Table of Contents
2010/02/25
Run diary
| Time | |
|---|---|
| 11:00 | Measure Ic at base t 29.3mK |
| 11:05 | Set HP3325A 100Hz, triangle, 280mVpp; set MC power 0.5uW |
| Read T when triangle wave distorts | |
| HP3325A: 260mVpp, MC: 0uW | |
| 20:43 | Fill N2 cold trap full. |
| 21:03 | Transfer LHe |
Ic vs T
By the time this measurement was taken, there was still no standard procedure to do this measurement. The way I did is as follows:
- Tune and lock SQUIDs, zero all QET biases,
- Cool the detector to base temperature,
- Send a 100Hz triangle wave down the QET bias line and sweep the amplitude from low to high, record the output at the feedback line. Ic can be calculated from the output voltage,
- Set the function generator output to values in the above list from high to low, add or remove power to the MC to increase and decrease the detector temperature, record the temperature when the transition starts.
There are problems in this measurement:
- In principle, Ic can be measured in Step 4. But the temperature changed so fast that if I took time to read the output voltage, then I would miss the temperature when transition happened. And the output is not stable when temperature is close to transition region, and Ic from the output might be biased.
- Where is the transition point? We are interested in the upper limit of the transition in temperature or current. At higher temperature or smaller Ic, the transition is a sharp one and easy to see. At lower temperature and larger Ic, the transition temperature range is broad and it is hard to define the transition point.
- How well can the detector temperature be measured? Temperature is controlled in open loop mode at this moment. There is no easy way to control the temperature or its ramp rate. There is temperature gradient between the thermometer and the detector. And this gradient varies from temperature to temperature and from time to time. Consistent if not correct measurement at this moment is not possible. I went as slow as my patient could tolerate. There is a need to use closed loop temperature control.
| Ic vs T | ||||||
|---|---|---|---|---|---|---|
| HP3325A (mVpp) | Ic(uA) | Tower T Up (mK) | Tower T Down (mK) | |||
| A | D | A | D | A | D | |
| 2 | 0.63 | 0.63 | 75.7 | 76.6 | 78.8 | 81 |
| 4 | 2.72 | 2.74 | 73.6 | 75.7 | 78.9 | 79.6 |
| 6 | 4.04 | 4.12 | 75.4 | 77.1 | 78.7 | 79.3 |
| 8 | 5.4 | 5.45 | 73.7 | 77.2 | 78.8 | 79.8 |
| 10 | 6.35 | 6.45 | 74.8 | 77.1 | 78.8 | 79.5 |
| 20 | 12.5 | 12.7 | 73.8 | 75.2 | 78.1 | 78.5 |
| 30 | 20.6 | 20.8 | 73.7 | 74 | 77.8 | 78 |
| 40 | 27.6 | 28 | 77.3 | 77.6 | ||
| 50 | 35 | 35.4 | 72.5 | 72.7 | 77.6 | 78.1 |
| 60 | 41.6 | 41.8 | 74 | 74 | 77.3 | 78.1 |
| 80 | 55.5 | 56.5 | 72.6 | 72.7 | 76.9 | 77 |
| 120 | 62 | 63.5 | 73.6 | 73.7 | 76 | 76.3 |
| 140 | 75 | 75 | 71.6 | 72.6 | ||
| 160 | 81 | 81 | 70 | 71.4 | ||
| 180 | 96 | 95 | 73 | 73 | ||
| 200 | 108 | 108 | 67 | 69 | ||
| 240 | 138 | 141 | 54 | 61 | ||
| 280 | 161 | 168 | 32.9 | 36.9 | ||
| Ic vs T plot of the above table |
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