Table of Contents
2010/06/14
Diary
| 10:05 | Check fridge running status in the morning |
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| 10:46 | Tower thermometer reads 75mK. This is too high. MC T=28mK, Cold plate 16.9kOhm, Still 4.49kOhm, P1=0.1mbar. Previously still=4.6kOhm at P1=0.06mBar. |
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| 11:05 | Adds 5uW to MC and tower temperature increases. The response is reasonable. There could be excess heat load on the tower from 4K stage |
| 11:07 | Add 2mW to still and see if I can bring down the tower temperature |
| 12:11 | It seemed one end of the tower resistor is shorted to ground. Need further check |
| Take noise traces run001 to 003 | |
| 15:00 | Turn on the FET heater |
| Take noise traces run004 and run005 | |
| 15:29 | Turn off FET heater |
| Qo (vacuum coax) microphonics test |
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| matlab fig |
Qo (vacuum coax) noise psd from DCRC.
- 'Knocking': a 1/4-20 x 11/2“ hex socket cap screw was used to knock on the Al plate to which the fridge dewar is bolted with a frequency of a few hertz.
- 'Big knock': a hand size plier was used to hit the Al plate during the data taking. These curves almost overlap except at low frequencies.
| Qi (regular coax) microphonics test |
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| matlab fig |
The curve with 'big knock' shows various peaks and baseline change due to mircophonics compared with the quiet one. After this, we decided to quantify the interference we introduced by dropping a 1/4-20×11/2 screw on to the fridge dewar at controlled heights. I looked at the SR760 while taking psd using DCRC. On the 10” dropping, there wasn't much change I could tell. On the 20“ and 30” dropping, new peaks at around 6kHz and 4kHz showed up. The curves on the plot were from average over 100 traces. The peaks are washed out a bit by this average.
| Qo and Qi comparison without knocking the fridge |
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| matlab fig. Low frequency part is at here. |
This comparison shows that the low noise conventional coaxial cable has comparable performance with the vacuum coax while quiet.
Data
| Run | Comment |
|---|---|
| 1 | Qo psd 100ms |
| 2 | Qi psd 100ms |
| 3 | Qo psd with knocking the fridge 100ms |
| 4 | Qi psd 10ms |
| 5 | Qo psd 10ms |
| 6 | Qo psd 10ms knocking the fridge with a screw |
| 7 | Qi psd 10ms big knock with plier |
| 8 | Qo psd 10ms big knock with plier |
| 9 | Qi psd 10ms drop a screw from 10“ above the dewar |
| 10 | Qi psd 10ms drop a screw from 20” above the dewar, can see 5.6kHz peak rose |
| 11 | Qi psd 10ms drop a screw from 30“ above the dewar, can see 4.4kHz peak rose |