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. 76           April 30, 1997

Table of Contents


    1. OPERATIONS UPDATE
    2. BEAM STABILITY AN ORDER OF MAGNITUDE BETTER THAN SPECS
    3. ELLIPTICALLY POLARIZING UNDULATOR MODEL COMPLETED
    4. ALS PROVES POPULAR AT CAL DAY OPEN HOUSE AND DAUGHTERS/SONS TO WORK DAY
    5. RESERVE YOUR COMPENDIUM NOW
    6. BEAMLINE INFORMATION ON THE WEB

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

Beam reliability for the last four weeks was 90.75% overall and 89.7% for user shifts. All outages were of short duration.

The ALS is in a planned shutdown for equipment installation and maintenance. (For details, see ALSNews Vol. 74, April 2, 1997.) User beamtime is scheduled to resume at 00:00 on June 10.

Weekly operations scheduling meetings will resume on Friday, June 6 at 3:30 p.m. in the Building 6 conference room. The Accelerator Status Hotline at (510) 486-6766 (ext. 6766 from Lab phones) features a recorded message giving up-to-date information on the operational status of the accelerator.

2. BEAM STABILITY AN ORDER OF MAGNITUDE BETTER THAN SPECS
(contact: r_keller@lbl.gov)

The ALS Stability Task Force continues to improve the stability of the electron beam. During the April 10 owl shift, beam position monitors in the ALS storage ring recorded its best electron-beam stability to date. The electron beam position was constant within about two microns vertically--ten times as good as the design specification--and within 20 microns horizontally--at least twice as good as the horizontal design value. This is the peak performance we can now reach without incorporating a closed-orbit feedback system. The keys to the high performance were improvement of the storage ring tunnel's air temperature control to about +/-0.1 degrees C (from 1 degree C) and avoiding other pitfalls such as crane movement and switching off the dipole magnets in the booster-to-storage ring transfer line.

With help from the Facilities Department, the Stability Task Force has also identified the cause of the "10-a.m. hump," one of the last remaining factors influencing the temperature stability of the storage ring tunnels. It is evidently caused by crosstalk between the Building 80 air-conditioning system and the tunnel air-chilling system. Adjustments to both systems appear to yield stable beam with no 10-a.m. hump.

3. ELLIPTICALLY POLARIZING UNDULATOR MODEL COMPLETED
(contact: s_marks@lbl.gov)

An elliptically polarizing undulator (EPU) magnetic model is now complete and under magnetic testing at the ALS. The purposes of this model are to commission a new magnetic measurement system, newly designed for measuring the magnetic fields of EPU-type insertion devices, and to develop techniques for identifying and correcting magnetic errors.

Two 5-cm-period EPUs (EPU5s, one of which is now under construction) and one 8-cm-period EPU will supply beams with variable polarization to Beamlines 4.0.1-2 and 4.0.3-4 (magnetic spectroscopy and magnetic microscopy), scheduled for availability in 1998. The model incorporates all the magnetic features planned for the full devices, including magnetic ends designed to prevent any net displacement or deflection of the electron beam. Its period length is 5.0 cm, and it has 6.5 periods, compared to 37.5 for the full EPU. The model and EPUs are the first ALS insertion devices to use a pure permanent-magnet structure (using neodymium-iron-boron magnets) rather than a hybrid structure with steel pole pieces between the magnetic blocks.

The EPUs can operate in a mode similar to that of existing insertion devices at the ALS to generate horizontally polarized light. Their special feature, however, is that their magnetic structure can be adjusted by users to generate vertically or elliptically polarized light, including circularly polarized light. This adjustment is manual in the model but will be automated in the full devices.

Generating high-quality light requires an extremely accurate magnetic structure. To bring this goal within reach, the EPU's design allows both for removal and/or interchangeability of periodic modules within the magnetic structure and for removal and adjustment of individual magnets within a module. Many field errors and optical phase errors can be corrected by selective swapping of periodic modules and mechanical shimming of individual magnet blocks.

The first phase of magnetic tests on the EPU model, now under way, includes commissioning a full-field integral measurement system and measuring the model's integral properties (those measured as sums over the full length of the device). Of particular interest are the effects of magnetic block adjustments on the magnetic field integral, and the degree of independence of the field integral with respect to the moveable quadrants' position. In the second phase of tests, a field scanning system for measuring local field effects will be commissioned. With this system, engineers will be able to establish the deflection and displacement properties of the model's magnetic ends and to measure local field effects due to magnet adjustment. This, in turn, will lead to procedures for magnetic tuning of the device.

4. ALS PROVES POPULAR AT CAL DAY OPEN HOUSE AND DAUGHTERS/SONS TO WORK DAY

The ALS was once again a highlight stop at the Cal Day Open House on April 19 at the University of California, Berkeley. More than 300 people ventured up the hill from campus to get an up-close look at the big machine. After an introductory talk by staff from the ALS and the Center for X-Ray Optics, visitors ventured on to the experiment floor where they had the opportunity to visit beamlines and talk to scientists about their research. The tour ended with the ALS's renowned "Cool Science Demo" team of Steve Lindaas and Tim Renner entertaining the crowd with fun science demonstrations that included everything from exploding bananas to bounceless rubber balls.

On Daughters and Sons to Work Day, April 24, nearly 400 children of Berkeley Lab employees took the opportunity to see their parents' workplaces and to take part in workshops around the Lab. As part of this special day, the ALS sponsored two workshops. In the first, after a quick introduction to the ALS and related hands-on activities, participants had an opportunity to interview people at work at the ALS with the goal of reporting on what they learned through the eyes of a technical communicator. Each communicator's curiosity took a different focus, from whether researchers like their jobs and what they do when the work gets tedious, to the particulars of an x-ray microscope's sample manipulation system, to how laser light is generated. In the second workshop, kids sporting safety goggles stalked the ALS floor with an eye toward potential safety hazards and warning signs. The discussion that ensued pointed out that for the most part the majority of the hazards that we have at the ALS are the same ones we have at home and school: slips, trips and falls, and electrical cords. The goal was to elevate the kids' safety awareness in their own environment.

Each participant went home with a deeper, more personalized knowledge of what goes on at the ALS; many thanks to the ALS employees and users who helped open the door to curious young minds!

5. RESERVE YOUR COMPENDIUM NOW
(contact: alsuser@lbl.gov)

The ALS Compendium of User Abstracts and Technical Reports for 1993-1996 is at the press, and now is your chance to arrange for copies to be sent to you and/or others in your research group. Representing three years' worth of results, the Compendium is over 600 pages, and we want to make sure it is distributed in an organized, cost-effective way.

The Compendium is designed to provide information useful to ALS users, prospective users, and others interested in the specifics of the ALS scientific program. It includes:

• 137 abstracts written by users, organized by beamline
• An index to abstracts by author and by general subject area
• Technical reports on various aspects of ALS operation, research, and development
• A list of publications related to work done at the ALS from 1993 to the present
• Technical information on each beamline (now also available on the Web; see item #6 below).

If you would like to receive a copy by mail, please send your name and complete mailing address via email to alsuser@lbl.gov with "Send Compendium" in the subject line. Compendium contact persons and active ALS users who have already requested a copy do not need to do so again.

6. BEAMLINE INFORMATION ON THE WEB
(http://www-als.lbl.gov/als/quickguide/index.html)

Tables of technical and contact information for each beamline (and many endstations) at the ALS are now available on the ALS web pages. The tables are designed to be a quick reference for current and prospective users and provide a convenient way to find out whom to contact for additional information. The tables can be accessed via the new Quick Guide for Users page.