A W-band gyro-twa based on a CUSP electron gun and helically corrugated waveguide

The latest experimental results of a W-band (75-110 GHz) gyrotron traveling wave amplifier [1] with a helically corrugated waveguide and cusp electron gun is presented. A waveguide with a helical corrugation on its inner surface has ideal dispersive properties which improve the bandwidth of the amplifier whilst maintaining the already good efficiency of operation [2,3]. The large orbit annular electron beam generated by the cusp electron gun [4] is ideal for driving the beam-wave interaction as the beam interacts resonantly with an optimum eigenwave existing in this particular interaction region. The fast-wave interaction is based on the cyclotron resonance maser. When driven by the electron beam of energy 40 keV and current 1.5A, the amplifier was simulated to output 5-10 kW (CW) with a 3 dB frequency bandwidth of 90-100 GHz and saturated gain of 40 dB. The gyro-TWA system includes a 3-layer microwave window, broadband input coupler and quasi-optical mode converter in the form of a corrugated horn. The electron gun has been designed and simulated [5,6] using both MAGIC and Opera and experimentally tested [7] to show the output of a 1.5 A, 40 Kv electron beam with alpha up to 1.56. Experimental results include electron beam profile, current and velocity ration, the microwave power, profile and bandwidth.