2015/08/20 (Thursday)
| Overnight status: 10 MHz C-filter on DIB2 at ebox, HV1/2 → DCRC50/55, DCRCs powered, 80 V bias left on the HV. | |
| Temperature slowly rising overnight, 0.3 mK/hour, up to 37.8 mK at 09:30 | |
| 0935 | No phonon pulses present. +80 V / 157.1 nA. Reduce HV to 0. Pulses return, temperature drops to normal base. |
| 0936 | Filled LN2 cold trap full |
| 0940 | MC/Tower/Cold Plate = 25.3/31.5/153 mK, Still = 1.32K / 0.11 mbar, G1/G2 = 150 mbar, 1K Pot = 1.74 K / 24 mbar. MC sensor = 41.3 mK. Still, MC sensor, and Cold plate temperatures reading implausibly high, as if something is wrong with the Fridge Out 1 cable. |
| 0945 | Main bath = 19.6%. Boiloff rate looks normal now, 1.6%/hour |
| 1030 | Studying HV leakage currents, comparing + versus - and the two Kepco DC power supplies. Voltages measured with multimeter. |
| HV leakage current | ||
|---|---|---|
| HV: | 10.00 V | -10.00 V |
| 0-1000 V supply | -18.9 nA | +18.1 nA |
| 0-40 V supply | -19.0 nA | 18.3 nA |
It seems that the two supplies produce about the same leakage current, but there's a difference between + and -.
| 1045 | Using 0-1000 V DC supply, measure current versus HV in both polarities with voltage low enough so that phonon pulses don't disappear. |
|---|
| HV (V) | Current (nA) |
|---|---|
| 5.00 | 8.5 |
| 15.00 | 27.2 |
| 20.00 | 35.6 |
| -5.00 | -9.2 |
| -15.00 | -28.7 |
| -20.00 | -39.1 |
at +20 V, HV1pA baseline starts to increase, slow to recover (~3 minutes). This is the limit for pulses.
| HV(V) | Current (nA) | Tower (mK, ± 0.5) | notes |
|---|---|---|---|
| 25 | 46.2 | 31.6 | |
| 30 | 56.2 | 31.6 | |
| 35 | 67.0 | 32.6 | |
| 40 | 77.8 | 33.3 | |
| 45 | 88.8 | 34.4 | |
| 50 | 100.0 | 35.2 | originally 100.4 nA, settled after a minute |
| 55 | 110.9 | 36.2 | |
| 60 | 121.4 | 37.0 | last measurement before LHe transfer |
| 60 | 122.1 | 36.6 | first measurement after transfer |
| 65 | 132.6 | 37.8 | |
| 70 | 144.0 | 38.7 | |
| 75 | 154.5 | 39.7 | |
| 80 | 166.4 | 40.7 | |
| 85 | 177.5 | 42.1 | |
| 90 | 188.8 | 43.4 | |
| 95 | 199.9 | 44.4 | |
| 100 | 211.0 | 45.5 |
| 1150 | Begin LHe transfer @ main bath = 16.3% |
|---|---|
| 1222 | Finish LHe transfer @ 96.0% |
| 1330 | Reducing HV, pulses return around HV=36V, 71nA |
| 1630 | Restarted DCRCs, zapped squids. Using settings from table on 2015/08/14 but increased HV2 PC QET Bias to 110 uA to account for filter on DIB2 |
| 1645 | Currently +11 V on HV kills the phonon pulses. Set to +10 V (13 nA) (Vcrystal = 4.27 V), see pulses. |
| 1650 | Tried to look for current from HV leaking into QET lines by setting QET bias to zero and looking for changes in baseline as we adjusted HV below the threshold of heating. But realized our QET current resolution is only on the order of 100 nA, so unlikely to see anything. Besides the total leakage currents we are seeing are much too small to heat the QETs. |
| 1710 | Tried to find a Tc transition in HV1pA by heating with HV. But we were doing it wrong by simply leaving the QET bias at zero - normally you also apply a 10 mVpp triangle signal to the QET. In the process we cranked the HV to the highest values yet. Here are some examples: |
| HV (V) | HV current (nA) | Vcrystal (V) | Tower (mK) |
|---|---|---|---|
| 244.4 | 460 | 8.54 | 75.8 |
| 304.7 | 637 | 23.8 | 90.9 |