One of the major challenges in designing the beam line was the small
clearance of ∼ 7.5 cm along beam axis between the collimators of
the anti-Compton shields. A stainless steel beam tube of 6 cm diameter
(top-left figure) has been used inside the array. The backward array
can slide back on its guide rails without disturbing the beam line.
The scattering chamber is made of 2″ diameter glass tube to minimize
the attenuation of γ-rays in the chamber walls. Wilson seal
couplings are used between the scattering chamber and beam tubes at
both ends. The target is mounted on four rods inserted along the beam
tube. The beam tube downstream of the target is mounted rigidly on the
mechanical structure of the forward array.
Outside the array, 4″ diameter stainless steel tubes are used for
transporting the beam. A Turbo-molecular pumping system backed by a
rotary pump, with dedicated home-made control unit has been installed
in the beam line. A removable collimator of 5 mm diameter with current
readout is put at 1.5 m upstream of the target. In actual operation,
the current intercepted by this collimator is minimized for centering
the beam on target.