Collisionless Plasma Shocks in Striated Electron Temperatures

The existence of low frequency waveguide modes of ion acoustic waves is demonstrated in magnetized plasmas for electron temperatures striated along the magnetic field lines. At higher frequencies, in a band between the ion cyclotron and the ion plasma frequency, radiative modes develop and propagate obliquely to the field away from the striation. Arguments for the subsequent formation and propagation of electrostatic shock are presented and demonstrated numerically. For such plasma conditions, the dissipation mechanism is the "leakage'' of the harmonics generated by the wave steepening

Phase space structures generated by an absorbing obstacle in a streaming plasma

The dynamic behavior of an ion flow around an obstacle in a collisionless plasma is investigated. The obstacle consists here of an absorbing cylinder, and a 2 dimensional electrostatic particle-in-cell simulation is used to study the flow characteristics. The formation of irregular filamented density depletions, oblique to the flow, is observed. The dynamics of these structures depend on the physical parameters of the plasma. The structures form at the edges of the wake behind the obstacle, in a region with a strong velocity shear, and are found to be associated with phase-space vortices, observed specially in the velocity direction perpendicular to the flow. The results can be of interest in the interpretation of structures in space plasmas as observed by instrumented space crafts

Weakly nonlinear ion waves in striated electron temperatures

The existence of low-frequency waveguide modes of electrostatic ion acoustic waves is demonstrated in magnetized plasmas for cases where the electron temperature is striated along magnetic field lines. For low frequencies, the temperature striation acts as waveguide that supports a trapped mode. For conditions where the ion cyclotron frequency is below the ion plasma frequency we find a dispersion relation having also a radiative frequency band, where waves can escape from the striation. Arguments for the formation and propagation of an equivalent of electrostatic shocks are presented and demonstrated numerically for these conditions. The shock represents here a balance between an external energy input maintained by ion injection and a dissipation mechanism in the form of energy leakage of the harmonics generated by nonlinear wave steepening. This is a reversible form for energy loss that can replace the time-irreversible losses in a standard Burgers equation

The Eulerian-Lagrangian transformation in two-dimensional random flows

The relation between the Eulerian and the Lagrangian correlation functions is studied in two spatial dimensions. Simple analytical expressions for the full space-time varying Eulerian correlation are derived solely on the basis of the one-dimensional wavenumber power spectrum of the velocity fluctuations. It is demonstrated that an extension of the arguments giving the foregoing results allows also for derivation of analytical expressions for the Lagrangian autocorrelation function. The results are supported by direct numerical solutions of the non-dissipative Euler equations for the fluctuating velocity. The calculations are initialized by a flow with equilibrium spectral energy distributions. The Lagrangian correlation function is obtained by tracing a large number of passively convected test particles