%The 2m Chamber                                 Steve Chappell

\chapter{The 2m Chamber at ANU}

Experiments requiring specific configurations of MEGHA modules, gas
hybrid telescopes, strip detectors and large area PSD's etc. may use
the 2m scattering chamber on ``Line 3'' of experimental area 1 at the
ANU.  Detector signals can be patched to the MEGHA data acquisition
system in the Linac Hall. In total 128 signals may be transferred
to/from the MEGHA DA and the patch panel adjacent to the 2m chamber.
Operating procedures relevant to using the 2m chamber are described in
this appendix.\footnote{Gas \& Vacuum cycling procedures adapted from
the document ``2m Chamber Vacuum Cycling...'', M.J. Leddy, S.J. Hall \&
C.D. Jones.}

\section{The Gas \& Vacuum Handling System}

The 2m chamber is pumped by a combination of carbon-vane pumps, which
take pressure down from atmospheric to around 40 mbar, vac-sorbs which
take pressure to 35 microns ideally and finally a cryo-pump which
maintains the operating pressure in the $10^{-7}$ torr range. The gas
handling is done by a unit similar in principle to the Daresbury units
(although a fraction of the size!) backed by a small rotary pump. The
layout of the system is shown figure \ref{2mgasfig}.
\begin{figure}
\centerline{\psfig{file=./figs/2mgas.ps,height=15cm}}
\vspace{1.0cm}
\caption{Layout of the 2m chamber gas \& vacuum handling system.}
\label{2mgasfig}
\end{figure}

