2018/05/03 (Thursday)
| Found leak into IVC at 77K. Warming to room temp. Puming out cryostat vacuum jacket overnight. | |
| 0915 | MC(Cernox) = 274.6 K |
| 0920 | Turbo = 3.4 nbar, cryostat vacuum jacket = 34 nbar. Stop pumping out cryostat vacuum jacket. |
| 0935 | Lower main bath. |
| 1020 | Clean and inspect bottom IVC indium o-ring surfaces. On the bottom piece, no scratches seen in the o-ring area. Clean thoroughly with swabs and with wipes wrapped around plastic scraper. Also cut wooden swab sticks at a sharp angle to clean into the corner as tightly as possible. On the bottom rim of the middle IVC piece at the fridge, saw some scratches extending from the o-ring surface to a screw hole. These may have occurred when attaching the bottom can - trying to find the screw hole, if you miss you could scratch that area with the screw. Use scotch-brite to try to buff out these scratches. Careful to move the scotch-brite in a circular direction around the diameter, so that and new scratches produced are parallel to the o-ring rather than perpendicular. Some of the worst scratches in terms of path to a screw hole seem to be gone now. Other scratches are deeper and still present, but don't necessarily look like they would produce leak paths. |
Photo before polishing:  |
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| 1050 | Attach bottom IVC can. Begin pumping IVC with scroll pump. |
| 1100 | Begin pumping IVC with turbo pump |
| 1200 | Turbo on IVC = 140 nbar. Leak = 3.5 pbarL/s with turbo valved in, 44 pbarL/s with turbo valved out |
| 1245 | Rig up a series of LN2 level resistors, in case we see a leak to bath at 77K again. Three ~750 Ω resistors in series, taped to IVC seals at bottom, middle, top. 2.15 kΩ total at room temperature. Resistances of each go up by a few 100 Ω when they are cooled to 77K. Wires come out main bath port at top of fridge, threaded through a stopper. |
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| 1255 | Turbo on IVC = 86 nbar. Leak = 2.6 pbarL/s with turbo valved in, 40 pbarL/s with turbo valved out |
| 1305 | Squirt-check all IVC seals. At flange on stripline elbow, leak increases 40→110 pbarL/s. At knurled rings on stripline elbow 53→73 pbarL/s. No leaks seen elsewhere. |
| 1500 | Raise main bath |
| 1510 | Quick electrical check of all 3 DIBs. Checked relevant phonon channels, all look OK, nothing open, no shorts. Check cross-channel resistances, see continuity. |
| 1530 | Pump out fridge lines with scroll pump |
| 1530 | Turbo on IVC = 34 nbar. IVC = 860 nbar with turbo valved out for a few minutes |
| 1535 | Leak detector on IVC. IVC = 36 pbarL/s. |
| 1545 | Let mixture from 3He pump through cold LN2 Trap 1 into fridge lines, both sides. (Most mixture still in dump.) Leak signal does not change. |
| 1550 | Check pressure in 1K Pot: 26 mbar on P2, about 0.1 bar on mechanical gauge above IGH. Pump out with scroll pump. |
| 1555 | Pump out main bath with scroll pump to <1 mbar on P2. |
| 1605 | Pressurize main bath with helium to 255 mbar above 1atm on G3. Also let He into 1K Pot. No increase in IVC leak. |
| 1605 | Let 5.4 mbar He exchange gas into IVC |
| 1610 | MC(Cernox) = 288.7 K, Sorb = >249 K (max), IVC = 5.4 mbar, G1 (fridge) = 212 mbar, Old Level resistor = 0.986 kΩ, New level resistor = 2.150 kΩ |
