An Instrumented Collimator for Enhancing the Degree of Linear Polarization
Abstract
We have successfully employed an instrumented collimator of aperture 2 mm for the g8 run (summer, 2001) in Hall B of Jefferson Lab. The instrumentation of the collimator consists of four radially mounted scintillator + lightguide + PMT elements possessing a left-right, up-down symmetry. We made use of the physical fact that the emission angle of the coherent bremsstrahlung photon component is correlated with its energy for enhancing the degree of polarization of the photon beam. We can extract the spectral peak by tightly collimating the beam and thereby reduce the incoherent background, which further serves to increase the degree of polarization. The maximum polar angle is limited by the opening angle of the collimator, which gives the lower limit for the coherent bremsstrahlung photon energy. To achieve polarizations exceeding 75%, we must collimate the beam to better than one half of a characteristic angle. This means for a collimator-goniometer distance of 22 m, the aperture of the collimator should be ~ 2 mm for an incident electron energy of E_circ= 5.7 GeV. We will report on the design and implementation of this device.
- Publication:
-
APS Meeting Abstracts
- Pub Date:
- October 2001
- Bibcode:
- 2001APS..HAW.KE009C