant 1 of the Spear Ring was renovated to add three southarc alcoves for the straight sections 2S3, 3S4 and 4S5. The height of Quadrant 1 was also increased from 6'-6" to 10' in height. The project was completed in September 1995. In conjunction with the new alcove installation, the footprint of Building 131 was extended westward to provide more than 4000 square feet of experimental floor space and storage for equipment and experimental apparatus. This new metal building will house the future Beamline 11 which is scheduled to be installed in the next two years. This project was completed for occupancy at the end of 1995. In order to provide better and easier access to the western part of Building 131, the old injector lines 16 & amp; 17 were removed during the summer of 1996. The removal of the old injector lines also created some sorely needed temporary outdoor storage space.
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Frame work erection for the Buildings 120 and 131 connection looking from the trestle going down to SPEAR. |
The new modular office is a compound of four sections. One section was rigged on the foundation from the building 137 parking lot. |
As a result of the findings of the newly chartered " Seismic Evaluation Committee", Building 131 was identified as being in need of additional seismic upgrade to comply with the current seismic requirements. In July 1997, an earthquake brace, constructed with concrete encased structural beams, was installed at the northeast corner of 131.
In order to meet SSRL's continuing need for storage and equipment setup space, a smooth, weatherproof pathway between Building 120 & 131 was installed during the summer of 1996. The fabrication of a one story metal building with approximately 3500 square feet of area is scheduled to be completed here in November 1997. While this new extension is part of Building 131, it is directly connected to Building 120 with a weatherproof metal enclosure.
One other improvement of the SSRL facilities is somewhat subtle but significant. An air conditioning system was installed in Building 140, the injector building. In the past, during the hot days in the summer, the electronic equipment in 140 was very susceptible to failure due to high temperatures. The installation of the cooling system was completed in May 1996.
With the planned implementation of SPEAR3 and with the anticipated beamline installations and upgrades, SSRL can certainly envision a continuing process of facilities improvements in the coming years.
New 10' high concrete formwork for the South Arc alcove. |
We heard you! The color orange has been banished from the SSRL user kitchens! You now have a choice of two color-coordinated, comfortable, and modern kitchen/lounge areas to retreat to after those countless hours at the beamline. The new user areas provide refrigerators, stoves, and microwaves. There is even an overhead monitor so that you can keep an eye on SPEAR while sipping that 12th cup of coffee and savoring that frozen pizza. We've also added quiet lounge areas that are equipped with telephone and network connections so you can retreat from the hubbub of the experimental floor when you need to communicate with the rest of the world. The kitchen/lounge in building 120 was completed in May 1997, while the building 131 mezzanine level kitchen should be completed in early November 1997. A third user retreat area is in the planning stage and will be located in the Beamline 9 area of building 120. This new Beamline 9 retreat will contain a small kitchen complete with sink, refrigerator, and microwave. There will also be a small lounge area that will accommodate 5-6 people, and a computer area with network connections.
Another recurring request we heard from the user community was the need for a quiet, computer-equipped area to process and analyze beamline data. The new user computer room is located on the mezzanine level of building 131. It is equipped with three separate work areas with active network connections. One of these work areas has a PC running Windows NT 4.0 and another has an X-terminal to access any of the SSRL servers or beamline computers. The third network connection is open and can be used to connect your laptop computer. A laser printer is also available for general use.
In response to the proposal by Helmut Wiedemann and others that the magnet structure and vacuum chamber of SPEAR be upgraded (see the article by Bob Hettel in this Newsletter), SSRL, the SSRL Users' Organization, and the SSRL faculty sponsored a one and one-half day workshop on May 29-30, 1997.
The goal was to assess and document the impact of this new lattice, known as SPEAR3, on current and future science and technology research programs of the users of SSRL. The hard and soft X-ray beams produced at SSRL are used in a number of different scientific and technological disciplines. The workshop was organized by defining a set of areas of science and technology covering the basic activities at SSRL and inviting key people from outside Stanford to work with the SSRL faculty and staff in a set of topical groups on estimating the impact of SPEAR3 on their respective fields and developing a vision of the future opportunities.
The roughly 70 scientists who attended the workshop were split into 8 working groups, namely:
Biological
Macromolecular Crystallography
Biological Small-Angle X-ray
Scattering and Diffraction
Biological X-ray
Absorption Spectroscopy
Molecular Environmental Science
Materials X-ray Absorption Spectroscopy
Imaging/Tomography/Topography
Condensed Matter, Materials Science and Technology
VUV and Soft X-ray Science
Prior to the convening of the working groups, details of the proposed upgrade were presented by Sean Brennan, Bob Hettel and Tom Rabedeau. Gordon Brown spoke about the impact of SPEAR3 on his field, molecular environmental science.
Each working group created a document detailing the impact of SPEAR3 on their field. In addition, some groups were able to identify new beam lines which would be particularly attractive with the new lattice. These include an undulator beam line for the 1-4 keV energy regime, and a vertically polarized wiggler for the 10 keV region. The reports were combined, along with an executive summary and a technical description, into report "SPEAR3 Workshop: Making the Scientific Case", SLAC Tech. Pub. SLAC-R-513.
The conclusions of the workshop were:
The conclusions drew
clear praise from the SSRL
Users Organization Executive Committee, which included a
letter
expressing their strong and enthusiastic support
for the proposed
upgrade.
For more detailed information, the executive summary is available on
the WWW, at:
http://ssrl.slac.stanford.
edu/pubs/reports/spear3_report.html
SSRL is proposing to upgrade the SPEAR2 storage ring, which is itself an upgrade of the 2.4 GeV SPEAR1 ring which dates back to 1974. This upgrade, along with an upgrade of the synchrotron radiation beam lines, will significantly enhance the research capabilities of the Laboratory. By replacing the ring magnets and vacuum chamber (Fig. 1), the natural 3 GeV electron beam emittance of SPEAR3 will be reduced from the present 130 nm-rad to 18 nm-rad and the stored beam current will be raised from 100 mA to 200 mA. The injection energy will be raised from 2.37 to 3 GeV to eliminate energy ramping and its impact on orbit reproducibility. While it will be possible to ramp SPEAR3 to 3.5 GeV, the RF system, which will be reused with minor enhancements, will initially limit the maximum current at 3.5 GeV to about 75 mA. Careful optimization of the magnet lattice and vacuum system design should yield a beam decay lifetime of approximately 40 hours at 200 mA.
Figure 1: SPEAR2 and SPEAR3 magnet girders. |
The smaller beam size (Table 1) and higher current in SPEAR3 will increase the focused photon flux densities for insertion device beam lines by an order of magnitude (Fig. 2). The photon beam brightness for future 4 meter undulators will exceed 1018 in the 5 keV range (Fig. 3). The new lattice has shorter bending magnets with a smaller radius of curvature, raising the critical photon energy from the present 4.8 keV to 7.1 keV at 3 GeV. The resulting bending magnet focused flux density at 20 keV will be more than two orders of magnitude greater than it is presently, and will be comparable (over the whole spectrum) to the focused flux density produced now by the BL10 wiggler. The higher photon beam power density and brightness will be accommodated by upgrading beam line masks, slits and windows, by installing LN2-cooled monochromators on most hard X-ray insertion device beam lines, and by improving mirror and other optical component performance. This will allow the SPEAR3 beam lines to take full advantage of the source improvements.
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Table 1: Electron beam dimensions at SPEAR2 and SPEAR3 source points with 1% horizontal-vertical coupling. |
A key feature of the SPEAR3 project is the minimization of the interruption of the SSRL's user program. This will be accomplished by limiting conversion downtimes to a series of normal 2-month shutdowns and one longer shutdown period of about 6 months. This concept has been the basis of the scope and planning of the SPEAR ring conversion. To minimize the amount of work that must be done in the 6-month down time, the new magnets will be mounted on existing support girders which, (with the exception of the four girders flanking the two long symmetry straight sections), will remain in place. Existing components such as magnet bussing, cabling, and water connections, will be reused wherever possible. Beam line alignment will remain unchanged except for a minor 5 mrad angular shift needed for each of the four bending magnet lines.
