CHESS RUNNING
Problems & Improvements ( Thur - Wed = Q F S S M T W )
CESR Tuning - Partial positron losses during electron injection.
As a last ditch attempt to get a run in for chess, changed the positron bunch pattern from 4t5b to 5t4b and only filled to 6ma/bunch. Changed the electrons from 5t4b to 4t5b and filled to 8ma/bunch. S
Vacuum - Linac HV not ready, e+ Snout 4 vacuum PS tripped off. Reset OK from remote panel. S
Notice pressure large spikes between fills around Q3W/B3W. It appears that the spikes occurs when the electron beam was dumped. Suspect a leak in the region. Need a leak check in Monday morning. S
Leak checked B3/Q3W region for possible leak. a leak was found on the B3W north / Vat oval gasket connection. Tightened flange bolts on gate valve. M
The gasket leak at Q3W GV/B3W opened again. Tighten the gasket, the leak went away. T
filled to 409ma total current..the rf tripped on w1 quench at very high power (200kw or so), we could probably get another 10ma by loading the east slightly more (1 unit or so, but this might bring us back to the e1 quench trip when the east is at high power), then vacuum was bad at 3 or 4 east. W
Linac Magnets - linac quad hf 10 readback went full scale, no e- beam. Retuned. Later, current driver card replaced. T
Linac RF - Linac Modulator 1 Thyratron was breaking down and firing at times other than the trigger time. Lowered reservoir. Still a problem, Linac tripping off every few minutes on PS overcurrent (slow). Replace thyratron with new style (never used here before) Litton L4888 (the most popular Thyratron at SLAC). Set reservoir at 4.2 V (the value recommended by the manufacturer - we have not tested its range yet). Also removed Sola constant voltage transformer for the reservoir, (it's really not needed anymore as the incoming Warm-up voltage is already regulated) because it was limiting the current we could put on the reservoir with the new higher voltate transformer previously installed. Q
Worked again today to improve flow in the Linac test 5 meter cavity cooling system. Found two of the 480vac phases crossed causing the pump to run backwards. Fixed wiring and started the system. All looks good with input end (north) of the cavity having about 8GPM and the other end about 6.5 GPM. The temp. regulation was turned on and the cavity warmed up to 44C. When the water was turned on, and heated up (see previous note) the vacuum rose from 20 nTorr to 500 nTorr. Turned off water pumps and heaters, and vented water pressure from cooling lines. T Pressure recovered overnight.
Feedback - CESR Horizontal Feedback Changes that affect performance:
Horizontal Feedback: Used a single bunch of electrons to observe the beam induced signal of the horizontal feedback kicker. The bad news is that the signal (suspected of blowing out the ENI amplifiers) is about 5Volts/mA peak with the present pretzel, and is sensitive to the pretzel amplitude. The good news is that the induced signal consists of pulses which might be reduced considerably by adding filtering at the kicker. T
Longitudinal Feedback: Observed the signal induced in the longitudinal feedback kicker. Also connected the Travelling Wave Tube amplifier to the cavity with a single bunch e- present. No oscillations induced. Succeeded in driving the beam with the cavity kicker at a low level. Good progress. T
E+ and E- Current Scales: Adjusted after much feedback front-end work, including lowering the gain by a factor of 4 (2 on the card and 6 dB attenuators). W
CESR Magnets - Poor e- injection. Hardbend trim at 47east was tripped off for some time. Replaced fuse, and reset 47east, then during ramp it trips again, so would assume that the ramp that was done this afternoon resulted in a 47east trip S
HB4(HB47E) chopper and fuse changed. M
CESR RF - During CHESS running, do west RF phase processing with program [cesr.rf]wpp will try to maintain west rf fwd-refl power and west window vacuum within specified ranges.
Processed W1 cavity with WPP program. The forward-reflected power level went up to 141 kW from 126 kW trip level seen earlier. M More processsing, got up to 163 kW. T
E2 Quench trips. Lowered tuning angle. Took a look at COMET data from E2 quench trips overnight. There doesn't appear to be any RF (or beam) action at all prior to the RF turning off. This plot shows some E2 signals. The E2 cavity field (which, as I understand is the thing that is looked at to determine a quench) does absolutely nothing until the RF is turned off. Ditto for other E2 signals. Why are we getting E2 quenches?. T
1. Adjusted RF phase and W1 tuning angle.
2. Took RF power data for relative cavity position/phasing.
3. W1 processing: Pf-Pr limit is now higher than 170 kW, see winlog plot here. All trips were W1 quench detector trips and we suspect that they are not real cavity quenches, but phase or tuning angle loop regulation problem. This remains to be checked.
4. Injected 200 mA of e+ and then e- to 372 mA total. E2 quench detector tripped RF. Then got another E2 quench detecor trip after next 200 mA e+ fill while playing with tuning angles. The nature of E2 trips is unknown yet. T
Looking at the maximum transmitted power (forward minus reflected power) that has been achieved on all of the cavities since start up, it appears that all three cavites are tripping on the Quench interlock at the highest transmitted power. The highest beam current that has been achieved (409 mA) is within 10% of the limit set by the RF system. W