2013/08/29

0400	Fill N2 cold trap full.
0450	Finished LED tests. As it is difficult to view the LED pulses themselves, we can test their effect indirectly by monitoring the fridge temperature. Four new DAQ configuration files were produced, each for 0 V bias but flashing only one LED to test each one in turn. LEDs were flashed for a total of 10 minutes and the peak mixing chamber temperature recorded. The fridge was left to cool down for 10 minutes before another flash of duration 6 seconds. The results are detailed below:

0400

Fill N2 cold trap full.

0450

Finished LED tests. As it is difficult to view the LED pulses themselves, we can test their effect indirectly by monitoring the fridge temperature. Four new DAQ configuration files were produced, each for 0 V bias but flashing only one LED to test each one in turn. LEDs were flashed for a total of 10 minutes and the peak mixing chamber temperature recorded. The fridge was left to cool down for 10 minutes before another flash of duration 6 seconds. The results are detailed below:

Table 1: Results from LED Tests.
		10 minute flash		6 second flash
DIB	LED	Initial MC Temperature [mK]	Peak MC Temperature [mK]	Initial MC Temperature [mK]	Peak MC Temperature [mK]
1	1	88.8	102.3	89.7	89.9
1	2	88.9	95.6	89.6	89.6
2	1	89.0	108.7	90.9	91.2
2	2	89.4	95.1	89.6	89.7

0505	All LEDs appear to be working. Did try running a couple in reverse bias and fridge did not warm up, so we've been using the correct polarity. It is known from tower continuity checks that LED 2 on DIB 2 does conduct under reverse bias, so shouldn't be used. Stick with three LEDs: LEDs 1 & 2 on DIB 1; and LED 1 on DIB 2.
	There is little indication of why the peak temperatures are so low. Reading registers back from the DCRCs show that the correct bias (and polarity), and flash on & flash off times have been written to the boards. It may be best to flash for longer than 6 seconds. Performed a quick test, flashing for 30 seconds and 1 minute, to determine whether the fridge would cool back down to base temperature within 20 minutes. The mixing chamber successfully cooled down to base temperature after reaching peaks of 95.5 mK (88.9 mK at start) for 30 second-flash and 100.7 mK (88.8 mK at start) for 1 minute-flash. Decided to use 30 seconds just in case - this should be more than enough.
	Start data acquisition with initial 8 hour flash followed by cool down. Data acquisition/flash/cool down shall be 5 minutes/30 seconds/20 minutes. Acquire 4 data series at each bias in the following order: +/-4 V; -/+4 V; +/-3 V; -/+3 V; +/-2 V; -/+2 V; +/-1 V; -/+1 V. Once completed, will repeat this test tomorrow, switching order of biases (ie. +/-4 V will be last data series taken) to check crystal has been neutralised.
1120	Filled LN2 coldtrap full.
2140	Fill N2 cold trap full.