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ALSNews           Vol. 14           February 28, 1995

Table of Contents


    1. HIGH-QUALITY BEAM FOR USER OPERATIONS DELIVERED ON SCHEDULE
    2. OPERATIONS SUMMARY FOR FEB. 28 - MAR. 15
    3. ALS GAINS SELF-SUFFICIENCY IN SURVEY & ALIGNMENT

1. HIGH-QUALITY BEAM FOR USER OPERATIONS DELIVERED ON SCHEDULE
(contact: robin@lbl.gov)

With scarcely a glitch, the ALS delivered beam for user operations on Feb. 22 as promised. The beam lifetime at 400 mA is now better than 8 hours and improving daily. These accomplishments are during a period when the operations crew has been making the transition to a new weekly operations schedule that requires the machine to be "started up" on Wed-Sun before the day shift begins (see Operations Summary below). The control room operators have already reduced the startup time for the machine each morning down to less than one hour, an exceptional achievement.

The nearly "instant success" of the startup is primarily due to the hard work of the ALS Operations, Accelerator, and Mechanical and Electrical Engineering Groups, who have coordinated their efforts during the last few weeks to characterize post-shutdown ALS machine performance, make improvements as required, and restore quality beam. Here are a few of their results.

**CLOSING BEAMLINE 7.0 UNDULATOR TO MINIMUM GAP**
During the shutdown a narrow-gap vacuum chamber was installed in straight section 7, allowing the undulator gap to close to 14 mm (this limit was 23 mm before the shutdown). With 25 mA of beam in the storage ring, the undulator gap was reduced from 210 mm to 14 mm. The beam remained stable, with a lifetime of over 10 hours.

**NEW CATHODE PERFORMANCE**
A new electron gun cathode was installed during the shutdown. The gun, which is pulsed once every second, can run in two different configurations: 1 bunch/pulse mode and 4 bunch/pulse mode. Measurements showed a current yield of about 1 nanocoulomb per bunch for the new gun, at least 10% greater than the yield of the old cathode.

**BOOSTER AND STORAGE RING INJECTION EFFICIENCY**
In 1 bunch/pulse mode the booster is capturing and accelerating about 75% of the injected beam from the linac to 1.5 GeV. In 4 bunch/pulse mode this figure is about 50%. The injection efficiency from the booster to the storage ring is about 50% in both modes. This gives a storage ring fill rate of about 0.5 milliamps/second in single-bunch mode and 1.5 mA/s in 4-bunch mode. Producing these results required a careful energy matching of booster to storage ring transfer line, as well as a good vertical orbit through the new narrow-gap chamber in the Beamline 7.0 undulator. Future studies will aim to improve the capture and acceleration efficiency of the booster and storage ring.

**BEAM ORBIT**
The orbit of the electron beam in the storage ring has shifted somewhat relative to its position before the shutdown. The most likely cause is ground motion in the vicinity of straight 7, where shielding blocks and the undulator were moved during the shutdown. Orbit corrections have brought the beam orbit back to displacements (relative to beam position monitors) similar to those existing before the shutdown.

2. OPERATIONS SUMMARY FOR FEB. 28 - MAR. 15
(contact: rmmiller@lbl.gov)

The new weekly operations schedule is in effect. The 9 shifts of user operations are now during day and swing shifts only (no owl shifts) as per user request.

Reminder: Weekly operations scheduling meetings take place in the Building 6 conference room at 11:00 a.m. each Monday.

1.5-GeV, 400-mA, 320-bunch operation for users:
    Wednesdays, 16:00-23:15
    Thursday-Sunday, 08:00-23:15
Maintenance:
    Mondays, 08:00-16:00 with startup Monday evening 16:00-23:15
Accelerator Physics:
    Tuesdays, 08:00-23:15
    Wednesdays, 08:00-16:00

3. ALS GAINS SELF-SUFFICIENCY IN SURVEY & ALIGNMENT
(contact: g_krebs@lbl.gov)

The ALS Survey and Alignment Group, using new and innovative technology, is no longer dependent upon outside help in surveying the ALS reference coordinates. In its earlier days, the ALS relied on the Precision Alignment Group from Stanford to make surveys of ALS monuments, the 100-plus markers in the ALS floor which form the basis for precision alignment of storage ring and beamline components. (This network of monuments is essential for maintaining proper storage ring alignment, which contributes to longer beam lifetimes, and for accurately aligning new beamline components. Careful initial alignments, coupled with high-quality design and engineering, have allowed ALS beamlines to obtain publishable data within days of their first commissioning efforts.) Now, however, the ALS has developed its own solutions to the demands of such large surveys, allowing survey work to proceed as the needs of the ALS dictate.

In preparation for the most recent monument survey, ALS survey and alignment staff designed and developed the monopod, a carbon-cylinder-based surveying stand which decreases the time required for monument surveys while increasing their accuracy (for more on monopods, see ALSNews Vol. 7, Dec. 13, 1994). The mekometer, an electronic laser distance meter, keeps long-distance measurements superbly accurate, and precision theodolites measure horizontal angles to 1/3-arc-second resolution. A computer program called StarNet facilitates the task of processing the large number of measurements necessary for a monument survey. StarNet uses a least-squares fit to determine the location, horizontal error ellipse, and vertical error bar for each monument. The results of this fit for the recently completed monument survey were outstanding: the typical error was 70 microns or less for storage ring monuments, compared with a storage ring diameter of 60 meters.