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. 32           July 25, 1995

Table of Contents


    1. LAST CHANCE-- 1995 USERS' MEETING T-SHIRT DESIGN CONTEST
    2. OPERATIONS UPDATE
    3. NEW INJECTION PROCEDURE PROVIDES MORE USER BEAMTIME

1. LAST CHANCE-- 1995 USERS' MEETING T-SHIRT DESIGN CONTEST
(contact: jccross@lbl.gov)

Just a friendly but urgent reminder that August 1 is the deadline for designs for ALS T-shirts to be available at this years Users' Meeting.

T-shirt designs should be no larger than 22 cm high by 28 cm wide (8.5 by 11 inches) and should use four or fewer colors. Rough drawings or concepts are acceptable as well as more polished artwork.

Send your designs to:
Jane Cross
Advanced Light Source
Lawrence Berkeley Laboratory, MS 2-400
1 Cyclotron Road
Berkeley, CA 94720
or fax to Jane Cross at (510) 486-7696.

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

Beam availability for the last two weeks was 94% overall and 93% during user shifts. Causes of the brief loses of beamtime during user shifts were problems with a booster rf auxiliary power supply and a fuse in one storage ring magnet power supply, front end water flow adjustments on beamlines 7.0 and 9.0, and a beamline interlock trip.

Operations summary for July 25 - August 13
1.0-GeV, 400-mA, 320-bunch operations for users:
    July 26, 08:00-16:00
    July 27-30, 08:00-23:15
    August 2, 08:00-16:00
    August 3-6, 08:00-23:15
1.5-GeV, 400-mA, 320-bunch operations for users:
    August 9, 08:00-16:00
    August 10-13, 08:00-23:15
Accelerator Physics:
    July 25 and August 1 & 8, 08:00-23:15
    July 26 and August 2 & 9, 16:00-23:15
Maintenance:
    July 31 & August 7, 08:00-16:00, with startup 16:00-23:15

3. NEW INJECTION PROCEDURE PROVIDES MORE USER BEAMTIME
(contact: ajackson@lbl.gov)

A new injection procedure in use at the ALS is providing 25-50 more minutes of beam per shift, a significant improvement in the availability of beam for users. The new procedure stems from experiments performed during the April-May accelerator outage to determine the outage's cause and restore beam.

For several months, for reasons that are not fully understood, the ALS had experienced a gradual decline in injection efficiency (the percentage of electrons from the booster that make it into orbit in the storage ring) at the magnet settings for storing user beam. In early 1995, accelerator physicists adopted a temporary solution, using an "injection tune" (produced by a group of storage ring magnet settings designed to provide good injection efficiency) to fill the machine, and then changing to the "user tune" in a way that ensured repeatable orbits for users. The disadvantage of this procedure was that each time an electron fill was required, operators had to dump the entire electron beam, cycle the storage ring magnet currents to the "injection tune" settings, fill the ring, and ramp the magnet currents to the user tune. This process could take up to 30 minutes.

Experiments performed during the outage showed that the booster and storage ring energies were not exactly matched, and that steering the stored beam closer to the injected beam in the injection straight could improve injection efficiency. Using these two pieces of information, accelerator physicists have produced injection efficiencies of better than 80% into the "user tune" (injection efficiency under the old, two-tune system was 30-50%). This has two major effects on accelerator operation: the high injection efficiency means that beam can now be injected in five minutes or less, and the ability to inject into the "user tune" means that beam dumping and magnet cycling are no longer necessary. New fills simply add more electrons to those already circulating in the ring.

If you like a good experiment story, read on to see how the key discoveries were made...

Betatron tunes (loosely defined as the number of times a perturbed electron beam oscillates vertically or horizontally in one trip around the storage ring), which affect beam size and stability, are routinely measured using stored beam. During the outage, however, the obstruction caused by the broken flex band prevented beam from being stored, so tune measurements were made on beam as it was injected (for the story of the outage investigation, see ALSNews Vols. 25 and 26, May 16 and 23, 1995). Accelerator physicists later matched the booster and storage ring energies by adjusting the booster energy until the tunes for injected and stored beam were the same.

The electron orbit that finally allowed beam storage, ending the outage, contained a global orbit distortion that caused it to oscillate around the normal electron orbit. Accelerator physicists began superimposing "local bumps" (orbit shape distortions affecting a single area of the ring) on the distorted orbit in various parts of the ring, "ironing out" those parts of the orbit to match the normal orbit. When they did this in sector 2, the stored beam disappeared; the distortion was necessary at that location to miss the obstruction. When they "ironed out" the distortion in sector 1 (the injection straight), injection efficiency decreased; the distortion in that part of the storage ring increased injection efficiency by bringing the electron orbit closer to the injection septum. Therefore, after the outage, a single local bump in the injection straight was introduced into the normal orbit to achieve the same effect.