Chemical Engineering @ Carnegie Mellon

Andrew J. Gellman Group S.O.P.

Pumping and baking a vacuum chamber

  1. Close any valves that are open to air. Molecular sieve traps on the mechanical pumps should be removed and baked in a fume hood before pumping process begins.
  2. Reinstall molecular sieve traps. Turn on mechanical pumps. Pump chamber and rotary stage with mechanical pump.
  3. When chamber pressure is below 10-2 torr, turn on turbopump. Close valve between chamber and mechanical pump and open valve between chamber and turbopump.
  4. Open valve between turbopump and 2nd stage of rotary stage.
  5. If chamber pressure does not reach 10-6 torr (this may take several hours), it is possible there is a leak in the chamber. Check the system for loose bolts on the flanges that were most recently opened.
  6. At this point, it is safe to open the gate valve to the ion pump or cryopump. The chamber is ready to be baked.
  1. Remove micrometers, motors, electronic cables, and other heat-sensitive parts from the chamber. Keep flammable materials away from chamber during baking process.
  2. Wrap the chamber in aluminum foil or fiberglass insulating sheets.
  3. Do not overlap heating tapes. Avoid placing heating tapes directly on flanges or gate valves. Heating tapes should be attached to the body of the chamber.
  4. Connect the power to the heating tapes.
  5. Heat the chamber to 150°C while pumping the chamber with the turbopump for the first 4-6 hours.
  6. The baking process should be attended for the first 5 hours, or until the chamber reaches its maximum temperature.
  7. Close the gate valve to the turbopump and open the gate valve to the ion pump or cryopump.
  8. If using cryopump, monitor cold head temperature. If cold head temperature exceeds 19 K, reduce power to heating tapes. Cryopump will not function properly if the cold head temperature exceeds 20 K.
  9. Continue bakeout for at least 12 hours on ion pump or cryopump.
  10. Disconnect power to heating tapes and allow chamber to cool. Do not operate any instruments until the chamber has completely cooled.

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