Particle acceleration with associated generation and absorption of electromagnetic radiation in solar plasmas

Abstract

The heating of solar chromospheric internetwork regions is investigated by means of the absorption of electromagnetic (EM) waves that originate from the photospheric black body radiation. It is studied in the framework of a plasma slab model. The absorption is provided by the electron-neutral collisions in which electrons oscillate in the EM wave field and electron-neutral collisions damp the EM wave. It is shown that for plausible physical parameters, the absorbed heating flux is between 20% and 45% of the chromospheric radiative loss flux requirement. Further, 1.5D particle-in-cell simulations of a hot, low density electron beam injected into magnetized, Maxwellian plasma were used to further explore the alternative non-gyrotropic beam driven EM emission mechanism, which was first studied in Ref.[83]. Variation of beam injection angle and background density gradient showed that the emission is caused by the perpendicular component of the beam injection current, whereas the parallel component only produces Langmuir waves, which play no role in the generation of EM waves in our mechanism. When the beam is injected perpendicularly to the background magnetic field, any electrostatic wave generation is turned off and a purely EM signal is left. Finally, a possible solution to the unexplained high intensity hard x-ray emission observable during solar flares was investigated via 3D particle-in-cell simulations. A beam of accelerated electrons was injected into a magnetised, Maxwellian, homogeneous and inhomogeneous background plasma. The electron distribution function was unstable to the beam-plasma instability and was shown to generate Langmuir waves, while relaxing to plateau formation. Three different background plasma density gradients were investigated. The strong gradient case produced the largest fraction of electrons beyond 15vth. Further, Langmuir wave power is shown to drift to smaller wavenumbers, as found in previous quasi-linear simulations.