Polarized Electron Sources for Linear Colliders ”

A&TRACT Linear colliders require high peak current beams with low duty factors. Several methods to produce polarized e’ beams-for accelerators have been developed. The SLC, the first linear collider, utilizes a photocathode gun with a GaAs cathode. Although photocathode sources are probably the only er@ical alternative for the next generation of linear colliders, several problems remain to be solved, including high voltage breakdown which poisons the cathode, charge limitations that are associated with the condition.of the semiconductor cathode, and a relatively low polarization of ~50%. Methods to solve or at least greatly reduce theimpact of each of these problems are at hand. .1 COLLIDER REQUIREMENTS AND POLARIZED SOURCES _ -. _ The accderator of choice for pushing higher the energy _. . . frontier for electron-positron collisions is the linear collider [l]. The linear collider concept has been demonstrated with the SLC, and already the designs of the next generation linear colliders are well underway. A comparison of electron sour& parameters for several new collider designs is given in Table 1 along with the SLC source parameters. The KEK, DESY, and SLAC designs require a electron source similar to that employed by the SLC but with a macropulse structure consisting of a string of micro-bunches whose total charge is somewhat larger than that of the SLC source:-