Short-wavelength plasma turbulence and temperature anisotropy instabilities: recent computational progress

Abstract

Plasma turbulence consists of an ensemble of enhanced, broadband electromagnetic fluctuations, typically driven by multi-wave interactions which transfer energy in wavevector space via non- linear cascade processes. Temperature anisotropy instabilities in collisionless plasmas are driven by quasi-linear wave-particle interactions which transfer particle kinetic energy to field fluctuation energy; the resulting enhanced fluctuations are typically narrowband in wavevector magnitude and direction. Whatever their sources, short-wavelength fluctuations are those at which charged particle kinetic, that is, velocity-space, properties are important; these are generally wavelengths of the order of or shorter than the ion inertial length or the thermal ion gyroradius. The purpose of this review is to summarize and interpret recent computational results concerning short-wavelength plasma turbulence, short-wavelength temperature anisotropy instabilities and relationships between the two phenomena.

Keywords: instabilities; simulations; turbulence.

Figure 1.

Reduced magnetic fluctuation energy spectra in (k_∥,k_⊥) space from a PIC simulation of the whistler anisotropy instability at four times as labelled [38]. Initial conditions here include β_∥e=0.10 and T_⊥e/T_∥e=3.0. (Online version in colour.)

Figure 2.

Results of a gyrokinetic simulation with β_i=β_e. 1D magnetic energy spectra as functions of perpendicular wavenumber. The solid black line represents results from the simulation; the dashed-dotted and dotted lines represent two model predictions and the dashed line represents a fixed spectral index of −2.8. (Adapted with permission from [49].) (Online version in colour.)

Figure 3.

Results from a 2D PIC hybrid simulation of turbulence for an initially isotropic spectrum of magnetosonic fluctuations and β_i=0.02. Here k_x=k_∥ and k_y=k_⊥. (Adapted with permission from [68].) (Online version in colour.)