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