Investigation of space-charge flow in magnetron injection guns

A combined theoretical and experimental study has been carried out on the space-charge flow in a magnetron injection gun (MIG). The theoretical analysis considers both nonrelativistic and relativistic cases and is concerned with the beam current density, perveance, axial- and rotational-kinetic energy of the electrons and relates these quantities to conditions at the cathode. An understanding of hollow beam space-charge flow has been obtained from the experimental investigation of a MIG which has been designed for maximum operating flexibility. The accelerating anode consists of six separate discs which may be biased independently thus providing a means for varying the potential distribution in the gun and suppressing or enhancing emission from any portion of the cathode. Three separate conical cathodes have been investigated with half-angles of 4, 8 and 12 degrees. The guns have been tested in an electron beam analyzer in which the beam is intercepted by a movable collector-aperture system. By varying the emission from the cathode, it has been observed that the flow is quasi-laminar. High magnetic fields were observed to alter the current density distribution but did not appreciably affect the thickness of the beam. Evaluation of the results provides a better understanding of the space-charge flow and is helpful in leading to the design of an optimum MIG configuration.