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.

Previous Issues are available.


ALSNews           Vol. 34           August 22, 1995

Table of Contents


    1. OPERATIONS UPDATE
    2. FEEDBACK SYSTEM RUN DURING USER SHIFTS
    3. EDITORS TAKE A BREAK, NOT A HOLIDAY

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

Beam availability for the last two weeks was 93.1% overall and 90.8% during user shifts. Causes of lost beamtime included three beam dumps due to Beamline 10.3.2 hutch interlock trips, rf system trips, and more frequent refills due to shorter beam lifetime with feedback on.

Note: The operating energy for 2-bunch operation this week has been changed to 1.9 GeV, instead of 1.5 GeV which was originally scheduled.

Operations summary for August 22 - September 11
1.9-GeV, 2-bunch operations for users, feedback on:
    August 23, 08:00-16:00
    August 24-27, 08:00-23:15
1.0-GeV, 400-mA, 320-bunch operations for users:
    August 30, 08:00-16:00
    August 31-September 3, 08:00-23:15
1.9/1.5-GeV, 2-bunch operations for users (the exact schedule of operating
energies will be determined at the weekly scheduling meeting):
    September 5-11, 08:00-23:15
Accelerator Physics:
    August 22 & 29, 08:00-23:15
    August 23 & 30, 16:00-23:15
Maintenance:
    August 28, 08:00-16:00, with startup 16:00-23:15
Holiday:
    September 4, Labor Day

Weekly scheduling meeting: Fridays, 3:30 p.m. in the Building 6 conference room.

2. FEEDBACK SYSTEM RUN DURING USER SHIFTS
(contact: r_keller@lbl.gov)

Last week the ALS reached a new milestone in performance by running the multibunch feedback system during user operations for the first time. The feedback system acts to decrease the energy spread and therefore the horizontal size of each bunch, and it produced a much brighter and more stable beam than was available before the feedback system's commissioning. High-brightness operation is beneficial for many ALS experiments, especially microscopy and high-resolution spectroscopy. However, because smaller bunches have higher electron densities, the Touschek effect (scattering of electrons within the same bunch) shortens the beam lifetime.

In their preparatory shifts, accelerator physicists had found they could increase the time between fills from 30-45 minutes to just over three hours while retaining a significant gain in brightness. They did this by moving the working point (a combination of the betatron tunes, which describe the oscillations of the electron beam as it circles in the storage ring) near the coupling resonance, thereby increasing the beam size and decreasing charge density and brightness. Still longer uninterrupted working time was achieved during one shift by allowing the beam to decay below the normal refill point of 200 mA.

The accelerator group's next goal in improving feedback-aided operation will be to match the optimal working point to the full range of undulator gap conditions. When undulator gaps change during user operation, different working points are required to provide maximum beam lifetime. Prior to last week, however, the accelerator group had found the best working point only with all undulators at their minimum gaps, so they made the necessary adjustments by hand.

The ALS feedback systems were developed in collaboration with a group from Stanford Linear Accelerator Center under John Fox and a group from LBNL's Center for Beam Physics led by John Corlett and Walter Barry.

3. EDITORS TAKE A BREAK, NOT A HOLIDAY

The writers of ALSNews are busy putting the finishing touches on the ALS Activity Report for 1994, and, in a quest to preserve some sanity, have limited this edition of ALSNews to vital information only. This year's Activity Report is designed to provide an overview of the ALS scientific program for 1994-1996, as well as to highlight some of the most important achievements and R&D activities of the ALS. If all goes as expected, the publication will go to the printer in early September for October delivery. Copies will be available at the ALS Users' Association Annual Meeting on October 23-24.