A High Current Electron Gun Suitable for Use down to 1 Nanosecond Pulse Length

A triode electron gun is described which has been developed to meet the increasing interest in short pulse high current operation. The gun is of variable perveance capable of injecting at least 15 amps under short pulse conditions (1 nanosecond) and 1.5 amps under long pulse conditions (5 microseconds) with a beam diameter of 1 cm. Considerations of beam geometry have lead to the choice of a convergent flow Pierce-type gun incorporating an intercepting grid giving an amplification factor μo of 100 and a maximum beam perveance of 0.7μP for the high current condition. A conventional oxide cathode is used. The cathode-grid structure, which is plug-in replaceable, forms part of a 50 ohm co-axial system mounted on the gun base from which a matched 50 ohm co-axial feeder is taken to the modulator. Some experimental results for long and short pulse operation are given.