Cooling down with LHe
Last updated
Last updated
Preliminary setup and change of the dewar should be done together with a beamline scientist. This instruction is only for the case when the needle valve is already inside the dewar.
Check that helium line is deep inside the dewar, ca. 5 cm above the bottom.
Check that Helium pump is running (see panel inside the frame from the side of the load lock):
3. Check that black valve below the frame is open:
4. Make sure that helium recovery line is connected to a He return port on the wall-panel.
5. Use ladder and open the needle valve 1 full turn. Rotate counter clockwise if you look from below.
6. Wait until temperature reading starts to steadily go down by 0.01 K. If this doesn't happen in 10 minutes - it is likely that there is a problem (*).
7. When sample temperature reaches ca. 40K start closing needle valve in small steps and wait for the temperature to stabilize. Try to close as much as possible to reduce helium consumption, but don't let temperature to go up.
8. The lowest temperature reading is ~12-20 K.
To reach the lowest possible temperature on the sample one can improve thermal contact by tightening the screws on the sample pocket of manipulator head. See here for more details.
Check that helium line is not at the very bottom of the dewar. If it slides down, retract at least 5 cm back. This way there is less chance that it will freeze inside.
Make sure that the needle valve part is straight, if not - adjust the support.
Underpressure in the LHe dewar should be avoided at all times! If this happens, air can reach inside the dewar and moisture will turn into ice that freezes on cold parts inside. This ice can block helium line from moving, then it cannot be neither closed normally nor taken out to change the dewar. Too much ice may lead to a dangerous condition!
(*) As a first step try to disconnect helium recovery line from the wall and check if there is a flow of gas coming out of it.
