Whistler turbulence: Particle-in-cell simulations

Two-dimensional electromagnetic particle-in-cell simulations in a magnetized, homogeneous, collisionless electron-proton plasma demonstrate the forward cascade of whistler turbulence. The simulations represent decaying turbulence, in which an initial, narrowband spectrum of fluctuations at wavenumbers kc/omega(e) similar or equal to 0.1 cascades toward increased damping at kc/omega(e) similar or equal to 1.0, where c/omega(e) is the electron inertial length. The turbulence displays magnetic energy spectra that are relatively steep functions of wavenumber and are anisotropic with more energy in directions relatively perpendicular to the background magnetic field B-o=(x) over capB(o) than at the same wavenumbers parallel to B-o. In the weak turbulence regime, the primary new results of the simulations are as follows: (1) Magnetic spectra of the cascading fluctuations become more anisotropic with increasing fluctuation energy; (2) the wavevector dependence of the three magnetic energy ratios, vertical bar delta B-j vertical bar(2)/vertical bar delta B vertical bar(2) with j = x, y, z, show good agreement with linear dispersion theory for whistler fluctuations; (3) the magnetic compressibility summed over the cascading modes satisfies 0.3 <= vertical bar delta B-x vertical bar(2)/vertical bar delta B vertical bar(2) <= 0.6; and (4) the turbulence heats electrons in directions both parallel and perpendicular to Bo, with stronger heating in the parallel direction. (C) 2008 American Institute of Physics. [DOI:10.1063/1.2997339]