Cryogenic Handling

General Remarks

Liquid Nitrogen

Most of our cryostats and cryo-magnets have an outer liquid nitrogen jacket to reduce the heat load on the helium bath.
The storage dewars are prepared by the sample environment staff and can be picked up at the preparation area (between FOCUS and MARS).
The dewars provided are self pressurizing systems with a mechanical level indicator at the top as shown below.

The dewars are always pressurized.

• Ensure that the hose is firmly connected to the vessel and the nozzle is not pointing towards a person before opening the valve.

• Make sure that you wear protective leather gloves when handling cold parts.

When using the automatic nitrogen refill

• test the automatic to assure that the filling hose remains in the cryostat filling port and that the system switches off correctly

Liquid Helium

Liquid Helium dewars are provided by the sample environment staff at the sample preparation area.
At PSI we run a Helium recovery system.

• Please make sure that the dewars are always connected to the recovery line when not in use
• Remember to close the valve on the recovery line when taking a dewar away and to open it after return
• Always measure the Helium level in the dewar before you take a Dewar away
• When using the crane be aware that no equipment (or dewar) should be moved over the DMC detector

Helium Transfer:

• Before you open the extraction port you should release the pressure in the dewar which might have built up during transport by opening one of the release valves
• Insert the Helium siphon first into the transport dewar.
• close all manual pressure release valves
• slowly lower the siphon into the dewar observe the pressure rise in the dewar (try to stay below 0.2bar)
• you should see gas streaming out on the other end of the siphon
• don't put your hands in the gas stream
• when it starts to turn white you can insert this end into the cryostat Helium filling port
• continue to lower the siphon into the transport dewar until you reach the bottom and lift it up by 10 cm
• switch on the compressed Helium gas line and connect the gas hose to one of the pressure release valves
  

• stop the pressure line
• release the dewar pressure before you remove the siphon.
• make sure that the extraction and filling ports are properly sealed

Automatic Cryostat Control and Monitoring

All our cryostats are monitored and controlled with SEA.
All instruments are equipped with a temperature controller (Lakeshore 340) for the temperature control
and a cryostat control unit (CCU) for the control of pressures, levels and valves.
The CCU will only work with a correctly configured SEA instance. It can read the pressure in the VTI pumping line
(see orange cool down and set the needle valve accordingly.
It reads the analog output of AMI Helium level meters and serves as a level indicator for our 2 point liquid Nitrogen level meter.
The Unit is used to energize the electromagnetic valves involved in the automatic Nitrogen/Helium refill.