2020/03/06 (Friday)
| Setup | Run 72. DIB 1/3/4 → Stripline 43/41/48 → Cable 3/2/1 → nothing/nothing/accessory_interposer → HV_Conn 1/3/2 → HV 1/2 → DCRCX(4)/DCRC55(1). DCRCs on overnight. Lead/poly shield erected (4 lead walls, 2 poly walls). |
|---|---|
| Overnight: After flash Tower fell to 54.0 mK by 8:05pm, then the LN2 trap bath was filled and Tower rose to 57.8 mK, fell at a steady rate to 56 mK at 11:40pm, then for some reason fell much faster to 54 mK at 12:10am, then steadily tp 52.3mK at 3:25am, then rose a bit (to 53.0 mK) before starting to fall again - another early-morning excursion. Another small excursion at 7:25am, from 51.6→52.0 mK. | |
| 0925 | Tower/MC/Coldplate = 51.7/34.2/196 mK, Still = 1.6±0.1 K / 0.220 mbar / 8 mW, G1/G2= 592/529 mbar, 1K Pot = 2.23 K / 22 mbar. MB = 69.1% |
| 0945 | Fill LN2 cold trap bath |
- Yesterday's -250V data shows an even lower Luke gain, implying an effective bias of 24.5 V, which is 16.5% of what we expect with a 1mm gap
- Contrast +250V data, Luke gain implies 59.9 V, 39.5% of expected
- This agrees with a Run 69 observation showing lower apparent Luke gain for negative bias
| 1045 | Tower = 53.8 mK. As usual it rose after the LN2 fill, now it seems to have peaked and is starting to fall, slowly. |
|---|---|
| Yesterday we increased the Still heater. Now not surprising the Circulation pressures are higher. 1K Pot temperature is higher and pressure a little lower. Maybe try opening the 1K Pot needle valve more. | |
| 1050 | Open 1K Pot needle valve wider, 35° → 45° |
| 1135 | Tower = 53.5 mK, not much change. 1K Pot = 2.28 K / 30 mbar, higher. G1/G2 = 605/538 mbar, a little higher. |
| We're going to try measuring the HV where it enters the E-box, at the end of the cables and pi-filters. Make sure it's doing what it should. | |
| 1140 | Turn off MIDAS DAQ programs (triggerfe, towerfe, dcrc_driver) and power down the DCRC1/4. Change ODB settings to disable DCRC1/4 and make DCRC2 “free-running”. So we should be able to control HV with DCRC2. Turn programs back on. |
| 1320 | Powering down DCRCs caused Tower to fall from 53.6→52 mK. |
| 1520 | We've been attempting to measure the HV at the end of the cable just short of the E-box: |
- Studying Nick's wiring diagram for the HV box, determine that Cable 1 pin1 and pin3 should be the HV leads (connects to Conn2, far left at back of HV box)
- also Cable1 pin7/5/38/36 are QETC/QETCret/QETD/QETDret, all of which are readout channels, so these should all be grounded at the DCRC ground plane
- Try applying a couple of Volts HV and reading it with a multimeter at the end of the cable - reading close to 0V
- Disconnect HV box from cables and DCRCs and study the box. Conn2 pins 1 and 3 do indeed connect to HV through the large 400MOhm resistor (used Fluke in nS mode)
- Try reading HV at HVside of 400MOhm resistor - reads 2.4V… at the far side only reads 0.06V.
- Realize that this is an internal resistance issue - Rinternal of Fluke is 10 MOhm, so it draws current, most voltage drops across the 400MOhm resistor, 1/40 of it drops across the meter - so this measurement is consistent
- Trying to figure out if there's a convenient high-impedance way to measure the voltage.
| 1710 | Tower temperature has been rising since we disconnected the cables from the HV box. Why??? 51→62 mK in the last 90 minutes or so. |
|---|---|
| 1715 | Fill LN2 cold trap bath |
| 1720 | Plug Cable1 back into Ebox and all 3 cables back into HV box. Maybe the fridge will be happier that way. |
| 1730 | Tower temperature stopped climbing, starts hovering at 66 mK |