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Detector gas handling system
Required controls and monitoring
The gas handling systems for both Focal Plane gas-filled detectors – the Ion Chamber and the CRDCs – are remotely controlled via a single LabView application running on the computer S800FP-PC in the S3 vault. This computer can be accessed remotely via the devop1 computer in Data-U6.
Note that since the same roughing pump drives the gas handling systems for both gas-filled detectors, extra precautions must be taken to protect one detector from the pressure of the other detector. The fact that the same pump drives both systems is not indicated on the graphics for the LabView control application
LabView Control Program
To start the gas handling system control application, click on the LabView icon FPGHS_TCPIP_Corrected_V01 on the S800FP-PC desktop.
Preparation of Gas bottles
In Data-U6
Ensure I265GV is closed to isolate focal plane vacuum chamber from the rest of the beamline
Confirm that the focal plane chamber is under vacuum
Confirm that the only open gas handling system valves are 4, 5, 6, 20, 21, and 22
In the S3 vault
Ensure that the gas handling system roughing pump is running and has a good vacuum
The pump sits on the floor under the focal plane behind the south support post
The display unit for the pressure at the pump has a needle indicator and is mounted under the focal plane on the south support post
Ensure that the main valves on the gas bottles are open
Ensure that the gas bottles are not empty
The gas regulators are not normally adjusted. They should all be set to provide a pressure around 20 psi.
The bottle supplying the P-10 gas for the ion chamber is secured to the cross-brace of the south support for the focal plane chamber. It has an electronic Ashcroft pressure gauge upstream of the regulator (toggle on and off with the “on/off” switch) and a mechanical pressure gauge downstream of the regulator.
The bottle supplying CF4 (tetrafluoromethane) gas for the CRDCs is secured to the cross-brace of the south support for the focal plane chamber. It has an electronic Ashcroft pressure gauge upstream of the regulator (toggle on and off with the “on/off” switch) and a mechanical pressure gauge downstream of the regulator.
The bottle supplying isobutane (C4H10) for the CRDCs is secured to the south support post for the focal plane chamber. It sits on a scale for monitoring the isobutane consumption – the electronic display for the scale sits on the chiller unit under the focal plane chamber. It has a mechanical pressure gauge downstream of the regulator. (PICTURE GOES HERE)
Filling Ion Chamber with Gas
Fill Ion chamber
Enter the desired fill pressure and start the automatic filling process
Click on the tab labeled Slot 8 (M-card) IC to access the page with the pressure set point control
Enter the desired pressure (typically 300 Torr) in the field under the knob labeled Set Point
Click button labeled Return to AUTO Mode on left to start filling/regulation
Click the Valves tab at the top of the LabView window to return to the overview display of the gas handling system to monitor filling. The flow readings for MFC #1 will increase and eventually disappear as the readout value overflows the display field (this is normal behavior)
If necessary, the filling process can be stopped at any time by pressing the valve button labeled Close MFC #1
Open valve 9
The filling process will take several minutes
Filling CRDC1 and CRDC2 with Gas
Fill CRDCs
Enter the desired fill pressure and start the automatic filling process
Click the Zero Sensor button
Click on the tab labeled Virtual Ch. 0 (CRDC) to access the page with the pressure set point control
Enter the desired pressure (typically 40 Torr) in the field under the knob labeled Set Point
Click button labeled Return to AUTO Mode on left to start filling/regulation
Click the Valves tab at the top of the LabView window to return to the overview display of the gas handling system to monitor filling. The flow readings for MFC #2 and MFC #3 will increase. The LabView application controls the gas mixing ratio based on the flow ratio (scaled with a calibration constant)
If necessary, the filling process can be stopped at any time by pressing the valve button labeled Close MFCs #2 & #3
Open valve 25
The filling process will take several minutes
Removing Gas from Focal Plane Detectors
Monitor the pressure of the focal plane vacuum chamber (as read out via the I264IG ion gauge) while gas is being removed from detectors; the pressure normally stays below 5E-5 Torr
Ensure that the system is in the normal state for flowing gas through the detectors
Confirm that the focal plane chamber is under vacuum
Confirm that the only open gas handling system valves are 2, 4, and 9 for the Ion Chamber and 10, 12, 15, 17, 20, and 25 for the CRDCs
Confirm that the detector pressures as indicated by the displays labeled P.T. #1 for the Ion Chamber and P.T. #2 for the CRDCs show the correct fill values (typically 300 Torr and 40 Torr, respectively)
Ensure that I265GV is closed to isolate focal plane vacuum chamber from spectrograph
Stop the gas flow into both detectors by clicking valve buttons labeled Close MFC #1 and Close MFCs #2 & #3
Isolate the gas supply by closing valves 2, 12, 17, 10, and 15
Open valves 5 and 21
IMPORTANT: CLOSE VALVE 25 to protect CRDCs from Ion Chamber pressure
Empty Ion Chamber to a pressure at or below the pressure of the CRDCs
Open valve 8
Wait for the Ion Chamber pressure to reach or drop below the pressure in the CRDCs; this process will take several minutes
Finish emptying both detectors
Open valve 25
Open valve 24
Wait for the pressure in both detectors as indicated by the displays labeled P.T. #1 and P.T. #2 to reach 0.5 Torr or less; this process will take at least an hour
Close valves 9 and 25
Close valves 8 and 24
Open valves 6 and 22
Enter vault and close main valves on gas bottles: P-10 for Ion Chamber isobutane (C4H10) and CF4 (tetrafluoromethane) for CRDCs