Maintenance for M9A
During the commissioning of the M9A beamline and conditioning the separators to high voltage, electrons emitted from ground potential accelerated toward the positive electrode of Sep#2 putting a hole in the ceramic separating the SF6 and vacuum spaces. The hole was about 1 inch from the bottom of the ceramic at 5 o’clock. This happened only to Sep#2 while Sep#1 did not have this problem!
Early in 2024 two new ceramics were painted (paint information) and a shield was designed to protect the ceramic from such events. After installing the new ceramic, the shield and running in the summer we had a similar issue with Sep#2 +ve. This time the hole was at a similar orientation to the first one but above the shield about 4 inches from the bottom. The new hole was smaller than before, the SF6 losses were small which allowed us to finish the run.
During the mini-shutdown Sep#2 was craned to the cleanroom. A detailed check of all the dimensions and surfaces was done, scratches on the lower set of Aluminum shields around the magnetic shims were observed. The shim covers were removed and re-polished while the 2nd painted ceramic installed. Initial observation from conditioning looks positive, however, final verdict will have to wait for few weeks.
Pictures can be seen in this link.