| 0853 | MC/Tower = 52.0/66.6 mK, G1/G2 237/214 mbar, Still = 4mW / 1.08K / 0.16 mbar, 1K Pot = 1.73 K / 22 mbar, Cold plate = 9.47 kΩ / 307 mK, MC sensor = -39.2 kΩ / 68.8 mK, Main bath = 36.6% |
| 0904 | Fill LN cold trap Dewar |
| 0914 | One-shot test to study the cryogenic situation: monitor MC, Tower and Cold Plate temperatures. Observations: |
| 1 | MC temperature fell to near 30 mK in 10 minutes, then began to rise again. Tower temperature followed along with Tower-MC increasing from 15 mK to about 20 mK. |
| 2 | G2 pressure increases linearly as mix is collected in dump. Temperature minimum occurs at G2 = 77 mbar. Stop one-shot when G2 = 100 mbar. |
| 3 | Cold plate initially gets warmer. After about 5 minutes it begins to cool along with the MC. CP-MC starts at about 215 mK, increases to 234 mK, then stays roughly constant. |
| 4 | Still gets colder. Still pressure falls by roughly 1/2. (Still heat was left at 4 mW - likely if it were heated more during the one-shot an even colder minimum could be achieved.) |
| | #3 above has interesting implications in terms of heat leaks. There are four main paths of heat from the CP stage to the MC stage: through the heat exchanger, through the tower, IR radiation, and through the tower thermometer wire assuming there is a touch. Since the CP got initially warmer, one of these must have been “disconnected” - of course that's the heat exchanger path, because returning mixture is what makes the thermal connection between MC and CP at the heat exchangers. But when CP-MC gets large enough, one or more of the other heat paths becomes strong enough to cause further cooling. |
| 0934 | Restore circulation, with 100 mbar of mixture in dump. MC gets warmer, to 196 mK. |
| 1006 | Move all mixture from dump into circulation. MC cools to 61 mK, seems to get stuck there - try increasing still heat from 4 mW to 8 mW. MC cools back to previous base, 53 mK. |
| 1025 | MC/Tower = 53/67 mK, G1/G2 = 282/256 mbar, Still = 8 mW/ 1.09 K / 0.20 mbar, 1K Pot = 1.70 K / 16 mbar, Cold plate = 9.51 kΩ / 306 mK. (note: 1K Pot needle valve was closed a bit at one point. It could be that with a lower pot temperature you want a higher still temperature for optimal cooling.) |
| 1051 | Tried connecting 3 DCRCs, DIB 1/2/3 = DCRC 31/50/33. But the interference problem returned repeatedly - could get rid of it by power cycling the DIB1 FETs but only for a couple of seconds. |
| 1130 | Connect DCRC31 → DIB1, DCRC33 → DIB2. |
| 1212 | All SQUIDs zapped and set, QET biases set, timing link set. Try to find a stable crystal bias… goal is nominally -4V/+4V, so 8V total - could be asymmetric but probably want some non-zero bias on either side, otherwise a lot of charge will be collected on guard rails (highly reduced charge collection efficiency for that side). |
| 1224 | Try many biases to test for stability, defined as how long it will last before slipping into the interference state (hopefully indefinitely). Side 1/2 = 0V/+3V, -2V/0V, and 0V/+8V all seemed stable. Tried -0.5V on Side 1 and various settings on Side 2… anything above +4.5 V on Side 2 seemed to only be stable for a few minutes. -0.5V/4.5V may have been stable, at least lasted for 13 minutes one time. |
| 1520 | With charge biases at zero (to avoid interference) tried setting the QET gains all to Front End = 50, Output = 7. This generally worked - in all cases I could find an appropriate Driver Offset so that pulses appeared in the window (this is easier to do with the y-axes range constant, e.g. -1.3 V to +1.3 V). |
| notes: | with DIB2 pC, any Front End Gain greater than 7 caused high-frequency noise in all the other channels from that DIB. With DCRC31, I am pretty sure that changing Front End Gain has no effect. This is based on comparing it to DIB2/DCRC33, where changes in the QET Front-End Gains always caused noticeable changes in the phonon channel displays, e.g. change in the baseline offset position. |
| | more evidence that the DCRC31 Front-End Gains aren't working: if you trigger on a phonon channel, there are certain threshold settings (around 500 to 800 ADC units) where there is a marked difference in event rate if you modify either gain setting significantly - this is seen in DCRC33 and in the Output Gain for DCRC31, but it is not seen in the Front-End Gain for DCRC31. |
| 1602 | Main bath = 26.2%. Hopefully it will last until tomorrow morning. |