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Date
Attendees
Meeting Notes: CM01 Field Emission Discussion
- Background: CM01 cavity 4 started showing field emission over the weekend
- Put the decarads on CM01 during access yesterday, found cavities 2 - 5 have notable field emission
- Worst cavity is 4
- Cavity 4 went up to 150 mR/hr at 16 MV - immediately shut it off
- Today: investigating this problem is the first priority. Beam off
- Gun off, trying to see if CM01 is getting worse
- With beam off, see 10 R/hr at cavity 4
- Field emission onset at 6 MV?!?!
- Decarads could be fried? But no, the response in cavities
- Since the trip last night, buncher tripped, but the rest of the linac on
- False arc fault, per Andy and Feng
- Is the loss pattern related?
- CM01 cavities turned off at the same time, flagged as a quench
- Check timestamp generation for faults, see if there is something similar with the gun and buncher
- Possible material deposition in the cavities?
- CsTe? YAG? Valve? Collimator?
- Look at temperature/vacuum around heater collimator
- Lower beam energies at CM01 -> more material damage possible on valves
- CsTe deposition in cavities was ruled unlikely in a Dave Dowell study, but worth revisiting
- Hydrocarbon contamination from the gun
- Look at gun RGA
- Something bigger that got hit and sputter deposited?
- Up to 1.5 GeV of dark current
- Chicanes go the wrong way for dark current hitting CM01 (bend the wrong direction). Possible to hit the wall and have something accelerate
- Unlikely that a direct hit from dark current would cause field emission - possible that damage from deposition after dark current hit something else
- Who do we reach out to for SRF operations insight?
- Julien
- Marc Ross
- Dave Dowell
- Planning for lit review of field emissions this afternoon
- Recharacterize Q?
- Warm up CM01 not to room temp, but 80 K?
- Could see if there’s gas on the surface
- Does it make sense for gas to cause field emission?
- More plan
- Turn cryomodule on with cavities at 4-5 MV for now
- Plasma processing in the future - requires heating up the linac
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