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2016/07/15 (Friday)

Previous Day

Status Third day of circulation. DCRCs on overnight.
Setup: iZIP mode, DIB1/2/3 → cables → 3.2 MHz filters → DCRC55(1)/33(2)/50(3)
0835 Tower/MC/Coldplate = 38/36/161 mK, Still = 2 mW / 1.48 K / 0.130 mbar, G1/G2 = 95/95 mbar, 1K Pot = 1.47 K / 3.6 mbar
0840 Fill LN2 cold trap Dewar
0845 Turn off still heater
1115 Some temperature spikes have occurred in the Tower thermometer over the last two hours. 6 or 7 spikes at random times, sharp rise then normal fall times back to base, different heights but as high as ΔT = 9 mK
1120 1K Pot down to 2.6 mbar. Open 1K Pot needle valve a few degrees more.
1130 Tower/MC/Coldplate = 38.0/36.0/157 mK, Still = 0 mW / 1.40 K / 0.130 mbar, G1/G2 = 105/105 mbar, 1K Pot = 1.65 K / 22 mbar, MB = 60.9%
note The boiloff rate is indicative of the fast-boiloff that we get when we don't release pressure. So we should continue to release pressure from the bath after a fill.
1155 Setup DCRCs 1/2/3 with QET Bias values from the beginning of Run 56. Values shown below:
Ibias (μA)
DIB 1 pA 114.2
pB 127.1
pC 117.8
pD 100.8
DIB 2 pA -112.6
pB -112.6
pC -138.8
pD -97.7
DIB 3 pA 110
pB 100.7
pC 92.5
pD 119.2
1235 After grappling with some slow-computer issues, all channels are alive and showing pulses.
1320 Start one 30min background series at -4/+4 V with FG=5/2/5, OG=3, with 1000 initial randoms, 1000 ending randoms, with 30s flash and 25 minute cooldown between series. Trigger on DIB1 phA with threshold of 30ADC bins, with 150 us pileup cut window.
1430 Lower mu-metal shield 23.2 cm below its standard height. (Standard position is marked by red tape on cryostat, bottom edge of tape = top edge of shield).
Begin warming tower above 1.2 K
1435 Close V6 to stop circulation. Tower → 0.2 K, G1/G2 → 50 mbar, P1 → 4.5 mbar
1440 Close V13B and turn off 3He pump.
1445 Turn on MC heater to 1 mW. Currently Tower = 0.35 K. Begins to warm more quickly.
1450 Still (P1) has risen to 38 mbar. Condenser (G1) has fallen to 15 mbar. Open V3. P1 rises a little and G1 falls a little. So apparently condenser pressure was higher.
1500 Still (P1) = 450 mbar, Condenser (G1) = 16 mbar. Both are rising. But these are actually the same pressure, V3 open, so P1 of course reads too high at this pressure.
1507 Tower = 1.0 K
1530 Still (P1) = “1000” mbar, Condenser (G1) = 23 mbar.
1536 Commence LHe transfer (51.5%).
1540 Tower/MC(H35)/MC(Cernox) = 1.63/1.80/1.65 K
1550 Tower = 1.7 K. Good enough, start cooling again. Turn off MC heater. Turn on 3He pump.
1555 Close V3, open V13B. G1 goes up (20→35 mbar), G2 goes down (43→30 mbar). Wait for them to settle.
1600 Start circulation again, open V6 to >12%. See response at 13.4%, G1/G2 begin to rise.
1605 V6 = 13.4%, Tower/MC = 1.65/1.66 K, Still = 1000 mbar, G1/G2 = 75/75 mbar, 1K Pot = 1.48 K / 4.0 mbar
1605 Recommence LHe transfer (43.3%).
1615 Open 1K Pot needle valve a few degrees more
1625 V6 = 13.6%, Tower/MC = 1.65/1.85 K, Still = 1000 mbar, G1/G2 = 185/180 mbar, 1K Pot = 1.65 K / 24 mbar
1627 Finish LHe transfer (after changing Dewars) at 92.6%
1635 V6 = 13.8%, Tower/MC = 1.47/1.60 K, Still = 130 mbar, G1/G2 = 215/210 mbar, 1K Pot = 1.63 K / 18 mbar
1640 Release pressure from Main Bath.
1655 V6 = 14.2%, Tower/MC = 1.31/1.45 K, Still = 17 mbar, G1/G2 = 280/270 mbar, 1K Pot = 1.61 K / 14 mbar
1705 V6 = 14.6%, Tower/MC = 0.99/0.90 K, Still = 3 mbar, G1/G2 = 200/190 mbar, 1K Pot = 1.59 K / 11 mbar
1710 Fill LN2 coldtrap full. Also, top off HPGe detector LN2 dewar. This should last over the weekend.
1720 V6 = 16.0%, Tower/MC = 287/317 mK, Still = 0.7 mbar, G1/G2 = 195/180 mbar, 1K Pot = 1.57 K / 9 mbar
1725 Open V6 100%
1730 Tower/MC = 145/317 mK, Still = 0.16 mbar, G1/G2 = 170/160 mbar, 1K Pot = 1.57 K / 8 mbar
1748 Starting overnight HPGe run. Bias=3.502kV, Course/Fine Gain = 100/1?(Sketchy knob), Shaping time=6us, Output Range=+6V. DCRC X, PA trigger= 30ADC(4.6mV).
1752 Tower/MC = 40.1/31.7 mK, Still = 0.11 mbar, G1/G2 = 122/116 mbar, 1K Pot = 1.54 K / 7 mbar
Opening 1K pot additional 30 degrees.
1830 Tower/MC = 38.2/28.5 mK, Still = 0.14 mbar, G1/G2 = 145/138 mbar, 1K Pot = 1.67 K / 30 mbar
1835 Place Cf source at detector height at back of fridge.

Preparing to test phonon collection efficiency as a function of mu-metal shield height. This requires heating the tower then recooling it with the mu-metal shield at the desired height (in order to trap flux in the Al fins of the QETs). The following procedure is abstracted from the warmup/cooldown in Run 56 on March 14:

Procedure for warming above 1.2 K then cooling again with mu-metal shield at a particular position

Warm tower (takes about 1 hour 45 minutes)

  1. Close V6 to stop circulation. Tower temperature will rise, G1/G2 pressures will fall, Still pressure will rise.
  2. Close V13A or V13B and turn off 3He circulation pump.
  3. Set MC heater to 1 mW.
  4. Still pressure (P1) will continue to rise. When it gets above 500 mbar open V14 to release pressure to dump.
    (Is this necessary? Maybe just open V3 to make sure there isn't a buildup on one side of the fridge or the other. If pressures get high, then release to dump.)
  5. Optional: to check still pressure close V14 and open V3, see if G1 changes. Then close V3 and open V14 again.
  6. At any point before beginning cooling again, move mu-metal shield to desired position
  7. When Tower temperature ≥ 1.7 K you can begin to cool to base again

Cool to base again (takes about 2 hours 20 minutes)

  1. Turn off MC heater. Turn on 3He pump. Open V13A or V13B. (Leave V14 open.)
  2. Begin circulation in standard way by opening V6 to > 12.5% in steps, allowing G1/G2 to settle between steps.
  3. When Still pressure (P1) < 0.6 mbar or so close V14. This should happen about 1 hour after beginning cooling.
  4. Continue cooling to base.
  5. After tower is cold (<0.2 K) raise mu-metal shield back to standard height before taking measurements.

end

Note the above procedure has been updated, so that pressure is not released into the dump.

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