\subsection{Evacuation}
{\bfseries\itshape Ensure biases are off all the detectors!}\\
{\bfseries\itshape Ensure hand valve is open \& beamline connected!}\\
{\itshape The hand valve is open when the handle is pointing towards the chamber
and the bellows are UNcompressed.}\\
\\
{\bfseries 1) Starting from:}\\
2 valves to chamber (A and B) OPEN.\\
2 valves to vacsorbs CLOSED.\\
Valve~D below transducer OPEN so that digital gauge reads pressure.\\
Ensure that the vacsorbs are cool or at least on the way.\\
\\
{\bfseries 2) The gas-handling valves should be in the following configuration:}\\
Gas-in valve (GD) on chamber wall CLOSED.\\
Chamber equalisation valve (GH) OPEN.\\
Detector input valve (GE) OPEN.\\
Gas out valve (GF) to left of roughing line CLOSED.\\
Beamline valves A and B SHUT. Beam hand valve OPEN.\\
\\
{\bfseries 3) Lower the chamber lid:}\\
{\itshape Make sure everything is clear and no plastic etc. has been
left in the chamber.}\\
Switch control to Down (no surprises there) and the lid will lower to
within 1 inch of closing.\\
Check the O-ring is seated and all is clear, then hold down the ``inch''
button until the motor stops itself---{\itshape don't just stop because
the lid looks like it is down.}\\
\\
{\bfseries 4) Close valve~C:}\\
{\itshape If the airlock over the target region is to be used, ensure that the
large bore tube leading from the middle of the chamber lid is
connected to the roughing line (in front of the large plastic valve
handle on the right hand side of the line---valve~C in the figure) and
valve~C open. Two bolts is enough. If the airlock is not to be used,
close valve~C.}\\
\\
{\bfseries 5) Switch on carbon vane and open valve E:}\\
The thermocouple gauge should start to drop and the gas rack transducer
reading should also fall. {\itshape If hybrid gas detectors are being
used then do not exceed 1mbar/sec pumping rate.}\\
\\
{\bfseries 6) When the gas rack transducer reads less than 40 mbar:}\\
Close valve~E.\\
Switch off carbon-vane.\\
Open valve on small vacsorb. {\itshape If the vacsorb is active you
should hear a hissing sound and the pressure should drop quite
rapidly.}\\ Close valve~D. This isolates the gas rack transducer from
the system. Note that the transducer reading may rise at this point due
to a small leak in the gas lines.\\
\\
{\bfseries 7) After 10-15 minutes:}\\
Close small vacsorb.\\
Open large vacsorb.\\
{\bfseries\itshape The pressure must fall below 75 microns on the
vacsorb transducer before it is safe to open to the cryo pump and
usually the large vac-sorb can bring it down to about 35 microns.}\\
Wait for thermocouple to drop below 60 microns and vacuum good/bad 
lights to turn to green.\\
If this does not happen and you are impatient the protection on the
thermocouple can be switched off by moving the 2m thermocouple toggle
switch on the Target Line Vacuum Protection Unit to
bypass---{\bfseries\itshape Only if the Roughing line Thermocouple is $<$
75 microns.}\\
\\
{\bfseries 7) At pressure $<$ 75 microns:}\\
Close chamber valves~A and~B.\\
Close vacsorb valves.\\
Switch the 2 litre per second to {\itshape bypass} on the target line vacuum 
protection unit (TLVPU).\\
Turn the range switch on the 2 litre per second gauge to start.\\ 
{\itshape The orange vacuum fail light will illuminate on the 2l/s ion pump
control unit.}\\
Open the valve to the cryo-pump, called valve A on the TLVPU.\\
{\itshape The Thermocouple control unit should shoot down and the vacuum good light come on. The 2 l/s ion pump control unit gauge should
follow and the range can be set to 10 mA or 1 mA as needed.}\\
\\
{\bfseries 8) When all vacuum good lights on TLVPU turn green:}\\
Switch all bypass switches to protect.\\
Ensure chamber 2l/s pressure $<$ 70 $\mu$A and beamline valves A, B are shut.\\
Open beamline valve B between chamber and beamline.\\
{\itshape Note that it is possible to hurry things along if necessary.
In this case ensure that the chamber 2l/sec gauge reads $<$ 120$\mu$A.
Then on the line valve control unit (near quads) swith the line 2l/sec
to bypass and open valve B between chamber and beamline. The vac fail
light may come on but the line 2l/sec should read $<$ 120$\mu$A which
is OK. Pressure should continue to drop and the vac fail light should
go out. At this point switch back to protect. Open valve A to
beamline.}\\
{\bfseries\itshape The line 2l/sec pump is located just upstream of the
line A quads. The reading is taken from a meter underneath the quads.
If reading goes higher than 10mA then shut valve B and let the pump
recover. If this is not done the pump can overheat.}\\
\\
{\bfseries 9) With the system operational the following readings are typical:}\\
Gas rack transducer: 020 (nb - This is isolated from the chamber).\\
Thermocouple control unit: 3 microns. Vacuum good light on.\\
TLVPU: Valve A open. Valve B shut. All vacuum good lights on.\\
2 l/s ion pump control unit: $\sim$30 $\mu$a on 100$\mu$a setting.\\
Mains light on.\\
Carbon vane pressure transducer: 0. Thermocouple: full left ($<$1000
$\mu$m).\\