In the past several months considerable effort has been invested in designing the proposed lattice, maximizing beam lifetime, optimizing beam source point parameters, and developing component designs. The resulting design has required that a defocusing quadrupole gradient be added to each bending magnet and that the two bending magnets on each support girder must be moved apart to create room for sextupole magnets, making bending magnet beam line realignment necessary. Another consequence of lattice development is that the four magnet cells adjacent to the East and West symmetry straight regions will be moved towards the old colliding beam interaction points, lengthening four straight sections from 2.7 m to 4.5 m and providing two 8.5 m symmetry straight sections. While these developments benefit beam quality and enhance the potential for future insertion device development, they also increase the amount of work that must be done in the 6-month conversion period.
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Figure 2: Focused flux density for several beam lines and the existing SPEAR source, the proposed SPEAR3 and beam lines from other existing synchrotrons |
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Figure 3: Brightness curves for a 4 m version of an APS Undulator A installed on SPEAR3 |
A high degree of beam stability is crucial for exploiting the low emittance beam properties of SPEAR3. Limiting beam motion to small fraction of its transverse dimensions implies that electron beam position for focused beams or for highly collimated undulator beams should be stable to the order of 20-40 µm rms horizontally and 5-10 µm rms vertically. Angular stability should be <10% of the photon beam opening angle, characterized by 1/g = 170 mrad at 3 GeV; this divergence is reduced by a factor of 10 for an undulator having the order of 100 periods, implying microradian stability will be needed for this type of source. To attain these stability requirements, magnet girder and optical component vibration will be suppressed, thermally induced motion of ring and optical components will be minimized, and feedback systems will be used to attenuate orbit disturbances and transverse coupled bunch instabilities. A longitudinal multibunch feedback system will also be used to reduce energy oscillations induced by vacuum chamber and RF cavity impedances that can spoil beam energy resolution.
The accelerator upgrade portion of the SPEAR3 project is being planned as a 3-4 year project, beginning as early as FY 99. The beam line upgrades will take place over a 5-year period, beginning as soon as FY 98. Special funding for the project is being sought from the DOE. All beam lines will be operational at the end of the 3-year accelerator conversion, although another year will be required for monochromator improvements on several insertion device side stations. With future funding, the Beamline 4 and 7 electromagnet wigglers can be replaced with permanent magnet devices similar to the one used for Beamline 9. By upgrading the RF system and increasing the power handling capacity of the beam lines, the SPEAR3 operating current could be increased to as much as 500 mA, thereby taking full advantage of the capacity of the new vacuum chamber.
Several significant improvements to SPEAR were completed in 1997, reflecting marked progress in the development of accelerator hardware and software. Improvements to the orbit feedback system largely concentrated on the Beam Position Monitor (BPM) processor, multiplexor switch equipment, and interface to the digital control hardware. Extensive hardware development was carried out to complete the installation of wide-bandwidth, low-loss cables to all BPMs in SPEAR. Four remote multiplexor stations (MUXs) were installed around the storage ring tunnel, complete with sophisticated low loss, high isolation RF circuits and shielded boxes. A new rack was installed in the SPEAR control room to house the signal processor (Harris chip) and MUX circuits that access the four remote MUX stations in the tunnel.
To enhance the data transfer protocol, the signal processor (producing quadrature components for the individual BPM button signals) was interfaced with the DSP chip (signal processor and control algorithm) via a CPLD (Programmable Logic) which implements a communication port compatible with the one on the DSP board. The CPLD accepts commands, an initialization sequence, MUX settings, and attenuator settings from the DSP, and sends the button data from the Harris chip to the DSP. The CPLD software has not yet been fully implemented, but the DSP data acquisition and button averaging process has been tested by emulating the CPLD/Harris chip on the DSP board. The emulation test included DMA data transfer through the communication port to memory on the DSP board. Simulated turn-by-turn BPM button data were processed on the DSP retrieved by the VME crate controller (MicroVAX) and placed into the SPEAR database where the data can be accessed for machine operations. We also carried out a successful demonstration of the complete data transfer sequence from BPM buttons through the MUX circuitry to the processor. Improvements to the software are now focusing on the final implementation of the global and local (beamline) feedback components.
A new method to power the linear accelerator was put into place. For the last 4 years the SSRL injector linac system has been powered by one SLAC 5045 klystron and one XK-5 klystron. After the current upgrade, the system will be powered by one 5045 klystron at an increased RF power output. The two major changes are: 1) reconfiguration of waveguide systems for even RF power distribution to three linac sections, and 2) modification of the modulator for improved stability and reliability. This change was motivated by problems with the continued use of the old XK-5; there are no resources available to manufacture or refurbish this aging klystron. The performance of the tube has been deteriorating over time; some of the spare XK-5 klystrons are not even operational. On the other hand, the SLAC 5045 klystron is in production on site. Spare tubes are readily available, and its reliability has been continuously improved.
A number of improvements to the modulator are also being carried out. These include upgrading the high voltage power supply regulation, improving the reproducibility of the thyratron performance, and increasing system protection through an interlock revision. A new LCW control panel was also installed to allow automatic monitoring and control of the status of the system.
The present thrust of the accelerator modeling studies is to calibrate a linear model of SPEAR using a response matrix measurement. Information contained in the corrector-Beam Position Monitor (BPM) response matrix is used to fit the parameters of the model.
In the case of SPEAR, the matrix contains 3,596 measured data points. These data points are compared to a calculated model response matrix. The singular value decomposition (SVD) method is used to analyze the difference between the model and the measurements; and calibration factors can be calculated for the various elements of the accelerator.
The modeling program has the following objectives:
Thus far our analysis has produced accurate models of the linear optics of SPEAR. The accuracy of the model is determined by measuring the rms difference between the measured and model response matrices. These differences have been below 20 micrometers. Another measure of the success of the model calibrations is to assess how well the machine functions of the model match the measurements. The matching is good, and the model has been used to calculate new magnet settings that reduce the beta function beating due to individual field errors within magnet families. The modeling has also been useful as a diagnostic tool for identifying faulty magnets and position monitors. At present, measurements made during the last run are being analyzed to calculate the best configuration for the coming run.
A study of the parasitic resonances driving longitudinal instabilities has promoted interesting insights into the frequency and strengths of the modes in the accelerating cavities. With these findings it was possible to optimize the position of the cavity tuners and to suppress the longitudinal coupled bunch oscillations, thus delivering a more stable beam to the users.
A phase space monitor system for studying the non-linear dynamics in SPEAR has been operational on SPEAR since 1996. The system consists of a pair of fast kickers that excite the bunch oscillations in the transverse plane and the turn-by-turn beam position monitors that allow recording of the beam motion following the kick. The data can then be transformed to visualize the dynamics in phase and frequency space. The system has been used to analyze the time variation of the tunes caused by ground motion, power supply ripples and other effects.
A study of the electron bunch characteristics following the launching of an oscillation in SPEAR revealed that the oscillation is not damped by the tune spread (Landau damping) when the chromaticity is set at some negative values. Under these conditions filamentation does not play a role in the turn-by-turn mapping of the accelerator and the beam acts as a fine probe of phase space.
All in all, the improvements made to SPEAR and to the accelerator physics program in 1997 have increase stability and reliability, raised the level of our confidence in our programs, and enhanced our ability to implement new technologies and ideas.
SSRL made substantial progress in the design study that will form the basis of a formal proposal for the development of a 4th generation light source, the Linac Coherent Light Source (LCLS). The LCLS is an X-ray Free Electron Laser (FEL) operating on the Self-Amplified-Spontaneous Emission (SASE) principle. Its operation principles and general layout were described in the last two issues of this Newsletter. The continuing study is a collaboration that involves several divisions of SLAC and a number of other scientific institutions. Progress was made in all areas of the Design Study; a few of the highlights include:
Progress in the analysis of FEL related questions through the use of sophisticated simulation tools continued during 1997. A variety of simulation codes such as Ginger and Fred3D, (both developed at LLNL) and TDA3D (originally developed at MIT) have been used to characterize the physics of FELs. A detailed list of parameters has been developed; parameter sensitivities and tolerances have been studied.
The LCLS will utilize a high performance photoinjector employing a low-emittance rf electron gun. Work continues on the development of a high-gradient 1.6-cell S-band normal conducting rf gun with a copper photocathode illuminated by intense optical pulses at 260 nm provided by a system comprised of a Nd:YAG-pumped Ti:sapphire (with tripled fundamental frequency). This gun has evolved from a collaboration that includes SLAC, Brookhaven National Laboratory, and the University of California at Los Angeles. Initial measurements on prototypes of the gun have been very encouraging. The Team is attacking a number of challenging design issues that directly affect the system performance, including emittance compensation and temporal pulse shaping.
