The ARS cryostat is a closed cycle cryogenic refrigerator consists of a water-cooled compressor, that compresses helium gas, and an expander, that gets cold. The expander uses the Gifford-McMahon refrigeration cycle. The expander has two helium gas line connections, one is high pressure and the other is low pressure. There are three electrical ports A,B, annd C. Ports A and B are used by the temperature controller. Port C is used for electrical measurements. There is an KF flange used to pump a vacuum around the cold head.
Pfeiffer Vacuum TSH 071 E Turbomolecular Drag Pumping Station
The Pfeiffer Vacuum TSH 071 E is a completely self-contained vacuum pumping station. It uses a diaphragm pump as a pre vacuum pump for a turbomolecular pump and is therefore completely oil free. A Pfeiffer Compact Full Range Gauge is used to measure the current pressure inside the vacuum system.
In the magnet laboratory, the vacuum system is used to thermally insulate the cold head of the cryostat with a high vacuum in the order of magnitude of E-4 mbar when starting the cooling process to E-6 mbar after sufficient time and at low temperatures.
There is a switch on the back for the membrane pump and a switch on the front inside the cutout in the lower right corner. Once these switches have been turned on, the controller boots and this takes a minute. There is a black vent knob on the back of the turbomolecular pump. Make sure this is closed before tuning on the pump. After the controller is ready, press the power button on the controller.
Operating instructions
How to cool down:
Inspect the cold head of the cryostat and ensure yourself that the radiation shield and the vacuum shroud are closed.
Open the cooling water drainage valve and then the cooling water inlet valve.
Verify that the vacuum valve at the cold head of the cryostat is open (as shown in figure VacuumSystemValve), this valve should never be closed.
Turn on the Pfeiffer Vacuum Single Gauge with the switch on the back side of the gauge.
Turn on the vacuum pump system with the switch that is lowered inside the lower right front side of the Pfeiffer Vacuum Turbomolecular Drag Pumping Station TSH 071 E and wait a few seconds for the system to boot.
Press the Key Right on the Display And Operating Unit DCU 001 until you are at “309: Act rotspd” to display the rotational speed of the turbomolecular pump. (The set rotspd at 308 should be at 1500 Hz.)
Close the venting screw on the backside of the vacuum pump head (right handed screw thread) until it is firmly closed.
Start the vacuum pumps with the Key Pumping Station ON/OFF on the DCU 001. The diaphragm pump will start instantaneously and when the pressure is low enough the turbomolecular pump will slowly start to work. The rotary speed can be observed at the display and will rise to 1500 Hz as the pressure drops.
Wait for the pressure to reach a value in the order of magnitude of E-4 mbar on the pressure gauge. This takes about 11 minutes.
Now you can engage the ON switch of the ARS-4HW Compressor to start the cooling process.
How to warm up:
Shutdown the cooling by turning off the ARS-4HW Compressor.
If the cooling water is not needed anymore (i.e. the compressor and the magnet are not in use), you can close the water inlet valve and the water drainage valve.
Wait for the cryostat to warm up.
The temperature inside the cryostat (all 4 temperature sensors) needs to be at least higher than the freezing point of Water (> 273.2 K) before the Cryostat can be vented. This, depending on the method, can take a long time.
