Quasi-optical internal mode converters for 110 GHz gyrotrons

Summary form only given. We have designed both internal and external versions of quasi-optical converters. We discuss an internal converter which was designed for use inside a Varian 110 GHz gyrotron producing the TE/sub 22,6/ cavity mode. This design consists of four reflectors which are fed by a Denisov-type launcher. The output is a microwave beam perpendicular to the axis of the tube and having a profile which is nearly flat over the center portion of the vacuum window of the tube. The window is a 4" diameter double-disk type window consisting of two parallel sapphire disks separated by a gap through which a coolant is pumped. It is desirable to have an output profile at the window which is nearly flat over the center part of the aperture to spread the heat deposition over a broader area and allow for higher transmitted power. A series of two additional reflectors are placed outside the tube to convert the flat-top beam to a Gaussian profile to be injected into a 1.25" diameter corrugated waveguide. Design techniques for the reflector system are discussed and experimental results are presented.