The LCLS requires a very high electron peak current. The Design Team has developed and refined an LCLS bunch compression and acceleration system comprised of a series of linac sections and magnetic chicanes arranged so that processes that degrade the beam quality are partially canceled. Simulations indicate that the accelerator section will produce an electron beam that will meet the stringent requirements of the undulator.
Using simulations and semi-analytic models, a planar undulator approximately 100 meters long has been designed. As the design effort progressed during the last six months, it was determined that the undulator could be designed to be segmented rather than continuous. This has allowed the adaptation of a "lumped focusing strategy" and the relaxation of some of the more demanding tolerances. A great deal of attention has been given to undulator alignment; four very promising approaches have been examined in detail.
Scientists using the LCLS will work in a hutch housing two experimental stations. To cover the full spectral range of the system, both specular (for wavelengths longer than 4.5 Å) and crystal (for wavelengths shorter that 4.5 Å) optics will be employed. The effect of radiation of this extraordinary intensity on optical materials is still, to some extent, unknown. The experimental area will include attenuation systems for controlling the extremely intense photon beam and optical components for directing it to experimental setups.
There were many programmatic advances during the year. Memoranda of Understanding were put in place with LANL and LLNL for joint R & D projects. Technical reviews were held for the undulator, the photoinjector, and the linac; a cost review was held for the preliminary cost package. The reports from all of the reviews supported the view that the LCLS concept, design and planning were on the on track for meeting project goals.
As pointed out in articles in past volumes of this Newsletter, our
Design Team is
inspired by the fact that the remarkable
characteristics
of LCLS radiation have the potential
for opening up a number of important
new scientific frontiers. This source would create a photon beam of
unprecedented
brightness, coherence and peak power, far
surpassing anything
available in 3rd generation
sources today. Design parameters are a peak
brightness of 5 x
1033
photons /(s-mm2
-mrad2-.01% bandwidth)
(13 orders of magnitude
greater than any existing radiation sources) and a
peak power of 10 GW in the wavelength region 1.5-15 Å. Furthermore, the
accompanying spontaneous radiation will be 4 orders of
magnitude greater than
radiation from existing 3rd generation sources. The Design Team
is in the
process of producing a design report, with a construction schedule and a cost
estimate by late 1997.
Late in the night of July 19, 1997 a new accelerator began operation at SLAC -the Gun Test Facility (GTF) located in the shielded vault of the SSRL injector linac. Graduate students Mike Hernandez and David Reis along with SSRL's John Schmerge and Herman Winick witnessed the first glimmer of light produced by an approximately 4 MeV electron beam on a phosphor screen. The GTF is an R&D facility aimed at developing the high-brightness electron source that will be needed for future linac-based X-ray free-electron lasers (FELs) such as SLAC's proposed Linac Coherent Light Source (LCLS).
The LCLS requires a high-brightness electron source to reach saturation down to 1.5 Å wavelength in a single pass through a 100 m long undulator. Electron beam brightness is a measure of the concentration of the beam and is exactly analogous to photon beam brightness. The product of the beam transverse size and divergence is called the geometric emittance. The lower the emittance, the higher the brightness. Since the divergence angle is reduced as the particle is accelerated, the normalized emittance, which does not vary with energy, is defined as the product of the geometric emittance and the dimensionless electron energy (Lorentz factor). In the current LCLS design the source must produce a beam with at least 1 nC of charge per 10 picosecond or shorter pulse with no greater than 1 pi mm-mrad normalized rms emittance. A 3.5 kA, 1.5 pi mm-mrad normalized emittance beam would be delivered to the wiggler after acceleration approximately 15 GeV in the last third of the SLAC linac using two magnetic bunch compressors at 0.3 and 6.5 GeV. This emittance is approximately the diffraction limit for 4 Å (3 keV) photons and can also be used to drive a single pass FEL such as the LCLS at even shorter wavelengths. An increase in brightness would allow the use of a shorter wiggler at substantial cost savings.
The most promising technology to date for the required source is the emittance-compensated photocathode RF gun, pioneered at Los Alamos National Laboratory (LANL) in the 1980's. In such a gun, electrons are generated by the photoelectric effect, rather than by thermionic emission (electrons boiled off the cathode surface with applied heat) as is done in the SSRL injector gun. Therefore, a high peak power, near IR laser with roughly 1 picosecond long pulses has been assembled at the GTF. This laser is frequency-quadrupled into the UV (263 nm wavelength) before the beam strikes the cathode so that the photons have sufficient energy to overcome the work function of the copper cathode currently in use.
The GTF laser is designed to have sufficient energy to produce up to 2 nC (nominally 1 nC) of charge with a copper cathode. With so many electrons packed so closely together in space and time their mutual repulsion results in a spreading out of the beam; i.e., an increase in emittance and a reduction in brightness. However, the self-induced magnetic field from an electron beam confines the electrons and would exactly cancel the electric field repulsion if the beam could travel at the speed of light. Thus, the electron beam is accelerated as quickly as possible to reduce the time during which this spreading, or emittance degradation, can take place. The GTF gun photocathode is immersed in a high-gradient (up to about 150 MeV/m) accelerating field which boosts the emitted electrons to nearly the speed of light (6 MeV) in a distance of about 8 centimeters. This acceleration is done in a 1.6 cell S-band RF structure similar to that used in the SLAC linac. The residual spreading is further reduced, or compensated, by refocusing the beam emerging from the gun structure using a solenoid magnet. Hence the electron source is called an emittance-compensated photocathode RF gun.
A collaboration led by Herman Winick which includes SLAC, Brookhaven National Laboratory (BNL) and the University of California at Los Angeles has designed and fabricated an emittance-compensated photocathode RF gun aimed at meeting the demanding requirements for the LCLS. Dennis Palmer of SLAC, a graduate student of Roger Miller, played a major role in the design and initial testing of the first copy of this gun at BNL as part of his Stanford Ph.D. thesis. A second copy, with some modifications made by SSRL's Jim Weaver, has now been installed on the GTF for more detailed characterization. A critical component of the GTF is the 10 MW few picosecond long laser which drives the gun. The laser system for the GTF was designed, constructed, and is now being commissioned by University of Rochester graduate student David Reis under the supervision of Professor David Meyerhofer. It makes use of part of the laser system developed by the Rochester group for SLAC experiment E144 at the Final Focus Test Beam. The GTF diagnostics were designed, built and are now being commissioned by SSRL graduate student Mike Hernandez under supervision of Professor Helmut Wiedemann. A group at Argonne National Laboratory is also collaborating with the GTF. All technical aspects of the construction, commissioning and the continued experiments at the GTF are coordinated by John Schmerge of SSRL.
The best measured emittance to date with 1 nC of charge is approximately 2 pi mm-mrad at both BNL and LANL using emittance-compensated photocathode RF guns. Simulations of the GTF gun indicate that it is possible to produce an electron beam with an emittance of 0.9 pi mm-mrad emittance and 1 nC of charge. In order to produce this low emittance, careful shaping of the laser pulse both longitudinally and transversely is required. The reduction in emittance with this laser pulse shaping as well as full gun characterization as a function of the major input parameters is currently the main focus of research at the GTF. Generating high brightness electron beams and preserving their brightness during transport, acceleration, and compression, are major areas of R&D for future facilities for both the synchrotron radiation and high energy physics user communities, the two constituencies which SLAC serves. Thus SLAC, with its strong accelerator physics capabilities and unique experience with the SLC is the ideal place to pursue this R&D.
In addition to those mentioned above, many at SSRL and SLAC contributed to the design and construction of the GTF, particularly Mike Nalls, Gary Woodcock, Sam Park, Dennis Palmer and Dian Yeremian, plus many others in the machine shops, radiation physics group, SPEAR operations group, and the SSRL Mechanical Services and Electronics groups. Finally, both the SLAC and SSRL Business Services Division provided much needed assistance during procurement of the many sub-systems of the GTF.
Synchrotron-based techniques have proven to be essential tools for solving problems in environmental science, such as the characterization of metal ion speciation in heterogeneous natural materials and probing structure-reactivity relationships of molecular species at environmental solid-liquid-gas interfaces. Synchrotron-based spectroscopic and X-ray scattering measurements have also become increasingly important for characterization of high-level radioactive wastes and engineered waste forms. The usefulness of XAFS and micro-XAFS spectroscopy, among other synchrotron-based methods, has driven the growth of a new interdisciplinary field, Molecular Environmental Sciences (MES), and has stimulated rapid increases in demand for MES beamtime and facilities at SSRL and other U.S. synchrotron light sources.
