Demands on polarized electron sources by future parity violating experiments

The next generation of parity-violating electron-scattering experiments at Jefferson Lab will require even greater control of the electron beam under polarization reversal. These experiments require faster transitions between polarization states with smaller associated changes in the beam. In this paper, recent experience at Jefferson Lab is reviewed and the requirements of future experiments are discussed. Potential developments are briefly examined, including the possible use of a Kerr cell to change the helicity of the laser and hence the electron beam.