| 1615 | Begin LN2 transfer. |
| 1625 | MC(Cernox) = 288.8 K, IVC = 5.4 mbar, G1 (fridge) = 212 mbar, Old Level resistor = 0.990 kΩ, New level resistor = 2.152 kΩ |
| LN2 Dewar valve is completely open but looks like another very slow transfer. Should stop and let it warm up. | |
| 1635 | Warm up LN2 Dewar fill outlet to room temperature with heat gun. |
| 1640 | Begin LN2 transfer again. Hose is vibrating, seems like there's liquid flowing now. |
| 1640 | MC(Cernox) = 286.8 K, IVC = 5.4 mbar, G1 (fridge) = 211 mbar, Old Level resistor = 0.990 kΩ, New level resistor = 2.152 kΩ |
| 1645 | MC(Cernox) = 286.1 K, IVC = 5.4 mbar, G1 (fridge) = 211 mbar, Old Level resistor = 0.993 kΩ, New level resistor = 2.156 kΩ |
| 1650 | MC(Cernox) = 284.8 K, IVC = 5.4 mbar, G1 (fridge) = 211 mbar, Old Level resistor = 0.999 kΩ, New level resistor = 2.170 kΩ |
| this is too slow again. We tried this before when the Dewar got “stuck”. Each time it happens when the Dewar is still cold from recent use. I think there's nothing to do but close it and let it sit for an hour or two then try again. | |
| 1650 | Close LN2 Dewar, stop transfer. Put ping-pong ball on fridge outlet. |
| 1915 | MC(Cernox) = 262.7 K, G1 (fridge) = 209 mbar, IVC = 5.4 mbar, Old Level resistor = 0.986 kΩ, New level resistor = 2.163 kΩ |
| 1920 | Restart LN2 transfer |
| Seems slow again. Attempt to pressurize LN2 Dewar through its vent outlet using a hose connected to the N2 cylinder. Note this cylinder is nearly empty so not sure I'll get much pressure from it. | |
| 1925 | MC(Cernox) = 262.4 K, G1 (fridge) = 209 mbar, IVC = 4.6 mbar, Old Level resistor = 1.000 kΩ, New level resistor = 2.167 kΩ |
| 1930 | MC(Cernox) = 261.4 K, G1 (fridge) = 209 mbar, IVC = 5.4 mbar, Old Level resistor = 1.017 kΩ, New level resistor = 2.184 kΩ |
| 1935 | MC(Cernox) = 260.1 K, G1 (fridge) = 208 mbar, IVC = 5.4 mbar, Old Level resistor = 1.031 kΩ, New level resistor = 2.215 kΩ |
| 1935 | Check N2 pressure at one of the outlets on the wall. Much higher than usual. So the Dewar pressure must be higher than the cylinder pressure. Stop trying to pressurize the Dewar, close the vent valve. |
| 1940 | MC(Cernox) = 256.6 K, G1 (fridge) = 208 mbar, IVC = 4.0 mbar, Old Level resistor = 1.033 kΩ, New level resistor = 2.261 kΩ |
| 1945 | MC(Cernox) = 250.1 K, G1 (fridge) = 208 mbar, IVC = 4.0 mbar, Old Level resistor = 1.036 kΩ, New level resistor = 2.279 kΩ |
| 1950 | MC(Cernox) = 245.4 K, G1 (fridge) = 208 mbar, IVC = 4.0 mbar, Old Level resistor = 1.044 kΩ, New level resistor = 2.314 kΩ |
| 1955 | MC(Cernox) = 238.5 K, G1 (fridge) = 208 mbar, IVC = 3.4 mbar, Old Level resistor = 1.053 kΩ, New level resistor = 2.512 kΩ |
| big jump in new level meter, must have hit the resistor at the bottom flange | |
| 2000 | MC(Cernox) = 231.7 K, G1 (fridge) = 208 mbar, IVC = 3.4 mbar, Old Level resistor = 1.063 kΩ, New level resistor = 2.530 kΩ |
| 2005 | MC(Cernox) = 224.0 K, G1 (fridge) = 208 mbar, IVC = 3.4 mbar, Old Level resistor = 1.075 kΩ, New level resistor = 2.557 kΩ |
| 2010 | MC(Cernox) = 214.6 K, G1 (fridge) = 208 mbar, IVC = 3.4 mbar, Old Level resistor = 1.103 kΩ, New level resistor = 2.601 kΩ |
| transfer is going about half as fast as the last normal one | |
