On 04/04/18:

We mounted S2 2323-18 (496um) in the downstream position with 12um mylar

We mount the central and downstream iris arms, we set the central arm position to 14.0mm and the downstream arm position toe 1.5mm - opening both irises.

We started Ecodry 1 and 2, we checked T1600 Backing valves was closed. At 10:11 cracked open the gate valve. After several minutes of pumping Ecodry 1 cutoff, suggesting a big leak.

The downstream chamber lid was sitting at a slight angle, we vented the chamber and reset the downstream aperture to 82.5mm. We removed the downstream aperture. Lifting off the downstream lid we found the O-ring between the lid and collar was not correctly in its groove, this was corrected.

We closed the downstream lid and remounted the downstream aperture. We set the aperture back to 1.5mm (iris open). We closed the turbo vent valves ready for a second venting attempt.

There was a problem with the Labview DAQ, Guiseppe and Raffaele fixed this.

Ecodry 1 and 2 were switched back on, at 11:20 the gate valve was opened. At 11:28 the gate valve was fully opened and pressures read < 1mBar on all 6 gauges. T1600 Backing valves was opened allowing Ecodry 2 to pump on chamber. At 11:31 all 7 turbos were switched on.

During pumping we began mounting the preamp boxes onto the chamber. We discovered the preamp box to be mounted on the central lid needed its holes enlarging to accomodate the bolts for mounting the preamp box to the spacer box.

We mounted the downstream preamp box first, currently holding preamp 2 with the now copper taped preamp - feedthrough signal cable. We then mounted the central preamp box, holding preamp 1 with a copper taped preamp - feedthrough signal cable.

We daisy chained the preamp -15V and +15V cables for the two S2 preamp boxes and the diode preamp, we also daisy chained the +ve test input for the two S2 preamp boxes.

Originally, the central S2 HV was connected to the Silena module CH1, the downstream S2 HV was connected to Silena CH 2, and the diode HV was connected to Silena module CH3.

Powering the diode to -70V, leak I = 0.00uA.

However when powering the S2s to -130V, no leakage current was observed. It turned out the silena CH2 did not work, moving the downstream S2 HV to silena CH4 and powering to -130V reads 1.69uA leakage current.

For the central S2 the problem was found on the respective preamp box. It turned out the SMA connection of the BNC->SMA feedthrough was loose, tightening this and powering the central S2 to -130V reads a leakage current of 2.47uA.

The target ladder was set to position VII - alpha source facing downstream.

Checking RAL signals for central detector, RAL X, XII, XIII, R, S, Q all looked good, RAL U CH 6 was dead, RAL W channel 0 and 1 were dead.

We discovered RAL I (dowsntream S2) showed poor noise, for a 0.2V pulser setting, the amplified signal on RAL I CH 2 was ~5V with noise ~400mV. See 20180404_Pulser_PreampLid_ON.jpg

I emailed Tom Davinson for ideas, he suggested checking what happens when the preamp is disconnected from the vacuum feedthrough.

When the preamp was disconnected from the vacuum feedthrough the amplified signal on RAL I CH 2 was ~1.5V with noise ~40mV. 20180404_Pulser_DisconnectedFromFeedthrough.jpg

We collected vias vs leakage current curves for the two detectors. See attached S2_2323-18_496um_Bias_Vs_Leakage_Current.png for the downstream S2 and S2_2623-26_505um_Bias_Vs_Leakage_Current.png for the upstream S2.

I suspected the new cable between the downstream S2 and vacuum feedthrough is damaged - perhaps it has a short.

I also checked the central S2, again for a pulser setting of 0.2V RAL X CH 1 showed a 1.2V signal with ~50mV noise, which seemed a better case than for the downstream S2.

The time was 20:20, we decided to stop for the day. The turbos, Ecodry 1 and 2, both S2s, the diode, and the preamp power were switched off ready for dismounting the downstream S2 for a cable change the next day.