CRYOSTATION ORIGINAL VACUUM SYSTEM
The Cryostation provides a high vacuum environment in the sample chamber. The initial vacuum is created by pumping a roughing pump in the Control Unit that brings the pressure down to 2 Torr before cryo-pumping engages. The roughing pump stays on until the pressure reaches 400mTorr, before cryo-pumping completely takes over. There are several charcoal adsorbers inside the system to create the vacuum, which reaches about 10-7 Torr in the sample space. The original vacuum space is shown below.
ADDING A TURBO PUMP
In some instances users may want to use a turbo pump to:
- Lower the pressure quickly in the sample space
- Pump down prior to cooling
- Have samples that are sensitive to atmospheric pressure and therefore continually want to keep the system under vacuum.
This can be done by installing the turbo pump on the system in a couple of ways, but first the Control Unit must be capped off and separated from the system. A Swagelok ¼” VCO cap was originally shipped with the system covering the vacuum port, this should be replaced on the VCO fitting at the back of the Cryostation.
The turbo can be added in two places, at the top of the Cryostat where the vacuum line comes out, in which case the user may need an adaptor between VCO and the fitting on the turbo pump line, usually a KF25. The user can also add a turbo into a window port of the system, again using a KF adaptor on the window port. These two options are shown below.
USING THE SYSTEM WITH A TURBO PUMP
Start the turbo pump and make sure that the pressure is at least 2 Torr or below. Once the sample space is under 2 Torr of vacuum, the software can be turned on. With the cap on the Control Unit the volume to be pumped out inside the Control Unit is very small, when cool down is pressed the system should rapidly drop in pressure to below 2 Torr. The compressor will then turn on and cryo-pumping will begin inside the system. The pressure displayed in the software will be incorrect, the user must either read off the pressure from the turbo pump or a user installed pressure gauge.
Users can run the turbo pump until the cryo-pumping starts and then valve-off the turbo pump. If necessary, the customer can run the turbo throughout the cool down. If the user wishes to have access to the N2, a third option is to keep the vacuum line hooked up, manually pump and purge the chamber with nitrogen, then turn off the pump, close the valves, and begin the turbo pump. The turbo pump will also have to purge the vacuum line, this will not take much extra time. As long as the pump is not on and no valves open, the roughing pump in the control unit will be safe.
After the system is warmed up the system can then be vented. It is not recommended that the system vent prior to all temperatures reaching 285K.