| 2015 | MC(Cernox) = 206.1 K, G1 (fridge) = 207 mbar, IVC = 2.5 mbar, Old Level resistor = 1.114 kΩ, New level resistor = 2.651 kΩ |
| 2020 | MC(Cernox) = 193.9 K, G1 (fridge) = 206 mbar, IVC = 2.5 mbar, Old Level resistor = 1.130 kΩ, New level resistor = 2.738 kΩ |
| I think the level may have hit the second resistor in the new level meter around this time. This is also where the bath diameter gets wider and IVC diameter gets smaller so we are starting to fill the larger volume, level will go up much more slowly. | |
| 2025 | MC(Cernox) = 186.0 K, G1 (fridge) = 206 mbar, IVC = 2.5 mbar, Old Level resistor = 1.145 kΩ, New level resistor = 2.819 kΩ |
| 2030 | MC(Cernox) = 176.2 K, G1 (fridge) = 206 mbar, IVC = 2.5 mbar, Old Level resistor = 1.169 kΩ, New level resistor = 2.840 kΩ |
| 2035 | MC(Cernox) = 168.2 K, G1 (fridge) = 206 mbar, IVC = 2.2 mbar, Old Level resistor = 1.190 kΩ, New level resistor = 2.860 kΩ |
| 2040 | MC(Cernox) = 157 K, G1 (fridge) = 205 mbar, IVC = 2.2 mbar, Old Level resistor = 1.220 kΩ, New level resistor = 2.890 kΩ |
| 2045 | MC(Cernox) = 152.5 K, G1 (fridge) = 205 mbar, IVC = 2.2 mbar, Old Level resistor = 1.235 kΩ, New level resistor = 2.906 kΩ |
| 2050 | MC(Cernox) = 147.7 K, G1 (fridge) = 205 mbar, IVC = 2.2 mbar, Old Level resistor = 1.248 kΩ, New level resistor = 2.922 kΩ |
| 2055 | MC(Cernox) = 141 K, G1 (fridge) = 205 mbar, IVC = 2.2 mbar, Old Level resistor = 1.263 kΩ, New level resistor = 2.941 kΩ |
| 2100 | MC(Cernox) = 136.9 K, G1 (fridge) = 204 mbar, IVC = 1.9 mbar, Old Level resistor = 1.273 kΩ, New level resistor = 2.954 kΩ |
| 2105 | MC(Cernox) = 132.3 K, G1 (fridge) = 204 mbar, IVC = 1.9 mbar, Old Level resistor = 1.283 kΩ, New level resistor = 2.966 kΩ |
| 2110 | MC(Cernox) = 128.1 K, G1 (fridge) = 204 mbar, IVC = 1.9 mbar, Old Level resistor = 1.291 kΩ, New level resistor = 2.977 kΩ |
| 2115 | MC(Cernox) = 123 K, G1 (fridge) = 204 mbar, IVC = 1.9 mbar, Old Level resistor = 1.299 kΩ, New level resistor = 2.987 kΩ |
| 2120 | MC(Cernox) = 120.6 K, G1 (fridge) = 204 mbar, IVC = 1.9 mbar, Old Level resistor = 1.303 kΩ, New level resistor = 2.992 kΩ |
| 2125 | MC(Cernox) = 117.5 K, G1 (fridge) = 203 mbar, IVC = 1.9 mbar, Old Level resistor = 1.309 kΩ, New level resistor = 2.997 kΩ |
| 2130 | MC(Cernox) = 114.4 K, G1 (fridge) = 203 mbar, IVC = 1.9 mbar, Old Level resistor = 1.313 kΩ, New level resistor = 3.002 kΩ |
| tired of this. stopping the transfer and going home. If we need to we'll transfer again tomorrow. |
| Cryocleaning mixture | |
|---|---|
| 1220 | Check pressure in warm LN2 Trap 2, from a cleaning a few days ago: 2.4 mbar. Pump out with scroll pump. |
| 1235 | Start cryocleaning mixture through cold LN2 Trap 1, V6 = 12.8% |
| 1250 | Increase V6→13.1% to speed up flow |
| 1320 | Increase V6→13.2% to speed up flow |
| 1345 | Stop cryocleaning. Trap 1, 70 minutes. |
| 1405 | Start cryocleaning mixture through cold LN2 Trap 2, V6 = 13.3% |
| 1410 | Increase V6→13.4% to speed up flow |
| 1510 | Stop cryocleaning. Trap 2, 65 minutes. |
| 1520 | Check pressure in warm LN2 Trap 1: 10.6 mbar. Pump out with scroll pump. |
| Cryocleaning log | |||
|---|---|---|---|
| date | trap | duration (minutes) | contaminants removed (mbar) |
| May 3 | 1 | 70 | 10.6 |
| May 3 | 2 | 65 | 18.2 |