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

The axial velocity spread is measured using a pin-hole and phosphor screen. The measured data is compared with the theoretical estimation. The theoretical calculations are performed by using a new single-cusp gun theory that shows the possibility of fairly low velocity spreads. In this experiment, 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. The result of the preliminary measurement of the axial velocity spread follows closely the theoretically estimated values. The minimum value of the axial velocity spread is about 2%.