(Note: Tom Davinson is now in CIRCE until the 21st)

On 19/02/2018 we performed the following:

This morning we gave CIRCE technician Antonio slanted spacer boxes (for mounting preamps) and also the Al box (used for target ladder) for minor modifications

I needed to unmount the Al box from the target chamber. As I did so some air rushed in as I unmounted the box, indicating the chamber was not back at atmosphere from pumping on Friday.

I also removed the central lid with the iris attached. I discovered the iris was broken beyond repair. We will need to order a new one and some spares.

Learning note: To avoid damage always have irises fully opened when pumping down the chamber.

In the meantime Tom D has been wiring up the rest of the electronics setup. He discovered the CAMAC crate was not supplying any voltage. We removed the crate and double checked the connection between the rear power box and the crate – it was not fully screwed in on the bottom. After fixing this we remounted the CAMAC and found all voltages read out correctly, including a current readout of -10A at the -6V voltage.

Next we set out to vacuum test the chamber. In total today we performed four vacuum tests.

In each test the diode mount, lemo feedthrough, 64-way vacuum feedthrough, and an iris mounts were installed in the central section (the iris mount in the central chamber had no iris due to damage mentioned above). The iris mount with an iris (fully opened) and 64-way vacuum feedthrough were installed in the downstream section. The Al spacer box for the target ladder was also installed, however the target ladder was not because Antonio was not finished with modifications. Instead of the target ladder a blank flange was installed. The two actuators for opening and closing the irises were also installed in the central and downstream chamber sections.

The first two vacuum tests showed a high leak rate, high 10^-4 mBar even without helium injected close to the chamber.

In the first test we found the two 64-way vacuum feedthroughs were causing a leak, after venting the chamber these were removed and mounted flat to the lid using four bolts, one at each feedthrough corner. We then started the second test.

In the second test we discovered a leak was caused by the lemo vacuum feedthrough on the central lid. After the test we put additional grease on the o-ring and around the flange section of the feedthrough (atmosphere side) to help it seal.

On the third vacuum test after ~ 20 minutes of running the up and downstream turbos the pressures levelled to:

Up = 3.6e-4 mBar, down  = 3.4e-4 mBar

We then switched off the turbos and continued monitoring the vacuum. After ~30 minutes from turning off power to the turbos, they had completely stopped spinning, the pressures read:

Up = 6.5e-1 mBar, down = 6.5e-1 mBar

We found during this test the lemo feedthrough was still not sealing, and in addition neither was the Al spacer box for the target ladder.

After venting we found a hair on the lemo feedthroughs o-ring. The hair was removed and additional grease was applied to the o-ring and lid. We also confirmed the nut was tight. For the spacer box we found the bolts used were slightly too long, and so removed ~ 2mm from the threads. The box was then remounted and looked flush with the side of the chamber.

After this test at ~16:00 Antonio had finished and delivered both the modified spacer boxes for the preamps and the target ladder mounting box, now it correctly uses a 16mm centering ring.

We then started the fourth vacuum test, now with the target ladder actuator mounted too (as well as all the other parts from tests 1-3):

At 16:43 the roughing pump in the leak test was started. At ~16:50 the turbos were started, both up and downstream from the chamber.

At 17:04 (~15 minutes later) the pressures in the chamber read: Up = 3.1e-4 mBar, Down = 2.8e-4 mBar.

We declared victory for the vacuum and decided to mount the detectors and an alpha source.

On the central lid we mounted the Si diode with 0.9um mylar and a 1mm collimator at ~28 degrees rotation (relative to the central lid) -> currently this is performed using an angle measuring app on my android phone and one screw, so this angle selection needs to be better reproducible for the future.

We discovered there was no way to mount the S2 detector on the central lid -> either the legs of its connectors collide with the lid, or when the iris mount is rotated 180 degrees (moves detector slightly upstream) the iris then collides with the target ladder. The way we mount the detector on the central lad needs redesign -> I will take the central lid with irises and diode mount back to Edinburgh to address and fix this problem. I can also use this opprtunity ot find a better mounting procedure for the Si diode.

We did mount the S2 2323-18 (496um) detector to the downstream iris mount. 12um mylar was placed in front with a central hole of max width <20mm to allow the beam to pass trough.

On the target ladder we mounted an alpha source at position 5mm. The alpha source specifications are:

Type: EAX

Prod No: 111109-1242002

Radionuclide: 241Am + 239Pu

Activity: 8.153 kBq

Reference Date: 25/3/2010

At 20:49 with the single S2 detector, diode detector and the alpha source mounted in the chamber we started the roughing pumps.

At 20:54 we started the turbos, including not only the up and downstream turbos but also the large turbo located below the chamber. The pressures read: Up = 1.3e-4 mBar, Down = 1.5e-4 mBar.

We went to dinner. Raffaele had fish.

22:19 The pressures read: Up = 1.4e-5 mBar, Down = 3.7e-5 mBar

We mounted the preamp box on top of the chamber with preamp 2 inside. The cables for the detector bias, +15 and -15V preamp power, +ve pulser, and ribbon signal cables were connected.

Biasing the S2 to -130V we read a leakage current = 1.16 uA. Powering the preamp we read currents: V=+15V -> I = 0.9A, and V=-15V -> I = 0.4A, as expected. The pressures read: Up = 1.4e-5 mBar, Down = 3.2e-5 mBar

Using DSO we observe

• RAL 1 CH 0->7 pulser OK, no alpha
• RAL 2 CH  0 no pulser or alpha
• RAL 6 CH 1->7 pulser OK,  no alpha
• RAL 8 CH 6 no alpha, pulser not connected to n+n ohmic strips

We declared today a good day and left the lab.