2016/05/05 (Thursday)
| Setup: HV mode, DIB1/2/3 → -/-/Phonon reroute board → cables → 3.2MHz Filters → HV board → HV1/HV2 → DCRC55/50, DCRCs unpowered overnight | |
| Y-Be source and Cf source near mu-metal shield at detector level for overnight activation | |
| Temperature stable overnight | |
| 0910 | Tower/MC/Coldplate = 45.6/44.6/275 mK, Still = 1.18 K / 0.090 mbar, G1/G2 = 115/110 mbar, 1K Pot = 1.58 K / 4.0 mbar, Main Bath = 47.6% |
| 0910 | Remove Y and Cf sources from fridge and return to safe |
| 0915 | Fill LN cold trap bath |
| 0920 | Open 1KPot needle valve a few degrees more. Settles to 1.64 K / 6.0 mbar. |
| 1040 | Remeasure leakage current versus voltage (DCRCs off). |
| HV [V] | Vtest [mV] | ||
|---|---|---|---|
| 0.000 | -0.002 | 0.000 | -0.100 |
| 10.010 | 10.010 | 12.600 | 11.500 |
| 19.995 | 19.995 | 31.200 | 31.300 |
| 30.005 | 30.010 | 51.900 | 52.000 |
| 35.000 | 35.000 | 62.400 | 63.000 |
| 40.000 | 39.990 | 73.200 | 73.500 |
| 45.005 | 44.990 | 84.000 | 83.800 |
| 50.010 | 50.020 | 94.700 | 94.300 |
| 55.000 | 54.990 | 105.400 | 104.100 |
| 60.000 | 60.000 | 116.300 | 117.400 |
| 55.010 | 55.010 | 106.000 | 106.700 |
| 50.000 | 50.000 | 95.200 | 95.800 |
| 45.000 | 45.000 | 84.200 | 85.100 |
| 40.000 | 40.000 | 73.600 | 74.100 |
| 35.000 | 35.000 | 63.400 | 63.600 |
| 30.000 | 30.000 | 53.100 | 53.000 |
| 20.000 | 20.000 | 31.700 | 33.500 |
| 10.000 | 10.000 | 12.200 | 12.900 |
| 0.003 | 0.004 | -3.200 | -0.400 |
| supply off | -0.300 | 0.200 | |
| Second value is after waiting a few minutes | |||
These results are very similar to yesterday's results (with less evidence of anomalous negative Vtest values at zero HV).
Again a total resistance of 500 MΩ is implied, leakage resistance of 100 MΩ, so Vcrystal ≈ HV/5.
| 1345 | Power DCRCs and zap SQUIDs. |
|---|---|
| 1355 | Set up phonon channels on HV2 (on HV1 the phonon channels are unrailed, but unbiased). HV2 pB currently in a mode of not showing pulses. A sample screenshot shown below: |
 |
| 1400 | HV2 pC and pD are looking good with Frontend Gains set to 5, Output Gains set to 8. Power on HV supply and bring it up to 150V reading on voltmeter (should be ~30V across the crystal.) |
|---|---|
| 1410 | Set HV to 150.0V and test resistor is reading 314.4mV. Both HV2 pC & pD looking good. Set phonon trace length to 3.2768ms and set HV2 pC to a phonon threshold trigger of 20ADC bins. |
| 1415 | Those numbers indicate a voltage across the crystal of only ~11V, which means something's changed. Take a few more points. |
| HV [V] | Vtest [mV] |
|---|---|
| 150.0 | 314.4 |
| 125.0 | 259.5 |
| 100.0 | 204.5 |
| 82.1 | 165.8 |
| Note: At this point, I had to use the rough Voltage Adjust knob to change to the 0.1kV regime. As such, the HV went from 82.1V → ~0V then back up to 75V. |
|
| 75.0 | 149.5 |
| 50.00 | 95.5 |
| 25.00 | 42.8 |
| 0.001 | -4.7 |
| supply off | -3.5 |
- These actually match the previous curve but my analysis was overly approximate. Rleak falls off something like 1/x (closer to x^-0.85) with HV. At HV = 150 V, Rleak falls to 34 MΩ.
- It looks as though the leakage current goes as Vcrystal^3.25
- Situation is pretty dire, it's hard to get a decent bias on the crystal:
- The Vcrystal versus HV curve above fits reasonably well to Vcrystal[V] = 1.95*(HV[V])^0.356
- Even at HV = 1000 V this only gives Vcrystal = 23 V
- Note it appears significantly worse today than yesterday, because yesterday we had Vcrystal = 15 V when Vbias = 60 V. (However with the 7 V shift in HV on yesterday's data, they look about the same…)
- Another approximate fit formula: Gleak[nS] = 0.22*Vcrystal[V]^2
| 1600 | Commence LHe transfer (36.4%). |
|---|---|
| 1620 | Adjusted HV while monitoring ColdPlate temperature, to see if there's an effect. Increased HV to 120 V then back down to 0 V. CP varied randomly, between 270 and 275 mK, but seemed unaffected by application of HV. |
| 1645 | Finish LHe transfer (93.9%). |
| 1654 | Release pressure from MB for 30 s |
| 2012 | Fill LN2 cold trap full. |