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.5           November 29, 1994

Table of Contents


    1. ADMINISTRATIVIA  
    2. OPERATIONS OVERVIEW  
    3. BEAMLINE BREAKTHROUGHS
    4. SINCE YOU ASKED
    5. TIMELY TOPICS

1. ADMINISTRATIVIA
(contact: alsnews@lbl.gov)

The first few issues of ALSNews are being sent to a standard distribution list of people we thought might be interested in subscribing. In early December, only those persons who have asked to be placed on the permanent newsletter distribution list will continue to receive ALSNews. If you haven't responded yet, please email alsnews@lbl.gov and include your complete internet address in the body of the message. We would also appreciate receiving suggestions for the information or topics you would like to see covered in ALSNews.

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

Maintenance time for December will be two days per week, to minimize the length of the January shutdown by completing some tasks early. Weekend user operations have been scheduled to offset the additional maintenance days.

Operations for Wednesday, Nov. 30, through Wednesday, Dec. 14:
Standard 320 bunch, 400 mA operation for users:
    Nov. 30, 08:00-24:00
    Dec. 1-2, 08:00-24:00
    Dec. 8-10, 00:00-24:00
One/two-bunch operation:
    Nov. 30, 00:00-08:00
    Dec. 1-2, 00:00-08:00
Maintenance and startup:  Mondays and Tuesdays
Accelerator physics: Dec. 7 and 14

3. BEAMLINE BREAKTHROUGHS

**ULTRA-HIGH-RESOLUTION SPECTRA FROM BEAMLINE 9.0.1**
(contact: berrah@wmich.edu)

Measurements using double-bunch operation have been conducted by a group led by Nora Berrah (Western Michigan U.) on the atomic and molecular physics branch of Beamline 9.0.1. The two-bunch timing structure was needed since their experiments were carried out using up to three time-of-flight spectrometers (see Item #4 below for descriptions of two-bunch mode and time-of-flight methods). The electron signal triggered the experiment's time-to-amplitude converter, while the ring timing signal provided the stop signal.

Berrah's group obtained high-resolution measurements with 5-meV steps, impossible to achieve without the brightness of the ALS and the high resolution of the monochromator. Specifically, they measured autoionizing resonances in Ne, Ar, Kr, and Xe along with new measurements of the electron angular distribution. They also made the first measurement of the Xe 4d(-1)6p --> 5p(-2)6p resonant Auger transition using the Auger resonant Raman effect. The group's measurements are essential for a better understanding of electron correlation in systems other than He.

4. SINCE YOU ASKED

**MOTIVATIONS FOR ONE/TWO/FEW-BUNCH OPERATION**
(contact: fred_schlachter@lbl.gov)

Have you been wondering about the shifts scheduled for one/two bunch operation? Here's some background on why this mode is useful for research. "Few-bunch" refers to the mode in which the storage ring contains only one, two, or a few bunches of electrons, usually at 20 mA per bunch, instead of the usual 320 bunches at a total of 400 mA ("multi-bunch mode"). Beam lifetime in two-bunch mode is a few hours at the coupling resonance (with reduced brightness) or about 40 minutes at maximum brightness. ALS operators can fill any pattern of bunches in the storage ring's 328 "buckets." Accelerator physicists are working to improve single-bunch purity by reducing the current in supposedly empty buckets adjacent to filled buckets.

Few-bunch operation is used for time-of-flight (TOF) experiments, in which one detector records an event (e.g., the ionization of an atom) and a second detector some distance away records the arrival times of particles (e.g., electrons) generated by that event, yielding a complete energy spectrum of ejected particles. Using this approach considerably reduces background noise levels compared to using electrostatic or magnetic spectrometers with the storage ring in multi-bunch mode. TOF methods can be used to determine charge states or charge-to-mass ratios of ions produced by x rays bombarding atoms or molecules; in this case the ions are generally accelerated in an electric field. TOF has been used at other facilities to determine the ratio of double to single ionization of helium, important in studying electron correlation. Item #3 above describes some of the first TOF results to come from the ALS.

5. TIMELY TOPICS

**HALBACH SYMPOSIUM ON MAGNET TECHNOLOGY**

Ever wondered whom you should thank for all those great insertion device x rays? Start with Klaus Halbach, the primary force behind today's permanent magnet wigglers and undulators. To honor Klaus, the ALS is sponsoring a special Halbach Symposium on Magnet Technology on February 3, 1995--with a day long symposium of scientific and informal talks, the release of a volume of his famous notes, and a festschrift in his honor written by the alumni of the Halbach Institute of Technology. (The festschrift is a tradition in which the students and colleagues of an individual of distinction publish a volume of their creative work and dedicate it to him.)

For more information contact
ALS Administration
Re: Halbach Symposium
Lawrence Berkeley Laboratory, MS 80-101
Berkeley, CA 94720
Fax: (510) 486-4960

Writers: jccross@lbl.gov, deborah_dixon@macmail.lbl.gov