\subsection{Venting}
{\bfseries\itshape Ensure biases are off all the detectors!}\\
\\
{\bfseries 1) Starting from Evacuated Chamber:}\\
Shut beamline valves A and B.\\
Shut hand valve to beamline and insert holding pin if you want to leave this under vacuum. If not leave open.\\
{\itshape This valve is shut when the handle is pointing away from the
chamber and the bellows are compressed.}\\
Close cryo-pump valve (valve~A on vacuum control unit).\\
Ensure gas in valve~(GD) and gas out valve~(GF) on chamber wall are shut 
and the chamber equalisation valve~(GH) is open.\\
Open transducer valve~D.\\
Check pressure in roughing line indicated on the thermocouple above the
carbon-vane. If at atmospheric, rough out the line using the
carbon-vane. If the target line is attached, make sure the valve~(C) is
open so that this line is roughed out as well. If the line is not
attached make sure that C is shut.\\
If necessary attach nitrogen line to the roughing line.\\
\\
{\bfseries 2) Open valves~A and~B SLOWLY:}\\
Allow nitrogen to enter the roughing line and chamber.\\
{\itshape Keep an eye on the transducer reading---approximately 1 mbar
per second seems the usual rate to vent at.\\
Watch the transducer reading and stop nitrogen flowing when
it reads approx 900 mbar (local atmospheric pressure).}\\
{\itshape\bfseries If nitrogen is allowed to flow beyond this pressure,
the chamber lid will lift and the O-ring may be damaged.}\\
\\
{\bfseries 3) At Atmospheric pressure:}\\
Slowly open the valve to the target line (valve~C), assuming the line
itself is not attached, so that the chamber is open to the
atmosphere.\\
{\itshape If the line is attached, the valve should be open so that the
target line is at the same pressure as the roughing line. If this has
not been done, open the valve now, slowly. Then DISCONNECT the line, or
it will be torn out when the lid is lifted!}\\
Lift the lid by about an inch, then check that the O-ring
has not lifted with it. This usually happens, so run a steel ruler
above the O-ring and let it drop back into place.\\
Raise the chamber lid to the required height.

\subsection{Replacing Targets Under Vacuum}

{\bfseries\itshape Protect the beamline! Close beamline hand valve and
beamline valve A.}\\
\\
{\bfseries 1) Starting from Evacuated Chamber:}\\
Ensure that the chamber valve on top of the chamber is shut, that valve
D is shut and the vacsorbs are cool.\\
Connect the target line to valve C and the N$_{2}$ line on top of the chamber.\\
Use carbon vane to pump out the target line up to the chamber lid valve.\\
The Pressure can be measured on the gauge on top of the chamber.\\
Close valve E and open vacsorb valve.\\
This will have removed most of the gas from the system. The vacsorb
should be left open at this point as a safety.\\
Place the 2l/sec pump on the cryo on bypass and open the
valve on top of the chamber.\\
The pressure in the chamber will rise but should stay below 1mA before
starting to drop again.\\
\\
{\bfseries 2) Replace target using target rod:}\\
Remove target rod and shut valve on top of chamber.\\
Shut the vacsorb valve and valve C.\\
Place the target at 90$^{\circ}$ to the pumping line.\\
Open the N$_{2}$ line to the target replacement system and take line up to atmosphere.\\
Open flange on top of chamber and remove target.\\
{\itshape As long as the vacuum is good then the chamber 2l/sec ion
pump can be placed back on protect and the scale changed back to
100$\mu$A.}\\
The pressure in the chamber may now be slightly worse than
the pressure in the beamline. Therefore, put the beamline 2l/sec ion pump on
bypass before opening up the handvalve.\\
Wait for beamline 2l/sec ion pump to recover. Put beamline 2l/sec to
protect and open valve A to tandem.

\subsection{The Gas Handling system}

The gas flow is from a bottle behind the cryo-pump, through the
{\itshape transducer} panel to the control unit, through the gas-in and
detector in valves on the chamber wall, through the detectors, out via
the gas-out on the chamber wall and through a rotary pump.  There are
2 sensors in the control unit, one labelled HI, in the output line
which ranges up to atmospheric pressure, and one labelled LO in the
input line which reads up to about 10 torr. For our purposes the HI
sensor will always be used assuming we are running at pressures $> 10$ torr.\\
\\
{\bfseries While the chamber vacuum is being cycled the valves should be in the
following status:}\\
2 valves before the transducer (GA and GB) CLOSED.\\
Transducer valve CLOSED (valve D).\\
Gas-in on control unit CLOSED (GC).\\
Exhaust valve on control unit CLOSED (GG).\\
\\
{\bfseries In the triangle of valves on the chamber wall:}\\
Gas-in CLOSED (GD).\\
Detector in OPEN (GE).\\
Chamber valve OPEN (GH).\\
Gas out valve to the left of the roughing line CLOSED (GF).\\
Proportional control valve set to `close'.\\
\\
Valve below gas-out is redundant but should be closed.\\

