Review of experimental results from high brightness DC guns; Highlights in FEL applications

高輝度電子銃実験結果のレビュー; 自由電子レーザーへの応用のハイライトと限界

西森 信行

Nishimori, Nobuyuki

Future energy recovery linac light sources and high repetition rate X-ray FELs require high-brightness and high-current electron guns capable of delivering an electron beam with an emittance lower than 1 mm-rad and currents up to 100 mA. A DC photoemission gun is one of the most promising candidates for such guns, because a record high current of 65 mA and generation of high brightness beam with 90% normalized emittances of 0.3 mm-mrad with bunch charge of 77 pC were recently demonstrated at the Cornell photo injector with a 350 kV photoemission gun. Further increase of the gun high voltage is desirable to reduce space charge induced emittance growth especially for high bunch charge application such as X-ray FEL. Employment of a segmented insulator is a key to reach higher voltage. This technique led to generation of 500 keV beam from the JAEA gun with 160 mm acceleration gap, conditioning voltage more than 500 kV at the Cornell gun with gap /lt 50 mm, and demonstration of 500 kV holding for 10 hours at the KEK gun with 70 mm gap. In this talk, we present recent experimental results of high brightness DC guns and discuss highlights and limitations in FEL applications.