2015/05/22 (Friday)
| 0840 | Fill LN trap Dewar |
|---|---|
| 0841 | Detector baking, Tower = 99.5 mK and steady. MC = 58.4 mK, G1/G2 = 333/303 mbar, Still = 8 mW / 0.22 mbar, 1K Pot = 1.59 K / 5 mbar (rather low…) |
| 0845 | Turn off flashing (use rd 30 on Putty sessions to confirm: last digit is 0, would be 3 if flashing) |
| 0915 | As yesterday, DCRC33→DIB1, DCRC31→DIB2, DCRC50→DIB3. Try setting all phonon gains and biasing crystal to +4/-4 V |
| Observation: on DCRC33/DIB1 all channels get noisier if the Front-end Gain on pC is raised above 7. | |
| 1000 | Having difficulties losing the phonon pulses. The traces rail to 1.25 or -1.25 V. A typical fix is to set the Front-end Gain of the phonon channel down to 1 than back to 50 - often they simply come back as normal. Other times it is necessary to readjust the Driver Offset. |
| 1010 | Also having difficulties losing charge pulses on DCRC31/DIB2. There was a problem in the past with DCRC31 that the FETs would spontaneously lose power. This is what the symptoms looks like (a certain sort of choppy noise in the charge channels). |
| 1020 | DCRC31 has stopped responding to changes in front-end settings. Cold reboot of DCRC31. (Note: yesterday's observation that DCRC31's phonon channels do not respond to changes in Front-end Gain seems to have been a temporary problem, because today they definitely do respond to gain changes.) |
| 1036 | More problems with DCRC31/DIB2 charge. Lose charge pulses, restore them by heating FETs. Causes some heating of the tower. |
| 1100 | Discovered that 1K Pot ran dry an hour ago. 1K Pot at 2.58 K / 4.5 mbar. Base is about 10 mK warmer than before. Still rose at 0.7 mbar, G1/G2 rose to around 800 mbar (so some mixture was released to the dump). |
| 1102 | Disconnect all DCRCs and turn off still heat. Open needle valve wider to restart 1K Pot. |
| 1104 | Pot = 1.75 K / 20 mbar. G1/G2 = 630/580 mbar and falling. Still = 0.24 mbar and falling. MC = 70 mK and slowly falling. |
| 1152 | All mix returned to circulation lines. MC/Tower = 55/69 mK, G1/G2 = 350/318 mbar and stabilizing, Still = 8 mW / 0.20 mbar, 1K Pot = 1.66 K / 9.0 mbar - has been drifting downward |
| 1206 | Needle valve opened wider, 1K Pot = 1.74 K / 26 mbar |
| note concerning interference problem: | A similar problem was seen in Run 41 on DIB2 using SQUET ZC-23, which is the same SQUET we have on the current problem DIB (DIB1). These images look familiar. |
|---|---|
| actually this is incorrect: in Run 41 the pattern appeared whether ZC-13 or ZC-23 was used. But the side coax used on the problem DIB then was the same used on DIB1 now: ZB1-6. |
| 1252 | Discover that we cannot set DIB1(DCRC33) charge biases with DIB1 FETs off. There is clearly no effect on the DIB2 charge pulses when we modify the DIB1 charge biases if the DIB1 FETs are off. However with the DIB1 FETs on, applying -4 V to Side1 causes many inverted charge pulses to appear on DIB2. This of course is a problem since leaving the DIB1 FETs on will surely induce the interference problem. Will have to leave Side1 grounded. |
|---|---|
| 1315 | Trying 0/- polarity biases. Breakdown at 0/-4.5 V or greater. 0/-4.0 V seems stable. |
| 1500 | Have become frustrated with trying to set all phonon gains without the phonon channels railing. Often some event will cause all phonons to rail, so you have to go back and fix ones you already fix… uphill battle, seems to be unwinnable. Give up trying to take data. |
At the meeting, Nader suggested that a leaky capacitor in the side coax could be responsible for the interference problem. We hooked up DIB1 and DIB2 for comparison to the breakout box and tried to check for this with the multimeter:
| +/- leads | DIB1 | DIB 2 |
|---|---|---|
| QiFB / QiBias | open | open |
| QiBias / QiFB | open | open |
| QiFB / QiDrain | 19 nS | 18 nS |
| QiFB / QiSource | 19 nS | 18 nS |
| QiDrain / QiFB | open | open |
| QiSource / QiFB | open | open |
so no obvious problem with DIB1 in this regard.
| 1540 | Cryo test: try banging the cryostat from the west (back) side - sort of a shove at roughly mid-height. The idea is that if there is a touch of the 100 mK can to something, this may make it worse or better. MC rises from 54.5 to 57.5 mK and stays there. But Cold Plate = 268 mK (10.47 kΩ), lower than it has been yet this run. |
|---|---|
| 1554 | MC temperature decreases to 47 mK, best this run. Cold Plate = 261 mK. |
| 1610 | MC = 47 mK, stable (still adjusted to 6 mW - tried 4 mW but the temperature oscillations returned) |
| 1614 | Bang the cryostat again. Cold Plate rises 20 mK then falls back down. MC settles at 46 mK. |
| 1618 | Go to one-shot mode. This time adjust still heat to try to maintain 0.20 mbar pressure. |
| 1625 | MC minimizes at 32 mK when G2 = 85 mbar, then rises again. Still increased to 10 mW. |
| 1632 | When G2 = 130 mbar, MC starts to warm more quickly: 40 to 100 mK in 8 minutes. |
| 1646 | Still = 16 mW / 1.13 K / 0.20 mbar |
| 1647 | when G2 = 215 mbar, MC reaches 152 mK then begins to fall again |
| 1653 | when G2 = 215 mbar, MC reaches minimum of 134 mK then begins to rise. At this time Still at 1.29 K and rising, 24 mW, 0.18 mbar. |
| 1657 | when G2 = 262 mbar, sudden drop in Still pressure to 0.055 mbar (at 40 mW, 6.5 K). Also G2 curve hits a cusp here (previously quite linear). MC warming much more quickly. |
| 1703 | End test and recover mix. Close 1K Pot needle valve, speedivalve, valve 4a, valve at pump, and turn off 1K Pot pump (scroll pump). Set MC to 20 mW, Still to 200 mW. |
| 1724 | Pump cold trap contents to dump. |
| 1757 | Open/close V6 from 26.0% to 25.3% to alternately pump out mix / allow MC to warm to around 2 K. Pumping both sides (V6, V3, V1 open). |
| 1820 | 792 mbar recovered to dump, MC = 8.8 K. Isolate fridge & dump (all valves closed). Turn off 3He pump. |
| Barometric pressure currently 30.175 “Hg, so true dump pressure is 801 mK. |