Irvine, S. W. A. (2018) Collective instability and physics of the anomalous Doppler resonance in fusion plasmas. PhD thesis, University of Warwick.

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Abstract

The anomalous Doppler instability (ADI) is a key relaxation mechanism for suprathermal electrons in magnetic confinement fusion (MCF) plasmas. The ADI involves a shift from parallel to perpendicular electron motion, accompanied by the excitation of waves at frequency and wavenumber satisfying the anomalous Doppler resonance condition. In this thesis we split effort between studying the physics of the anomalous Doppler resonance and developing a new code to address linear calculations in magnetized plasmas characterized by arbitrary gyrotropic velocity distribution functions. This fully relativistic code is more general than the analytical linear theory which has been performed previously. This code is benchmarked against many problems in plasma physics.

We perform 2D3V particle-in-cell (PIC) simulations of the ADI for an energetic electron tail oriented in the magnetic field direction. For the first time we verify, via fully kinetic simulation, that the long standing conjecture, that it is possible for the ADI to self consistently drive a positive slope in the parallel electron velocity distribution, is correct. We show that the presence of this positive slope excites waves in a separate region of frequency and wavevector space to the ADI. We show that the simulated linear and quasilinear stages of instability demonstrate strong agreement with the linear solver which we have constructed. We also show that the addition of a second simulated spatial dimension is necessary to capture nonlinear three-wave coupling which can be driven by the ADI. The location of this three-wave triad, which has not previously been explored, is consistent with what would be predicted by the wave matching condition and a cold plasma model.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Plasma (Ionized gases), Thermal electrons, Nuclear fusion, Plasma turbulence
Official Date:	September 2018
Dates:	Date Event September 2018 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Chapman, Sandra C. ; Dendy, R. O.
Format of File:	pdf
Extent:	xiii, 131 leaves : illustrations, charts
Language:	eng

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