A Project to Put New Quads Downstream of the Moeller setup

This file: ~moller/downst_quads.html, last updated: Thu, 03 June 1999
moller@jlab.org
There are several requirements to the optics settings in Hall A:
  1. A good beam spot on the main target
  2. A small beam spot in "X" projection in the Compton polarimeter chicane
  3. Settings in 3 "Moeller" quads optimized for Moeller polarimeter measurements
With the present beam line configuration there is no way to satisfy all the requirements at the same time. Changing the magnets to/from the Moeller settings takes on average 20min. In order to provide a common setting satisfying all the requirements the accelerator division suggested to install 2 new quads downstream of the Moeller dipole.

There is a potential drawback of such a change in the beam line configuration. Such quads may increase the background for the Moeller detector. At the moment the beam pipe downstream of the Moeller dipole is 4" thick. It turns to a 1.5" pipe about 200cm downstream of the end of a Moeller detector box, of about 1000cm from the Moeller target. Multiple scattering in the Moeller target smears off the beam considerably. For a 0.8GeV beam the deflection is about RMS=1cm at 1000cm from the Moeller target.

A quad with a 1" beam hole placed above the Moeller detector may create a considerable background since 10-40% of the beam passed