2020/02/20 (Thursday)
| 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 turned off overnight. No shield. |
|---|---|
| overnight: tower temperature falling at constant rate, 0.22 mK/hour, 5.3 mK/day | |
| 0905 | Tower/MC/Coldplate = 68.4/33.2/195 mK, Still = 1.61 K/ 0.240 mbar / 0 mW, G1/G2= 147/123 mbar, 1K Pot = 2.21 K / 50 mbar. MB= 24.8% |
| 0915 | Fill LN2 cold trap bath from 25L bomb Dewar |
| 0935 | Try running a DC current through Motor A in a setup like yesterday's screw terminal test. With 200 Ohm series resistor and 0.7 V, current on Fluke is initially > 0.1 mA but then falls. Fridge heats to 0.47 K. Current falls to 0.01 mA. Disconnect circuit. Fridge starts to cool again. |
| 1130 | Start LHe transfer @ MB = 20.1 % |
| 1213 | End LHe transfer @ MB = 91.8% |
| 1300 | The transfer “shock” on the fridge seems to have put the 1K Pot (and circulation pressures) into a new lower state: Still = 1.57 K / 0.200 mbar / 0 mW, G1/G2= 133/110 mbar, 1K Pot = 2.09 K / 34 mbar That's colder than the 1K Pot ever got yesterday, although it's still high compared to other runs. |
| 1430 | Set up a circuit to run current through the motor coils. From the DC power supply to a 1.336 kΩ resistor to the Fluke ammeter to the coil. Apply some voltage and watch current and temperature change. |
| V_supply [V] | I_motorA [mA] | Tower temperature [mK] | wait time [min] |
|---|---|---|---|
| 0.1 | 0.08 | 67.3 | 1.5 |
| 0.7 | 0.53 | 84.1 | 3.0 |
| 1.7 | 1.30 | 194.3 | 3.0 |
| 3.1 | 2.28 | 365 | 3.0 |
| I_motorB [mA] | |||
| 3.0 | 2.23 | 95.8 | 3.0 |
| 4.9 | 3.63 | 152.2 | 3.0 |
| 6.1 | 4.55 | 196 | 3.0 |
| Series resistor: 1.336 kΩ | |||
- We can compare to similar measurements from the last run. It's not a big improvement, at least with Coil A: last time 2.5 mA heated the fridge to 290 mK, this time 2.3 mA heated it to 365 mK - that's worse actually. Not sure how long they waited for it to stabilize last time.
- The results for motor Coil A are consistent with a resistance at the MC stage around 10 or 20 Ω - this would imply heating power values around where you'd expect to explain the amount of heating. It's not obvious from this that any part of the NbTi wire is being driven normal.
- Motor Coil B does a little better. It's as if this coil is only 1 or 2 Ω. This one wasn't measured this way in the last run.
- We could do a little better by measuring the supply voltage with a meter - we just used the supply readout. Then we could get a better direct estimate of the resistance of the coil&connections at the MC stage.
| 1615 | Plug in DCRCs, zap SQUIDS, and adjust the channels a bit. Got pulses on all but one channel, adjusted QET bias to get strong pulses (generally much lower QET biases than Run 70 when we were at <40 mK). The one that isn't working yet is DCRC4pA (Side1pE). We looked at the SQUID modulation curve and adjusted the lock point. It looks OK. But the trace has no pulses and does not respond to changes in QET bias. |
|---|---|
| 1620 | Tower = 67.4 mK |
| 1630 | MB = 88.2% |
| 1730 | Fill LN2 cold trap bath from 25L bomb Dewar |