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Procedure for cooling down the PT NIKA cryostat

1) "Rapide" (ev5=1; ev2=1; ev1=ev17=ev19=0) with J2 initially at 750mbar (J4 around 3500mbar), going down slowly. Continue this way until T_still = T_4K (usually satisfied at about 20K; takes roughly 16h).

2) J2=500mbar (ev5=1) until further flattening; then J2=300mbar (ev5=1) until further flattening.

3) When (T_still < 10K and T_BM < 10K), close ev5, ev5=0. Steps 2 and 3 together take about 4-6 hours. From now on ev5 stays closed.

4) When flattening again, the only other choice is passing through the pump (ev2=0, ev1=ev17=1, compressor ON, J1=15-20mbar); now it should be 24h roughly from the beginning. Pay attention to the J1 zero-point, could be not zero.

5) Leave this way (ev2=ev5=0; ev1=ev17=ev19=ev3=ev6=1; ev7=ev8=1; preref ON regulating J2 at 300mbar; compressor ON) for the night or in any case for about 8 hours until (T_still < 7K and R_BM > 1240-Ohm). If they're still cooling down reasonably when you arrive there, you might leave further until flattening. Very important to leave the "preref" switched ON. Otherwise, when the 4K reaches the LHe temperature a large part of the gas circulating condenses, leaving with a largely insufficient gas flux to cool down. So you basically lose the night entirely.

6) If (T_still < 7K and R_BM > 1240-Ohm) you could try to condense the mixture. To do that, simply close ev7, thus ev7=0, and switch ON the condensation procedure to regulate J4 at 4000mbar. Open ev18 to help the still and BM cooling. In case, increase slightly the pressure to J4=4500mbar (never more than that) but then decrease the target regulation value to 4000mbar.

7) At some point at the beginning of the condensation (e.g. after a few cycles of ev11 open/close) you might want to close ev18 to open it again when J5<50mbar. Or not, it depends on how it goes. Condensation should take no more than 12 hours (TBC).

8) When (J5 < 10mbar and J4 < 2000mbar) open ev18 if it's closed. ev18=1. Switch ON the turbo and stop the condensation procedure. Now just a matter of waiting it to reach base T.

CoolingPTcryostatNIKA (last edited 2013-07-16 09:37:33 by NikaBolometer)