Design and development of 42GHz transmission line for ECRH application

Abstract

This work represents the design and development of overmoded circular waveguide- based mode converters. It transforms unpolarized mode into linearly polarized mode used in plasma applications. This transmission line system (TLS) consists of TE03 to HE11 mode converters, corrugated waveguides, and other components. These are used to carry 200 kW power generated from gyrotron at a frequency of 42±0.2 GHz to the applicator or dummy load (in offload condition).A conservative design goal of insertion loss (1.5 dB) for the TLS is used as a design driver. It consists of different overmoded circular waveguide mode converters, miter bends (MBs), and corrugated waveguide. For efficient transmission of power between components, proper phase matching and accurate calculations of geometrical dimensions (perturbation amplitude, bending angle, and many more) are prerequisites. Analytical study, design technique, manufacturing process and simulation studies of TLS are discussed and summarized. After carrying out simulation studies of the various TLS components, the estimated insertion loss of the TLS is approximately 1.3 dB.The TLS along with seals is compatible to high vacuum (10−6 torr) and pressurization of 1 bar absolute pressure. Similar joints have been used at the joints of the various components in the TLS. The worst case leak rate of any of the TLS joint seal is 10−6 mbar liter per second.