DESIGN OF HIGH-PERVEANCE CONFINED-FLOW GUNS FOR PERIODIC-PERMANENT-MAGNET-FOCUSED TUBE

摘要

Immersing the cathode of an electron gun in a magnetic field produces a beam which is less sensitive to transverse forces. This technique, called confined flow, is used extensively to diminish beam scalloping due to the transverse velocities of thermal electrons and to improve beam transmission under rf operation with solenoid fields. Confined flow can also be used to provide stiffer beams which resist the magnetic perturbations inherent in periodic-permanent-magnet (ppm) focusing. This report gives an approach to the design of high-purveyance, low-compression guns in which confinement is used to stabilize the beam for subsequent ppm focusing. The computed results for two cases are presented. A magnetic-boundary-value problem is solved for the scalar potential from which the axial magnetic field is computed. A solution is found by iterating between Poisson's equation and the electron trajectory calculations. Magnetic-field values are varied in magnitude until a laminar beam with minimum scalloping is produced.