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. 46           February 21, 1996

Table of Contents


    1. OPERATIONS UPDATE
    2. ALS USERS' HANDBOOK WINS PUBLICATION AWARD
    3. FUN AND FASCINATING FACTS
    4. DATE SET FOR 1996 ALS USERS' MEETING

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

Beam availability for the last two weeks was 89% overall and 93.2% during user shifts. Causes of lost beamtime included problems with a bend-magnet power supply on the booster-to-storage-ring transfer line (diagnosed and repaired) and loose connections on a 480-V circuit breaker panel feeding several storage ring power supply and vacuum equipment racks (inspected and re-tightened). Most lost beam time occurred during accelerator physics shifts.

Operations Summary for February 21 - March 11

Feb 21, 00:00-16:00           Accelerator Physics
Feb 21, 16:00- Feb 26, 07:15  1.5-GeV/400-mA/320-bunch user operations
Feb 26, 07:30-24:00           Maintenance & Startup
Feb 27, 00:00-24:00           Accelerator Physics
Feb 28, 00:00-08:00           User Scrubbing & Special Operations
Feb 28, 08:00- Mar 04, 07:15  1.9-GeV/260-mA/320-bunch user operations
Mar 04, 07:30-24:00           Maintenance & Startup
Mar 05, 00:00-24:00           Accelerator Physics
Mar 06, 00:00-08:00           User Scrubbing & Special Operations
Mar 06, 08:00- Mar 11, 07:15  1.5-GeV/400-mA/320-bunch user operations

Weekly operations scheduling meetings: Fridays at 3:30 p.m. in the Building 6 conference room.

2. ALS USERS' HANDBOOK WINS PUBLICATION AWARD

The ALS Users' Handbook received a Distinguished Technical Communication award (the highest level of award possible) in the "Non-Computer User Documents" category in the Northern California Technical Communication Competition held February 10. The competition, which attracts over 300 publications and online entries from throughout the region, is an annual event sponsored by the Society for Technical Communication (STC). The publications are judged on clarity, precision of language and thought, organization of material, and effectiveness of page layout and graphics. The handbook was a team effort of Jane Cross, Deborah J. Dixon, Joan Minton, Elizabeth Moxon and Greg Vierra (graphic design), all of the ALS.

Winners of the Distinguished award are entered in the STC international competition which will be held in May 1996. Another ALS brochure, "The Advanced Light Source - America's Brightest Light for Science and Industry" received an award of excellence in last year's international competition.

3. FUN AND FASCINATING FACTS

** HOW STRONG ARE THE PERMANENT MAGNETS AT THE ALS? **

To get a sense of their strength, imagine pulling a typical refrigerator magnet off your freezer door. For a pretty strong one, this takes a force of about 2.7 newtons (about half a pound, or the weight of a 0.27-kg object). By comparison, if the upper and lower magnetic structures of the wiggler soon to be installed for beamline 5.0 were placed 14 mm apart (their minimum gap), it would take a force of almost 170,000 newtons (38,000 pounds) to separate them--over 63,000 times as much force! ALS physicists and engineers don't even like to think about what would happen if we let the magnets touch--this could result in damage to their magnetic properties, so wigglers and undulators are engineered with sturdy structures to hold the magnets apart against extremely large forces.

For you physicists, the peak field of the wiggler at minimum gap is 20,000 gauss or 2 T, and we assumed a field of 1000 gauss for the refrigerator magnet.

** HOW POWERFUL IS THE ALS? **

The heat flux from an ALS undulator beam is about equal to that inside a rocket nozzle. The following table shows approximate heat flux levels for various processes.

                            Approximate heat flux
Process                           W/mm**2

Meteor entering atmosphere        100-500
Fusion reactor components         0.05-80
Sun's surface                     60
Commercial plasma jet             20
Interior of rocket nozzle         10     <---- ALS
Fission reactor cores             1-2

** WHAT ARE WE DOING TO THOSE ELECTRONS? **

If you've ever wondered just what we are putting those electrons through in the ALS, here is an account of their energies, speeds, and cumulative distances traveled.

             At end of       At end of        At end of       After 4 hours
             electron gun    linac            booster cycle   in storage ring

Time (s)     400 billionths  800 billionths   0.33            4 hours
Distance     1 m             5 m              98,000 km       4.32 billion km
Speed (%c)   59.5            99.9948          99.999994       99.999994
Energy (eV)  120,000         50 million       1.5 billion     1.5 billion

** WHY DOES THE ALS SPEND SO MUCH TIME VACUUMING? **

When we check for vacuum leaks in the ALS, we look for leaks so small that if a car tire had one, it would take 10,000 years for the tire to go flat. Why? Well...the scattering cross section of a high energy particle is so high that the ALS electron beam would propagate only a few meters in atmosphere because of the number of collisions with air molecules etc. the beam would experience. Thus, to maximize electron beam lifetime (i.e., keep collisions to a minimum), the ALS vacuum system is designed to maintain a very low pressure inside the vacuum chamber. In fact, the ALS vacuum chamber has fewer atoms per unit volume in it than there are in outer space, i.e., the pressure (approx. 1e-9 torr) is about one trillionth that of the atmosphere. The ALS vacuum is so good that improving it would have almost no effect on beam lifetime; lifetime is chiefly limited by intra-bunch scattering of electrons (the Touschek effect), not by electrons scattering from gas molecules.

To manufacture the final vacuum chamber sections, each half of the 12 full-sized vacuum-chamber sectors was cut from a single sheet of aluminum 10 cm thick, 1.5 meters wide, and 10 meters long. Each of the 24 sheets needed cost $17,500. Scraps from the sheets were used to make the vacuum chambers and magnet mounting frames for ALS insertion devices. The machining costs were $900,000 (not including welding the two halves together, cleaning in preparation for vacuum, etc.).

4. DATE SET FOR 1996 ALS USERS' MEETING

The annual meeting of the ALS Users' Association Meeting has been set for Monday and Tuesday, October 21-22, 1996. This meeting provides an opportunity to hear about new science from the ALS and about progress in refining and augmenting the tools available at this national user facility. ALSNews will carry more information about registration for the meeting in future months. Mark your calendars now!