\documentclass{chowto}

\title{Changing SOS Gas Cerenkov PMTs}
\howtotype{expert} % ``expert'', ``user'', ``reference''
%\experiment{Name of experiment} % Optional
\author{Glen Warren}
\category{sos} % Subject area of this document
%\maintainer{Name of person maintaining document} % Optional
\date{July 7, 2003} % Can use \today as the argument

\begin{document}

\begin{abstract}
Instructions on how to remove and install PMTs for the SOS gas
Cerenkov detector.
\end{abstract}

\section{Introduction}

The detector employs four Burle 8854 PMTs. These are large 5''
diameter, 14 stage tubes. They are housed in magnetic shields, and
look through Winston cones, parabolic mirrors that funnel photons
to the photocathode. 

\section{Removal}

To remove a phototube from the detector, do the
following: 

\begin{enumerate}

  \item {\em Remember never to touch or apply force to the phototube
  face. This glass/metal seal is very fragile!}

  \item Loosen the hose clamps that connect the phototube and base and
  remove the base.

  \item Remove the six brass nuts that hold the phototube flange to the
  detector tank.

  \item Remove the whole phototube assembly (tube, flange, Winston cone
  and support) taking care not to bump the Winston cone on the hole in
  the tank. The assembly is somewhat ``off balanced'' and a little
  heavy. It has been found that a round office waste basket is very
  useful in supporting this assembly, tube up, on a work bench.

  \item Loosen, but do not remove, the three, small, regular head
  screws that hold the Winston cone back against the phototube face.

  \item Undo the three Allen bolts that connect the aluminum ring
  (connected to the back of the Winston cone) to the flange (via the
  brass rods). The Winston cone should now be free.

  \item Now wiggle the magnetic shield, with the tube inside, free of
  the aluminum cylinder and flange. Take care not to let the phototube
  fall out of the shield. It's a little tight because there is an
  O-ring inside that forms the gas seal.

  \item Finally, remove the plastic ring from the face of the tube,
  and then remove the tube from the magnetic shield.


\end{enumerate}

\section{Installation}

To replace a phototube, do the following: 

\begin{enumerate}

  \item {\em Remember never to touch or apply force to the phototube
  face. This glass/metal seal is very fragile!}

  \item Place the flange on top of an office waste basket with the
  aluminum cylinder pointing down.

  \item Insert the O-ring into the back of the wide part of the
  magnetic shield, slide the phototube in, and place the plastic ring
  around the face of the tube.

  \item Wiggle the magnetic shield into the aluminum cylinder/flange.

  \item Place the Winston cone assembly onto the front of the magnetic
  shield. The three small, regular screws should be loose. Note that
  the shield should catch on the small lip on the inside of the
  aluminum ring connected to the cone. Tighten the three Allen bolts
  that attach the cone assembly to the flange via the brass rods.

  \item Center the Winston cone on the phototube by gently pushing the
  cone up against the plastic ring around the phototube. There is no
  need to apply force! Tighten the small screw holding the cone in
  place.

  \item Once you're sure that everything is secure, pick up the whole
  assembly and place it (Winston cone first!) into the detector
  tank. Making sure the flange O-ring is in place, tighten the six brass
  bolts slowly, and in a star pattern.

  \item Place the hose clamp collar around the phototube base housing,
  and slide it up along the housing such that the white phototube
  socket is the furthest thing out. This will enable you to see the
  pin alignment hole as you connect it to the phototube pins. Once the
  tube is connected (take care not to touch the pins, there is a
  strong argument that this increases dark current) slide the hose
  clamp collar down, such that it is centered between phototube and
  base. Tighten the hose clamps as needed. (Note that the center of
  the phototube and base are often not quite collinear. This is
  normal, and a little bit of ``tweaking'' is necessary. Try to maintain
  that fine line between being gentle and forcing it.)

\end{enumerate}

\end{document}

% Revision history:
% $Log: sos_gc_pmt_change.tex,v $
% Revision 1.1  2003/07/07 20:30:25  saw
% Initial version
%
