Beam Line 9: A Newly Commissioned Station

- T. Rabedeau

The past year has marked the transition of Beam Line 9 from a collection of designs and components to a functioning beam line with one commissioned station and two more close behind the first. The full extent of this transformation was apparent to those who watched tape lines on the building 120 floor metamorphose into hutches, girders, optics, and vacuum hardware.

The transformation started in earnest with the installation of the Beam Line 9 wiggler into SPEAR during the summer 1995 shutdown. Following the startup of SPEAR in the fall, Beam Line 9 engineers in conjunction with the SPEAR operating staff investigated the field compensation required to ensure that this 8 period, 2 Tesla wiggler would not adversely affect SPEAR operations. After several machine physics shifts the wiggler compensation was fully characterized and attention shifted to the beam transport system and instrumentation and controls suite.

From a scheduling perspective, the installation of hardware in the SPEAR alcove behind the SPEAR shielding concrete provides an enormous challenge as SPEAR operations must be interrupted. With the exception of the M0 mirrors and associated slits and masks, all the in-alcove hardware had been installed during or prior to the summer 1995 shutdown. Initial plans to install the remaining mirrors and slits prior to the SPEAR fall 1995 startup or during the Christmas break were scrapped as technical difficulties in the fabrication of the water-cooled mirrors by an external vendor delayed their delivery until late spring 1996. Instead, a short installation access to SPEAR was scheduled for the first week of June. The arrival of the first of the mirrors in mid-April was followed by a flurry of activity as vacuum shop staff and a SLAC alignment crew assembled, aligned, and baked the mirror system. Lessons learned in this assembly proved valuable as the last of the two remaining mirrors arrived at SSRL a scant three weeks prior to scheduled installation. Nonetheless, all three mirror systems stood ready for installation at 6 am on Sunday, June 2nd, as the SPEAR shielding block rolled open -precipitating a mad scramble by Beam Line 9, vacuum shop, operations, and alignment staff. When the dust settled 100 hours later, the three mirror systems, two water-cooled masks, and six water- cooled slits had been successfully installed in the Beam Line 9 alcove.

With the alcove transport system complete, attention turned to the remaining systems nec-essary to conduct light into the 9-1 experimental hutch. In rapid succession, the 9-1 hutch table, shutters, monochromator slits, and drift tubes were installed. Several years of effort by the beam line instrumentation and controls team culminated in the certification of the personnel protection system and the commissioning of the new Allen Bradley programmable logic-based machine protection system.

The last essential optical component on Branch Line 9-1, the side- scattering focusing monochromator, was installed on June 17th. This monochromator represents a significant departure from other side scattering monochromators at SSRL. Instead of employing a back-cooled, triangular crystal in the monochromator, John Cerino and the protein crystallography group opted for a side-cooled crystal configuration to reduce thermal distortion of the crystal figure. To facilitate side cooling, the asymmetrically cut crystal was configured with a cube root thickness variation along its length as pioneered for cylindrically bent mirror applications by Howells and Lunt. With the introduction of this innovative monochro-mator, the 9-1 branch line was ready for commissioning.

In contrast with most other SSRL beam lines, first white light was extracted from Beam Line 9 at an entirely civilized hour. . . 1830 on June 18th with the wiggler field at 1.92 Tesla and SPEAR at 2 mA/3 GeV. Over the course of the next eight hours, the beam was steered onto the photon monitor port, and the 9 -1 optics were illuminated and tuned to produce a monochromatic, focused ( 0.75 mm x 3.0 mm) spot in the 9-1 hutch.

As with all beam line development projects, the extraction of first light provides a major milestone for the project. First light from Beam Line 9 marked an important personal milestone as well. When John Cerino accepted the Beam Line 9 project management responsibilities he stipulated that he intended to retire in the summer of 1996. With the extraction of first light, John achieved his final objective at SSRL. So it was, that at the end of June, with two canoes strapped on top, a trailer behind, and a set of golf clubs in the back, John and Katherine Cantwell's truck departed SSRL bound for adventures in this new phase of their lives. We at SSRL wish them well.

Extracting first light from a beam line often involves tracking the beam progressively down the beam line. Here John Cerino adjusts a fluorescent screen just down stream of the 9-1 monochromator.

Following John's departure, 9-1 commissioning consumed much of the remainder of the run. Beam Line 9 and biotech staff characterized and fine tuned the optics resulting in a 0.175 mm x 1.15 mm focus. The effectiveness of the improved cooling of the branch-line optical elements is demonstrated by the 25 µm stability of the focus (typical peak-to-peak vertical motion observed over one shift). In August, a MAR-Research imaging plate data collection system, kindly loaned to SSRL for these trials by the manufacturer, was installed and a number of initial data sets were collected by the SSRL scientific staff and outside collaborators as described elsewhere in this newsletter.

In parallel with the commissioning activities of 9-1, the first of the new double crystal monochromators designed for Branch Lines 9-2 and 9-3 was assembled by biotech staff and initial mechanical tests were conducted. Unfortunately, the monochromator just missed being ready for synchrotron beam testing at the end of the run. Thus full power tests of this monochromator and the associated new pinpost crystal design await the restart of SPEAR in November. Preliminary x-ray measurements of the pinpost crystals using a conventional x-ray tube source reveal very little residual strain in the crystal diffracting volume.

The last major optical components of Branch Lines 9-2 and 9-3, the refocusing M1 mirrors, are scheduled for installation over the Winter shutdown. Branch Line 9-3 commis-sioning should start at the beginning of the new year with Branch Line 9-2 commissioning starting in February or March.

Since Branch Line 9-2 will be used for both monochromatic experiments (MAD-phasing studies, high resolution data collection, the collection of data from large unit cells and/or microcrystals) and white beam experiments (time-resolved Laue-diffraction studies), a large experimental enclosure has been built for this branch line to conveniently accommodate the large array of equipment that is being provided to support each of these experiments. A large/fast MAR-Research imaging plate detector system and a 2 x 2 matrix CCD detector system from ADSC are on order for the two protein crystallography lines.

The Beam Line 9 project is being funded by the DOE Office of Health and Environmental Research (OHER). The project has also been accomplished in part through efforts of staff supported in part by the NIH NCRR SSRL Biotechnology Resource.

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December 2, 1996