METHODS AND ANALYSIS OF THE HSX TRANSMISSION LINE WITH SMOOTH-WALL AND PERTURBED-WALL LAUNCHERS

[摘要] Gaussian beams are electromagnetic waves with Gaussian distribution amplitudesin the transverse directions and are important for electron cyclotron heating (ECRH) inmany plasma fusion experiments. Systems that have the ability to transform the non-Gaussian output of some gyrotrons are of particular interest and it is important tounderstand the limits of the methods used in designing and simulating these systems.The computational propagation of Gaussian beams is important in the design andmodeling of complex and high-power systems. Therefore it is important to understand thelimits of where current approximate analytical solutions and computational methodsdiffer. The first objective of this thesis is to analyze two computational methods ofpropagation, the Fourier Transform method and the Finite-Difference Time-Domainmethod, and compare the results to the paraxial approximation solution for Gaussianbeams. Specifically, these methods are tested for initial beam waist radii in the region ofa wavelength or less than a wavelength. It was found that there was good agreementbetween each method and that it would be advisable to use FFT for narrow beam freespacepropagation and FDTD for domains consisting of scatterers.A perturbed-wall launcher designed by Ungku Fazri Ungku Farid was implemented in the HSX microwave transmission system and simulated using Surf3d.The original smooth-wall Vlasov launcher HSX microwave transmission system was alsosimulated and found to have 63% of the input power propagated to the dual-modewaveguide, while the perturbed-wall launcher only propagated less than 10%. Theoriginal launcher also propagated a beam to the dual-mode waveguide containing significantly more Gaussian content than the perturbed-wall launcher beam. This significant performance decrease is due to the HSX microwave transmission systembeing designed using geometrical optics for shaping the output beam of the smooth-wallVlasov launcher and, if redesigned for the perturbed-wall launcher, the system couldrealize increased propagated power. For the perturbed-wall system there should be lesspower loss and less spillover loss in the system due to a better output beam from thelauncher.

[发布机构] University of Wisconsin

[效力级别] electromagnetic waves

[关键词] electron cyclotron heating;electromagnetic waves;Gaussian beams