Fabrication and Test of Electron Gun for CW High-power C-band Klystron

Abstract

The Lower-Hybrid Current Drive (LHCD) system for a nuclear fusion reactor (e.g. KSTAR, ITER) requires a klystron that has a 5-GHz frequency and CW 500 kW power output. We have been developing this high-power klystron tube in sub-components; i.e., electron gun assembly, RF cavity section, and beam collector system. The electron gun is a diode type to simplify high voltage power supply and use air cooling for easy maintenance. We chose the design parameters: beam voltage 68 kV, beam current 15 A, maximum electric field 7 kV at full power, and 0.85 μPerveance. The electron gun includes a scandate-type dispenser cathode that operates under 1000 ℃. The E-GUN code (SLAC beam trajectory program) was used for the beam trajectory design, and the ANSYS code was used for the hot cathode thermal design analysis. Field Charge Interaction (FCI) code is used for the design of RF cavity section, CST Particle Studio was used for cross verification of the beam characteristic. As a part of the klystron development program, we have manufactured the full-scale electron gun assembly and have conducted tests of the beam perveance and the beam envelope evolution along the beam axis. This paper provides details of the design and fabrication processes and the performance test results are described.