2017/09/26 (Tuesday)

Previous Day

	Overnight bake using IR LEDs on DIB4. 5V bias was accidentally left on.
0745	Tower temp = 520 mK
0748	End bake.
0905	Dang, 5V bias still applied, I forgot to turn it off before last night's bake.
0907	Turn off 5V bias. Enable DIB4 IR LEDs to begin bake. Took about 30 minutes to cool back to base.
0908	Fill LN2 cold trap full.
1208	Disable DIB4 IR LEDs to end bake.
1247	Tower temp = 76.5 mK
1249	Apply 10V bias to contact free electrode. Can see strong pulses.
1250	Start data series of contact-free/readout=10V/0V data with DIB1/3/4 = DCRC 1/none/2 = master/none/slave, 1000 beginning randoms, and a 50ADC bin threshold trigger on DCRC1 q[1] = qC
1340	End data series.
1343	Ground detector and flash for 30s with DIB4 IR LEDs. Note: it only takes about 10 minutes to cool back to base.
1355	Apply 10V bias to contact free electrode.
1356	Start data series of contact-free/readout=10V/0V data with DIB1/3/4 = DCRC 1/none/2 = master/none/slave, 1000 beginning randoms, and a 50ADC bin threshold trigger on DCRC1 q[1] = qC
1437	End data series.
1438	Measure V_leak = 0.00 mV using both Fluke 87V and Fluke 8600A meters.
1439	Ground detector.
1446	Plug DIB3 cable into breakout box to check LEDs. UV LEDs (on QET biases B,D) have measurable voltages with the meter in diode test mode. The IR LEDs (both on DIB itself and electrode) don't register a voltage, but the measurement heats the fridge as though they are still illuminating. We usually don't measure LED voltages at base temp, so this heating may be signs that the LEDs are still healthy. Not sure why I had trouble operating them with the DCRC this DIB on saturday.
1555	Flash for 30s with DIB4 IR LEDs with electrode grounded.
1605	Tower/MC/Coldplate = 78.3/61/378 mK, Still = 1.2 K / 0.140 mbar, G1/G2 = 140/135 mbar, 1K Pot = 1.67 K / 45 mbar. MB = 47.7% Still thermometer less stable today.
1612	Apply 20V bias to contact free electrode
1613	Start data series of contact-free/readout=20V/0V data with DIB1/3/4 = DCRC 1/none/2 = master/none/slave, 1000 beginning randoms, and a 50ADC bin threshold trigger on DCRC1 q[1] = qC. Switched bias polarity at 16:49, see below
1630	Raw file sizes seem to be a good first indication of when we start to lose neutralization. For the earlier two data series at 10V the raw file sizes seemed to hold at ~100 MB for 5 minutes, then drifted down, ending up at about 20 MB. For this 20V series the 100 MB file size lasted 11 minutes.
1644	Dial down voltage to zero. I was going to try reversing the bias while data was still going. But I think the grounding scheme makes that difficult. I tried flipping the plug to the power supply, but then I couldn't dial the voltage up, I think because the BNC ground on the diverter board is shared with the negative jack on the power supply, because the negative jack is wired to ground on the power supply. (But it seems like these should be isolated grounds…)
1649	… no that's wrong - I had simply turned off the power supply “output” button and forgotten. So now I've swapped the polarity and dialed up to 20 V, which is -20 V on the electrode. We'll take data for a little while like this.
1650	File sizes increased after dialing the bias to zero, for the five minutes that it was at zero volts. Could be extra noise, or it could be that the built-up surface charge was now producing its own bias. After applying the -20V electrode bias the file sizes are still about the same, around 100 MB.
1715	File sizes are still high, maybe a bit higher. Could be that charge buildup on the surface is still stuck there, and the applied and surface-charge components of the field are adding constructively, or something. Eventually it should build up on the other side. This is about 25 minutes of large files. Anyway, we'll want to look at the data to try to interpret this.
1718	Dial HV down to zero, short the electrode leads, then end data series.
1720	Start 14-hour detector bake with DIB4 IR LEDs with electrode grounded. Using the DCRC Control flashandflash tool on the DCRC_UI, set to 60 seconds on, 5 seconds off, 14 hour duration. Tower rises to 510 mK.

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