Lai, W. N., Chapman, Sandra C. and Dendy, R. O. (2013) Self-consistent nonlinear kinetic simulations of the anomalous Doppler instability of suprathermal electrons in plasmas. Physics of Plasmas, Volume 20 (Number 10). Article number 102122 . doi:10.1063/1.4827207 ISSN 1070-664X.

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Abstract

Suprathermal tails in the distributions of electron velocities parallel to the magnetic field are found in many areas of plasma physics, from magnetic confinement fusion to solar system plasmas. Parallel electron kinetic energy can be transferred into plasma waves and perpendicular gyration energy of particles through the anomalous Doppler instability (ADI), provided that energetic electrons with parallel velocities v ≥ (ω + Ωce )/k are present; here Ωce denotes electron cyclotron frequency, ω the wave angular frequency and k the component of wavenumber parallel to the magnetic field. This phenomenon is widely observed in tokamak plasmas. Here we present the first fully self-consistent relativistic particle-in-cell simulations of the ADI, spanning the linear and nonlinear regimes of the ADI. We test the robustness of the analytical theory in the linear regime and follow the ADI through to the steady state. By directly evaluating the parallel and perpendicular dynamical contributions to j · E in the simulations, we follow the energy transfer between
the excited waves and the bulk and tail electron populations for the first time. We find that the ratio Ωce /(ωpe + Ωce ) of energy transfer between parallel and perpendicular, obtained from linear analysis, does not apply when damping is fully included, when we find it to be ωpe /(ωpe + Ωce ); here ωpe denotes the electron plasma frequency. We also find that the ADI can arise beyond the previously expected range of plasma parameters, in particular when Ωce > ωpe . The simulations also exhibit a spectral feature which may
correspond to observations of suprathermal narrowband emission at ωpe detected from low density tokamak plasmas.

Item Type:	Journal Article
Subjects:	Q Science > QC Physics
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH):	Electrons, Mathematical physics
Journal or Publication Title:	Physics of Plasmas
Publisher:	American Institute of Physics
ISSN:	1070-664X
Official Date:	December 2013
Dates:	Date Event December 2013 Published
Volume:	Volume 20
Number:	Number 10
Page Range:	Article number 102122
DOI:	10.1063/1.4827207
Status:	Peer Reviewed
Publication Status:	Published
Copyright Holders:	AIP
Date of first compliant deposit:	25 December 2015
Date of first compliant Open Access:	25 December 2015
Funder:	Research Councils UK (RCUK), European Union (EU)
Grant number:	EP/I501045 (RCUK)

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