High-Power, Annular-Beam Klystron Amplifiers

Annular beam klystron amplifiers are being developed at L‐band and at X‐band. These devices are designed to operate at power levels of hundreds of MW to ∼1 GW, with pulse durations up to 800 nsec. The L‐band amplifier uses an 11‐cm‐diameter, 3‐mm‐thick annular beam (450 kV, 4.5 kA) inside an open beam tube with large‐gap cavities. The X‐band amplifier employs a 12‐cm‐diameter annular beam that propagates between inner and outer grounded cylinders and cavity structures. At higher frequencies or power levels, this so‐called triaxial configuration provides a significant advantage over the open‐cylinder configuration. In effect, it is a sheet‐beam klystron bent into a full circle, thereby avoiding the edge effects. Alternatively, it can be thought of as the continuum limit of the multi‐beam klystron.