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Installation of focal-plane scintillator

In June 2019, a new Turbo Pump with magnetically-levitating bearings (Leybold MAG 2200iP) was installed in the S800 focal-plane chamber. This pump has a dry-N line connected to it that is purging continuously the bearings. This creates an extra pressure in the foreline, which must be pumping down continuously. Therefore, it is critical turn off the turbo pump whenever the foreline valve needs to be closed.

Instructions on how to vent/pump-down the focal-plane chamber are described below.

Vent focal-plane chamber

  • Open the HV Remote Control GUI and ensure that the gas focal-plane detectors (both CRDCs and the Ion Chamber) are unbiased
  • Make sure that the CRDC grid gate is off (HV is in dU6)
  • Make sure that the CRDC preamps and interface boards are turned off (it is located in the NIM crate attached to the S800 focal-plane chamber)
  • In order to avoid condensation from the cooling system, turn off the chiller sitting under the S800 focal-plane chamber. Wait for at least a couple of hours before venting the chamber.
  • Open the Labview gas handling system and verify that there is no gas in the CRDCs and IC. Make sure that the only open valves are 4 (IC supply), 5 (IC bypass), 6 (IC focal-plane bypass), 7 (Ion Chamber vent), 20 (CRDC supply), 21 (CRDC bypass), and 22 (CRDC focal-plane bypass) and 23 (CRDC vent). The rest of the valves should be closed
  • Ensure that the manual venting valve located on the south side of the chamber is closed (see figures below) FP chamber manual venting valve FP chamber manual venting valve
  • Ensure that the FP ion gauge (I264IG) is off (see details here)
  • Open PanelMate and select S800vac file in directory \\exp\files\control\ncsdata\General\Qt\Templates, and go to page 07 (see figure below)

Panel Mate Vacuum FP chamber

  • Close I265GV (gate valve separating FP box from rest of beam line) is closed.
  • Click on the VENT STATUS window and begin the venting procedure. The VENT VALVE I260VV window will turn red and display “OPEN”. The pressure should remain constant because the manual venting valve is still closed. The turbo GV I260GV will be closed, isolating the turbo pump from the focal-plane chamber.
  • Gently open the manual venting valve until the pressure displayed in the Pirani Gauge (see figure below) increases by ~1 torr every 15 seconds (see figures below)

FP chamber manual venting valve

  • Make sure that pressure inside the CRDCs and IC detectors (LabView) increase at the same rate than the pressure in the chamber. Otherwise, stop the venting process inmediately.
  • Wait until the chamber is vented (few hours). The I261PG Pirani Gauge should read slightly above atmospheric pressure (due to the dry N2 flow pumped to the chamber). The window VENT STATUS in PanelMate should display “VENT VALVE OPEN”. The window PUMPDOWN STATUS should display “PUMPDOWN STOPPED”
  • Meanwhile, turn the turbo pump off using PanelMate S800vac: select box Turbo pump focal plane detector I260TP can clock “Stop”. It will take several minutes to fully stop (you can check the turbo-pump speed in box I260TP SPEED, or using EPICS channel I260TP_FR_RD)
  • When the Turbo pump is fully stopped, switch off the chiller located near the S800 electronics rack
  • When the chamber is fully vented, select VENT STATUS and click STOP VENTING PROCEDURE. This will automatically close the vent valve I260VV
  • Close the manual vent valve

Open focal-plane chamber

  • After venting the FP chamber, the pressure inside the chamber is slightly above atmospheric due to the dry N2 pumped. Before opening the chamber, it is recommended to vent the extra N2 by “forcing” the pressure-relief valve with e.g. a screwdriver screwdriver-flange.jpg
  • Unlock the padlock protecting the power brakers of the switch controls to open the chamber, and press the START button Padlock
  • Turn the switch to open the clamps holding the FP chamber. The weight held by the hydraulic piston will increase Switch clamps Clamps holding FP chamber Scale FP chamber
  • Turn on the switch to activate the motor opening the chamber. It takes about 10 minutes to get the chamber totally opened Motor switch to open FP chamber

