by Ina Reichel
With all the changes due to COVID-19, it is no surprise that this summer’s ALS shutdown was also affected. It began later (August instead of July) and was shorter than originally scheduled (about six weeks instead of three months). The original two drivers of the shutdown—installation of new modulators for the linac rf and the storage ring alignment—were postponed. Nevertheless a number of smaller activities, many in preparation for the ALS Upgrade (ALS-U), were accomplished.
A long-term project to upgrade the fast orbit feedback progressed during this shutdown. The upgrade will increase the fast orbit feedback bandwidth from the present hundred Hz to kHz-class, allowing better control of the electron beam position in the ring and ultimately better photon position in the beamlines. In order to upgrade the orbit feedback, new vacuum chambers were installed in six corrector magnets. The old ones were aluminum, whereas the new ones are stainless steel, allowing changes to the magnetic fields from the corrector to penetrate faster through the wall due to their lower conductivity. Many chambers have already been installed during previous shutdowns. The final four will be installed in January 2021.
Other work included an upgrade of the sprinklers, swapping of the cold head on the spare superbend magnet, repairs to the kicker magnet system interlock, and the installation of new power supplies and cables for some ion pumps. Three-dimensional Matterport scans were also taken of the storage ring and some beamline areas (see previous examples here). Since in-person work is limited due to COVID work restrictions, these scans will help enable work planning remotely. There was also a surprise opportunity to replace the Gemini beamline’s photon stop with a dummy, which allowed the beamline to see light for the first time.
Work in preparation for ALS-U included electrical utility upgrades for the accumulator ring, RSS (radiation safety system) wireway installation, and core drilling and saw cutting for cabling. These are necessary to provide electrical power to the new accumulator ring for the upgraded ALS. The upgraded machine does not need a substantial increase in electrical power compared to the current ALS, but it needs it at different locations. In addition, some changes in code requirements necessitate additional routes for cables through the shielding walls. This work will be completed during the two-day shutdowns leading into the January 2021 shutdown when the RSS cabling will be installed in its new location.
The shutdown also provided an opportunity to attempt a repair of the large liquid nitrogen (LN) tank. The tank had been broken for awhile, leading to losses of LN. The repair required the tank to be empty, which is ideally avoided during user operations. While the problem was unfortunately not resolved, there is a steady supply of LN again, and another repair will be attempted in the January 2021 shutdown.
Overall the shutdown was successful despite complications due to COVID-19 protocols necessitating social distancing. Anyone who has ever been inside the storage ring can probably imagine some of the difficulties, like simply not being able to pass someone working on something and instead having to walk around the ring in the opposite direction to get to where one wants to get.