2020/09/30 (Wednesday)
- Lab in-person: Matt
- Virtual partner: Derek
| Setup | Run 73. DIB 1/3/4 → Stripline 43/48/41 → pi-filters 1/2/3 → Cable 3/1/2 → nothing/nothing/accessory_interposer → HV_Conn 1/3/2 → HV 1/2 → DCRCX(4)/DCRC55(1)-master; DCRC33(2) → HV control. DCRCs off. Lead/poly shield erected (4 lead walls, 2 poly walls). |
|---|---|
| Status | 1K Pot is not working. Warming up to clean it out. Mixture in fridge+dump+trap, helium in IVC and CVJ. MC/Still heaters = 20/30 mW. 1K Pot pumped out and isolated. |
| 0200 | Recovery = 0.31 cuft/hour, 387365.05 cuft |
| 0200 | MC(Cernox)/Sorb = 81.1/168 K. |
| 0600 | Recovery = 0.14 cuft/hour, 387365.80 cuft |
| 0600 | MC(Cernox)/Sorb = 103.5/220 K. |
| 0805 | Matt Fritts body temperature = 97.4 F |
| 0845 | MC(Cernox)/Sorb = 117.6/249.3 K. |
| 0910 | Recovery = 0.10 cuft/hour, 387366.05 cuft |
| 0910 | MC(Cernox)/Sorb = 119.6/>250 K. |
so we are already way above LN2 temperature. Todo:
- Turn off heaters
- check CVJ pressure
- Start pumping out CVJ (can refill if pot still seems clogged)
- Throughput-check 1K Pot, see Sep 17 14:50
- If Pot seems OK:
- pump out pot, CVJ (how long?), IVC
- proceed to LN2 transfer
- If Pot not clearly better:
- recover mixture, let things warm up.
| 0920 | Matt arrives in lab |
|---|---|
| 0920 | Turn off MC&Still heaters |
| 0930 | Cryostat vacuum jacket = 86 ubar. Start pumping out CVJ with Turbo Pump |
| 0935 | Check pressure in 1K Pot: about 0.02 bar on mechanical gauge. Pump out with Scroll Pump. |
| 1005 | Perform 1K Pot throughput test (at MC = 122 K). Close needle valve then pump out 1K Pot, isolated from MB. MB is full of helium gas, after bath boiloff yesterday. Pump out 1K Pot, then stop pumping and watch the pressure rise at P2. Then repeat, but after stopping pumping open the needle valve a certain amount. Measured the amount of time to rise from 0.5 mbar to 3.0 mbar. At needle valve = 0/10/20/30/60°, risetime = 900/97/67/68/18 seconds. 0/10/20/30/60° → 0.17/1.5/2.2/2.2/8.3 mbar/min |
| OK, what to make of this. These times are slower than on Sep 17, and fridge is colder. I would normally expect colder helium to flow faster, not slower. Does that mean there's still a problem? How warm is the 1K Pot? Well above 77 K, so frozen air is gone, but likely below freezing. | |
| 1050 | Recovery < 0.05 cuft/hr, 387366.05. Close Recovery valve from MB (and also from 4He Pump outlet) |
| 1055 | Insert the lab thermometer probe into the LN2 transfer stick. The 1K Pot is about 31.5“ down from the port. Insert the stick to position the thermometer near the 1K Pot. Readout falls to -30 C, then reads LL.L - apparently it can't read that cold. Clearly it's pretty cold down there. |
| from the rate that it was rising, I predict that Sorb is near 273 K now. But it's surely lower, simple linear extrapolation is wrong. | |
| 1125 | At 20“ above 1K Pot level, MB = -37.0 C = 236.2 K. At 19” above 1K Pot level, MB = -46.8 C = 226.4 K. |
| 1130 | With 1K Pot speedivalve and needle valve closed, pump on Main Bath with scroll pump. Once P2 < 2 mbar, open 1K pot speedivalve and needle valve (5 turns) to pump out 1K pot volume to < 0.5 mbar on P2. |
| 1140 | Close off scroll pump, then pressurize main bath and 1K Pot (both sides) with helium to 120 mbar +1atm on G3, then close 1K Pot speedivalve and needle valve. |
| 1145 | Pump out 1K Pot again with Scroll Pump, → 0.024 mbar. |
| 1145 | Perform 1K Pot throughput test (at MC = 130 K). Close needle valve then pump out 1K Pot, isolated from MB. MB is full of helium gas. Pump out 1K Pot, then stop pumping and watch the pressure rise at P2. Then repeat, but after stopping pumping open the needle valve a certain amount. Measured the amount of time to rise from 0.5 mbar to 3.0 mbar. At needle valve = 0/10/20/30/60°, risetime = 970/220/125/104/38 seconds. 0/10/20/30/60° → 0.15/0.68/1.2/1.4/3.9 mbar/min |
| This is slower throughput than the previous test. Maybe just because it's a little warmer? Anyway it is still a lot slower than on Sep 17, which was done at warmer temperature. So, there may still be a problem - there might be water ice in there. Let's not try to cool down today. | |
| 1215 | As a quick check, pressurize 1K Pot to 330 mbar+1atm. Pressure falls slowly with needle valve closed, not much faster at 30° (8 mbar/min). But with needle valve open 2 full turns, it falls pretty quickly (100 mbar/min). |
| 1225 | Pump out 1K Pot, close Speedivalve, then open Needle valve 2 full turns. We'll leave it open to the MB on that side. Just in case something expands in the pot, this will allow it to depressurize into the bath. (Not likely really - should just be water ice, which may melt but it won't boil.) |
| 1230 | Start pumping mixture out of fridge and LN2 Trap 1 into dump: close V13a, turn on 3He pump (V9 is open), open V6→12.8%. When G1<10 mbar open V6→21% |
| 1235 | Turbo on cryostat vacuum jacket = 19 nbar. With Turbo valved out for 1 minute, CVJ = 0.25 ubar |
| 1235 | Let 5.4 mbar N2 gas into vacuum manifold. Then open cryostat vacuum jacket valve to let this into the vacuum jacket. Vacuum Jacket → 250 ubar. |
| 1245 | At 20“ above 1K Pot level, MB = -37.1 C = 236.1 K. Basically no change from 11:25 |
| 1245 | MC(Cernox) = 132.5 K |
| 1315 | G2(dump) = 752.5 mbar and pretty flat. Barometric pressure = 28.91 inHg, temperature 61 F, gives sea-level pressure 29.73 inHg. Corrected dump pressure = 746.1 mbar. Compare with last time (743.9 mbar), a little higher. |
| 1315 | Close V9 and turn off 3He pump |
| 1320 | Cryostat vacuum jacket = 0.14 mbar. Close CVJ port valve. |
| 1320 | Matt leaves lab |
| 1615 | MC(Cernox) = 143.3 K. Rising faster since adding N2 to the CVJ. 3.7 K/hour Given lab temperature = 298 K this implies warming tau = 41.8 hours. MC will reach 273 K on Saturday at 8:27 pm. |
| 1650 | Turn on MC & Still Heaters to 20/30 mW |
| 2220 | MC(Cernox) = 166.7 K. Rising 3.8 K/hour |
| 2225 | Matt Fritts body temperature = 97.2 F |