2020/03/10 (Tuesday)
| 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 on overnight. Lead/poly shield erected (4 lead walls, 2 poly walls). |
|---|---|
| Status | Stopped circulation yesterday. Switched to one-shot, so we are pumping out of fridge and trap to dump. Suspend 1K Pot operation - 1K Pot is pumped out and isolated (maybe still has some LHe in it?) |
| 0931 | He recovery meter = 341037 cuft, rate 16 cuft/hour |
| 1000 | Tower/MC/Coldplate = 1.1/1.5/2.6 ± 0.1 K, Still = 21 ± 2 K / 0.022 mbar / 0.0 mW, G1/G2= 1.2/529.4 mbar, 1K Pot = >7K / 0.026 mbar. MB = -1% |
| 1100 | Turn off DAQ programs and power down DCRCs 1&4. |
| 1115 | Try measuring detector+electrode capacitance. Using the HP LCR meter. Leave DCRCs plugged in so that they connect all the Side1 channels to ground. Connect one meter lead to the shell of the HV input (Detector Side1 channels) and the other lead to the shell of the test resistor cable (to electrode). |
| 1125 | At low oscillation-level setting, capacitance reading was really low. Turn it up to something like 0.7 V, reading is more reasonable. Expecting something like 20 pF. But we are getting various values - sometimes around 30 pF, but as high as 170 pF, not very stable. |
| 1130 | Try various frequencies. “Q” is maximum (12.2) at 2 MHz. At this frequency C = 130 pF. |
| Freq [Hz] | Q | C [pF] |
|---|---|---|
| 10e3 | CF | 70-100 |
| 20e3 | CF | 90-120 |
| 40e3 | CF | neg 300-500 (??) |
| 100e3 | -1.4 | 78-80 |
| 200e3 | -2.4 | 84 |
| 400e3 | -12.4 | 93.8 |
| 1e6 | -2.71 | 82 |
| 2e6 | -21.1 | 119.7 |
| 4e6 | 19.59 | 128.13 |
| 10e6 | 0.9 | 34 |
| 1200 | Let's connect the HV side to Pin 1 at the cable, instead - this bypasses the 40 MOhm resistors. But this gives some nonsensical results. |
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| 1300 | Set up to measure R and C using Wavetek Function Generator and oscilloscope, apply AC voltage at test resistor, measure Vinput and Vtest with scope. |
Sine-wave measurement:
| measurements: | ||||
|---|---|---|---|---|
| freq | Hz | 11.67 | 3.347 | 0.334 |
| I shift | s | -6.00E-03 | -2.20E-02 | -0.625 |
| Vin | V | 9.68 | 9.68 | 9.68 |
| Vtest | V | 0.24 | 0.216 | 0.068 |
| calculations: | ||||
| phase | radians | -0.439948635 | -0.462656067 | -1.311614933 |
| omega | Hz | 73.32477253 | 21.02982122 | 2.098583893 |
| RC | s | 0.02897268 | 0.095339259 | 0.126344816 |
| I | A | 2.40E-07 | 2.16E-07 | 6.80E-08 |
| C | pF | 793.9344846 | 2377.33359 | 3463.062931 |
| R | MOHm | 36.49253279 | 40.10344151 | 36.48354606 |
- In the above table RC constants are calculated from measuring V at two different times.
- Vtest measured across 1 MOHm test resistor, gives the current
- Expected R is 21 MOhm, this is the two 40 Ohm resistors to the HV in parallel
Square-wave measurement:
| measurements: | |||
|---|---|---|---|
| with pi filters | without pi filters | ||
| RC | s | 0.119223742 | 0.035690445 |
| Vmax | V | 10 | 9.9 |
| Vtestmax | V | 0.288 | 0.36 |
| calculations: | |||
| I | A | 0.000000288 | 0.00000036 |
| R | MOHm | 34.72222222 | 27.5 |
| C | pF | 3433.643769 | 1297.834364 |
- These function-generator measurements give huge capacitances.
- Removing the pi filters definitely changes the result
| 1320 | In the square-wave measurements there's also a very short initial fall, 300-400 us. Divided by 20 MOhm implies 20 pF. Well that's interesting… |
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| For the fast time constant case: RC/Vin/Vtest = 0.4ms/9.9V/7.0V → R/C = 1.4 MOHm / 282 pF |
OK, a muddled and confusing picture all around.
Note: none of the function-generator observations gives any indication of a polarity asymmetry. So nothing giving a clue to the polarity asymmetry in Luke gain.
| 1331 | He recovery meter = 341100 cuft, rate 15 cuft/hour |
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| 1355 | Open 1K Pot speedivalve to check pressure: about 0.2 bar on the mechanical gauge. Pump out 1K Pot in steps with the 4He pump. Note that 1K Pot temperature does not fall. How warm is it? 1K Pot > 7K; Sorb = 10.2 K. So Pot is well above 4K but well below 77K. |
| 1415 | 1K Pot is down to 0.5 mbar and flat. Stop pumping 1K Pot and isolate it again. |
| 1425 | G2 (dump) = 585 mbar and rising. G1 (condenser) = 0.9 mbar, slowly falling. P1 (still) = 0.020 mbar, slowly falling. Tower = 1.07 K, behaving as a 1K Pot as we continue in one-shot mode. |
| 1430 | Isolate fridge (close V1 and Still Gate valve) then open V3 to pump remains of cold LN2 Trap 1 directly to dump. Tower temperature starts to rise. |
| 1435 | IVC = 54 ubar. (We stopped pumping it yesterday, hasn't gone up much.) |
| 1440 | Isolate LN2 Trap 1 and remove it from the LN2 bath to warm up. |
| 1440 | Tower = 1.53 K and rising |
| 1445 | Close V6 to stop pumping mixture. Open fridge to GHS again. Then let mixture from dump into both sides of fridge through V4 & V3. Tower rises quickly to 3.7 K. |
| 1450 | Tower/MC(H35) = 3.5/3.4 K |
| 1500 | Let some He gas into the IVC, less than a tube-length. IVC → 40 ubar. Tower temperature rises quickly above 4K. Fridge pressure rises, G1 500→560 mbar. 1K Pot falls to 6.1 K, then rises again. |
| Isolate IVC then connect turbo pump manifold to cryostat vacuum jacket port | |
| 1500 | Tower/MC(H35) = 5.0/5.0 K |
| 1503 | He recovery meter = 341123 cuft, rate = 15 cuft/hour |
| 1515 | Let 1.9 mbar He gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vaccum Jacket → 0.046 mbar. Recovery meter speeds up. |
| 1524 | He recovery meter = 341148 cuft, rate = 192 cuft/hour |
| 1535 | MC(Cernox) = 5.66 K and rising |
| 1610 | MC(Cernox) = 8.21 K and rising. G1 (fridge) = 584 mbar. |
| 1615 | Start pumping mixture from fridge (both sides) to dump. |
| 1607 | He recovery meter = 341230 cuft, rate = 90 cuft/hour |
| 1630 | MC(Cernox)/Sorb = 8.51/16.0 K and rising |
| 1630 | G2(dump) = 701.0 mbar, still rising slowly. (Around 701.7 before turning off the pump.) Fridge pressure has bottomed out. Stop pumping out fridge. |
| 1717 | He recovery meter = 341300 cuft, rate = 46 cuft/hour |
| 1800 | Around this time recovery meter starts moving a lot more slowly. MC(Cernox) = 22 K |