Instructions for turbo vacuum system for pumping out cryo stages
NB: Do not operate unless you are sure how to use the turbo pump. It is very expensive and can be damaged by incorrect operation.
At least once per week, before use: make sure dewar is under high vacuum. Needs pumping 1h (min)-overnight, with heating to 550° for about 4 hours once every few times (see next page for heating instructions). Never let the dewar up to atmospheric pressure. After use, the tip must also be pumped. Before 1st insertion into the 2010, the tip must be turbo pumped, to avoid crashing the microscope vacuum.
- Connect the pump-out tool to the vacuum outlet
- Pull the handle on the pump-out tool outwards and push the open end over the pump-out port on the holder dewar. Then push in the handle of the pump-out tool and engage the end into the hexagon socket of the pump-out port.
- Turbo pump cooling water must be ON. (tap with reinforced hosing).
- Rotary must go on FIRST. On plug board, rotary and air cutout must be permanently on. Switch is at top of pump.
- Rough out line to turbo. Red valve must be CLOSED. Also close air inlet valve (silver one at top). AVOID sudden or fast air flow through the turbo pump - this will damage the blades. Never leave running with air flowing through.
- Plug in combigauge (TMP combi). Shows rotary pump pressure.
- Open red valve to rough out pumping tool (holder still shut - never let dewar vacuum up to air).
- Plug in turbo (frequency cv). Wait for lights on control panel to go out. Press start. Accel light should go out after ~1 min, & normal light should come on. Oil at base of turbo will show some outgassing for 1st ½ hour. Once turbo is running normally, slowly and gently open pump out tool - 5 turns anticlockwise.
5x10-4 mbar is final vacuum. Pumping time 1 hour - overnight.
- Close pump out tool - watch for leaks. Clockwise, don't overtighten.
- Close red valve. Gently open air inlet valve (silver tap).
- Gently remove pump out tool from holder - no mechanical strain.
- Stop turbo. Wait at least 1 min to let the blades slow down.
- Slowly open red valve. Rotary pump noise should increase when open to air. Switch off rotary once it is open to air.
- Unplug freq conv and combigauge.
- Close red valve and air inlet.
- Leave cooling water on as long as turbo blades are running - they take about 30 min to stop after switching off. Close tap 30 min after shut down.
Pumping out the tip of the cryo holder
- Connect the tip to the pump out tool as above.
- Close silver and red valves
- Switch on rotary pump
- After a few minutes, open the red valve, then open the pump out tool
- Pump until the holder is completely warmed up. It can be left overnight if necessary.
- When done, close pump out tool, close red valve, open silver (air inlet) valve.
- Remove tip
- Open red valve and when rotary pump is open to air, switch it off.
Operation of Oxford ITC4 temperature controller
Heating sorb to release adsorbed contaminants, once high vacuum is reached.
- Connect the sorb lead (not the same as the temperature sensor lead) to the holder and to the ITC4 temperature controller.
- Set the control panel as follows:
- power on
- control - lock & local
- heater - sensor 1 & manual
- display - sensor 1
- normal settings - do NOT change: prop 4, int 2, deriv 10, set limit +55°C
- Heater - switch to auto (takes ~20 min to reach preset temp)
- Leave for 4 h - overnight
- Close valve on holder dewar
- Switch heater to manual; set temp limit to -255°C; reduce heater amplitude to zero
- ITC4 power off