In the past year SSRL has taken several significant steps to provide increased support for its large and growing MES user community. On January 17 and 18, 1997, a working group of MES scientists and engineers from SSRL, other U.S. synchrotron sources, universities, and national labs met at SSRL to discuss the types of MES research being undertaken at synchrotron light sources, to document the rapid increase in demand for beamtime by MES users, to take inventory of US synchrotron facilities currently available for MES research, and to predict the future facility and infrastructure needs of the MES community at synchrotron light sources. It was concluded that current and planned U.S.-DOE synchrotron facilities should be adequate in the near future, i.e., 1997 and 1998. Beyond this time frame, however, it was anticipated that additional MES synchrotron facilities will be needed, due to projected increases in the use of synchrotron-based spectroscopic and X-ray scattering methods in applied environmental research and engineering efforts, such as routine environmental monitoring and remediation programs. MES operations and user support models were also discussed, and recommendations were made for future facilities. A report of this DOE-sponsored workshop can be obtained from Todd Slater (slater@slac.stanford.edu).
In December, a new staff scientist, John Bargar, was hired to assist in MES user and laboratory support and to conduct MES research. Subsequently, a commitment has been made by DOE to provide funding for technical and support staff for operating BL 11 and associated experimental facilities, including the hazardous sample experimental enclosure, a new state-of-the-art 30-element Ge array detector, and other instrumentation. The new detector will be equipped with a digital signal processing (DSP) system, which will provide substantially greater data throughput and processing capabilities than an analog spectroscopy amplifier. Extensive tests of the DSP system have been performed by Paola de Cecco (SSRL Biotechnology group) at SSRL beamlines using existing 13-element detectors. The results suggest that DSP should be robust and user-friendly.
On the beam line 11 front, the capital equipment project is proceeding despite some technical difficulties. During the summer 1997 shutdown of SPEAR, the beam line 11 front-end components were installed along with many of the in-alcove components. The remaining in-alcove items are scheduled for installation during the Christmas shutdown. Notably absent from the components installed this summer are the 26 pole wiggler and its vacuum chamber. The installation delay was necessitated when the vendor, Danfysik, found that oxidation initiated during the magnet block manufacturing process resulted in magnet block fragmentation into the constituent sub-blocks. (Typically, insertion devices requiring large magnetic blocks utilize composite blocks composed of several smaller magnetic blocks glued together. Composite blocks generally provide better magnetic performance at the price of increased assembly complexity and potential for adhesive failure. Ironically, the oxidation of the wiggler blocks resulted from a processing step used in the application of an anti-corrosion coating on the blocks.) This setback necessitated refabrication of all the magnetic blocks by the magnetic material subcontractor, Vacuumschmelze. After extensive environmental testing of several glues and anti-corrosion coatings, a suitable adhesive and anti-corrosion coating has been selected. The wiggler is now on track for delivery to SSRL in early 1998. Rather than interrupt SPEAR operations during the run, the insertion device will be installed during next summer's shutdown.
Construction is complete on BL5-4, the new low energy (10-40 eV) branch line based on a dedicated high resolution SCIENTA photoelectron spectrometer and a Normal Incidence Monochromator (NIM). The branch line is located between the old BL5 monochromator and BL6. The monochromator was delivered in mid June. A lot of hard work was put in by both vacuum and mechanical staff to install the mono and the beam line components before the end of the run. Commissioning was started on July 25th with first light through the entire system on July 28th.
Commissioning will continue during the FY '98 run, interspersed with user running on 5-2 and 5-3. There are a number of major tasks still to be done. First is integration of the control system software and hardware. This should be ready for testing by the start of the run. Delivery and installation of the full set of three gratings is expected in early November. The platinum coated glass horizontal refocusing mirror will be replaced with a silicon mirror with higher reflectivity. With the beam line in its final configuration the goals are to optimize the performance and characterize the monochromatic light with a gas cell. The dedicated end station with the SCIENTA spectrometer will then be moved on line and used to characterize the higher order contamination. Commissioning should be completed during this year's run.
Just prior to the end of the last running period, the protein crystallography group just received a Quantum-4 CCD detector system from Area Detector Systems Corp. (ADSC). This detector employs 4 individual CCD detector chips each linked to an X-ray phosphor using a tapered fibre-optics coherent light guide. The four individual modules are arranged in a 2 x 2 matrix that has a total active area of 188 mm x 188 mm, with a total of 2304 x 2304 pixels that are each 82 µm x 82 µm. During an initial trial on beamline 1-5AD, our tunable-wavelength bending magnet beamline used for MAD experiments, it performed very well. This detector has the ability to read out an entire high resolution diffraction image in approximately 9 seconds, and will clearly dramatically increase the speed of protein crystallographic data collection at SSRL. The detector will be placed on our new MAD beamline 9-2 when that beamline has been completed sometime early next year. In the meantime, we plan to make this new CCD detector available to users on our existing MAD beamline 1-5AD from the beginning of the next running period, for a few months.
At the end of September 1997, we received our new "fast" MAR-Research imaging plate data collection system, called the MAR345. We are currently installing this new system on our recently c ompleted beamline 9-1, and plan to make it available to users after some initial tests on that line at the beginning of the next run. This new imaging plate detector has a programmable plate diameter of up to 345 mm, and a readout time that is approximately three times as fast as the MAR300 systems that have been used on both BL7-1 and BL9-1 in the past (MAR-Research kindly loaned us a second MAR300 for use on beamline 9-1 for the past year during the development of their new MAR345 detector system). The pixel size of the MAR345 can be set to either 100 µm or 150 µm, compared to 150 mm for the MAR300. To give you an example of the speed of the new MAR345 detector, the total readout and erasure time for an imaging plate diameter of 300 mm and a pixel size of 150 µm, is 66 seconds, compared to 210 seconds for the MAR300. Our new MAR345 also incorporates an extra long base unit that will allow the crystal-to-detector distance to be varied between 75 mm and 800 mm. When the maximum imaging plate diameter of 345 mm and the minimum pixel size of 100 µm is selected, each diffraction image requires 23.8 MB (uncompressed) and approximately 4 or 5 MB (compressed) of storage. For this reason, we have purchased a disk farm capable of storing ~80 GB of data on BL9-1.
The MAR300 imaging plate system, that has given us excellent service for many years on our wiggler beamline 7-1, was sent back to the factory in Hamburg after the end of the last run for a complete overhaul. The imaging plate, lasers, power supplies, etc., have been replaced, and the system has been recalibrated. It has already arrived back at SSRL, and has been reinstalled on beamline 7-1 ready for the next run.
SSRL has just taken delivery of a Huber Kappa-geometry goniometer (Kappa angle of 60 degrees) for use on our new MAD beamline 9-2 when that line has been completed. This goniometer, recently developed by Huber in collaboration with Wilfried Schildkamp (of BIOCARS at the APS and the Univ. of Chicago), incorporates a number of excellent features for protein crystallographic experiments. One of the greatest virtues of a Kappa-geometry goniometer is the ease of access to, and the unhindered space surrounding, the sample crystal. The simple counterweighted 3-axis system (without a large chi plane) provides a "sphere of uncertainty" at the center of the machine of approximately 12.5 µm radius. This will allow us to very accurately align, in any general orientation, and collect data from very small protein crystals. The sample crystal support incorporates motorized X, Y and Z translations, with enough translation along the phi axis (+/- 12.5 µm) to accommodate a large range of cryogenic mounting equipment, pressure cells, flow cells, etc. Using a CCD TV telescope, these automated alignment translations X, Y and Z will permit us to align the sample from a remote computer terminal, inside or outside the experimental enclosure. The motion of the omega, kappa and phi axes are sufficiently rapid to make it feasible to collect anomalous scattering data using the inverse beam technique. In contrast to Eulerian-geometry goniometers, the Kappa-geometry also permits a greater angular range to be covered before the goniometer hardware would interfere spatially with the input X-ray collimator or the X-ray detector. Since we are working towards the goal of providing similar experimental apparatus (and software interfaces) on each of our protein crystallography beamlines, for the convenience of our user groups and to simplify upkeep, two more of these goniometers are now on order. We plan to equip each of our new advanced detector systems with such a Kappa-geometry goniometer in the next two years.