\subsection{Introducing Gas}

{\bfseries\itshape Gas should only be introduced into the detectors
after the chamber pressure has dropped below 250$\mu$A on chamber
2l/sec ion pump.}\\
\\
{\bfseries 1) Starting from Evacuated Chamber:}\\
Shut beamline valves A and B.\\
Turn on rotary pump below gas control panel and open gas out~(GG) on
control panel. This pumps from the rotary pump, through
exhaust valve~(GG), to chamber gas out valve~(GF).\\
Shut gas bottle valve and gas regulator valve just above bottle.\\
Switch on carbon vane and open valve~E.\\
\\
{\bfseries 2) After lines pumped out:}\\
Close valve~E and switch off carbon vane.\\
Switch proportional valve to LO.\\
Open vacsorb valve and transducer valve~D. This evacuates between the propane bottle and the chamber gas-in valve~(GD).\\
The proportianal valve readout should read 0 by the end of pumping.\\
\\
{\bfseries 3) At the end of pumping:}\\
Open valve GA.\\
Open valve GB.\\
Open valve GC.\\
Switch the proportional valve rotary pot to OPEN.\\
{\itshape You should see -ve gas flow in the flow rate meter at this stage}.\\
Set proportional valve toggle switch to HI.\\
\\
{\bfseries 3) When lines have been roughed out:}\\
Close transducer valve~(D).\\
Close valves~(GA and GB).\\
Leave vacsorb open for emergencies.\\
Close chamber~(GH) valve on chamber wall.\\
Check that exhaust valve~(GG) is open.\\
Open gas-out valve~(GF) and then slowly open gas-in valve~(GD).\\
{\itshape Recheck that proportional valve is reading 0, that the
proportional valve is on the 10~V full scale setting and that the HI
setting has been selected.}\\
Put the control switch on {\itshape AUTO} on the control box and ensure
i/p line pressure is approx zero and the green status light is lit, as
opposed to the red one.\\
Close valve GC as a safety.\\
\\
{\bfseries 4) The system should now be in its equilibrium state:}\\
{\itshape This means that the proportional valve is fully closed. This valve is
adjusted using the rotary pot, which may not read zero for fully closed
but probably will be near.}\\
Fully open the valve on the centre of the gas cylinder lid.\\
Open the pressure regulator on the side of the gas bottle until the 200
line can be read.\\ 
Open the left hand valve on the {\itshape transducer} panel one
turn or less~(GA).\\
Open the valve~(GB) very slowly. {\itshape This is the needle valve
which controls the gas supply pressure (eventually you will want this
to give a reading of about 1000 mbar (usually 1077 mbar) on the
transducer valve's digital read out). If the transducer won't go up to
$\sim$1077 mbar then open GA a bit further.}\\
Open GC fully.\\
{\itshape The flow meter should register but the green 
status light remain lit.  Pressure in the detectors is then controlled 
by the control pot. The central digital meter on the gas control box 
gives you the pressure in VOLTS (where for the HI 
range 10 V~=~1 atmosphere, approximately 760 torr, and on the LO 
range 1 V~=~1 torr ).}\\
{\bfseries\itshape  Do NOT touch the toggle switch when the control is
set to auto. If the toggle is changed, the proportional valve will go
crazy.}\\
\\
{\bfseries 5) Ready to Introduce Gas into the detectors:}
\\
{\itshape Monitor the digital pressure readout of the proportional
valve, the flow rate meter and also the 2l/sec readout below the vacuum
protection unit. This 2l/sec readout is important as it monitors the
pressure in the chamber.}\\
Open proportional valve slightly using the control pot.\\ 
{\itshape The status light on the proportional valve should remain
green. If it goes red then you are opening too fast, stop and wait for
it to recover.}\\
\\
{\bfseries 6) With some gas in detector ($\sim$0.2~V on digital readout):}\\ Close the gas exhaust valve~(GG) until flow meter $\sim$100~scc/min.\\
Introduce more gas  by opening proportional valve control pot until
required pressure is reached {\itshape (while continually checking
2l/sec pressure, if this goes very bad then wind down the proportional
valve control pot and open valve D to the vacsorb). As you do this keep
closing exhaust valve~(GG) to keep flow rate at $\sim$100~scc/min.\\
If the flow rate goes off scale and the control pot status light remains green 
then no worries! It just means that you should shut GG slightly.}\\
\\
{\bfseries 7) After reaching the required pressure (eg. 1~V $\equiv$ 76
torr):}\\
Ensure that the flow rate is $\sim$40-60 scc/min.\\
Close vacsorb and switch gas control, on bottom of gas control unit, to
protect.\\
\\
{\bfseries 8) During the run monitor:}\\
Gas flow rate ($\sim$40-60 scc/min).\\
Detector gas pressure ($\sim$1~V Digital readout on gas control).\\
Transducer Pressure ($\sim$1077~mbar).\\
Chamber pressure ($\sim$70 $\mu$A 2l/sec gauge below vacuum protection unit).\\
Status green on proportional valve control pot.

