Study of ICRF Wave Propagation and Plasma Coupling Efficiency in a Linear Magnetic Mirror Device

Ion Cyclotron Range of Frequency (ICRF) wave propagation in an inhomogeneous axial magnetic field in a cylindrical plasma-vacuum system has historically been inadequately modelled. Previous works either sacrifice the cylindrical geometry in favor of a simpler slab geometry [1], concentrate on the resonance region (mode conversion)[21, use a single mode to represent the entire field structuref3], or examine only radial propagation{4j. This thesis performs both analytical and computational studies to model the ICRF wave-plasma coupling and propagation problem. Experimental analysis is also conducted to compare experimental results with theoretical predictions. Both theoretical as well as experimental analysis are undertaken as part of the thesis. The theoretical studies simulate the propagation of ICRF waves in an axially inhomogeneous magnetic field and in cylindrical geometry. Two theoretical analysis are undertaken an analytical study and a computational study. The analytical study treats the inhomogeneous magnetic field by transforming the (r, z) coordinate into another coordinate system (p,4) that allows the solution of the fields with much simpler boundaries (Plasma-vacuurr: boundary at p = 1, conducting wall at p = n). The plasma fields are then Fourier transformed into two coupled convolution-integral equations which are then differenced and solved for both the perpendicular mode number a as well as the complete EM fields. The computational study involves a multiple eigenmode computational analysis of the fields that exist within the plasma-vacuum system. The inhomogeneous axial field is treated by dividing the geometry into a series of transverse axial slices and using a constant dielectric tensor in each individual slice. The slices are then connected by longitudinal boundary conditions. The experimental accomplishment of this thesis include the design, construc2 tion, and operation of a linear magnetic mirror device, the PPEX machine. A full set of heating systems has been installed on the PPEX device 400kW of ICRF power, 2kW of ECH startup power. Diagnostics to monitor diiferent plasma properties have been either designed and constructed from scratch or modified from existing designs. Experiments to examine ICRF wave propagation were conducted. Thesis Supervisor: Jeffrey Freidberg Title: Professor of Nuclear Engineering Thesis Supervisor: Ted F. Yang Title: Research Scientist, MIT Plasma Fusion Center