SLSP 5246-4 activated well on April 7th Used LLGUN2 modestly for remaining SAD and Physics start-up OK through April 24th
Field Emission begins? on April 24th (QE has fallen significantly already)…
Opportunistically hi-pot HV chamber on 4/27. Reach ~120kV each time … finally, viewer flashes (light, not electrons?) Anode current reduced from ~60pA to ~30pA Wafer preserved in PREP =>
Beam orbit drifting for last few days (over April-May weekend…) Tunnel investigation on May 1 Lasers check out OK Hall B laser spot fixed (result of bad beam tweeking…) QE now very bad (max ~0.07%) Found anode isolation bad (30k Ohm instead of 50 Ohm) Limp along with spot moves, but QE falls rapidly….
FE emission begins 4/24, orbit drift with hi-potting 4/27, but stabilizing ….
Gun2 wafer activated May 6th very well (1 Gun2 wafer activated May 6th very well (1.2%), OK for program, but continues to drop… Connected picoammeter to anode for investigation (anode connection good) Anode current >20pA always (except when HV off) Calibration of HVPS/anode suggests ~120nA FE per 1pA of anode current Anode current: <50pA beam ON, but up to 150pA when beam OFF
May 11th : Vacuum burps even when HVPS has been off… vary IP voltage May 11th : Vacuum burps even when HVPS has been off… vary IP voltage? Ground cage?