There may be no user beamtimes at DESIREE during the summer months, but that doesn’t mean that nothing is happening! Summer is a busy period for machine upgrades and maintenance. It takes a full month just to bring the inner DESIREE vacuum chamber up to room temperature and back down to 13 K again, so every detail must be carefully planned to minimize downtime and maximize availability to users.
This summer, in addition to routine maintenance, a few notable upgrades were made to the DESIREE storage rings that may be of interest to users. These upgrades are intended to improve the measurements of stored ion beam currents i.e. the number of ions still circulating in the rings at the end of one injection cycle. These measurements are important for normalizing user data for shot-to-shot variations in injected ion current, deriving absolute cross sections, and confirming the long-time stability of ions which may have low neutral yields.
Up until now, these measurements have been performed by dumping the beam into one of two Faraday cups (labeled FCS and FCA in the picture above) located near the injection deflectors at the end of each cycle. These deflectors have been replaced with new ones of an improved design. This will eliminate the possibility of the ion beam being partially scattered off the edge of the deflector plates, instead of into the Faraday cup. This will improve the accuracy of beam current measurements for most users. Deflector plates of a similar design were installed last summer on the merging section, which was found to improve flexibility in steering the beams into and out of that section.
Speaking of the merging section, the other beam-current related upgrade this year saw fortified electrical feedthroughs connected to the “de-merging” deflectors following the merging section. This will enable users to rapidly switch the voltages on these deflectors, just like the injection deflectors currently. For very low ion currents, for example at the end of a long storage cycle, users will now be able to dump the beam onto one of the MCP detectors (the Imaging Detector ID or the Fragment Detector FD), which have far greater sensitivity than the Faraday cups.
These upgrades will open new possibilities for users to more accurately measure the current of their stored ion beams in DESIREE.