Ionization Chamber (IC) Instructions	8 August 2002

Authors: J. D'Auria, D. Hutcheon, U. Greife, A. Chen and C. Jewett

A. TO PUMP DOWN FROM ATMOSPHERE THE IC AT THE END OF THE BEAM-LINE 

Ensure that the MCP (microchannel plate detector) and foil are retracted by checking on the actuator at the pumping cube, and also by going to EPICS.

Close valves 0, 1, 3, 7, 11, 12, 20 and 20B.

Go to EPICS and close valves IV61 and RV61.
 
Open valves 4, 5, 6 and 21.

Open valve 2 by giving it three turns from the fully closed position.

Open the MFC (mass flow controller) valve.  The MFC valve switch is the channel 1 switch on the black MFC box.

Bypass the EPICS interlock on SV62, and open the isobutane supply valve SV62 with EPICS.

Plug in the pump (RPX) that is located on the floor beneath the IC.

Record the pressure differential readout.

Open valve 0.

Slowly open valve 1 until you observe a change in the pressure differential display.  The pressure differential value should be between 0 and 1 torr.

Continue adjusting valve 1 in order to maintain a pressure difference that is less than 1 torr relative to the value recorded earlier.

When valve 1 no longer has an effect on the pressure difference, then it is safe to completely open valves 1 and 2.

When the readout from the convection gauge CG61 reads less than about 0.6 torr, reset (RST) SV62, and remove the SV62 bypass.  Close valve 2.  Check for good vacuum in the final slit box (IG52 should be on).  Next turn off ion gauge IG52, bypass the interlock for IV61, close IV51, and open IV61.

Close valve 0, and open valve 2 to further evacuate the IC behind the window.

Remove the bypass on the interlock for IV61.

Turn on IG52, reset (RST) the interlock condition on IV61, and remove the interlock bypass for IV61.







B. TO FILL THE IC WITH ISOBUTANE

You must first pump out the IC (see procedure A).

Check to be sure that isobutene is ready to flow from the gas shack.

To set up for pumping on the upstream end of the window, close valve 2.  Close IV61, and open RV61 in EPICS.

Close valve 6.

Open valve 7, and close valves 4, 0 and 12.

Open valve 11.

Set the mfc valve to auto.

Set the pressure differential set point to the desired IC pressure.  To do this, push index, use the up and down arrow keys to adjust the value, hit enter, and then hit index.  Because the isobutane pressure fluctuates wildly at first, it would be best to set the pressure differential to about 2 torr, and then to increase it to the desired pressure.

Bypass the SV62 interlock, and then open SV62 in EPICS.  

Check that valve 21 is open.

Open inlet valve 20, which is the isobutane valve.

The value in the flow reading is given in cc/min.  A good flow rate is 100 cc/min.  If necessary, adjust needle valve 5 until the flow rate is 100 cc/min.

Let the isobutane flow for 30 to 45 minutes to remove eventual contaminants from the system.  After the desired pressure differential has stabilized, close RV61, and turn off RP21.  Bypass the IV61 interlock, open IV61, turn IG52 back on, and reset (RST) the IV61 interlocks.  If necessary, remove the IV61 bypass, reset (RST) SV62, and remove the SV62 bypass.




















C. TO USE THE IC

1. Applying bias

When the pressure differential has stabilized, apply the appropriate biases to the electrodes.  Apply biases slowly (( 10 V/sec)!

2. Changing pressure

Before performing pressure changes, close IV61 and open RV61.  Set the pressure differential set point to the desired IC pressure.  To do this, push index, use the up and down arrow keys to adjust the value, hit enter, and then hit index.  Because the isobutane pressure fluctuates wildly at first, it would be best to set the pressure differential to about 2 torr, and then to increase it to the desired pressure.  After the pressure change, close RV61, bypass IV61, and open IV61.  Finally, remove the bypass on IV61 again.









































D. TO EMPTY THE IC OF ISOBUTANE, AND THEN BRING IT BACK TO 760 TORR OF AIR

First, slowly turn down, and then off all of the biases applied to the IC.  The Bertan units marked IC anode and cathode located in rack 27B supply the bias voltages to the IC.

Next, pump out all of the isobutane (never let air in with the isobutane, since air mixed with isobutane can explode!). 

Close valve 20.

Close IV61 and ensure that the IV61 bypass has been removed.  Ensure that RV61 is closed.

Set the MFC to open.

Open valves 6, 7 and 4.

Check that valve 2 is closed, and then open valves 0 and 1.

Slowly open valve 2 by three turns of the valve handle.

Close SV62, and set the MFC valve to close.

After the IC has reached vacuum (check the pressure gauges PG2 and CG61), let air into the IC by performing the following steps.

Close valve 0, and then ensure that valves 1 and 2 are closed.  Close valves 6 and 7.

Unplug the pump.  Open vent valve 3.  Open valve 0, and then open valve 2 halfway by giving it three turns.

Very slowly open valve 1, while watching the readout on the pressure differential.  Do not permit the pressure difference to exceed 1 torr.  Open valve 1 further to let air in more quickly, but do not let the pressure difference exceed 1 torr.