Design of a high perveance ACP gun for the Litton 95 GHz harmonic gyroklystron

Summary form only given. This paper describes a new advanced centerpost (ACP) gun for the Litton 95 GHz harmonic gyroklystron which provides roughly four times higher beam current than that available from the original gun. The magnetic focussing structure has been carefully matched to the beam in order to provide a very high quality, low velocity spread, axis-encircling beam. The level of magnetic field in the rf interaction region is consistent with fourth harmonic operation of the device (approximately 8500 gauss) which allows a conventional solenoid to be used. At an operating voltage of 30 kilovolts and a beam current of 6.4 amps, peak power in the beam from the new gun is 192 kilowatts. At this voltage and current, the perveance of the gun is 1.23 micropervs. Procedures, computer codes, and methodology used to design the gun and magnetic focussing system will be discussed in detail. Two key codes used in the design process were DEMEOS and POISSON. DEMEOS is a finite-element based variable triangular mesh electron beam dynamics code and POISSON is a variable mesh magnetic field code. Results from POISSON can be imported into DEMEOS. The first step was to develop a low spherical aberration gun in an x-y half plane (using DEMEOS) having the correct current density and as long a beam throw (cathode to beam waist) as possible. Next, code VAXSCALE was modified to reflect, rotate and shift DEMEOS data for solution in the actual problem space (the z-r plane). Both nonthermal and thermal beam models were used in the simulations.