The MAD phasing beamline 1-5AD was heavily used during the 1996-1997 run. The large majority of the users collected multi-wavelength data, principally from proteins genetically engineered to contain selenomethionine. Users have so far reported solving four structures using MAD data collected on this line this year. MAD data sets were also collected this year from other proteins for which the results are not yet available. We also collected data on three proteins that were not MAD projects but had unit cells too large to be accommodated on our other beamlines. During the first two months of the run a MAR-Research automated imaging plate detector was used on BL1-5AD. While no faster than the standard manual system used on BL1-5AD, data collection was much easier, and users had more time to evaluate their data while it was being collected.
For the bulk of the run we reverted to the use of Fuji imaging plates scanned off-line. A room near to the beamline was specially equipped for the scanner. This made scanning and erasing the imaging plates, and reloading the cassettes, considerably more convenient. In September, the computer that controls the Fuji imaging plate scanner was upgraded to a Power Macintosh.
Beamline 9-1 has been scheduled regularly for users since March 1997, and has produced a wealth of high quality data on many exciting projects. The first attempts were made to collect diffraction data to very high resolution (better than 1 Å) for which the X-ray wavelength was set to 0.77 Å. This allowed for the measurement of very complete and high quality data to a maximum resolution of 0.78 Å on a 29 kDa enzyme. The resulting electron density map is of astounding quality and reveals details not seen in proteins of that size before. Various modifications were made to beamline hardware, and data collection strategies were designed in the course of these tests. We anticipate ultra-high resolution data collection to become a routine experiment at SSRL in the near future.
The development of techniques for preparing heavy atom derivatives, to be used for the multiple isomorphous replacement (MIR) method of structure determination, has continued. An attempt at preparing a xenon derivative at cryogenic temperature proved to be successful and an apparatus to perform these experiments was designed and fabricated for general use at the crystallography beamlines. SSRL staff scientists, in collaboration with a number of visiting experimenters, were successful in producing heavy atom derivatives for a variety of proteins at cryogenic temperature. The success rate of xenon binding appears to be about 50% as observed for room temperature experiments.
Major instrumental developments and upgrades for small-angle scattering include a dedicated small-angle single-crystal diffraction instrument, a second vacuum flight path for recording scattering at intermediate angles, new signal processing modules for the linear detector system, and characterization/acquisition of a CCD detector system.
It is expected that single-crystal diffraction studies at very small angles, i.e. in the resolution range of 1000-10 Å, will become very important in virus crystallography, and for phase determination in macromolecular crystallography in general. Based on our experience last year in recording low-index reflections from a few different macromolecular crystal systems (see the 1996 Newsletter), we are building a dedicated instrument for this purpose on BL4-2 as part of the Biotechnology SAXS camera system. The instrument will be available for users in January 1998. A crystal flash cooler for single-crystal diffraction, based on the design developed by the protein crystallography group at SSRL, was made available on BL4-2 during 1997.
A second vacuum flight path was constructed and commissioned successfully. The flight path provides approximately 0.9 m of sample-to-detector distance, providing access to higher angles up to approximately 5 Å in Bragg spacing. This second scattering system, for intermediate angles, will be mounted on a horizontal sliding mechanism together with the primary small-angle scattering instrument, so that users can cover a wider range of angles during a short run.
We purchased several new signal processing modules to implement coincident event rejection capability with our linear detector system. We also adopted the modules and the software suite developed by the EMBL Hamburg Outstation. With the help of M. Koch (EMBL), we successfully commissioned the new data acquisition system in August. The new system is expected to widen the dynamic range of the detector system at high count rates by eliminating a very small amount of background signal due to coincident events. A new software suite, which is versatile and user-friendly, was also tested. We will keep the current data acquisition system during the FY98 user run, and at the same time we will provide a way to convert the new data file format to be compatible with the old format.
We have been collaborating with the group led by Y. Amemiya (U. Tokyo) to evaluate CCD X-ray detectors that they have developed for non-crystalline X-ray scattering experiments. A version of the CCD detector, that incorporates an X-ray image intensifier lens coupled to a full-frame rate CCD camera head, was found to have a very low noise level that is comparable to single photon counting detectors. This 2-D detector system allows circular-averaging of isotropic scattering from non-crystalline samples, thus improving data statistics. The detector system can handle very high count rates and, therefore, allows us to take full advantage of the high flux obtained with the multi-layer monochromator installed on BL4-2. In addition to static measurements and fibre diffraction experiments, we also conducted "snap-shot" time-resolved solution X-ray scattering experiments using this system. For example, we initiated an enzyme reaction with a stopped-flow mixer, and turned on the CCD detector system for a short time (e.g. 20 ms) after a certain time (e.g. 5 ms) had passed after the beginning of the reaction. Encouraged by the high data quality of this detector system, we successfully obtained funding from the DOE OBER at the end of FY97 to purchase a comparable detector system. We have just placed a purchase order for an improved version of the same detector system which is expected to arrive at SSRL in May 1998.
The past year saw major milestones reached on a number of beam line projects. Beam Line 5-4 was installed and initial commissioning activities successfully completed. This new branch line on the Beam Line 5 multi-undulator source features a normal incidence monochromator (NIM) for high resolution photoemission studies of collective phenomena in condensed matter systems. (This is discussed in more detail in the article by Michael Rowen.)
Beam Line 9, the new suite of three branch lines for structural molecular biology, has also moved from construction to user commissioning mode. The 9-1 protein crystallography side station completed its user trials with outstanding data collected on a number of systems. The past year saw first light and subsequent commissioning activities on X-ray absorption spectroscopy Beam Line 9-3. These commissioning activities included performance studies of the second-generation pin post monochromator crystals and associated new monochromator design. The protein crystallography End Station 9-2 should experience first light and commissioning in the fall. The Beam Line 11 front end and most alcove components were designed, fabricated, and installed this past year. The current schedule calls for wiggler installation during the SPEAR shutdown next summer.
A number of beam lines have seen less extensive upgrades. For example, Beam Lines 4-2 and 6-2 received new hutch tables which feature increased mechanical stability. Beam line 7-2 was fitted with a new, more spacious hutch. A new powder diffraction station was installed and commissioned on Beam Line 2-1; this capability will be enhanced when a new mirror, which is currently in fabrication, is installed this fall. A new mirror system is also currently in fabrication for Beam Line 7-2. This new mirror will extend the focused energy range of 7-2 while eliminating the platinum mirror coating resonant absorption lines from the 7-2 spectrum. In anticipation of the new mirror on 7-2, the mirror controller has been upgraded to the type of system employed on 4-2 and 6-2. The goniometer on the 4-2 monochromator has been upgraded with a more robust model. Crystals from a number of double crystal monochromators were realigned, cut, and etched to provide improved monochromator performance. The machine protection systems on Beam Lines 3, 4, and 7 were replaced with new Allen Bradley systems. Finally, the personnel protection systems on Beam Lines 3 and 4 were replaced.
The nature of defects introduced by ion implantation and their subsequent interaction during high temperature processing with the implanted ion species is of considerable technological and recent scientific interest. If ion implantation is to continue being used for future device generations, it is imperative that we understand and attempt to control the phenomenon of Transient Enhanced Diffusion (TED). TED is observed upon annealing ion implanted silicon, we notice that the diffusion of the ion implanted species is enhanced by several orders of magnitude compared to the bulk diffusivity. In addition, the phenomenon is transient and of limited duration depending on time and temperature. The phenomenon is illustrated in Fig. 1 which shows the concentration profiles of Boron implanted silicon versus depth as a function of annealing time at 800°C. Note the saturation of the diffusion profile at long annealing times.
At SSRL we have initiated a program in collaboration with our industrial colleagues at Intel Corporation and scientific colleagues at the University of Munich, Stanford University, the University of Illinois and the Lawrence Livermore laboratories to try to understand in a systematic way the defects introduced by ion irradiation and their subsequent interaction with implanted ions.
In particular we concentrate on identifying and characterizing point defects and point defect clusters too small to be observed by transmission electron microscopy. A powerful method for detecting point defects or defect clusters is to analyze the diffuse scattering in the tails of Bragg peaks or the weak scattering between Bragg reflections. In metals the use of these methods allows unambiguous characterization of point defects and clusters such as dumbell pairs.
Since the implanted layers are usually about 2000 Å from the crystal surface we use grazing incidence geometry to restrict penetration and to suppress bulk scattering. The diffracting planes are normal to the (001) crystal surface. Both radial and angular scans were taken around the (400) and (220) Bragg peaks using a position sensitive detector to map out a region in reciprocal space around the Bragg tails.
