The design of beam shaping mirrors for gyrotrons to aid injection of an electromagnetic beam into a corrugated waveguide

Gyrotrons can be used to produce high-power high-frequency electromagnetic beams to help heat a plasma by Electron Cyclotron Resonance Heating (ECRH) in order to achieve fusion. The purpose of this research is to develop and improve techniques associated with the transmission of the electromagnetic power that is radiated from the launcher in a gyrotron to the injection of the electromagnetic beam into a corrugated waveguide transmission line system. This consists of many parts including investigating the coupling of a Gaussian beam into the HE11 mode of a circular corrugated waveguide. Improved techniques in iterative phase reconstruction and iterative mirror design in a planar geometry are developed. These improved methods help correct for some measurement errors as well as use new techniques that force the mirror surfaces to be smooth. A pair of planar-based mirrors has been designed from a planar phase reconstructed field using these new techniques. They were then fabricated, and tested. The fraction of power coupled between the planar phase reconstructed beam at the output of the system and the target beam is 0.982. Finally, new techniques in iterative phase reconstruction and iterative mirror design in a cylindrical geometry are investigated. A pair of cylindrical-based mirrors has been iteratively designed from the simulated output of a launcher. These mirrors were then fabricated and tested. The fraction of power coupled between the planar phase reconstructed beam at the output of the system and the target beam is 0.961. The cylindrical phase reconstructed beam obtained from cylindrical amplitude scans of the launcher is numerically propagated through the mirrors and compared with measurements at the output of the mirrors. These improvements and new techniques used in designing the mirrors in the internal quasi-optical mode converter will help increase the amount of electromagnetic power produced by the gyrotron being delivered to the plasma and decrease the internal heating in the gyrotron.