A study of global kinetic stability of the field-reversed configuration

Peter George Papanikolaou, Purdue University

Abstract

A field reversed configuration (FRC) is a toroidal plasma device presently being investigated as a potential magnetic confinement scheme for a fusion reactor. If the FRC is to be a candidate for use as a fusion reactor, it must achieve good confinement of particles and energy. The amount of reversed magnetic flux that is contained in the FRC is believed to play an important role in the confinement of particles and energy. In this thesis the linear stability properties of an FRC are studied. Currently, most stability analyses rely on averaging or perturbative technique to approximate the linearized Vlasov-Maxwell system. In an FRC, however, these techniques break down near the field null and near the separatrix. In this thesis we develop a practical method of analyzing the linear stability of an FRC(1). The method is to expand the perturbed distribution function in eigenfunctions of the equilibrium Liouville operator. The perturbed potential is expanded in a computationally convenient set of basis functions (not eigenfunctions of the Maxwellian operator). This model uses the properties of one-dimensional Hamiltonians to provide a computationally tractable form of the dispersion relation. The bounded, periodic nature of the equilibrium particle orbits allows a closed-form representation of the orbit integrals. A code has been generated and several instabilities have been investigated. No high frequency $(\omega\sb{\rm r}\approx\omega\sb{\rm p})$ instabilities were found. In the middle range of frequencies, the Lower-Hybrid Drift instability was found. For the most part, however, the instabilities found were in the low-frequency regime $(\omega\sb{\rm r}\approx\omega\sb{\rm ci}).$ The instabilities include ion-cyclotron drift and universal drift waves. The instability with the most globalization is a mode similar to the drift cyclotron mode, but that depends on gradients in the electron density. This mode also extends throughout the interior of the plasma but not to the field null. None of the unstable modes has a large amount of globalization. The modes that propagate in the interior of the plasma do not extend to the field-null and seem to dissipate near the higher magnetic fields of the separatrix.

Degree

Ph.D.

Advisors

Choi, Purdue University.

Subject Area

Nuclear physics|Fluid dynamics|Gases

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