In order to produce samples with a preponderance of one defect type we have adopted the following procedure for sample preparation. Floating zone dislocation-free silicon crystals were cleaned and implanted with a high Boron dose at 32 keV. The wafers were then Rapid Thermal Annealed (RTA) at 1070°C in order to anneal the implant damage and to locate the Boron predominantly in substitutional sites. The wafers were then implanted with a lower dose of Silicon at 80 keV and annealed at 750°C for various times. We expect that defects introduced by the silicon implant will be captured during annealing by the substitutional Boron already present and thus produce a defect population largely consisting of Boron, B-Si interstitial pairs or small clusters.
The contours of diffuse scattering around (400) and (220) Bragg peaks are shown in Fig. 2 for the crystal containing a high B concentration (6·1015 cm-2) annealed at 1070°C for 10 seconds after subsequent silicon implant (4·1014 cm-2) and annealing at 750°C for 10 sec. Besides the expected diffuse scattering around the (220) reflection, we notice a rather unusual feature. There are lobes of intensity displaced from the Bragg peak in the [220] direction. For the (400) reflection the peaks are not as clear, however, we can clearly see four lobes of intensity extending in the [-220] and the [220] directions. The intensity lobes are more clearly seen for crystals with an initial concentration of B (6·1014 cm-2) that is an order of magnitude less than the previous case shown in Fig. 2. After annealing at 1070°C for 10 sec. and subsequent Si implantation (2·1014 cm-2) anneal at 750°C 10 sec. the intensity contours for the (400) and (220) reflections are shown in Fig. 3. For the (220) reflection the lobes in the [220] direction are clearly visible. Around the (400) reflection four lobes of intensity are observed in the two {220} directions.
In Fig. 4 we plot the intensity profile for the high B sample in the [220] direction. Besides the tail of the (220) Bragg peak satellite peaks on either side of the main peak are clearly visible. From the spacing q of the satellite peaks we obtain a period distance of 74 Å for the high B sample shown in Fig. 4 (a). A similar profile for the low B sample shows satellite peaks somewhat lower in intensity and a periodicity of 85 Å. Fig. 4(b).
The results are internally consistent since the (400) reflection shows as would be expected pairs of satellite peaks in the [-220] and [220] directions. This is especially clear for the low B case and less so for the high B (220) results.
While the results clearly indicate a periodicity in the <220> directions, it is difficult at this stage to propose a model for the origin of these satellites. At present we can only speculate that the data are consistent with a lateral modulation normal to the surface on the scale of 75-85 Å. Since the implanted layer is only 2000 Å from the surface, a surface-mediated strain induced periodicity may be the cause for the observed satellites. We intend to look at reflections other than those investigated in this report to shed further light on this rather unexpected result.
The original aim of this work was to characterize the defects introduced by ion implantation by analyzing the diffuse intensity in the Bragg tails. To aid in the defect characterization we have used molecular dynamics simulation methods to predict the defect types and impurity profiles. The predicted profiles will be compared to experimentally obtained SIMS (Secondary Ion Mass Spectroscopy) profiles and refined to fit the experimental data. Preliminary work indicates that the defects are mainly point defects as well as B3I and B4I2 clusters, where (I) refers to interstitial silicon. Atomic displacements around such clusters have been calculated using first principles methods by our collaborators at the Lawrence Livermore National Laboratories. All of this information will be used to calculate directly the diffuse scattering under Bragg reflections and compared to the results we have in contour form in Figs. 2 and 3. Experimental verification of the simulation results is important since it will provide a sounder basis for the simulations and provide additional confidence for including such data in process codes that are widely utilized in the semiconductor industry.
Our colleagues in this rather extensive project are listed below since the format of this Newsletter does not allow an extensive author list. Much time and diligent effort has been expended by U. Beck and C. H. Chang in the experiments and data analysis. At Munich the support and participation of J. Peisl is gratefully acknowledged. We are grateful for a travel grant from NATO that made this cooperative effort possible.
Our close collaborators in the myriad problems raised in these studies are our Stanford colleagues P. B. Griffin and J. Plummer, at Lawrence Livermore T. Diaz de la Rubia and M. Caturla, at Illinois B. Averback and K. Nordlund and at Intel M. Giles and B. Doyle. The diffuse scattering experiments were carried out at ESRF, Grenoble and SSRL. We gratefully acknowledge the expert assistance of J. Arthur, S. Brennan and G. Grubel. Finally one of us (JRP) would like to thank J. Carruthers of Intel for suggesting the TED problem and his encouragement and support for this work.
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Fig. 1. Boron profiles for several anneal times at 800°C. From A.E. Michel, W. Rausch, P.A. Ronsheim and R.H. Kastl, Appl. Phys. Lett., 50 , 416 (1987) |
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Fig. 2: Contours of diffuse scattering intensity from silicon containing a high B concentration 6·1015 cm-2 annealed at 1070°C 10 sec. after subsequent silicon implant 4·1014 cm-2 and annealed at 750°C 10 sec. |
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Fig. 3: Contours of diffuse scattering intensity from silicon containing a low B concentration 6·1014 cm-2 annealed 1070°C 10 sec. after subsequent silicon implant 2·1014 cm-2 and annealed at 750°C for 10 sec. |
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Fig. 4 Intensity profile along (220) direction. (a) high Boron concentration; (b) low Boron concentration. |
As part of the Scientific Facilities Initiative, a replacement program for all the beam line computers was initiated. After thorough evaluation of options, the choice was made to procure DEC Alpha computers and to replace the existing DSP CAMAC controllers with Kinetic Systems Grand Interconnect controllers. SSRL has purchased 14 computers and controllers in the first phase of this upgrade. Coupled to these purchases has been the development of a new low-level beam-line control and data acquisition software system. A staggered hardware and software implementation will take place at the beginning of the November 1997 run.
The decision was furthermore made to equip the beam lines with additional computer capability in the form of X-terminals, configured to enable access to a large number of computers labwide. Currently, 12 X-terminals have been installed on beamlines and in the new user computer area upstairs in Building 131. The new user computer area is also equipped with a PC running Windows NT 4.0 and a laser printer.
The Alphaserver 2100 (the new "SSRL" central computer) was fully commissioned in 1996, including database moves and application porting, getting RZ20 firmware upgraded, and setting up RAID sets for high reliability disk storage. As part of the conversion to the Alphaserver SSRL, SSRL01 and SSRL04 were clustered.
In response to a call from SSRLUO to make more of the user administrative process electronically based, SSRL's World Wide Web server was rehosted on the much-faster AlphaServer. Common Gateway Interface (CGI), a way to enhance World Wide Web communications, mail-to, and forms support have subsequently been implemented, allowing users to enter form responses over the net. Beamtime scheduling information was made automatically available over the WWW as well.
The Scientific Facilities Initiative, with additional funding from the DOE Office of Biological and Environmental Research, has also enabled a major upgrade of the SSRL lab wide computer network. The technical solution was defined, hardware procured and installation begun in 1996. The project will extend into 1998, but major milestones have already been achieved.
Cable Infrastructure. There were four major areas of improvements in the cable infrastructure; first 300 MHz CAT-5 cables and then fiber optics cables were installed throughout the SSRL area. The CAT-5 cables were terminated and certified to pass all 100 MHz certification tests. The fiber optics cables were installed by the network group, but were terminated by an outside company (All Systems). In preparation for the cable infrastructure, several wiring closets throughout the SSRL lab had to be created and refurbished. These closets were fitted with equipment racks, cable management devices and AC power. Several cable raceways were installed at various locations through the SSRL laboratory.
Equipment Installation. In the area of equipment improvements, the most important part was the installation of several Cisco Catalyst switches and 10BaseT hubs. The Catalyst switches were used to allocate single collision domains to devices that use network intensive applications, and to crate controllers that are critical to the operation of the accelerator. Providing each crate controller with its own switched port is necessary to avoid potential problems created by a faulty device in the same collision domain. The shared 10BaseT hubs were used to create small share domains in areas that do not have switched Ethernet resources.
The SSRL router was also connected to the SLAC FDDI ring, providing a fast communication link to the Wide Area Network (WAN).
In order to manage the switched networks, a software package called "Cisco Works for Windows" was installed. This package allows all areas of the switched network to be managed and configured. To manage the Legacy networks, a variety of Ether meters located at strategic areas of each shared LAN are being used.
