Today we started by mounting the central and downstream preamp box lids.

The pumps were left running overnight, at 9:06 CHUP = 2.1e-5mBar and CHDW = 5.8e-5mBar.

We biased the detectors

• central S2 bias = -129.9V, leak I = 8.09uA
• diode bias = -70.0V, leak I = 0.01uA
• downstream S2 bias = -130.0V, leak I = 1.66uA

The DAQ OR is all 3 detectors, DAQ DT = 82% and trigger rate ~ 6kHz. So the preamp lids made little difference. We saw particularly high rate in ADC 2 channels 1->4, 6 and 7, ADC 4 channels 6 and 31 (both of these are the downstream S2, ADC 5 channels 4 and 5 (central S2), and ADC 6 channels 1->7 (central S2) and 31 (diode)

Decided to ensure copper taped cable is isolated from preamp lid. I cut two sheets of plastic ~ 31 X 19cm and (after powering down the detectors and preamps) placed these between the copper taped preamp - feedthrough cable and the preamp box lid, for both preamp boxes.

Now when the DAQ is triggered from all 3 detectors DAQ DT = 7%, trigger rate ~ 2600Hz, event mult = 49.7

I saw ADC 3 (the "TDC-like" module) was not disabled, i set its ADC threshold to 2046 (out of 2047 channels).

I opened the irises in front of both S2s and moved the target ladder to position VII - alpha source facing downstream.

Now DAQ DT = 7%, trigger rate ~4100Hz, event mult = 18.6

I reset all of the RAL thresholds back to 15mV, I also disconnected the 2nd ECL-NIM converter channel 13 from the Lecroy quad coincidence module because the last 16 channels werent being used for the DAQ trigger anyway.

DAQ DT rose to 85% and trigger rate 32kHz, event mult = 11.8.

ADC 2 channels 1->4, 6, and 7, and ADC 4 channels 30 and 31 still show high rates. Disconnected RAL I and RAL VIII analogue and ECL outputs to remove these.

Now DAQ DT = 22% and trigger rate 8.5kHz, still see a high rate for the diode in ADC 6 CH 31

I tried plugging in the pulser to the diode preamp, pulser setting 0.3V. Ultimately after checking DAQ rate and signals on oscilloscope I raised the diode CFD threshold from 200 to 226mV and settled on this new value.

I decided to keep the diodes analogue delay set to 1us (same used in Feb 2018)

I realised I do need the 2nd ECL-NIM convertor channel 13 in the DAQ OR, because otherwise i could not trigger ADC 6 channels 0->31. This was now remedied

So, the DAQ trigger OR was from RAL II -> VII (downstream S2), RAL X -> "Q" (central S2) and the diode

At 12:03 we started data collection for a 15 minute alpha spectrum, save name  = 180406110805

DT = 78%, trigger rate = 10kHz, event mult = 12.5. DT had dropped to ~ 50Hz during this run. Still saw high rate in ADC 6 channels 1->7 and 31

I was unable to see alpha peaks with good statistics for the downstream S2

At 12:35 I started a 30 minute alpha spectru, save name: 180406114011. DT ~ 73%, trigger rate ~ 9.6kHz

I noticed the central detector leakage current had risen to 10.01uA (bias -129.9V). The diode leak I was still 0.00uA and the downstream S2 leak I was still 2.21uA

When the downstream S2 was connected to the DAQ OR and ADCs a high dead time is seen. Because of this we decided to try and collect some beam data with the central S2.