Maintenance for DR(Pandora)

Three issues developed in 2022 during the five month long run of the DR.

1)            A small air leak into the OVC that reduced the helium hold time to about 16 hours without pumping the OVC and about 20 hours with the pump on. Leak checking with the DR cold did not produce any response.

2)            A short in the internal z-coil used to zero the field. The short appeared when the DR was cold but not at room temperature.

3)            A leak through automatic valve 12 that plugged the nitrogen traps, it was a small leak when the valve moved. The valve could not be continuously used to condense the mixture but was okay to set flow.

We finished the beam time by pumping the OVC, using a floating power supply to zero the field and reduce the number of times Auto-V12 used.

Leak checking with the DR warm identified the internal coil’s feedthrough as the source of the leak into the OVC. This is a 2 pin Lemo connector at the bottom of the DR that was leaking through the connector and not the O-ring. The connector was changed.

When the internal room temperature coils were removed there was lots of damage to the wires that fit into the DR pocket from the Forward/Veto counters side. We changed the way the coil wires are connect and fed through the pocket as well as filling a small groove into the DR OVC jacket to make room for the wire (See pictures). Room temperature test with a grounded power supply used during experiments was successful. A cold test at Nitrogen temperature is planned.

Auto-V12.

Rahim removed the DR’s Auto V12 and replaced all the O-rings. While the valve was out, we had a better look at its operation and noticed that one of the two air sealing O-rings becomes exposed at 300 DAC (might be the source of the air leak we had during operations). With the leak detector we determined that the valve is closed at 300 DAC.

Once the valve was re-installed on the DR, I did few tests.

DR1) DAC from 300 to 440. Start with equal pressure on the Still side and the G4 side. Dumps closed (pumping into a very small volume on the G4 side). Very small increase in Pressure due to outgassing.

It looks like V12 Auto is closed between 300 and 440 DAC.

DR2) Same as above with Auto V12 at 460 and 450 DAC. Valve starts to open with a bit of flow.

DR3) Open Dumps- Large volume on the G4 side. DAC at 500, 480, 460 and 440.

>> I think we need to add an option in CAMP to set a minimum and maximum DAC value for Auto V12. Then we can start with a minimum of 400 DAC and adjust it later if needed.