Two-stage, high power X-band amplifier experiment

At output powers in excess of 100 MW we have noted the development of sidebands in many TWT structures. To address this problem an experiment using a narrow bandwidth, two-stage TWT is in progress. The TWT amplifier consists of a dielectric (ε=5) slow-wave structure, a 30 dB sever section and a 8.8-9.0 GHz passband periodic, metallic structure. The electron beam used in this experiment is a 950 kV ,1 kA, 50 ns pencil beam propagating along an applied axial field of 9 kG. The dielectric first stage has a maximum gain of 30 dB measured at 8.87 GHz, with output powers of up to 50 MW in the TM₀₁ mode. In these experiments the dielectric amplifier output power is about 3-5 MW and the output power of the complete two-stage device is ~160 MW at the input frequency. The sidebands detected in earlier experiments have been eliminated. We also report measurements of the energy spread of the electron beam resulting from the amplification process. These experimental results are compared with MAGIC code simulations and analytic work we have carried out on such devices