Preparation visit before Run6
In May 2013, 3 people come to the 30m to install the new 2mm array and replace the 1mm cold amplifier. Then, a cooling down will occur and the NIKA prototype stays cold until the Run6 proper starts.
Tuesday 14-May-2013: 10h (during maintenance) Open cryostat, replace array at 2mm and the 1mm cold amplifier. Install the new DC cables for the amplifier. Install a new 4K magnetic screen. Install electronics rack in the cabin and connect. Mount the anti-vibration legs on the pumping stage. In the evening, start cooling down.
15-17 May 2013: cooling down
18 May 2013: check resonances in a dark configuration and end the preparation as soon as it is ready. The cryostat stays cold until the observational run 6 in June.
Alessandro Monfardini, Martino Calvo and Nello D'Addabbo come by car from Grenoble.
Daily Reports
PreparationRun Sun 12/05
Left Grenoble by car in the morning, stopped at Calp
PreparationRun Mon 13/05
Arrived at the telescope around 3:30pm. Unloaded the car, installed archeops8, archeops9 and THz in the control room. Updated with SVN. Experiment file for next NIKA run: nika_iram2.txt
A few mbars of something in the cryostat (J1=50mbar).
PreparationRun Tue 14/05
GISMO electronics is still there. Thus first we'll have to wait that it's craned down before starting working on the cryostat. We re-pump the cryostat and the big pumping pipe before the intervention. Jpi is growing up a bit after pumping; 1e-3mbar per minute roughly. Not very dangerous, could be outgassing, but I have seen better. Could be a small leak at the O-rings. In any case we have to open later.
All planned operations completed. Furthermore, mu-metal screening on 4K and 50K stages:
- on 4K screen: (inner) METGLAS 2714A 2.0 inch x 0.6 mil std spec (bat), mu about 10000 @ 4K (see figure below); (outer) VITROVAC (same put on Sionludi @ Institut Néel)
- on 50K screen: only METGLAS
figure: METGLAS mu at 4.2K, real and imaginary parts.
Installed NICA_8f1 18nm IEF (litho at PTA) tested in run HE34 in Grenoble at 2mm. At 1.25mm left the NICA_8e 20nm IRAM we had for runs 4 and 5.
Cooling down started at 17:30. Everything seems correct. Only (known already) problem is a small leak (1.5e-7) while circulating for the preref. The leak is proportional to the flux.
Wednesday 15-May-2013:
Fixed a problem preventing the NIKEL boards to kick on automatically (still to be investigated in Grenoble with Olivier). Fixed an annoying problem preventing to control properly the cryostat. We have installed a brand new blue ethernet cable going directly from the main NIKA switch in the cabin down to the "automate" of the cryostat. Now the connection is OK, no more risks of losing control so far.
In the afternoon, taking advantage of bad weather preventing observations, we have installed the whole NIKA optics (curved M6) and laser-aligned the system in order to be ready for the next run. Replaced, with Santiago and Gregorio, one broken anti-vibration leg of the table holding the cryostat. We also made new semi-rigid cables for better connecting the electronics to the cryostat. Gregorio says we have used the VERY LAST one available at Pico Veleta. Since they break very often (every time more or less) not to be forgotten buying few more before the next run.
21h30. Snowing. T_4K=6K; T_still=8K; T_BM=9K. Reduced strongly the preref flux. Pumping through the 3He pump, injection pressure J4=1200mbar, on the pump input 15mbar (should be safe). Leak signal is now 3e-8. Refilled LN2 trap.
figures: Cryostat status at 21h30 today. J1 zero-point is at -15mbar actually, means the 3He pump in is at 15mbar.
Thursday 16-May-2013:
Problem during the bight: the "rapide" circulation was not correctly launched and when the first drops of He started to condense at the 4K coldest part the flux dropped drammatically. Thus we've lost roughly 6 hours of cooling down. In the morning, put again the "rapide" circulation" and started condensation at 10am. Not working immediately (still and BM heating up); had to open ev18 to have it started. At 14h everything seems OK. Still and BM are cooling toward 4K and the injection pressure J4 drops.
Procedure for cooling down the 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, only 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". 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. Now just a matter of waiting it to reach base T.
Availability of planets for Sunday 6-8 UTC slot this horizon plot