Abstract
Transmission of power from 42 ± 0.2 GHz gyrotron (TE
03
mode) to tokamak or dummy load requires a set of transmission line components. It includes a set of mode converters that converts circularly unpolarised TE
03
mode to polarised HE
11
mode. The mode conversion sequence is methodised in two steps; first from TE
03
to TE
01
mode and then from TE
01
to TM
11
mode. The proposed mode converters performance depends on the parameters such as waveguide radius, beat wavelength, number of ripples, its perturbation amplitude (η) and bending angle. These parameters are numerically optimised and verified in CST microwave studio. TE
03
to TE
01
mode conversion is realised by the generation of intermediate mode TE
02
. The mode conversion length for TE
03
to TE
02
mode converter is6λ
0
, (where λ
b
is the beat wavelength of corresponding mode conversion) which converts 99.15% of an incident circular TE
03
mode power into TE
02
mode power. Next, mode converter converts TE
02
mode into TE
01
mode with 99.06% efficiency along the optimal length of6λ
b
. For TE
01
to TM
11
mode conversion, two conversion methodologies have been proposed: first using axis arc bend (34.94°) technique to convert TE
01
into its analogous degenerate mode with 99.01% conversion efficiency and second using parabolic curve with 90° bend, which gives a conversion efficiency of 97.5%.