POLARIZED ELECTRON SOURCES
The nuclear physics program at CEBAF relies to a great
extent on the availability of highly polarized electron sources.
Significant progress has been made in the last few years
and has resulted in cw, highly polarized (~80%), low-emittance,
long-lifetime electron sources in the mA regime.
Nevertheless there is a continuing demand of polarized
electron sources of higher performance, in terms of polarization,
current, and lifetime. For example, electron-ion colliders
that are contemplated that will need 100 mA sources.
A research program on the development of polarized electron
sources could have several facets:
Lifetime improvement of polarized electron sources
At present, the lifetime of photocathodes is limited by ion
backbombardment. A better understanding of the mechanisms
and physics of ion backbombardment, as well a means of
eliminating or controlling, it would result in an increase
of the lifetime of the photocathodes
New photocathode materials
New materials (strained layers, superlattice, chalcopyrite, etc)
could produce polarizations in excess of 85%. An R&D program
would study these new materials and optimize their characteristics
and preparation parameters in order to maximize the electron polarization
New laser methods for synchronous photoinjection
New and existing polarized electron sources would benefit form
stable, reliable lasers with variable repletion rates and pulse
lengths. Future projects (free electron lasers, energy-recovering
linacs, electron-ion colliders) will require high-power, stable,
and reliable lasers operating at high repetition rates.