The benefits of the above mentioned improvements can be appreciated and summarized as follows: Central wiring closets provide an easy way to troubleshoot problems, therefore allowing technicians to quickly attend to trouble calls and new installation requests. Ethernet traffic congestion areas have been alleviated by the installation of Catalyst switches, allowing the users and staff to transfer files at a fast rate with no restrictions regardless of time of day or size of the files. The SSRL networking group has a variety of spare parts and adapters to help the staff and users to connect their various computers and lap tops to the new upgraded network.
As part of the network upgrade we are working on purchasing a Cisco Catalyst 5500. This Network switch will replace the existing Network Backbone Switch Catalyst 5000. The Catalyst 5500 will allow us to accommodate for the growth of the SSRL network. It will also increase the switching Backbone engine's bandwidth from 1.2 Giga bps to 3.6 Giga bps. The Catalyst Switch 5500 will support various Network technologies such as Conventional Ethernet, Fast Ethernet, Gigabit Ethernet, Ether channel and ATM.
As part of the preparation for the Response to Questions from the DOE BESAC Sub-committee on Synchrotron Science, a fair amount of time was spent in summarizing and internally formulating a picture of educational activities at SSRL. The extent of these activities came almost as a surprise to the laboratory, and we thought it might be of interest to share this information with a wider audience.
SSRL and Stanford University. From the very beginning, SSRL has had a very strong intellectual tie to Stanford University. Formally this has been (and still is) by way of faculty appointments joint with campus Departments (e.g., Applied Physics, Materials Science, Electrical Engineering, Chemistry). SSRL furthermore has its own academic faculty (the SSRL component of the SLAC faculty); the faculty chair is currently Sebastian Doniach. The SSRL faculty is augmented by term appointments from other Stanford University Departments. There is also a group of Affiliated Faculty, which consists of Stanford University faculty that have an intellectual interest in the science at SSRL and active research programs at the facility, and which serve in an advisory function to the SSRL Directorate. SSRL also has a group of Consulting Faculty from other academic institutions, industry and Government laboratories, whose role is to provide advice and expertise in diverse scientific fields.
Graduate Student Education. Because of these ties to Stanford University, graduate student education has always been an integral part of the SSRL program. As with SLAC, SSRL does not have its own graduate student program - all SSRL graduate students are formally graduate students within a campus Department (Physics, Applied Physics, Materials Science, Chemistry, etc.).
In addition to Stanford students, a very large number of graduate students from other institutions have based their theses on work done at SSRL, either having spent a long time at the laboratory as visitors, or as users. As new fields have been pioneered, graduate students have been, and continue to be, at the forefront in these developments, and have moved into important positions at other synchrotron and Government laboratories, in academia and in industry after completion of their theses.
As of June 1, 1997 a total of 349 Ph.D. and 11 M.Sc. theses had been reported to SSRL as being awarded based on work partially of fully performed at SSRL. The first thesis was completed in 1974, by C.A. Ashley, on "Extended X-ray Absorption Fine Structure" (S. Doniach, advisor), with P.E. Gregory, "Ultraviolet Photoemission Studies of the Surface States and Properties of the (110) Gallium Arsenide Surface and of the Oxidation of Cesium" (W.E. Spicer, advisor) and B.M. Kincaid " Synchrotron Radiation Studies of K-Edge X-ray Photo-absorption Spectra: Theory and Experiment" (S. Doniach, advisor) as runner-ups in 1975. There were in all 31 theses before 1980, many representing breakthroughs in several scientific fields. During 1980-1989, 154 theses were reported with a peak in 1986 of 23 theses. In the 1990s, 177 theses have been completed so far, and there are currently 19 reported to SSRL for the year 1997.
Graduate Student Program in Accelerator Physics. Recognizing a U.S. need for accelerator physicists, SSRL and the Stanford Applied Physics Department initiated an educational and training program for graduate students about ten years ago. SSRL faculty, now joined by SLAC high-energy physics faculty, offer a range of graduate courses in accelerator physics. Two interleaved biannual courses on "Introduction into Accelerator Physics" and "Electromagnetic Radiation from Relativistic Electrons" form the basis of this program and are supplemented by one or two specialized courses per academic year. Applied Physics and SSRL were the hosts for the 1992 US Particle Accelerator School, which offers a variety of full credit courses in accelerator Physics. This school will be repeated at Stanford in 1998.
A special training program has also been established by SSRL at the SUNSHINE (Stanford UNiversity SHort INtense Electron source) facility, and is headed by Helmut Wiedemann. This facility consists of an rf gun, a bunch compressor, a 30 MeV linac, a 4 m undulator and optical instrumentation. The purpose of this facility is exclusively for the training of graduate students while conducting forefront electron and photon beam research. This facility has been developed by the students to generate 100 f-sec rms electron bunches; develop an optical device to measure f-sec pulses; and produce coherent, polarized, far infrared radiation with radiance exceeding that of black body radiation by 5 to 8 orders of magnitude in the form of i) transition radiation (broad band, sub p-sec pulses), ii) stimulated transition radiation (broad band, sub p-sec pulses) (first observed at SUNSHINE), and iii) single pass FEL (narrow band, high radiance). Three of the six former graduate students are now working as accelerator physicists at APS, NSLS and SLAC. There are currently six students in training.
Two additional Stanford graduate students, supervised by SLAC faculty/staff, are currently performing longitudinal feedback and nonlinear map fitting studies using SPEAR. SSRL is also hosting accelerator physics graduate students from other universities (MAXlab/Lund University, Sweden and UCLA). Finally, there is a graduate student from University of Rochester working on the LCLS gun test facility.
Undergraduate Education. SLAC as a laboratory organizes a program called Summer Internships in Science & Engineering (SISE). SISE is a lecture and research participation program for undergraduate students who are traditionally underrepresented in science, such as women, and some minority groups, often from historically black colleges and universities. SISE is designed to encourage these students to pursue careers in science. From a national applicant pool, approximately 20 students are selected to spend 8 weeks at SLAC during the summer under the supervision of laboratory scientists. This program has existed for 26 years, and to date ca. 50 students have worked at SSRL. SSRL furthermore engages undergraduate students directly in work with its staff typically during the summer months, funded directly through the SSRL budget. Recent projects have spanned a wide range of topics, with just a few examples being: computer code development for VME modules in the ring feedback system, for 'corrector ironing' program on SPEAR, and for soft X-ray spectroscopy data acquisition; FEL computer simulations for the LCLS; and protein crystallization of the channel protein annexin. This activity has in several cases resulted in co-authorship on internal reports and scientific publications.
Undergraduate students are also to some extent direct participants as users in research at SSRL. This is a small activity, but one that is currently growing. Three representative examples of undergraduates working with/as SSRL users are:
Two seniors at University of California at Santa Cruz based their theses on X-ray absorption spectroscopy work with Prof. F. Bridges. Both students received the Dean and Chancellor Awards for Senior Thesis in their year: Eric Bauer, "Local structure study of two high temperature superconductors HgBa2CuO4+d and YBa2(Cu1-xCox)O 7-d), March 1996; and Zev Kvitky, "Using EXAFS spectroscopy to probe interatomic potentials in Ag, Au, Pb, and RbBr", January 1997.
As part of projects led by Dr. S.D. Conradson, LANL, Nicole Levy, California Polytechnic University, San Luis Obispo, worked at SSRL during the summers 1995, 1996. The work included study of local structure in actinide-containing materials and compounds, and chemical speciation in solutions and inhomogeneous solids. This activity is continuing with students Leilani Pastizzo, San Jose State University, and Dorota Rek, California Polytechnic University, San Luis Obispo, both summer 1996 - present.
Several students from the San Jose State University, California, are working at SSRL with Prof. Juana Acrivos on projects related to high Tc superconductor materials, using X-ray absorption spectroscopy as a method. The opportunity to do synchrotron research with Dr. Acrivos is through NSF support at SJSU. Among former students are K. Hathaway (CEO in Palo Alto), J. Reynolds (University of Florida, Gainsville), C. Bustillo (engineer at Apple), D. Gilbert (Michigan State University). Current students are C.M. Burch, M. Rose, L. Nguyen and T. Norman.
High School and College Teacher Education. SLAC also offers a two week program on particle physics for high school and college teachers (~30 participants/year) during the summers. The program consists of presentations and demonstrations from scientists and development of related classroom activities. Two days are spent at SSRL to gain insight into the use of synchrotron radiation. There is also a Teacher Research Associates program, where teachers participate in laboratory research for 6-8 weeks during the summer. During the 1997 summer one teacher intern, David Trapp, worked at SSRL.
