ALSNews is a biweekly electronic newsletter to keep users and other interested parties informed about developments at the Advanced Light Source, a national user facility located at Lawrence Berkeley National Laboratory, University of California. To be placed on the mailing list, send your name and complete internet address to ALSNews@lbl.gov. We welcome suggestions for topics and content.

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ALSNews           Vol. 30           June 27, 1995

Table of Contents


    1. OPERATIONS UPDATE
    2. IMPROVEMENT MADE IN BEAM STABILITY
    3. LABORATORY NAME CHANGES
    4. HOVERING PLATFORM INSTALLED AT BEAMLINE 8.0
    5. LONG-TERM SCHEDULE OUTLINE THROUGH SEPTEMBER 1995

1. OPERATIONS UPDATE
(contact: rmmiller@lbl.gov)

Beam availability for the last two weeks was 91.9% overall and 92.3% during user shifts. Outages during this period were caused by low-conductivity water flow problems associated with pump maintenance, difficulties with resetting control system display micro modules and intelligent local controllers, overcurrent trips on a booster-to-storage ring bend magnet power supply, and failure of a storage-ring focusing quadrupole power supply.

Operations summary for June 27 - July 16
1.5-GeV, 400-mA, 320-bunch operations for users:
    June 28 - July 3, 08:00-23:15
1.9-GeV, 250-mA, 320-bunch operations for users:
    July 7-9, 08:00-23:15
    July 12-16, 08:00-23:15
Maintenance: 
    July 5 & 10, 08:00-16:00, with startup 16:00-23:15
Accelerator Physics:
    June 27 and July 6 & 11, 08:00-23:15
Holiday: July 4

Weekly scheduling meeting: Fridays, 3:30 p.m. in the Building 6 conference room (no meeting on June 30).

2. IMPROVEMENT MADE IN BEAM STABILITY
(contact: ajackson@lbl.gov)

ALS staff and LBNL Facilities staff recently isolated and eliminated one type of motion in the ALS electron beam. This motion was discovered in late 1994, when a new electron beam position monitor indicated a vertical motion of the ALS electron beam that had a characteristic period between 10 and 15 minutes. The period was similar to variations in photon beam intensity observed in some beamlines, but the electron beam motion's magnitude was too small to explain the beamline variations. A good correlation was observed between the period of the beam motion and that of the temperature of the low-conductivity water (LCW) cooling system.

A joint ALS/Facilities working group set up dedicated monitoring systems, seeking to identify the source of the problem. This proved to be the temperature of the cooling tower water, which regulates the LCW water temperature via a heat-exchanger system, and whose temperature is itself regulated by fans to control evaporation rates. When these fans were run at a constant speed rather than cycling on and off, the 10-15 minute variations in water temperature and beam position disappeared.

The LCW cooling system is used both in the ALS storage ring and in various beamline optical systems, which helps explain why some variations in photon beam intensity were greater than the electron beam position changes could explain. Beamline optical elements (and, to a much lesser extent, storage ring components) are very sensitive to the temperature of the water used to cool them, regardless of its source. The next target of the beam stabilization working group will be beam motion with a period of about one hour.... Watch this space for updates.

3. LABORATORY NAME CHANGES

The sharper-eyed among you may have noticed the LBNL acronym on the first line of the previous article -- it's no mistake! As of June 16, Lawrence Berkeley Laboratory is now known as the Lawrence Berkeley National Laboratory, or LBNL for short. The new name correctly reflects LBNL's status as a national research facility. The name continues to honor the late Nobel prizewinner Ernest Orlando Lawrence, inventor of the cyclotron that spawned modern high-energy physics research, the discovery of many new elements, and nuclear medicine. At this time, "lbl.gov" electronic mail addresses remain valid.

4. HOVERING PLATFORM INSTALLED AT BEAMLINE 8.0
(contact: hill20@llnl.gov)

At several ALS beamlines, there are a number of user groups who share beamtime and use different endstations. In such situations there is a need for devices that will allow the photon beam to be switched easily from one endstation to another without breaking vacuum. This can often be accomplished in a matter of minutes, compared to hours for the dry tent process (which breaks vacuum but prevents the introduction of moisture into the beamline) or days for bakeout (required if vacuum is broken and any moisture reaches the inside of the beamline or endstation). So far exchanges under vacuum have been accomplished in at least two ways at the ALS. At several existing or planned beamlines, "pop-up" mirrors or other adjustable optics direct the beam into one endstation or another while the endstations remain stationary. A large rotating platform on wheels at Beamline 9.3.2 holds two endstations, either of which can be rotated into the beam. A new device called the Rotating Experiment Platform, installed in May at Beamline 8.0, accomplishes the same task without wheels by using hover craft technology.

The platform, designed by Randy Hill of Lawrence Livermore National Laboratory, was required to meet several design criteria. It had to position endstations accurately and repeatably, isolate the endstations from extraneous vibration, extend no more than 25 cm above the floor, and operate easily and reliably on an uneven floor surface, all at low cost.

The most noticeable features of the platform are the pneumatic bearings that bear its weight while it moves. These are circular pieces of thin rubber, joined around their edges and at their centers to the undersides of metal plates at the corners of the platform. When air is pumped into the bearings, they inflate, taking the shape of large doughnuts and jacking the platform off the floor. A hole toward the center of each rubber sheet lets air flow into the "doughnut hole" space in the middle of each bearing. As the air escapes between the rubber and the floor, it creates a film of air less than 0.03 mm thick on which the platform hovers, enabling a single individual to move several tons of equipment with ease.

Once the endstations are in the desired position, the pneumatic bearings deflate, setting the platform back down on the floor. The endstations, whose feet are slightly taller than the platform (which is 15 cm tall), decouple from it and bolt to the floor when they are not being moved. This scheme gives the endstations seismic stability, isolation from vibrations of other endstations, and positional accuracy of better than 0.5 mm (this accuracy is determined by the fit of the bolts holding the endstations to the floor).

The platform is built of 6-inch (15 cm) aluminum I-beam, joined in a grid pattern with steel plates and high-strength bolts. Its flexible structure is free to twist as it traverses the uneven floor surface. Thin plates of mylar-coated steel are bonded to the floor beneath the pneumatic bearings to give a suitably smooth, low-cost, easily repairable surface. These inexpensive materials were fabricated off-site and assembled at the ALS with pneumatic wrenches.

5. LONG-TERM SCHEDULE OUTLINE THROUGH SEPTEMBER 1995
(contact: fred_schlachter@lbl.gov)

In response to your requests in our reader survey, here is a week-by-week summary of ALS user operations through the beginning of our next shutdown. Our typical schedule now is 10 user shifts per week (08:00-23:15 on Wednesday through Sunday). During some weeks of this period, there may be 9 user shifts as the Accelerator Physics group completes testing of the longitudinal and transverse feedback systems. Other unusual numbers of shifts are noted below. Unless otherwise noted, 1.5- and 1.0-GeV operation are 320 bunches at 400 mA, and 1.9-GeV operation is 320 bunches at 250 mA.

June 28-July 3: 1.5 GeV (12 shifts)
July 7-9: 1.9 GeV (6 shifts)
July 12-16: 1.9 GeV 
July 19-23: 1.5 GeV
July 26-30: 1.0 GeV
August 2-6: 1.0 GeV
August 9-13: 1.5 GeV
August 16-20: 1.5 GeV
August 23-27: 1.5 GeV, two-bunch, 40-mA
August 30-September 3: 1.0 GeV
September 5-11: 1.5 GeV, two-bunch, 40-mA (14 shifts)