A gyrotron output transmission circuit

The chief virtue of gyrotrons, their capability of producing high average power efficiently at millimeter wavelengths, places special demands on separating high power microwaves in oversized waveguides from high power electron beams. It is possible to transmit the microwave power across a region bounded by a large diameter cylindrical collector through the use of two spherical mirrors. The optimization at low power levels of such an arrangement at 28 GHz is discussed along with the presentation of measurements of transmission and mode purity at the output. In a specific case, for the TE01^omode using 12-in.-diam spherical mirrors with a 2.5-in.-diam output waveguide, the optimum entrance diameter is 2.5 in. for a 16-in. focal separation. This yields a maximum TE01^omode transmission of 94%. Adding a 12- in.-diam cylinder between the mirrors to simulate the collector surface produces a transmission ripple of only ±0.2 dB provided that a O.5-in. gas is present at one mirror to load spurious modes.