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Self-consistent nonlinear kinetic simulations of the anomalous Doppler instability of suprathermal electrons in plasmas
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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
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Official URL: http://dx.doi.org/10.1063/1.4827207
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 > 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: |
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| Date of first compliant deposit: | 25 December 2015 | ||||
| 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 | ||||
| Funder: | Research Councils UK (RCUK), European Union (EU) | ||||
| Grant number: | EP/I501045 (RCUK) |
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