Beam Measurements on the Electron Injector for a High Current Betatron

The beam from a pulsed electron source for injection into a high current betatron has been investigated. Only cold cathode field enhanced emitters were considered. Carbon fiber bundles and hydrocarbon felt were tried in a gridded Pierce-geometry gun. The observed emittance was not acceptable at a current of 140 A and a diode potential of about 280 kV. An alternative source was investigated consisting of a single needle point cathode and a plane anode grid. At a current of 200 A an emittance of ¿ = 44¿ cm mrad was observed. The spherical aberration of the source was found negligible. The pulse length of the high voltage pulse was about 20 nsec. The turn-on delay times for the carbon fiber and the needle point cathode were around 10 to 15 nsec.