Experimental study on low-velocity-spread axis-encircling electron gun

Summary form only given, as follows. The axial velocity spread was measured using a pin-hole and phosphor screen and the result was compared with the theoretical estimation. The theoretical calculations had been performed by using a new single-cusp gun theory that considered the discrepancy of the electron beam line and the magnetic flux line in the area of the cathode and anode. The specific thing of the new theory is the possibility of a fairly low velocity spreads just by controlling the distance between the cathode and the magnetic cusp, under well optimized another parameters. In this experiment, to verify the validity the theory, a 30 kV, 1.0 A Pierce-type electron gun was used with a peak magnetic flux density of 4.38 kG. The magnetic field has an asymmetric magnetic cusp by which the electron beam can be made to be an axis-encircling electron beam. And the position of the cathode can be changed using a micrometer to control the distance between the cathode and the magnetic cusp.