ABSTRACT
The possible applications of high-power microwaves span a wide range of technologies. In materials processing, microwaves areutilised to heat food, textiles, wood products, polymers, minerals, structural and functional ceramics, composites, multilayer structures and chemicals. The plasma physics community has already taken advantage of recent advances in using high-power micrometre and millimetre waves in the areas of RF plasma heating for magnetic confinement fusion research, such as lower hybrid current drive (1–8 GHz), electron cyclotron resonance heating (ECRH) (28–160 GHz), electron cyclotron current drive (ECCD), plasma production (start-up) and plasma diagnostic measurements such as collective Thomson scattering or heat-pulse propagation experiments. Other important applications are multiply charged ion and soft X-ray sources, high frequency broadband electron spin resonance (ESR) spectroscopy, deep-space and specialised satellite communication, high resolution radar ranging and imaging in atmospheric and planetary science and drivers for next generation high-gradient linear accelerators in elementary particle physics. The high ohmic attenuation and low power handling capability of conventional metallic waveguides supporting the dominant mode are prohibitive for those applications. Thus, in order to design low attenuation waveguides, oversized or overmoded structures are preferred. Electron cyclotron emission (ECE) and microwave reflectoinetry plasma diagnostics also employ sucli oversized transmission lines. Since the gyrotron, the most important high-power mm-wave sonrce, operates in a higher order cavity mode, one needs novel mode conversion and transmission concepts in order to feed the applicator antenna by a pure mode with a well-defined polarisation state.
