The Electron Gun for the Stanford Two-Mile Accelerator

The design of the electron gun for an electron linear accelerator is of prime importance in achieving a small emittance volume and good reliability. This paper discusses phase space concepts useful in gun design, the design of the SLAC electron gun, and tests of its performance. A convenient definition for the effective area in phase space of a finite set of calculated points is proposed and a discussion of the increase in transverse phase space within a linear accelerator is presented. The SLAC gun is a Pierce spherical triode with a 50-ohm coaxial input to the grid. The gun is designed to operate with 80 kV dc between the cathode and the anode. The current in the beam can be varied from 2 A peak to less than 10-8 A peak by varying the grid to cathode voltage over a range of about 1000 volts. The design permits use of either an oxide cathode radiantly heated or a thoriated tungsten cathode heated by electron bombardment.