Foam Scattering Chamber

The (foam) scattering chamber, used for the e1d and later runs, has been added to GSIM (geometry taken from drawing no. 66840-E-03016). The old chamber had supporting ribs in line with the torus coils, in order to support the pressure from the vacuum. There are no ribs in the new chamber. It is made of Low Density Foam which is strong enough to withstand the required pressure. The image below shows a cut out view of the FOAM chamber with the e1-6a target cell inside.
Cut out view of FOAM chamber
with e1-6a target cell.

Cut out view of FOAM chamber
with e1-6a target cell.

The changes made are;

The volume FOIL has been split in to upstream (UPST) and downstream parts (FOIL) to allow the scattering chamber (and all downstream beam pipes) to be positioned independantly of FOIL.
New volume CHAM, added as a subvolume of UPST, which acts as the new scattering chamber.
New ffread card CHAMBER which decides between the old (RIBBED) and the new (FOAM) chamber. This decision is made in the file geom_foil_new.F.

Usage;
CHAMBER <1 or 2>
Takes one integer arguement where; 1=Old chamber and 2=New chamber.
(The default is 1=old for nothing specified.)
See the result of;
CHAMBER 1 RIBBED Chamber,
and
CHAMBER 2 FOAM Chamber.
The material definitions are as follows;

the chamber is made of low density foam, polystyrene,

the upstream exit window is Al (71microns thick),

the interior of the chamber is vacuum, which continues upstream for ~60cm.

New ffread card UPSTPOS which positions the UPST volume. This card can be used to position either the old or new chamber.

Usage;
UPSTPOS <x> <y> <z>
Takes 3 real arguements for the x, y and z coordinates.
(The default is x=0.0 y=0.0 z=0.0).

Views of UPST volume positioned relative to the mini torus;
UPSTPOS 0.0 0.0 0.0
UPSTPOS 0.0 0.0 -50.0

The behaviour of the SIGBEAM ffread card remains almost as before (it dictates whether the vertex follows the target cell or is given in the event file). Except that now with SIGBEAM>0.0 the vertex follows the TGPOS + UPSTPOS positions so that it will always follow the target cell. (NOTE: Still only in the z coordinate, not x & y).

Email comments to Steven Morrow