Design for a One-Gigawatt, Annular-Beam Klystron

Abstract

A one-gigawatt, annular beam klystron (ABK) is being developed by Los Alamos National Laboratory in collaboration with the Stanford Linear Accelerator Center (SLAC). The pulse length is 1 µs, the pulse repetition frequency is 5 Hz, and the operating frequency is 1.3 GHz. The beam voltage and current are 800 kV and 4 kA. Since the electron beam parameters are considerably beyond the state-of the-art, an aggressive cathode and electron gun design is required. The magnetron injection gun (MIG) configuration was chosen over the standard Pierce geometry that is typically used in klystrons. The tube design, design issues, and status are presented. 1 BACKGROUND For many decades accelerators and radar systems have used high power klystrons to provide the RF energy for their operation. The klystrons for these applications use electron beams with a solid cross-section. The beams are typically produced by thermionic electron guns using a Pierce geometry. As the need increases for higher peak power, the voltage and current of the beam must increase. Since raising the beam voltage above 800 kV is expensive and impractical, one must instead raise the beam current. For a klystron with 1 GW output and a nominal efficiency of about 30%, the required beam current is 4 kA. Not only is this beam current well beyond what has been previously used in klystrons, but beam potential energy considerations dictate that an annular beam, rather than a solid beam must be used. The beam injection energy is partitioned into two parts: the kinetic energy and the potential energy due to the space charge fields. In a conventional klystron the current is low enough that the beam potential energy can be ignored. However, in an intense beam klystron the beam