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ALSNews           Vol. 49           April 3, 1996

Table of Contents


    1. OPERATIONS UPDATE
    2. APRIL 16 POWER OUTAGE ON EXPERIMENT FLOOR
    3. BIOLOGISTS CONFIRM EXISTENCE OF NEW CELL STRUCTURES
    4. ALS OPENS STOCK ROOM FOR USERS
    5. REMINDER: USERS' TOWN MEETING APRIL 12

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

Beam availability for the last two weeks was 87% overall and 85.5% during user shifts. Causes of lost beamtime included component failures in the linac modulator #1 high-voltage system.

Operations Summary for April 3 - April 15

Apr 03, 00:00- Apr 08, 07:15  1.9-GeV/260-mA/320-bunch user operations
Apr 08, 07:30-24:00           Maintenance & Startup
Apr 09, 00:00-24:00           Accelerator Physics
Apr 10, 00:00- Apr 14, 24:00  1.5-GeV/400-mA/320-bunch user operations
Apr 15, 00:00-08:00           Accelerator Physics

The last weekly operations scheduling meeting before the shutdown will take place Friday, April 5, at 3:30 p.m. in the Building 6 conference room.

Owl shift on April 15 has been changed from user operations to accelerator physics. The reason for taking this particular shift is to perform an experiment that requires partial venting of the storage ring vacuum system. The experiment will probe an instability, known as the fast ion instability, which gets progressively worse as storage ring pressure increases. The goals are to identify the characteristic signature associated with the instability and to study how the instability varies as the gap in the bunch train is changed.

** FEEDBACK-ON OPERATION NOW DEFAULT AT 1.5 GeV **
The default operating condition for the ALS now includes coupled-bunch feedback at 1.5 GeV. The feedback-on lifetime is 2 hours 50 minutes at the maximum current of 400 mA. The comparable lifetime with feedback off is about 8 hours. Feedback-on operation narrows the energy range of storage-ring electrons, thereby increasing spectral brightness. Feedback-off operation can still be provided at user request.

2. APRIL 16 POWER OUTAGE ON EXPERIMENT FLOOR
(contact: rkthatcher@lbl.gov)

All electrical power to the experiment floor will be shut off from 7:00 a.m. to noon on Tuesday, April 16 for circuit breaker and maintenance work. All computers and beamline systems should be secured before 7:00 a.m. Users with questions, please contact Ray Thatcher (x7412).

3. BIOLOGISTS CONFIRM EXISTENCE OF NEW CELL STRUCTURES
(contact: Tony Stead, UHBT003@alpha1.rhbnc.ac.uk)

Using the XM-1 transmission x-ray microscope at the ALS, researchers from the University of London and LBNL have confirmed the existence of newly found cellular structures in Chlamydomonas, a unicellular green alga. These are the first cellular structures that scientists have been able to visualize only with soft x rays. Since the investigators had previously seen them with soft x-ray contact microscopy, but not with electron microscopy, the observations on Beamline 6.1 verified the existence of these novel cellular inclusions.

Soft x rays are particularly useful for studying cell structure because they can give better resolution than visible light and do not require the extensive tissue preparation that electron microscopy demands. X-ray photons in a specific energy range, known as the "water window," are absorbed by carbon but not by oxygen. Thus, many carbon-containing structures within a cell, such as plastids, are more x-ray dense (more x-ray absorbent) in this range than the surrounding cytoplasm. Furthermore, structures such as vacuoles, which contain only dilute solutions of carbon-based molecules, should be more x-ray lucent (transmitting more x rays) than the cytoplasm.

When imaging living material with soft x rays, one must consider the possibility of radiation damage to the specimen, especially if the exposure times are long. Here the XM-1 offers a key advantage over other soft x-ray microscopes. Imaging times as short as a few seconds are made possible by the high photon flux available at the ALS. The recent experiments with Chlamydomonas tested the ability of the XM-1 to image the alga before radiation damage became evident. Comparison of images taken with varying exposure times showed that the likelihood of the images being influenced by radiation damage was minimal as long as the exposures were less than 2 seconds.

The Chlamydomonas cells appeared to contain several x-ray-dense spheres that were not seen with conventional transmission electron microscopy. Each of these was about 1 to 2 microns in diameter. In some cases, the pressure within the holder used to mount the biological material was sufficient to cause the cells to burst and the spheres to be released. The fact that the spheres remained intact suggested that they were membrane bound. The newly found structures proved to be very sensitive to radiation while still in the cell. When isolated from the cell, they were even more radiation sensitive; exposures of 2 seconds already showed signs of radiation damage, and a 4-second exposure completely destroyed the spheres. The function of these structures remains a mystery, but since they are significantly more x-ray dense than the surrounding cytoplasm, it is very unlikely that they are vacuoles.

In future experiments at the ALS, the researchers hope to gain more information about the possible function of these structures by following their fate during the cell cycle and investigating the effects of changes in the conditions used to culture the algae. The addition of a cryo-stage to the XM-1 (scheduled for the April-May shutdown) will allow examination of frozen biological samples, which should be much less radiation sensitive.

This work was done by A.D. Stead (principal investigator) and T.W. Ford (Royal Holloway, University of London) and W. Meyer-Ilse and J.T. Brown (Center for X-Ray Optics).
Supported by the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.

4. ALS OPENS STOCK ROOM FOR USERS
(contact: rkthatcher@lbl.gov)

The ALS now has a stock room from which users can purchase commonly needed equipment. The current stock consists mostly of beamline vacuum parts (flanges, gaskets, tees, etc.). Ray Thatcher (email: rkthatcher@lbl.gov; phone: x7412) and the Operations Coordinators (x7464) welcome users' suggestions for items to add to the stock room supply.

Users with access to the AppleTalk network and Microsoft Excel can access a listing of the stock room inventory with prices. In AppleShare, select "als" zone, "USER INFO" file server (sign on as guest), "USER INFORMATION" volume, Stockroom Folder. There is also a printout of the list posted in the User Services Area near Beamline 9.0.1, or users can request a printout from Ray Thatcher. To make a purchase, contact Ray or an Operations Coordinator, and have an account number ready.

5. REMINDER: USERS' TOWN MEETING APRIL 12

A meeting of ALS management, users, and the ALS User Executive Committee (UEC) will occur on April 12, 1996, 9:00 - 10:30 a.m. in the Building 4 conference room. Please send any issues you may wish to raise at the meeting to UEC Chair Jeff Bokor (jbokor@eecs.berkeley.edu) in advance of the meeting.