The vacuum chambers of MAXIV are only 22 mm of diameter; the chamber size was chosen in order to fit inside the compact magnets of the storage ring. Due to the small diameter of the chamber, the conventional way of pumping using lumped pumps is not efficient nor practical, accordingly, the vacuum system of the 3 GeV storage ring is fully NEG (non-evaporable getter) coated vacuum system.
NEG coating provides the needed pumping and reduces the outgassing due to the photons hitting the chamber walls. For NEG coating to be pumping down it should be activated, activation means that the coating should be heated up to around 200˚C, consequently, any venting to atmosphere will cause the NEG coating to be saturated (can not pump) and should be followed with NEG activation to restore the coating performance. At MAX IV, in order to activate the NEG coating, a major intervention is needed, where the whole achromat (23 m) should be lifted and heated up inside an oven. Such an intervention would last from 2 weeks (if the achromat does not have insertion devices) up to 4 weeks (for achromats with insertion devices).
Neon venting is a procedure which has been used at LHC for interventions in the warm vacuum sections that are NEG coated, the procedure implies venting the chambers to atmospheric pressure using pure neon gas and keeping the sections at over pressure of neon gas during the intervention. Neon is a noble gas and it is not pumped down by NEG coating, and subsequently the performance of the NEG coating is preserved, and there is no need for activation.
MAX IV is the first synchrotron facility to test this procedure in the storage ring. During a short intervention that started on the 15th of June and finished on the 20th of June, two achromats were vented with neon and some faulty chambers were replaced, followed by machine commissioning which started on the night of the 20th of June to validate the process.
Signs of success were evident just after less than 24 hours of the restart of the machine (less than 1Ah), the beam lifetime was increasing, and the average pressure was decreasing.
Furthermore, after 6 days of the machine operation, the vacuum performance was back to the same level as it has been before the intervention, with no signs that the procedure has affected the performance of any other systems, and the procedure deemed successful!
Exciting news from the vacuum team at #MAXIV. They recently trialed a Neon Venting technique from @CERN which will dramatically decrease the time for interventions in the storage rings https://t.co/XyyKwm1TXk #synchrotron #physics pic.twitter.com/Bv4MMziKix
— MAX IV Laboratory (@MAXIVLaboratory) July 20, 2018