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The procedures to vent/pump the S800 Intermediate Image box, and/or filling the PPAC detectors with gas must be done carefully to ensure that the PPACs are not damaged. For instance, before venting the chamber, we have to make sure that the PPACs are empty and equalized with respect to the vacuum in the chamber. In order to avoid errors, an automated gas handling system (II-GHS) was designed to perform these tasks safely. The system is schematically illustrated in the figure below. It shows the status of the valves (red: closed, white: open) when the intermediate image chamber is under vacuum and the PPACs are filled with gas (NOTE: This figure was taken from the A1900 GHS included in Barney. A similar GUI for the S800 II PPACs is not yet available):
The II-GHS equipment (valves, flow-meter, pipes, isobutane gas bottle. etc.) are located on the west balcony of the top level in the S3 vault (see figure below):
Requirements: PanelMate files S3_Gas_Handling and S800Vac
Verify that PPACs are in automatic mode with gas removed (S3_Gas_Handling)
The “GH System Status box should read “Auto Mode Gas Removed”
If gas is removed but the system is not in the automatic mode, consult the Beam Physicists or Device Physicist. NOTE: the only valves that should be open in S3_Gas_Handling are the “Det Bypass” and “Chmbr Bypass
Verify that PPACs are not biased:
Open S800Vac and go to page 03 (“Intermediate image box vacuum system sec 15”)
Isolate chamber by closing gate valves I212GV and I215GV
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Check box “PUMPDOWN STATUS INTERMEDIATE IMAGE BOX”. It should read “Good vacuum”
.
Requirements: PanelMate files S3_Gas_Handling and S800Vac
Verify that Chamber is closed and pressure-relief valve (north side of the chamber) is properly closed (NOTE: sometimes, due to overpressure from dry N2 during the venting procedure, the O-ring in pressure-relief valve flange is moved out of place)
Verify that PPACs are not biased by opening the
HV GUI
IMPORTANT: Verify that manual roughing pump valve located near the intermediate-image chamber is closed
.
Insert PPACs/turn on light (Diagnostic Drives PanelMate) and verify condition through sight window on south side of the chamber (be careful no to bump the bullet camera).
Open S800Vac and go to page 03 (“Intermediate image box vacuum system sec 15”)
Check “PUMPDOWN STATUS INTERMEDIATE IMAGE BOX”; it should read “PUMPDOWN STOPPED”. Select that box and click on “START PUMPDOWN”. The chamber will not be pumped yet because the manual roughing pump valve is closed.
Slowly crack manual roughing valve
Start slow (< 1 Torr/sec). Chamber pressure is displayed in I215PG in S800Vac PanelMate. There is also a local display of the mechanical pump pressure on a Granville-Phillips 275 Mini-Convectron, which is helpful to control rate of pumping.
Verify PPACs changing shape through sighting window.
Pump to about 100 Torr before fully opening the roughing valve.
Once roughing valve is fully open, retract PPACs and turn lights off.
When the pressure in I215PG is below 200 mTorr, the Turbo Pump will start automatically through the following sequence:
I214RV will be closed
I214FV will be opened
I214GV will be opened
When the pressure ready by I215PG is few mTorr, you can turn on the ion gauge I213IG. Good vacuum will take ~1-2 hours.
NOTE: it sometimes happens that the foreline pressure rises above the trip point for the Turbo Pump (e.g. if the pumpdown timer expires before pressure is below 300 mTorr, or there is too much back-up pressure from the chamber when the foreline valve opens). In this situation, you will see that: (1) the turbo pump will stop, (2) the turbo gate valve I214GV will be closed, (3) the foreline valve I214FV will be closed and the corresponding PanelMate box will turn red and display an error message “Foreline pressure > 2 Torr”, and (4) the foreline pressure will be few Torr. In a situation like this, foreline valve needs to be bypassed open (in PanelMate) and the TP needs to be restarted:
Select box labeled “FORELINE VLVE I214FV” and the click on “BYBASS VAC INTERLOCKS OPEN” button
Select box labeled “TURBO PUMP INTERMEDIATE IMAGE BOX I214TP” and click “START”
Turbo pump will start ramping speed. When the TP reaches 40000 RPM, the I214GV will open automatically.
When foreline vacuum gets below 2 Torr, you can select “FORELINE VLVE I214FV” and click “REMOVE BYPASS”
(Note: sometimes it is necessary to repeat this operation a couple of times).
At the end of the procedure, close the manual roughing pump valve
Requirements: PanelMate files S3_Gas_Handling and S800Vac
Verify that PPACs are not biased:
Verify that PPACs are in automatic mode with gas removed (S3_Gas_Handling)
The “GH System Status box should read “Auto Mode Gas Removed”
If gas is removed but the system is not in the automatic mode, consult the Beam Physicists or Device Physicist. This typically requires to verify that the system is in a controlled status. In particular, the “I214BON_CONFIRM” box should indicate “PP BIAS OFF CONFIRMED”, and the only that should be open in S3_Gas_Handling are the “Det Bypass” (V5) and “Chmbr Bypass” (V6); the rest of the valves (Gas Sup V1, Gas Lin Pmp Out V2, Flow Bypass V3, Det Return V4, and I214V_NCL (enable) should be closed)
Confirm that PanelMate box “I214P_AUTO/MAN Pre Set” reads 5 Torr (the set gas pressure in the detector)
Open the gas bottle valve (sitting near the gas handling system)
PanelMate box “Gas Flow Control” should indicate “OK to Start Gas Flow”. Select that box and click on “Start Gas Flow”
Valve V2 (Gas lin pmp out) will be opened and I214V_NCL will change from closed to “ENABLED”
Valves V3 (Flow Bypass) and V4 (Det Return) will open
Valve V1 (Gas supply) will open, and V2, V3, and V6 (Chamber Bypass) will close
GH System status should indicate “Gas Flowing”
I214CM Press Rdg will gradually increase to the set value
When the detector is filled, valve V5 (Det Bypass) will close
GH System status will indicate “Flow Estab.”
I214BON_CONFIM will change to “PPAC BIAS ASSUMED ON”
The valves status will be: V1 (open), V2 (closed), V3 (closed), V4 (open), V5 (closed), V6 (closed, I214V_NCL (enabled)
You can now turn on the detectors
Verify that PPACs are not biased:
Verify that PPACs are in automatic mode with gas flowing (S3_Gas_Handling)
The “GH System Status box should read “Auto Gas Flow Estab”
If gas is flowing but the system is not in the automatic mode, consult the Beam Physicists or Device Physicist. This typically requires to verify that the system is in a controlled status. In particular, the “I214BON_CONFIRM” box should indicate “PP BIAS OFF CONFIRMED”, and the valves should indicate:
PanelMate box “Gas Removal Control” should indicate “OK to Start Gas Removal”. Select that box and click on “Start Gas Removal”
Valves V1 (I214 Gas Sup) and I214V_NCL will close
Valves V3 (Flow Bypass) and Det Bypass (V5) will open
I214CM Press Rdg will gradually decrease to zero
GH System status should indicate “Gas Removal”
When the gas is removed from the detector
Valve V3 (Flow Bypass) and 4 (Det return) will close
Valve V6 (Chamber Bypass) will open
GH System status will indicate “Gas Removed”
I214BON_CONFIM will change to “PPAC BIAS ASSUMED ON”
The valves status will be: V1 (closed), V2 (closed), V3 (closed), V4 (closed), V5 (open), V6 (open), I214V_NCL (closed)