Self-consistent nonlinear kinetic simulations of the anomalous Doppler instability of suprathermal electrons in plasmas
- Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)
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{sub ||}≥(ω+Ω{sub ce})/k{sub ||} are present; here Ω{sub ce} denotes electron cyclotron frequency, ω the wave angular frequency, and k{sub ||} 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 Ω{sub ce}/(ω{sub pe}+Ω{sub ce}) 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 ω{sub pe}/(ω{sub pe}+Ω{sub ce}); here ω{sub pe} denotes the electron plasma frequency. We also find that the ADI can arise beyond the previously expected range of plasma parameters, in particular when Ω{sub ce}>ω{sub pe}. The simulations also exhibit a spectral feature which may correspond to the observations of suprathermal narrowband emission at ω{sub pe} detected from low density tokamak plasmas.
- OSTI ID:
- 22218514
- Journal Information:
- Physics of Plasmas, Vol. 20, Issue 10; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CYCLOTRON FREQUENCY
DAMPING
ENERGY TRANSFER
KINETIC ENERGY
LANGMUIR FREQUENCY
MAGNETIC CONFINEMENT
MAGNETIC FIELDS
NONLINEAR PROBLEMS
PLASMA INSTABILITY
PLASMA SIMULATION
PLASMA WAVES
RELATIVISTIC PLASMA
SOLAR SYSTEM
STEADY-STATE CONDITIONS
TAIL ELECTRONS
TOKAMAK DEVICES