\subsection{Removing Gas \& Venting the Chamber}
{\bfseries\itshape Protect the beamline! Close valves A and B to the
beamline.}\\
\\
{\bfseries 1) Starting from Evacuated chamber, Gas filled detectors:}\\
Close valve A to the cryopump on Target Line Vacuum Protection Unit (TLVPU).\\
Switch from protect to bypass on gas control lower unit (below proportional control valve).\\
Close the proportional valve by winding down the control pot to 0 and switching it from auto to close.\\
Close GC and open GG fully.\\
{\itshape This should pump the gas out of the detectors
until eventually the flow rate is very low.}\\
\\
{\bfseries 2) When the digital pressure readout is $\sim$0 (usually
$\sim$0.05):}\\
Close GB and GA to stop any more gas entering the gas control
system. \\
Close gas bottle valves.\\
Close GF and GG to stop pumping of gas from detectors.\\
Switch 2l/s ion pump to bypass on TLVPU. (Otherwise it tries to shut
valve A to the cryo.)\\
Open GH to couple the detectors with the chamber.\\
{\itshape The transducer  will still be reading $\sim$1077 mbar. The
gas from here can be pumped out using the carbon vane.}\\
\\
{\bfseries 3) Ensure that chamber valves A and B are shut as well as
GA, GB and GC.}\\
Switch on carbon vane and open valve E (on carbon vane) and valve~D.\\
{\itshape This will pump out the carbon vane line down to $\sim$40 mbar.}\\
Close valve E and switch off carbon vane.\\
{\itshape If you've got a working vacsorb then you can pull more gas out of the carbon vane line, otherwise the remaining gas can be let into the chamber.}\\
Check that GF and GD are closed and that GH is open.\\
Slowly open valve A on chamber wall to release the gas into the chamber through
the detector.\\
\\
{\bfseries 4) After pressure in transducer has dropped to 0:}\\
Slowly open chamber valves A and B.\\
The N$_{2}$ can now be let into the chamber and detectors.\\
Slowly open N$_{2}$ valve on plastic tube and then open N$_{2}$
valve on pumping rig.\\
Transducer pressure should start to increase from 0 to 900 at a rate of $\sim$1~mbar/sec.\\
\\
{\bfseries 5) When transducer pressure reaches 900 mbar:}\\
Shut N$_{2}$ valves.\\
Open valve C.\\
Lift the lid.\\ 
Turn off rotary pump below gas control.
