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Last Updated: | 24 OCT 2001 |
| Content Owner: | L. Dunn | |
| Page Editor: | L. Dunn |
**** **** **** * * * * * * **** **** **** * * * * * * **** **** * * **** HEADLINES - a digital monthly publication
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1. 2001 Users' Meeting Program Set
(contact: Cathy Knotts, knotts@slac.stanford.edu)
An exceptional program has been planned for the SSRL Users' Meeting on
October 18-19th. The opening session features presentations by John
Hennessy (Stanford University President) and Patricia Dehmer (Director
of Basic Energy Sciences, DOE). Scientific presenters include: Frank
Bridges (UC Santa Cruz), Christopher Lucas (Univ. Liverpool), Geoffrey
Chang (TSRI), Daniel Herschlag (Stanford Univ.), Alain Manceau (Univ.
Grenoble), Ken Kemner (ANL), Greg Hirsch (Hirsch Scientific), Jeff
Kortright (LBNL), and Valeri Petrov (Michigan State Univ.). Full program
details and registration information can be found on the meeting website:
http://www-ssrl.slac.stanford.edu/conferences/ssrl28/
program.html
The full User's meeting is preceded by workshops on Wednesday, October 17 and additional details can be found on the SSRL web site.
2. Nature of Charge Order in the Layered Manganite
La1-xSr1+xMnO4
(contacts: Martin Greven, greven@loki.stanford.edu,
John Arthur, jarthur@slac.stanford.edu)
During the last two decades, some very unusual and potentially useful electronic and magnetic properties have been found in compounds based on copper, nickel, and manganese oxide. These properties, such as high-temperature superconductivity (the absence of electrical resistivity at temperatures well above absolute zero) and colossal magnetoresistance (or "CMR" -- a tremendous sensitivity of electrical resistivity to applied magnetic fields), derive from a complex interplay of interactions among the electrons in the crystal lattice of these materials. Although some general principles have been established, there is not yet a complete theory that explains how these properties come about. In order to further understand these unusual materials, other properties that might possibly be related, such as crystal structure and magnetism, are being carefully studied in transition metal oxide compounds. Recently, a group at Stanford University and SSRL grew a series of crystals of Nature of Charge Order in the Layered Manganite La1-xSr1+xMnO4 with different ratios of La to Sr. The variation of the La/Sr ratio had the effect of changing the electron concentration in the manganese-oxygen sheets that constitute the key building block of these crystals. They then used synchrotron x-ray scattering to observe the effect of this variation on the low-temperature crystal structure. The high intensity and collimation of the synchrotron x-ray beam allowed them to observe a small structural distortion, which changed as the electron concentration was varied. This trend is reminiscent of that seen in La1-xCaxMnO3, which is a CMR material. However, Nature of Charge Order in the Layered Manganite La1-xSr1+xMnO4 does not display CMR. This study, recently published in the August 27, 2001 edition of Physical Review Letters, may eventually help to unravel the mysteries of CMR and other correlated-electron effects.
More information regarding this research can be found at:
http://www-ssrl.slac.stanford.edu/research/highlights_archive/greven-highlight.html
3. BL10 Insertion Device Repair Successful
(contacts: Ben Scott,
bscott@slac.stanford.edu,
Tom Rabedeau, rabedeau@slac.stanford.edu)
Our last report on the BL10 wiggler appeared in the July edition of Headlines. Since then we have made substantial progress in restoring the wiggler to operational status. Thanks to the efforts of many groups at SLAC the wiggler was repaired and installed back into SPEAR by late August. All phases of the work were carried out on site.
To prevent a future recurrence of the failure, thin stainless steel bands were clamped around the magnetic keeper assemblies to retain the magnetic material. However, these bands come at the cost of slightly increasing the operating gap of the magnet. This causes a 10% loss in peak field for the immediate future. Over the long term we intend to fabricate a new vacuum chamber and to recover the old magnet gap.
The 10% peak field loss translates to a 10% reduction in fan width to the beam line. The BL10-1 soft x-ray side station nominally accepts light to the edge of the old fan, and so will suffer some loss of flux owing the fan narrowing. The quantitative extent to the loss of flux depends on the configuration of the optics, slits, etc.
The BL10-2 hard x-ray centerline station will suffer a 10% reduction of the critical energy. For the majority of the beam line utilization this will have a negligible effect on the beam line performance. Users of the highest energies will experience some flux loss.
4. Summer Shutdown Projects are Winding Down
(contact: Piero Pianetta,
pianetta@slac.stanford.edu)
The shutdown is starting to wind down and SPEAR will be "buttoned up" next week for pre-run checks. Startup activities will then begin with the linac and booster systems ready by the middle of October, keeping on track to have user beam ready by the end of October. Since the last report on shutdown activities in July, all of the shielding work in the West Pit area has been completed, including fully covering the SPEAR tunnel in this area and adding a bend magnet alcove between BL11 and the West Pit. We have also started construction of the beam line enclosure that will continue Building 131 up to the SPEAR injection line. By the time the run starts, the concrete slab will have been poured and the steel shell of the building will have been erected with completion expected in February.
Most of the repair/maintenance items discussed in the July Newsletter have been completed except for the reinstallation of the M0 mirrors for Beam Lines 9-2, 9-3, 11-1 and 11-2, which will occur during the coming month. The construction of the LN2 cooled monochromators for Beam Lines 6-2, 9-3 and 10-2 is proceeding with installation now being scheduled at the end of December for 9-3 while 6-2 and 10-2 will be installed later in the run.
5. DOE 2001 Pollution Prevention Award
(contact: Ben Scott,
bscott@slac.stanford.edu)
The Oakland Office recently presented awards to eight members of SLAC for their efforts in pollution prevention. Among these was Harold Morales, of SSRL, who was recognized for implementing the use of an alternative organic-based solvent in the cleaning of vacuum equipment.
6. User Research Administration Announcements
(contacts: Cathy Knotts, knotts@slac.stanford.edu,
Lisa Dunn, lisa@ssrl.slac.stanford.edu)
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7. SSRL Job Opportunities
(contact: Rochelle Roberts, rroberts@slac.stanford.edu)
SSRL currently has positions available for mechanical, electronic and
beam line engineers and technicians. More information is available at
the following web site:
http://www-ssrl.slac.stanford.edu/jobs.html
SSRL Headlines is published electronically monthly to inform SSRL users, sponsors and other interested people about happenings at SSRL. SSRL is a national synchrotron user facility operated by Stanford University for the U.S. Department of Energy Office of Basic Energy Sciences. Additional support for the structural biology program is provided by the DOE Office of Biological and Environmental Research, the NIH National Center for Research Resources and the NIH Institute for General Medical Sciences. Additional information about SSRL and its operation and schedules is available from the SSRL WWW site: http://www-ssrl.slac.stanford.edu/
You can subscribe or remove your name from the distribution list by sending a brief email with your request to Lisa Dunn, editor, at lisa@ssrl.slac.stanford.edu.