Pumping

A suggested sequence for pumping the cryo chamber is as follows:

1. IMPORTANT! Make sure that the convectron controller located on the cart under the air table (which is the one for the piezo interlock) is connected to the convectron gauge at the upstream (front) wall of the chamber. Otherwise the piezo may be under high voltage in low vaccum, which would cause sparking.
2. Inspect every flange. Especially look at the bellows at the airlock and underneath the chamber -- are they all ready to feel vacuum force?
3. Make sure the turbo is vented, and the chamber is at atmospheric pressure.
4. Make sure all up-to-air valves (green and black handles, Valves D and E) on prepump line and vacuum chamber are closed.
5. Open the valve between turbo and chamber by flipping the ``Turbo Valve override'' switch on the cryo interlock front panel and pushing the ``open'' button. Start the turbo. If it is a slow pumpdown, the turbo may shut itself off after five minutes or so. If that happens, just turn it right back on.
6. At $\sim 1$ torr, or when the turbo has reached 50% of its maximum speed, you can switch off the override for the turbo valve. This will ensure that the interlock closes the valve in case of (accidental) venting of the chamber. Also, the beamline valves will not be allowed to open as long as a valve override on the cryo interlock panel is on.
7. With the turbo, you will be able to pump into the low $10^{-6}$ torr range. For imaging, you may then want to open the ion pump. NOTE: The ion pump should always be pumping on itself when it is not pumping the chamber, therefore it should not be turned off but instead be isolated from the chamber by closing the gate valve. The gate valve to the ion pump can be opened by pushing the ``Ion Pump Valve open'' button on the cryo interlock. To protect the ion pump from high pressures, the gate valve will be closed by the cryo interlock when the chamber pressure rises above $5\times 10^{-6}$ torr.
8. If you choose to use the ion pump, you can close the electrically-controlled valve to the turbo. Turn the turbo off so it vents itself. (If the cryo chamber pressure rises during any of these steps, immediately turn the turbo back on).