Installing FP scintillator

  • The figure below shows the FP chamber open, with the “old” FP scintillator to be replaced by the new one FP chamber opened
  • Unplug the bases of the up and down phototubes. The platic tie holding the cable of the up phototube to the chamber needs to be cut UP base phototube DOWN base phototube
  • Using an allen wrench, unscrew the two bolts attaching the scintillator frame to the base of the chamber Scintillator frame
  • Climb to the chamber and pull the scintillator frame up. Once unplugged, handle it to a second person FP chamber opened FP chamber opened
  • With the help of a second person, hold the new scintillator by its frame and place it in the right spot. A second person should be ready to screw the frame to the base of the chamber
  • Connect the bases of the up and down phototubes. The later is quite difficult because one cannot see the pins
  • Using a plastic tie, attach the cable of the up phototube to the scintillator frame

Closing focal-plane chamber

  • Turn the switch to move the chamber to position “UP”, and keep it that way for about 10 minutes (the time it takes the chamber to be closed)
  • Check the display indicating the weight lift by the hydraulic system. When the chamber is close, the weight displayed will increase drastically due to the resistance experienced by the hydraulic system. At that point, stop immediately the lifting switch (otherwise, a weight-limit set point might be reached, disabling the hydraulic system)
  • Turn the knob to close the clamps
  • Inspect the clamps and chamber flange (no gaps) to ensure that the chamber is properly sealed
  • Before pumping the chamber down, make sure that the scintillator is properly connected. This can be done by biasing the detector and checking the signals, either from the scalers or with a scope. One should clearly see cosmic rays; if that is not the case, the phototubes are likely miss connected

Pumping focal-plane chamber

  • Make sure that the pressure-relief valve and the manual vent valve (see above) are closed.
  • Make sure that manual valve of the mechanical pump is opened (the valve I260RV will be automatically opened in the next step) Manual valve pump
  • Open the gas-handling-system LabView control and make sure that the only open detector valves are 4 (IC supply), 5 (IC bypass), 6 (IC focal-plane bypass), 7 (Ion Chamber vent), 20 (CRDC supply), 21 (CRDC bypass), and 22 (CRDC focal-plane bypass) and 23 (CRDC vent). The rest of the valves should be closed. The pressure inside the detectors should be ~760 Torr.
  • Open PanelMate S800vac and go to page 07. Make sure that the venting valve I260VV is closed (see last step of the venting process described above)
  • Make sure that the turbo pump is off (as seen in PanelMate s800vac, page 07, box Turbo pump focal plane detector I260TP)
  • Select window PUMPDOWN STATUS and click on button START PUMPDOWN. The PUMPDOWN STATUS and VENT STATUS windows should display “PUMPDOWN IN PROGRESS”
    • The vent valve I260VV and foreline valve I260FV will be automatically closed
    • After the rough valve I260RV is automatically open, the mechanical pump will start pumping.
    • The pressures in the mechanical pump (from I259PG) and beam chamber (from I261PG) will jump momentarily to very high values. They should go down slowly after few seconds (otherwise, the chamber is not properly closed).
    • Make sure that pressure inside the CRDCs and IC (LabView) decrease at the same rate as the chamber. Otherwise, stop the pump-down sequence immediately.
    • Note that during the rough pump-down sequence, pressure in the foreline I260PG will increase to few torr due to the purge line connected to the turbo pump. This is ok, as long as the turbo pump is OFF
    • When pressure in I261PG is ~95 mTorr, turn on the chiller providing cooling water to the turbo pump.
    • When pressure in the chamber (from I261PG) gets below 90 mTorr (at least 45 min), I260RV will close.
    • Open the foreline valve I260FV using PanelMate box Foreline vlve I260FV and clicking “Open”
    • When pressure in the foreline (I260PG) is below 200 mTorr, turn on the turbo pump. You will see the speed increasing in the PanelMate box I260TP speed
    • It takes about 8 min to get the turbo pump “At Speed” (as read in box Turbo pump focal plane detector I260TP). During that time, the pressure in the focal-plane chamber will slowly increase (it is not being pump down) by few mTorr
    • When the turbo pump is “At Speed” and pressure in the chamber (as read in I261PG) is below 175 mTorr, the turbo-pump gate valve I260GV will open
    • After I260GV gets opened, you will see a pressure spike in the foreline I260PG up to ~1 Torr. This is normal behavior. This pressure will slowly decrease below 200 mTorr in about 2 minutes. It will take at least 30 min to reach the nominal value (~60 mTorr).
  • Wait for few hours until vacuum is good. You can then turn on the ion gauge I264IG
installation_fp_sci.txt · Last modified: 2019/12/10 20:26 by pereira