Cryostat Pump Down

Before pumping down the main vac chamber each cryostat should be pumped over night. Kodi recommends no more than an hour between removing cryostats from pumps to beginning of main chamber pump down, but can live with a few hours (up to 5 or 6).

Each cryostat needs a separate pump cart which will fit in the narrow space between the chamber and the wall.

The valve on the cryostats can be finicky and has given us trouble on multiple occasions. Try using both actuators to see if one works better if you have problems closing the valve. If needed, bring cryostat to ambient pressure with a GN2 purge and clean threads on the plug.

The valves on the cryostats are “Oerlikon Leybold Sealing Valve, DN 40 KF Valve, PN 28323” and the threads on the cryostat are M30 x 1.5 mm straight thread, we believe this tap can be used if the threads on the cryostats need to be chased.

Chamber Pump Down

Note when turning on the roots pump, there are two toggle switches in the back, one for “Mains” one for “Pumping”. Toggling the mains on will power the pump, but one needs to toggle the pumping switch off and on to begin pumping.

Roots pump should be used to get the chamber down to about 0.5 torr. Then the turbo pump should be turned on.

Turbo Pump Control

The turbo pump can be controlled via a web interface accessible only from a browser on kpfserver. Launch Firefox from a kpfserver (blue) terminal and go to 192.168.23.125. Log in using the kpfdev account credentials.

Ensure system control is set to remote, and turn on the turbo pump using the green ‘START’ button at bottom center of page.

The user should immediately see the turbo pump speed and power draw start to increase.

It can take up to approximately 60 minutes for the pump up to reach a nominal speed of 1000 Hz. As the turbo pump spins up, the chamber pressure, and cart pressure will begin to decrease.

Transition to Cool Down

If possible pump out the main vac chamber to the e-5 level. During the Oct 2025 pump down the turbo pump was on for ~24 hours before the vacuum leveled out at the ~2.5e-4 for another 24 hours before beginning to drop again.

Pumping out any moisture trapped in the MLI is the goal for the pump down. In October 2025, we pumped down until the pressure was in the high e-5 range, but going longer would have been even better.

Original Procedures (LN2 Cooling Era)