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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 focal-plane detectors are unbiased
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)
Ensure that the FP ion gauge (I264IG) is off (see details
here)
-
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)
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 and select S800vac
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
Unlock the padlock protecting the power brakers of the switch controls to open the chamber, and press the
START button
-
Turn on the switch to activate the motor opening the chamber. It takes about 10 minutes to get the chamber totally opened
Installing FP scintillator
The figure below shows the FP chamber open, with the “old” FP scintillator to be replaced by the new one
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
Using an allen wrench, unscrew the two bolts attaching the scintillator frame to the base of the chamber
Climb to the chamber and pull the scintillator frame up. Once unplugged, handle it to a second person
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)
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)
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).
When pressure in the chamber (from I261PG) gets below 100 mTorr (at least 30 min), I260RV will close. Foreline valve I260FV will open followed by the turbo gate valve I260GV.
Wait for few hours until vacuum is good. You can then turn on the ion gauge I264IG