Table of Contents
2010/06/15
Diary
| 09:14 | MC temperature went up to 60mK |
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| 09:15 | Turn off still heater |
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| 11:00 | MC temperature went down to 26mK after transferring helium to 33.4% |
| 12:00 | Take charge noise psd at low frequency part with SR760 |
| Qi (regular coax) and Qo (vacuum coax) comparison |
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| matlab fig |
This is a comparison between Qi and Qo at frequency below about 3kHz. Noise psd is taken using SR760 and an oscilloscope probe to monitor the feedback line. Compared with the result using regular wire instead of the probe, the attenuation effect from the probe is not significant. That said, I used regular wire and cable in the tests later on.
The plot above shows the Qi (conventional coax) noise psd from SR760 which monitors the test points (TP5) on feedback line and from DCRC. Both are normalized to the feedback line output. They overlap well at lower frequencies. It is not clear why the baseline of the curve from SR760 is slightly higher around a few kHz. Below 1kHz, DCRC curves have more peaks around mutiples of 60Hz. Sten suggested to ground the digital ground to chassis. There is no effect I can tell by grouing the digital ground.
After conforming that DCRC and SR760 have consistent results. A comparison is made between Qi and Qo using DCRC with a higher frequency resolution. The three peaks around 26kHz on Qi are from the fluorescence lights. They can reduced by turnning off the lights near the fridge.
Data
| Run | Comment |
|---|---|
| 1 | |
| 2 | |
| 3 | Qi spectrum at TP5 on SR760, 4ms, average 100, exponential |
| 4 | QI spectrum from DCRC, 4ms, average 100, exponential |
| 5 | QI spectrum from TP5, SR760, 128ms, average 100, exponential, low frequency |
| 6 | QI spectrum from DCRC, 128ms, average 100, exponential |
| 7 | Qo spectrum at TP5 on SR760, 4ms, average 100, exponential |
| 8 | Qo spectrum from DCRC, 4ms, average 100, exponential |
| 9 | Qo spectrum from TP5, SR760, 128ms, average 100, exponential, low frequency |
| 10 | Qo spectrum from DCRC, 128ms, average 100, exponential |
| 11 | Repeat Run 7 |
| 12 | Repeat Run 7 |