• General information for focal-plane gas handling system
• LabView Control Program for focal plane detectors
• Preparation of Gas bottles for filling of focal-plane detectors
• Filling Ion Chamber with Gas
• Filling CRDC1 and CRDC2 with Gas
• Removing Gas from Focal Plane Detectors
• Filling and removing gas of Intermediate-image delay PPACs
• Tracking Gas bottles pressures from Barney
• Replacing Gas bottles

The gas handling systems for both Focal Plane gas-filled detectors – the Ionization 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 from the desktop of computer u6pc5, by clicking in the icon S800 Vault PC, or by typing xfreerdp /u:s800 /v:s800fp.nscl.msu.edu from a Linux terminal. A terminal will pop-up asking for the s800 password. Once the virtual session in S800FP-PC is open, the gas handling system can be opened by clicking in the corresponding icon on the desktop FPGHS_TCPIP-II. This icon opens the local directory C:/Users/s800/Desktop/FPGHS_TCPIP-II. Once there, run the Labview executable FPGHS_TCPIP-II.exe.

The Labview software communicates with a MKS gas handling system through a Moax Nport 5110 terminal server attached to the bottom of the focal-plane chamber. This terminal server has a hostname s800ghts.nscl.msu.edu, which currently has an static IP address assigned to it (10.65.40.135). When running Labview, go to the Initialization tab and make sure that the terminal server address (IP) and port number (2001) is correct.

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

Required controls and monitoring

• LabView gas handling system application FPGHS_TCPIP-II.vi
• PanelMate S800vac.ui page 07: Focal Plane Detector

To start the gas handling system control application, click on the LabView icon FPGHS_TCPIP_Corrected_V01 on the S800FP-PC desktop.

• The LabView program controls the gas handling system through a Moax terminal server. You have to verify that the address is correct.
  • Go to Initialization tab
  • Confirm that the IP address is 10.65.40.135 (or s800ghts) and the port number is 2001

• A log file should be specified before operating the gas handling system
  • A window automatically pops up asking for the name of the log file when the program starts
  • Use the number of the current experiment (or the date) as the name of the log file and save in the default directory /projects/s800/Gas logs
  • The On indicator next to Is VI running? will flash until a log file is specified and the program initiates communications with the hardware

• Click the Valves tab at the top of the LabView window to display the overview of the gas handling system (see Figure below)
  • The triangles on the valve control buttons (as well as the square valve status indicators near the control buttons) are red to indicate that a valve is closed (e.g., control 25 for the CRDC return above) and green to indicate a valve is open (e.g., control 22 for the CRDC bypass above)

• The gas handling control application should always remain open during the entire time either detector is filled with gas to ensure the log file is continuously updated

• Once both detectors are empty, this application can be closed with the “X” button on the upper right corner of the window.

• Ensure I265GV is closed (in PanelMate S800vac.ui page 07) 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, 7, 20, 21, 22 and 23
• (Check section on vacuum control for further details.)

• 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 (see pictures below)
• Open valves downstream of regulators in each bottle
• 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 ionization 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

• Follow instructions under Preparation of Gas bottles

• Monitor the pressure of the focal plane vacuum chamber (as read out via the I264IG ion gauge in PanelMate S800vac.ui page 07) while detectors are being filled with gas; the pressure normally stays below 5E-5 Torr.

• Confirm that the detector pressure as indicated by the display labeled P.T. #1 reads below a couple of Torr
  • To zero this display:
    • Click on the Slot 3 (PT1) tab to access the details page for PT #1
    • Click the Zero Sensor button
    • Click the Valves tab at the top of the LabView window to return to the overview display of the gas handling system

• Close valves 6 and 7

• Open valve 2; the flow reading at MFC #1 should jump momentarily

• 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 Update 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)
  • Open valve 9
  • If necessary, the filling process can be stopped at any time by pressing the valve button labeled Close MFC #1
  • The filling process will take several minutes

• When the detector is filled, close valve 5

• Follow instructions under Preparation of Gas bottles

• Monitor the pressure of the focal plane vacuum chamber (as read out via the I264IG ion gauge in PanelMate S800vac.MT2 page 07) while detectors are being filled with gas; the pressure normally stays below 5 x 10^-5 Torr.

• Confirm that the detector pressure as indicated by the display labeled P.T. #2 reads below a couple of Torr
  • To zero this display:
    • Click on the Slot 4 (PT2) tab to access the details page for PT #2
    • Click the Zero Sensor button
    • Click the Valves tab at the top of the LabView window to return to the overview display of the gas handling system

• Close valves 22 and 23

• Open valves 10 and 15

• Open valve 12; the flow reading at MFC #2 should jump momentarily

• Open valve 17; the flow reading at MFC #3 should jump momentarily

• Fill CRDCs
  • Enter the desired fill pressure and start the automatic filling process
    • 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 Update 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)
  • Open valve 25
  • If necessary, the filling process can be stopped at any time by pressing the valve button labeled Close MFCs #2 & #3
  • The filling process will take several minutes

• When the detector is filled, close valve 21

• Monitor the pressure of the focal plane vacuum chamber (as read out via the I264IG ion gauge in PanelMate S800vac.MT2 page 07) 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: Before opening valve 8 (next step), 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, 7, 22 and 23

• Enter S3 vault and close valves downstream of regulators in gas bottles: P-10 and CF₄ (tetrafluoromethane). Close the main valve for the C₄H₁₀ bottle.

A rather conservative rule of thumb that helps estimate how much gas will be consumed during the course of an experiment assumes that when the detectors are filled and with gas running through them, the S800 IC detector consumes ~10 psi/day of P10, and the CRDCs consume ~10 psi/day of CF4 and ~0.07 lb/day of Isobutane. The process of filling the detectors, is approximately equivalent to 1 day of gas consumption during normal operations.

In order to track the status of the gas bottles for the ionization chamber, the CRDCs, and the TPPAC, it is possible to monitor their remaining pressures from Barney. Just open the A1900 page, then Tools, and then Gas Status. The following window will be displayed:

The gas content of each bottle is tracked by measuring the pressure in regulators (e.g. P10 and CF4) or the weight of the bottle on a scale. Both types of measured values are encoded in EPICS PVs, allowing remote monitoring of the gas available. There are two alarm levels (low alarm and high alarm) that can be adjusted using the corresponding EPICS PV. For instance, for the isobutane bottles (5 lb net weight), the low- and high-level alarms trigger at 1 lb and 0.5 lb, respectively.

When installing a full bottle in a scale (e.g. isobutane), it is important to follow a procedure to account for the differences between the weight measured by the scale, and the actual gross weight. After removing an empty bottle, proceed as follows:

Adjusting the pressured reading from a scale (for instance isobutane) requires some special guidelines. In the case of isobutane, the following EPICs PVs are involved:

• Check the weight marked in the scale when it is empty (no bottle). If different than zero, press “set zero” and ensure that it marks 0 lb
• Check the gross and net weight in the bottle (as seen in the labels)
• Install the bottle in the scale and check its weight.
• Update the following EPICS PVs with the correct values:
  • I265DGWN: net weight, as marked in the bottle (e.g. 5 lb)
  • I265DGWG: gross weight, as marked in the bottle (e.g. 41.6 lb)
  • I265DGWS: weight, as read from the scale
  • I265DGWC: correction factor used to match the scale weight and gross weight when the full bottle is installed.
  • I265DGW: net weight deduced from the scale

In preparation