previous day
| | Overnight status: nothing plugged into ebox. |
| 0930 | MC/Tower = 24.5/31.6 mK, Still = 0.11 mbar, G1/G2 = 160 mbar, 1K Pot = 1.73 K / 26 mbar, Main bath = 55.4% |
| note: | boiloff rate unusually high again, about 1.8%/hour (usually it's less than 1.7%/hour) |
| 0940 | Fill LN2 cold trap Dewar |
| 1100 | Put 10 MHz C-filter on DIB1 at ebox, then set up HV board, HV1/2 → DCRC50/55. This will filter all HV1 phonon channels. I'd actually intended to try to filter the incoming HV, but this won't do that - we actually need three filters for that since the bias channels (6 phonon, 2 charge) are on all three DIBs. |
| 1125 | Remeasured current versus HV and tower temperature versus HV. Very similar results with yesterday (not surprising since we're not really filtering the bias voltage). |
| 1145 | Check whether current drawn from HV changes with time. Set to -10 V, current falls from -16.5 nA to -14.5 nA after a while. Compare with the measurements from yesterday with the ebox disconnected: 7 nA to 2.5 nA. It looks like the conductance at the cold end is greater and not time dependent. |
| 1150 | Set Side1 charge bias to 0 and observe HV1 pA with output gain set to 3, QET bias = 110 μA. |
| Phonon baseline versus HV |
| HV (V) | HV1pA baseline (V) | notes |
| -10 | -0.96 | |
| -13.5 | -0.94 | |
| -14.3 | -0.91 | |
| -15 | -0.66 | |
| -15.5 | 0.18 | |
| -16 | 0.26 | pulses very small |
| -16.5 | 0.26 | pulses almost gone |
| -17 | 0.26 | pulses gone |
| -20 | 0.26 | pulses gone |
Increasing baseline suggests decreasing TES current, suggesting increasing TES resistance, suggesting that the TES is being warmed. At -16 V it looks like TES is being warmed to its Tc.
| 1200 | Leave HV at -16.0 V (Side1 charge bias = 0) and observe HV1pA at different QET biases. |
| Phonon baseline versus QET bias |
| QET bias (μA) | HV1pA baseline (V) | notes |
| 110 | 0.26 | pulses very small |
| 100 | 0.32 | a little larger |
| 90 | 0.35 | a little larger |
| 80 | 0.36 | larger |
| 70 | 0.33 | larger |
| 60 | 0.28 | larger |
| 50 | 0.18 | larger |
| 40 | -0.3, unstable | quite large |
| 30 | < -1.25 (offscale) | adjusting driver offset looks like mostly noise and abnormal pulses, probably superconducting |
The baseline relationship is basically an IbIs measurement. As bias is decreased, initially the TES current decreases (as noted by the increasing baseline) but at low enough biases the TES current starts to increase as its resistance gets very low and it approaches superconducting.
| 1210 | At a HV1pA QET bias of 50 μA, the phonons still disappear when the HV is increased to -16.5 V. |
| 1215 | Try setting Side1 charge biases to +14 V then increase HV (crystal bias). Now it seems that there's a relaxation time: increasing the HV causes phonons to disappear initially but they come back after time. HV can be set as high as -16 V but it takes a few minutes for the phonon pulses to return. Note that HV current is about -24 nA so voltage drop across 400 MΩ bias resistor is -9.6 V, thus crystal bias is actually only -6.4 V. |
| 1225 | Set HV to -18 V (-27.7 nA). Phonon pulses disappear. Wait… |
| 1309 | Still no phonon pulses. Dial down to HV = -17 V (-26.2 nA) - pulses come back immediately. Crystal voltage = 6.52 V. |
| 1320 | Take IbIs measurements for HV1 pA at HV = -17 V and HV = 0 V (side1 bias = 0 in both cases). |
IbIs observations: the R_TES versus Ibias curve is shifted to higher Ibias for the filtered/HV=0 case than for either the unfiltered/HV=0 case or the filtered/HV=-17V case. It suggests that there is additional TES excitation in both the unfiltered and HV-biased cases. The Ibias values at which R_TES=200 mΩ are 107/97/93 μA in the filtered/biased/unfiltered cases. It suggests additional excitations of 0/3.4/4.6 pW in the three cases.
| 1555 | Perform a mini-bake, leaving tower at plateau temperature for 3 minutes. |
| 1601 | Immediately after mini-bake increase HV to max, -31 V (55.4 nA). This is emulating the CDMSlite operating mode. |
| 1623 | Tower has cooled to 36.2 mK, probably within 1 mK of base at this HV setting. HV current a little lower at 54.5 nA. |
| 1625 | Reduce HV until pulses return. Pulses return at -19 V, but it seems to be temporary. Pulses consistently present and strong at -18 V. |
| 1639 | Try increasing Side1 charge bias to +14 V. It can be done but generally after an increase pulses disappear, then reappear after some time. The higher the bias the longer the wait. (It may be better to set Side1 bias first, then increase HV.) Maximum: Side1 bias = +14 V, HV = -18 V / -28.4 nA (bias at crystal = -6.64 V). |
| 1642 | Try opposite polarity. First zero all biases, then set Side1 to -14 V, then increase HV. Phonons disappear at +19 V, reappear after reducing to +18 V / 30.5 nA. Measuring HV with meter gives 17.77 V. Maximum: Side1 bias = -14 V, HV = +17.77 V / +30.5 nA (bias at crystal = +5.57 V) |
| 1755 | Main bath = 39.4%. Again boiloff rate is high at 1.9%/hour |
| 1800 | Fill LN2 cold trap Dewar |
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