At line 0 added 4 lines. |
+ !!Orange Cryostat Cooldown Procedure |
+ |
+ For some general remarks on cryogenic handling at the Neutron guide hall [see|http://lns00.psi.ch/sinqwiki/Wiki.jsp?page=CryogenicHandling]. |
+ |
At line 1 added 1 line. |
+ This is normally done by a sample environment technician |
Line 3 was replaced by line 8 |
- * Pump main vaccum with a turbo pump, ideally over night. If the cryostat |
+ * Pump main vacuum through valve (V) with a turbo pump, ideally over night. If the cryostat |
At line 11 added 2 lines. |
+ [OrangeCryostatTopPictures] |
+ |
Line 14 was replaced by line 21 |
- * Increase the temperature of the heat exchanger to 100 K. |
+ * Increase the temperature of the heat exchanger to 100 K. (The better part of air will not condense at this temperature) |
Lines 18-22 were replaced by lines 25-51 |
- * Pump down and flush again with He gas, then pump down to a pressure between 10 and 50 mbar. |
- |
- !Cool down |
- |
- There are two possibilities, each has advantages and drawbacks. |
+ * Pump down and flush again with He gas. To remove all contaminants you should repeat this procedure an infinite number of times (at least 2x). |
+ * If you cannot reach 0 mbar (or -1 bar) on the mechanical gauges you might be faced with a leak into the sample chamber or with an offset on the gauge. |
+ * Pump down to a pressure between 10 and 50 mbar. |
+ |
+ !Cool Down |
+ |
+ # Connect helium pump to the pumping port (P). Switch on the pump and wait until |
+ the pressure stabilizes (should be less than a few millibars). Make sure that |
+ the warm valve (W) is closed, open cold valve (C) a little, the pressure at the |
+ pump should not exceed 20 mbar (30 on a maxi cryostat). |
+ In SEA, this could be done by switching the needle valve control to automatic |
+ and set 20 - 30 for the flow maximum. |
+ # Put a setpoint of 10 K on the heat exchanger. |
+ # When the heat exchanger is at 10 K and the sample near 10 K, reduce the pressure |
+ by closing the cold valve gradually until the heating power the temperature controller |
+ needs to keep 10 K has reached a value between 100 and 200 mW. |
+ With SEA, the regulation of the needle valve is done automatically, but the value |
+ for "flow set" should be optimized if not known from an earlier run. |
+ # Put the temperature setpoint to zero. The cryostat should cool to 1.6 K within 10 minutes. |
+ If the base temperature can not be reached or the "nv_Set" is oscillating, most probably |
+ the value for "flow set" was not determined properly, and must be increased slighly. |
+ |
+ ''Cool Down with warm valve'' |
+ |
+ In principle there is the possibility to cool down with the use of the warm valve, |
+ without He pump. As this is not recommended, it is mentioned only for information. |
+ Make sure that the warm valve is always closed except for preparation. |
Removed line 24 |
- *With He pump |
Removed lines 26-43 |
- ** Connect helium pump to the pumping port (P). Switch on the pump and wait until |
- the pressure stabilizes (should be less than a few millibars). Make sure that |
- the warm valve (W) is closed, open cold valve (C) a little, the pressure at the |
- pump should not exceed 40 mbar (20 on the ILL cold valve controller). |
- ** Put a setpoint of 10 K on the heat exchanger. |
- ** When the heat exchanger is at 10 K and the sample near 10 K, reduce the pressure |
- by closing the cold valve gradually until the heating power the temperature controller |
- needs to keep 10 K has reached a value between 100 and 200 mW. Wait half an hour |
- and check or change the cold valve setting again. |
- ** Put the temperature setpoint to zero. The cryostat should cool to 1.6 K within 10 minutes. |
- |
- *With warm valve |
- |
- ** Open cold valve (C), open warm valve (W) by about 3 turns. Close the valve (R) going |
- to the He recovery. |
- ** When the heat exchanger and the sample temperature have stabilized around at 4.2 K, |
- close the warm valve and reopen a little bit, just enough to held 4.2 K. |
- |
Line 50 was replaced by lines 60-75 |
- * Dry the sample stick. |
+ * Dry the sample stick with a hair blower (not a hot gun!) |
+ |
+ !He Flow Schematics |
+ |
+ [OrangeCryostatCooldownProcedure/NeedleValveControl.png] |
+ |
+ !Automatic Cryostat Control and Monitoring |
+ |
+ All our cryostats are monitored and controlled with [SEA|http://lns00.psi.ch/sinqwiki/Wiki.jsp?page=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 Helium gas pumping line 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. |
+ |
+ [CCU|CCU.png] |