Workshops and Conferences. Since 1987, SSRL has organized 17 workshops with subjects ranging from synchrotron sources and specialized beam lines to applications in trace impurity analysis for silicon processing, biological small angle scattering, X-ray absorption spectroscopy and protein crystallography data analysis. During the same period SSRL has hosted three international scientific meetings in addition to national gatherings. In particular the workshops have had a large impact on graduate students (and faculty members new to synchrotron radiation research) in providing them a good introduction to various fields of synchrotron radiation research. This is especially so with those that were arranged to provide hands-on experimental training. Many non-student participants have also been introduced to, for them, novel techniques this way and later returned to SSRL as users.
In January SSRL hosted the SLAC/DESY "International Workshop on Interactions of Intense Sub-Picosecond X-ray Pulses with Matter". Researchers from five countries and 12 different institutions attended the two-day event organized by SSRL staff members Roman Tatchyn and John Arthur, DESY staff members Gerd Materlik and Jupp Feldhaus, and ESRF staff member Andreas Freund.
The workshop was associated with two ongoing design studies of high energy, linac-driven Free Electron Lasers (FELs) intended for operation at Ångstrom wavelengths. The project under study at SLAC, the Linac Coherent Light Source (LCLS), will utilize a laser-driven rf photocathode gun injector and 1 km of the SLAC linac to drive an ultra-low-emittance 5-15 GeV electron beam through a 100 meter long undulator. The LCLS will produce coherent radiation with a fundamental energy range of ~900-8500 eV. The DESY project (TESLA FEL) has a similar goal, but it is basing its beam acceleration on superconducting linac technology, which should allow it to operate with a higher duty cycle (average output power). Both devices will initially operate as amplifiers in the so-called Self-Amplified Spontaneous Emission (SASE) mode, producing similar 100-300 femtosecond long X-ray pulses featuring full transverse coherence, 10-100 GW of peak power, and unprecedented peak power densities of 1015 to 1016 W/cm2.
Over the period 1992-1996 there have been several well-attended scientific workshops, hosted by both SSRL and DESY, on the potential scientific applications of this new category of radiation. A major concern common to most of the participating scientific communities has been the question of how the extraordinarily high peak power densities of the LCLS and TESLA FEL will affect the various experiments that have been proposed for these facilities. Specific concerns include: 1) damage to beam line optics and instrumentation, 2) damage to samples, 3) non-linear effects, and 4) saturation, and other loading effects on the physical processes being studied. The goal of the January workshop was to systematically address these concerns and to begin to formulate R&D plans and collaborations for addressing and resolving these physical issues.
The workshop program was structured as a sequence of invited tutorial presentations, contributed talks, and discussion sessions. The tutorial lectures reviewed the status of theory, experimentation, and computer simulation of the interactions of ultra-short, ultra-intense radiation pulses with matter. The contributed talks covered a number of topics related to experimental techniques and instrumentation, and the discussion sessions were spent reviewing the presentations and attempting to formulate plans for meaningful theoretical and experimental work.
Several conclusions were reached by the end of the workshop. Most importantly, representatives from LLNL, LANL, and other institutions expressed their intent to seek support for the extension of their existing theories and computer codes into the short-wavelength parameter regime of the LCLS. This would allow detailed calculation of the effects of X-ray FEL radiation on materials. This work is a natural outgrowth of programs at these laboratories based on high-power optical lasers; extension of the work into the X-ray region may uncover new fundamental physics that can be tested experimentally at LCLS, and it will also be useful for predicting the performance of LCLS optical components such as mirrors, crystals, and absorbers. As a result of the workshop, SSRL has entered into cooperative research agreements in this area with LLNL and LANL.
A second conclusion concerns the possibility of using existing sources to approximate the parameters of the LCLS beam for demonstration experiments. The consensus was that insertion devices on existing storage rings probably could not attain the required parameters. However, useful demonstration studies could possibly be performed with a partially completed LCLS using an undulator substantially shorter than the one required for the full-scale LCLS.
A workshop was held at SSRL on October 23, 1996 on "Approaches to Modern and Advanced Analysis of XAS Data". It consisted of four lectures followed by discussions. Robert Scott (Univ. of Georgia) introduced the topic and the questions with a talk "Extracting the Most Structural Information from EXAFS. Defining the Problem", which defined where the field has come, where it is heading, and what will be needed in the future. Matthew Newville (LLNL) then gave a lecture on how to use FEFF (a code base on ab initio theoretical calculations of EXAFS functions) for advanced data analysis with very recent examples from complicated data. John Rehr (Univ. of Washington), the physicist behind the extensive development effort of FEFF, continued the workshop with an overview of new improved theoretical simulations of the latest version of FEFF, FEFF7 and his own vision of planned and projected developments in the future. Graham George (SSRL) concluded the sessions with a description of his SSRL-available analysis software package EXAFSPAK - its current capabilities and future plans. The workshop received a most enthusiastic response by the 70 participants from all over the US who took part in often-lively discussions.
A mini-symposium was held at SSRL on the same day in conjunction with the dedication of the OHER-funded Beam Line 9. It consisted of four invited lectures focussing on protein crystallographic research that has utilized SSRL as its main synchrotron radiation data collection facility. Speakers were William Weis, Stanford University ("Structural Studies of Cell Recognition and Adhesion"), Robert Stroud, UC San Francisco ("The Mighty Javelin Approach of Antibacterial Channel Forming Proteins"), John Johnson, Scripps Research Clinic ("The Structural Basis for Viral Infection") and Doug Rees, California Institute of Technology ("Electron Transfer Reactions in Nitrogen Fixation and Photosynthesis: A Structural Perspective"). The symposium was attended by approximately 50 participants from all over the US. It was followed by the dedication of Beam Line 9 which was held at the extension of building 120 (specifically build to house the new beam line). Brief remarks were given by Artie Bienenstock, Keith Hodgson and by Roland Hirsch from the DOE Office of Health and Environmental Research. A reception followed, which was attended by the symposium and dedication speakers, workshop and mini-symposium participants and SSRL staff.
In late 1996, the Basic Energy Sciences Advisory Committee (BESAC), an advisory group to the Department of Energy's Office of Basic Energy Sciences (BES), began the formation of a subcommittee (referred to as the BESAC Panel on Synchrotron Radiation Sources and Science) to review the four BES-supported synchrotron radiation facilities. This Panel was given the charge of studying a broad range of issues of importance to the need for and the opportunities presented by each of the four light sources. The Panel's purview included topics such as: the scientific and technological demand for synchrotron radiation, the size and distribution of the user community, the capacity of the facilities, the funding needs of the facilities, and the vision of the future.
By mid 1997, the Panel (a group of 18) had been organized and the review process had begun. Dr. Robert Birgeneau of MIT served as Chairman, Dr. Z.-X. Shen of Stanford was Vice Chairman, Dr. Gordon Brown and Dr. Ewan Patterson from Stanford were Panel members and Dr. Keith Hodgson was SSRL's non-voting delegate to the Panel.
Before making site visits, the panel sent out a set of twelve questions that each facility was asked to address. The panel inquired about scientific and technological impacts of research, future trends and opportunities, educational impact, user demand, technical facilities, and budget issues. The synchrotron facilities prepared detailed responses to these questions that provided an in-depth look at the past and present status of synchrotron radiation-related science and technology as well as a projection of what the future may hold.
Following an initial meeting in May, the Panel visited each facility. They arrived at SSRL on July 8th for a day and a half of presentations and tours. After visiting the other three facilities the Panel met at the end of August to formulate their conclusions and recommendations. They presented their findings and recommendations to the full BESAC Committee at a meeting on October 8 and 9, 1997.
The full report of the Panel will be available to the public shortly after this Newsletter goes to press; a few of the highlights can be summarized very briefly as follows:
The Panel recommended specific priorities for facility operations and improvements. The highest priority recommendation was for continued effective operation of SSRL, NSLS and APS including inflationary growth in FY99 and beyond. Also included in their recommendations was funding for 4th generation R&D with proposals to be evaluated by a peer review group. SPEAR3 received strong support but DOE was urged to seek partnerships in funding this major upgrade given the strong growth and use of synchrotron radiation by communities like the life and molecular environmental sciences.
Overall, the Panel viewed SSRL in a very positive light. It was noted that in the user survey, SSRL was unique in having its users be "remarkably and astoundingly happy".