77
ZTKS0156 / Z31820 / Rev.: 03
Assembling
4.3.5 Cooling down to 4.2 K
Preconditions
• Helium vessel filled with cold nitrogen gas.
• Current lead inserted into the current lead turret.
• Power supply connected to the current lead.
• Upper and lower PT 100 temperature sensors show 80 - 90 K.
• Vacuum pumping unit connected; cryostat evacuated with vacuum less than
5x10
-8
bar).
• Stop valve (3) at the cold head flange connected with the transportation dewar with
warm helium gas.
• Transportation dewar with sufficient dry and warm helium gas ready.
• Transportation dewar with sufficient liquid helium ready.
Procedure
1. Close the vacuum valve (refer to ”Removing the Vacuum Valve” on page 4-53)
and remove the vacuum pumping unit from the vacuum valve.
2. Connect the one way valve (2) at the helium flow system with the vacuum pumping
unit.
3. Pump and flush the helium vessel with warm helium gas 5 times:
- Fill the helium vessel with dry helium gas until the quench valves open.
- Pump to the following pressures: 0.8, 0.5, 0.3, 0.1, 0.01 bar (11, 7, 4, 1.5, 0.1 PSI).
- Use short pumping times!
4. Connect the vacuum pumping unit to the vacuum valve and continue to generate
vacuum (refer to ”Generating the Vacuum” on page 4-52).
5. Check the zero reading of the helium level sensor.
6. Insert the magnet side of the helium transfer line completely into the helium fill-in
turret.
Figure 4.80: Helium Flow System during usual operation
1 Connector
2 One way valve
3 Stop valve
4 Cold Head
5 Quench valves
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