Relativistic electron generation in nonuniform underdense plasmas

Simulations of relativistic electron generation by stimulated Raman scattering are presented. The effect of a nonuniform plasma density, such as may occur in a laser fusion scenario, is investigated. A simple WKB theory accounts for the wavenumber shifts in the spectra

Amplitude modulation of kinetic Alfven waves and the formation of nonlinear structures

The theory of the amplitude modulation of finite amplitude kinetic Alfvén waves in a medium beta plasma is re-examined and extended. The modulational and filamentational instabilities as well as associated localized structures in magnetic field and plasma density are investigated. The relevance of our investigation to coherent nonlinear structures in the ionospheric plasma is pointed out

Cosmic ray injection at SNR shocks: a laboratory for radio galaxy plasma physics?

The standard paradigm for extragalactic radio sources assumes that a description in terms of single-fluid MHD, adiabatic work, and radiation losses should provide an adequate model for the observed radiation and morphology. However this approach omits several physical elements that are now standard in other branches of laboratory, space, and astrophysical plasma physics, and we examine whether current observations of extragalactic radio sources motivate extensions to the standard paradigm. Supernova remnants are analogous to extragalactic radio sources in producing synchrotron radiation from radio to X-ray wavelengths, and electron energies as high as 10(14) eV axe required in some cases. Diffusive shock acceleration can generate these electrons from a mildly relativistic population, but the 'injection' problem of prior acceleration of background electrons to mildly relativistic energies has remained. Here we describe the 'bootstrap' solution of the electron injection problem, by which a shock-reflected proton population drives collective plasma instabilities, which in turn excite waves in the plasma which accelerate thermal electrons to mildly relativistic energies. The physical processes incorporated in this solution lie outside the standard paradigm for extragalactic radio sources, and we discuss their potential relevance

Ponderomotive force acceleration of ions in the auroral region

A general description of ion acceleration by the ponderomotive forces of circularly polarized electromagnetic waves with arbitrary frequency in magnetized plasmas is presented. The time derivative parallel ponderomotive force turns out to play an important role for nonstationary ion acceleration. Our results can be useful in understanding the acceleration of escaping ions in the presence of intense electromagnetic waves in the auroral zone of the Earth's ionosphere

Wave generation by ion horseshoe distributions on auroral field lines

Recent observation by Freja satellite of ions in the auroral zone at the boundary of the plasma sheet and tail lobe reveal the presence of a ring or horseshoe type distribution function. The horseshoe type distribution function measured by the satellites has a field aligned component which is moving in the case of the Freja data in the down-going direction with a peak velocity of about 400km/sec. We show that the horseshoe type distribution is unstable to predominantly perpendicular ion waves with frequencies in the lower-hybrid range.</p