|
|
Electronics | Mr. Freeze (dilution refrigerator) | Mrs. Astra Principle of Operation | Cooling Down | Starting the Circulation | Warming Up | Pumping the Transfer Tube and the Top Loading Stick | Loading and Unloading the Sample
n. b. This is not a foolproof guide. It is very important that one has to know what he is doing, why he is doing it, and what’s happening in Mr. Freeze if he does it.
TOP LOADING INSTRUCTIONS
LOADING:Do not top-load or top-unload alone. Get help from somebody who knows the system.
1. Make sure that you have at least 40% level in the bath, and fill up the pot.
2. Tighten the brass piece to the sample holder (finger tight).
3. Make sure that the brass screw is tightened to the brass piece.
4. Tighten the brass screw to the top loading stick a bit harder, use a wrench.
5. Mount the top loading stick on the gate valve and the top-loading siphon in the leftmost hole. Connect the pump bellows.
6. Pump out the load lock with the roughing pump. When the pressure is below 10-1 mbar you can continue (this takes about 5 minutes).
7. Stop pumping on the lower part of the load lock (i.e. close the green valve) and open the gate valve.
8. Lower the top-loading stick to the pre-cool position. The cross should be 10 cm below the chimney. Do not go lower than this or you will damage the baffle. Check the pressure when going down. If it gets too high, stop, pump out, then continue again. When you are in position, mount the safety clamp.
9. Connect the siphon and the pump line. Start the membrane pump by throwing the switch on the shielded room wall. Precool until sample is cold. Monitor the sensor with a Fluke. When the sample is cold, the sensor will fluctuate about 1 kW. This should take about 30 minutes.
10. Increase the bypass threshold on the gas panel to 990 mbar.
11. Stop heating on the mixing chamber and the still.
12. Bypass the booster pump.
13. Now you are ready to do the actual top loading. It should be done fairly rapidly to avoid too much of the mixture from boiling off. Ask your copilot to look at the gas pressure of the mixture. If it gets close to 900 mbar, open valve 9 shortly to release the pressure to the dumps.
NOTA BENE. The following number of turns is true only for the gold plated SET sample holder.
14. Stop the membrane pump. Disconnect the siphon and the pump line. Open the baffle and lower the top loading stick. Always turn anti-clockwise when going down if the top loading stick gets stuck. The Fisher connector will fit at 11.30 seen from above facing the Membrane Pump Switch Panel.
15. Start turning clockwise. This takes about ≈4.5 turns before it begins to be hard to turn, and another ≈0.25 turns to release the brass screw/sample-holder thread.
16. Continue ≈11 turns to tighten the sample holder.
17. Continue ≈5 turns to release the top-loading stick from the sample-holder. The top-loading stick should be positioned at around 8 o’ clock seen from above facing the Membrane Pump Switch Panel. Pull up to precool position and close the baffles.
18. Pull up the top-loading stick completely and close the baffle, and then the gate valve. You will know that the baffle is closed after you turn about 20°. Make sure to pull the top-loading stick all the way up. You will know that the gate valve is fully closed when you hear the ‘click’ as you close it and when only about 0.5 cm of the silver part of the gate valve handle is exposed. Watch the pressure when going up as before.
19. Decrease the bypass threshold on the gas panel to 400 mbar.
20. Restart the circulation.
UNLOADING: Do not top-load or top-unload alone. Get help from somebody who knows the system.
1. Make sure that you have at least 40% level in the bath, and fill up the pot.
2. Mount the top loading stick on the gate valve and the top-loading siphon on the leftmost hole. Connect the pump bellows.
3. Pump out the load lock with the roughing pump. When the pressure is below 10-1 mbar you can continue (this takes about 5 minutes).
4. Stop pumping on the lower part of the load lock (i.e. close the green valve) and open the gate valve.
5. Lower the top-loading stick to the pre-cool position. The cross should be 10 cm below the chimney. Do not go lower than this or you will damage the baffle. Check the pressure when going down. If it gets too high, stop, pump out, then continue again. When you are in position, mount the safety clamp.
6. Connect the siphon and the pump line. Start the membrane pump by throwing the switch on the shielded room wall. Precool until sample is cold. Monitor the sensor with a Fluke. When the sample is cold, the sensor will fluctuate about 1 kW. This should take about 30 minutes.
7. Increase the bypass threshold on the gas panel to 990 mbar.
8. Stop heating on the mixing chamber and the still.
9. Bypass the booster pump.
10. Now you are ready to do the actual top loading. It should be done fairly rapidly to avoid too much of the mixture from boiling off. Ask your copilot to look at the gas pressure of the mixture. If it gets close to 900 mbar, open valve 9 shortly to release the pressure to the dumps.
NOTA BENE. The following number of turns is true only for the gold plated SET sample holder.
11. Stop the membrane pump. Disconnect the siphon and the pump line. Open the baffle and lower the top loading stick. Always turn anti-clockwise when going down if the top loading stick gets stuck. To make things easier and faster, position the top-loading stick at 9 o’ clock seen from above facing the Membrane Pump Switch Panel.
12. Start turning anti-clockwise. It takes ≈4 turns to tighten the top-loading stick to the sample holder.
13. Continue ≈11.3 turns to untighten the sample holder. It should feel just a little loose at around 11.3 turns if you turned it at a moderate speed. Do not go further than 12 turns.
14. Pull up the top-loading stick completely and close the baffle, and then the gate valve. You will know that the baffle is closed after you turn about 20°. Make sure to pull the top-loading stick all the way up. You will know that the gate valve is fully closed when you hear the ‘click’ as you close it and when only about 0.5 cm of the silver part of the gate valve handle is exposed. Watch the pressure when going up as before.
15. Decrease the bypass threshold on the gas panel to 400 mbar.
16. Restart the circulation.
Updated: August 9, 2004, Ian Jasper Agulo
|
|
| Last edited: | Disclaimer | ||
