by Ina Reichel
Last week the ALS returned to user operations after its summer shutdown. A lot of work was accomplished, including several large projects in the storage ring and maintenance and updates for the accelerator and beamlines.
The biggest task was the replacement of part of the heating, ventilation, and air conditioning (HVAC) system in the storage ring as part of a larger HVAC upgrade. The old HVAC system has to be moved because it is located where the ALS-U accumulator ring needs to be installed, and the air handler units had reached their end of life and needed to be replaced. During this shutdown five of the nine air handlers and associated ducts were replaced. The remaining four will be replaced during the next shutdown. The team was also able to make many preparations on the now-vacated areas of the shielding wall for the future installation of the accumulator ring.
The radio frequency (rf) loads for the storage ring were replaced (the loads provide proper termination of the high frequency system). Once the system is commissioned, this will allow operation with two klystrons, which provide the rf power for the cavities in the ring. This will allow a beam current of 500 mA even with all insertion devices closed to minimal gap. (The smaller the gap, the more power they take out of the beam, requiring the klystron(s) to feed more power into the rf cavities.) Although the system has already been tested at low current, it still needs more tuning and testing before being fully operational.
The shutdown team addressed several other projects for the accelerator. They replaced the cold-heads of the three superbend magnets, which needs to be done every 18 months. The cold-heads help ensure that the superconducting magnets maintain their cold temperature and thus superconducting capabilities. In addition, the team aligned the magnet girders in Sectors 1 through 3, completing the recent set of realignment campaigns. This was the final scheduled alignment before the installation of the upgraded storage ring as part of the ALS-U Project. Synchrotron light sources usually have tight alignment tolerances. As equipment can settle over time, it is necessary to check the alignment every few years and adjust positions of elements where needed.
In a future shutdown, the power supply that feeds the main bend magnets in the booster ring will be replaced. Some prep work for this installation was done during this shutdown.
On the beamline side, the primary mirror (M101) for Beamline 4.2.2 was replaced, which will give the beamline up to two times more flux. Then, the Survey and Alignment team scanned the exit port in support of ALS-U beamline realignment.
The team also removed QERLIN’s mirror M201 as it caused some bellows to kink. For now, a spool piece (a piece of vacuum chamber with flanges at each end) sits in place, but new optics will be installed in a future shutdown.
Work was also performed on Beamline 5.3.2.1’s exit slits. The exit slits (and the entrance slits) are part of a feedback system that corrects for small movements of the electron beam by detecting the resulting fluctuations of the photon beam and adjusting a toroidal mirror. In-vacuum wires needed to be reattached to the exit slits.
Projects at other beamlines included the start of a cleanroom installation at Beamline 11.3.2, a shutter replacement at Beamline 7.3.3, and the adjustment/alignment of the M121 mirror and higher order suppressors at Beamline 11.0.1.
After the shutdown, but before returning to user operation, the Electrical Maintenance technical team performed the annual top-off interlock test. This is required to make sure beam can be safely injected with the beamline shutters open, as is done during the top-off mode of operation. This activity, which requires about three full days of work, was successfully completed, allowing the ALS to return to user operations as scheduled. Because of the COVID-19 pandemic, the ALS is still operating in a “restricted” mode with a limited number of users physically present at the ALS, and with others sending in samples for remote work.