2021/03/04 (Thursday)

Lab in-person: Matt
Virtual partner: Derek

Status	Run 74 in progress.
	Setup: DIB1/2+acc → SL 41/43 → 3.2 MHz filters → cables 2/3 → nothing/motor_board+HV_board → DCRC50(3)/55(1). No lead/poly shield.
0855	MB = 68.9%
0900	Tower = 111 mK. Temperature is higher and less stable than it was before.
	We haven't been able to see the 60keV line in data. I've been worried that the Side2 electrode is not grounded as it should be, but instead is just floating. We tried 7V data with the diverter board in place and the HV lead shorted to ground, and we've tried it with the diverter boards removed and the cable attached directly to the DCRC (which should ground Side2) and yesterday we replaced the diverter boards and removed the HV short to let Side2 float intentionally - and the data looks the same in all three cases. So this seems like a real problem. A further test would be to try to apply a bias to Side2 - if it is connected we should easily be able to see triggered pulses when the bias is applied.
0920	Start 31min series of +9V data (bias applied after 1 min), with HV lead left floating, with 1000 beginning randoms, trigger threshold 80/80/80/80 on DCRC3qI/qO/DCRC1qI/qO, no in-run randoms, with 1.6384 ms pulses (8192 length) and 400 us prepulse (500 length). Use sequence r74_takeandflash_dcrcbias.msl
	Triggering looks OK
	Quick look at this data shows that the muon blob has again shifted upward significantly at 9V c/w 7V.
1430	Matt enters lab
1430	Tower/MC/Coldplate = 118/31.1/189 mK, Still = 1.46 K / 0.130 mbar / 0 mW, G1/G2= 216/190 mbar, 1K Pot = 1.67 K / 37±2 mbar.
1605	Attempting some troubleshooting: trying to apply bias to the HV lead at the diverter board. But this is not successful, because plugging into the power supply produces severe noise in the charge channels. Here are some observations:

Simply touching the shell of the HV BNC produces extra noise.
We tried isolating the power supply in our usual way: plug it into the variac, and plug the variac into the wall with the “cheater” cord (with the ground pin removed).
Using the multimeter we adjusted the HV supply to near zero (a few mV)
Plugging either HV lead into the power supply causes severe noise - the charge channels rail up and down.
Not what I was doing when it happened, but twice during the tests there were strong temperature events. The first caused the Tower temperature to rise to 0.6 K, the second to 0.4 K. It didn't heat suddenly, it took a few minutes in each case to warm up. Cooling curve looks pretty normal.
We tried measuring resistance from power supply chassis to DCRC ground to establish isolation. Possibly this caused the temperature spike(s), but we couldn't recreate it.

1645	Instead of using a Kepco power supply, tried biasing the detector with a battery. Tried 1.5 V and 9V. Observations:

First note that we are seeing occasional upright pulses - one every few seconds - even with no bias applied. It could be that the detector needs to be neutralized.
Applying bias using a battery does not produce the nasty noise that the power supplies produce.
Attaching to the battery produces a burst of noise but it goes away quickly.
With the 9V battery, it kinda looked like we were seeing a higher rate and taller upright pulses. But we may have been fooling ourselves…
Flipping the 9V polarity, we continued to see upright pulses at around the same rate. But if we were really biasing the detector we'd expect the bias to flip. So - doesn't seem like we are connected.

1700	Try again applying bias with DCRCs, first +4V, then +8V. Definitely see an increase in triggered event rate at +8V. Turning the bias back to 0V we see the rate fall again.
	Note - to further test the hypothesis that Side2 is floating, we can try to look for the buildup of counterbias that we would expect. We can take a very long series at moderate bias and see if the amplitude of muon-bulge events falls off with time. We can also try running at bias for a while then removing the bias, to see if we get reversed counter bias.
	In the end I left the HV lead shorted to ground, although it doesn't seem to matter.
1715	Matt exits lab
1845	Write sequence r74_takeandflash_dcrcbias_keepgoing.msl which starts like the other one - start data, wait 60s, apply bias - then removes bias and continue to take data for a while, then stop and flash.
1851	Start 31/120min series of +9V/0V data (bias applied after 1 min), with 1000 beginning randoms, trigger threshold 60/60/60/60 on DCRC3qI/qO/DCRC1qI/qO, no in-run randoms, with 1.6384 ms pulses (8192 length) and 400 us prepulse (500 length). Use sequence r74_takeandflash_dcrcbias_keepgoing.msl
	SEQUENCE ABORTED. Stopped sequence during randoms, before bias applied, because we are seeing terrible noise.
1900	Extreme noise seen in DCRC1qI (q4, center channel). Around 1e-3 at 10kHz. Somewhat elevated in other channels, slightly elevated in q1. Guess we can't take data now.

Next Day