VELOCITY SPREAD MEASUREMENTS ON A MAGNETRON INJECTION GUN BEAM

The parallel electron velocity distribution function has been measured on an electron beam from a magnetron injection gun (MIG) using an E parallel to B energy analyzer. The magnetic field, beam voltage, and beam current were scaled down from normal operating parameters. The perpendicular velocity spread, inferred under the assumption that the electrons are monoenergetic, is relatively constant for electron velocity ratios beta(perpendicular to)/beta(parallel to)>0.7 and increases approximately linearly with the beam current. The current scaling of the perpendicular velocity spread is also consistent with electron-loss currents measured at the control anode of the MIG. Observed perpendicular velocity spreads for the gun design parameters are substantially larger than computational values.