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Vacuum chamber for test setups in the Tigress lab (Room 156)

There is a vacuum chamber in the TIGRESS Lab (Room 156) that can be used for testing surface-barrier, PIPs, DSSD detectors etc. Here are some notes on reducing noise in the detector when using this chamber.

• Isolate the chamber from the turbo pump by using a delrin section of tube
• Ensure the chamber is not touching the detector pumping stand - this is a strong source of RF
• Using grounding braid between the chamber and the NIM crate in the rack (where preamp power and HV were supplied) did reduce the RF in the signal but introduced a different noise (not a ground loop) that was even worse!

Vacuum gauges and controls

[edit] Pumping Down

• Ensure all vent valves on the vacuum system are closed
• Switch on the black fan by plugging it in and point it towards the turbo pump. This is to ensure that the turbo pump stays cool
• Open the gate valve between the turbo and the roughing pump by plugging in the lead
• Plug in the roughing pump
• Observe the pressure change on the roughing pump gauge (Granville-Phillips 375 convectron) and TC2 on the main gauge box (Varian UHV2C)
• Wait until the roughing pump valve reads less than about 60 millitorr (It will get down to around 6 millitorr if left for a long time) NEVER START THE TURBO BEFORE THE PRESSURE IS LESS THAN 100 millitor
• Switch on the turbo by pressing 'start' on the control box (Varian, Turbo - V 301). The turbo pump takes about one minute to get up to normal operating speed of 56 krpm
• Once the turbo is up to speed switch on the EMIS IG by pressing 'EMIS' on the main gauge box
• The pressure should now be displayed on the 'IG' panel of the main gauge box
• Detector testing may proceed

Spinning down the turbo whilst venting with nitrogen gas

[edit] Venting

• Power down any detectors and switch off the preamp power supply
• Switch off turbo by pressing 'stop' on the control box (Varian, Turbo - V 301)
• Switch off roughing pump by unplugging the lead
• The safest way to spin down the turbo is by the vent valve on the turbo itself indicated in the photo to the right. Dont use the green valve of the vacuum system
  • Hold a supply of nitrogen close to the turbo vent valve so that nitrogen populates the vacuum system instead of air. This will make pumping down quicker next time
  • Carefully and slowly open the turbo vent valve whilst monitoring the pressure with the emis gauge.
  • Switch off the EMIS ion gauge when it reads 10^-4 and use the roughing pump gauge and TC2 instead
  • Let the pressure increase slowly up to atmosphere
• Switch off the black fan by unplugging it