A Precise Compton Polarimeter for Hall~C at Jefferson Lab

The $Q_{weak}$ experiment, scheduled to run in 2010--2012 in Hall~C at Jefferson~Lab, will measure the parity-violating asymmetry in elastic electron-proton scattering at 1.1\,GeV to determine the weak mixing angle $\sin^2 \theta_W$. The dominant experimental systematic uncertainty will be knowledge of the electron beam polarization. Following the accelerator upgrade to provide an 11\,GeV electron beam to Hall~C by 2014, parity-violating deep-inelastic scattering experiments will require a high-precision, continuous beam polarization measurement. With a new Compton polarimeter we aim to measure the beam polarization with a statistical precision better than 1\% in one hour and a systematic uncertainty of 1\% for an incident electron beam energy between 1.1\,GeV and 11\,GeV. A low-gain Fabry--P\'erot cavity laser system provides the circularly polarized photons. The scattered electrons are detected in radiation-hard diamond strip detectors, and read-out using FPGA logic boards. The photon detector uses a fast, undoped CsI crystal with sampling and integrating read-out. Coincident events are used to calibrate the detectors. The design and installation of the Compton polarimeter subsystems will be discussed.