2016/05/06 (Friday)
| Setup: HV mode, DIB1/2/3 → -/-/Phonon reroute board → cables → 3.2MHz Filters → HV board → HV1/HV2 → DCRC55/50, DCRCs powered overnight | |
| Cold plate temperature stable overnight | |
| 0835 | Fill LN2 cold trap. |
| 0835 | Tower/MC/Coldplate = 48.9/47.8/260 mK, Still = 1.22 K / 0.080 mbar, G1/G2 = 100/100 mbar, 1K Pot = 1.61 K / 5.0 mbar, Main Bath = 77.3% |
| Begin looking for hints as to the source of leakage current by trying various cable combinations. Biasing with 1kV supply, DCRCs unpowered. Leakage measured immediately after bias change, and again ~2 min later. |
| Bias [V] | Leakage [mV] |
|---|---|
| All DIBs connected | |
| 1 | 1 |
| 5 | 7.5 → 2.5 |
| 10 | 10 → 12 |
| 15 | 22 → 20 |
| 20 | 30 → 34 |
| 25 | 44 |
| 30 | 53 |
| DIB1/2 connected, DIB3 open w/o diverter | |
| 1 | 2 |
| 5 | 4 |
| 10 | 10 → 12 |
| 15 | 23 |
| 20 | 34 |
| 25 | 44 |
| 30 | 55 |
| DIB1 connected, DIB2 open, DIB3 open w/o diverter | |
| 1 | 2 |
| 5 | 7.5 |
| 10 | 12 → 7 |
| 15 | 11 → 2 (~5 min) |
| 20 | 11 → 0 (~5 min) |
| 30 | 15 → 4 (~5 min) |
| DIB2 connected, DIB1 open, DIB3 open w/o diverter | |
| 1 | 1 |
| 5 | 6.5 → 4 |
| 10 | 12 → 12 |
| 15 | 22 → 23 |
| 20 | 33 |
| 25 | 43 |
| 30 | 54 |
| So it looks like DIB2 is responsible for pretty much all of the leakage current. (It is certain at least that DIB2 leaks and DIB1 has no significant leakage. It's probable that DIB3 doesn't leak much either but it's not verified.) |
|
| 1500 | DIB3 warm end diverter board was not being used for this run. We modified it by removing the single jumper wire which had connected Pin4 on the male Dsub connector to Pin7 on the female Dsub. |
| 1514 | Using modified diverter board to target certain portions of DIB2. Other DIBs disconnected. |
| Bias [V] | Leakage [mV] |
|---|---|
| DIB2 QI/QO lines connected | |
| 1 | 1 |
| 5 | 8→5 |
| 10 | 10 → 5 |
| 15 | 12 → 7 |
| 20 | 14 |
| 25 | 15 |
| 30 | 20 |
| DIB2 PA lines connected | |
| 1 | 2 |
| 5 | 7 |
| 10 | 13 |
| 15 | 22 |
| 20 | 34 |
| 25 | 44 |
| 30 | 54 |
| DIB2 PB lines connected | |
| 1 | 2 |
| 5 | 7 |
| 10 | 12 |
| 15 | 16 |
| 20 | 19 |
| 25 | 27 |
| 30 | 38* |
| At this point a 4mK tower temp spike was observed. It continued to climb another ~0.2mk/min, but leakage current remained constant. Bias voltage was reduced to 0 and the tower temp quickly fell back to baseline (~42mK). Repeating above measurement. |
| Bias [V] | Leakage [mV] | tower temp (mK) |
|---|---|---|
| DIB2 PB lines connected | ||
| 5 | 3 | 42.5 |
| 10 | 11 | 42.5 |
| 15 | 16 | 42.5 |
| 20 | 17-18 | Rises to 44mK in 2mins, plateaus at 45 |
| 25 | 33 | Again begins to rise |
| 0 | 0 | Temp promptly falls back to base |
| 1610 | It seems that the DIB2 phonon channels, which are HV biased, are responsible for the bulk of the leakage current and can cause some temperature excursions. Should try and target specific phonon lines. |
|---|
| Bias [V] | Leakage [mV] | tower temp (mK) |
|---|---|---|
| DIB2 PB QET and QET return lines connected | ||
| 5 | 7 | 41 |
| 10 | 10 | 41 |
| 15 | 16 | 41 |
| 20 | 18 | rises to 45 mK |
| 25 | 29 | rises further |
| 0 | 0 | 41 mK |
| 1655 | Fill LN2 cold trap full. |
|---|