  Future colliders that require low-emittance highly-polarized electron beams
are the main motivation for developing a polarized rf gun. However there are
both technical and physics issues in generating highly polarized electron beams
using rf guns that remain to be resolved. The PWT design offers promising
features that may facilitate solutions to technical problems such as field
emission and poor vacuum. Physics issues such as emission time now seem to be
satisfactorily resolved. Other issues, such as the effect of magnetic fields at
the cathode-both those associated with the rf field and those imposed by
schemes to produce flat beams-are still open questions. Potential solution of
remaining problems will be discussed in the context of the PWT design.
