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.