In the center of the detector, a radial drift field is defined on the
inside by the high voltage electrode, which surrounds the beam pipe at
a radius of 8cm and a potential of -10KV, and on the outside by the Frisch
grid at a radius of 30cm and a potential of 0V. Towards both ends of the
detector, this field has to be isolated against disturbances from the outside
world. Here, 17 aluminum rings are set to potentials equivalent to a radial
field by a divider chain. To reduce radiation length, the rings are made
of 1cm diameter aluminum tubing with a wall thickness of 0.1mm. The rings
are mounted to support beams made of glass fiber loaded epoxy. The ring
radii have to be extremely precise to limit field distortions and danger
of sparking.
All mechanical work was done at the MPI workshop.