The effect of electron beam pitch angle and density gradient on solar type III radio bursts

Abstract

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 electromagnetic emission mechanism, first studied in Tsiklauri (2011). Variation of beam injection angle and background density gradient showed that the emission process 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. Particular emphasis was put on the case, where the beam is injected perpendicularly to the background magnetic field, as this turned off any electrostatic wave generation along the field and left a purely electromagnetic signal in the perpendicular components. The simulations establish the following key findings: i) Initially waves at a few w_ce/gamma are excited, mode converted and emitted at w_pe ii) The emission intensity along the beam axis is proportional to the respective component of the kinetic energy of the beam; iii) The frequency of the escaping EM emission is independent of the injection angle; iv) A stronger background density gradient causes earlier emission; v) The beam electron distribution function in phase space shows harmonic oscillation in the perpendicular components at the relativistic gyrofrequency; vi) The requirement for cyclotron maser emission, df/dv_perp > 0, is fulfilled; vii) The degree of linear polarization of the emission is strongly dependent on the beam injection angle; viii) The generated electromagnetic emission is left-hand elliptically polarized as the pitch angle tends to 90 deg; ix) The generated electromagnetic energy is of the order of 0.1% of the initial beam kinetic energy.

supplemental material at http://astro.qmul.ac.uk/~tsiklauri/sp.html

References in corpus (6)

• An alternative to the plasma emission model: Particle-In-Cell, self-consistent electromagnetic wave emission simulations of solar type III radio bursts
• Three dimensional particle-in-cell simulation of particle acceleration by circularly polarised inertial Alfven waves in a transversely inhomogeneous plasma
• Particle acceleration by circularly and elliptically polarised dispersive Alfven waves in a transversely inhomogeneous plasma in the inertial and kinetic regimes
• Electron beam induced radio emission from ultracool dwarfs
• The effect of electron beam pitch angle and density gradient on solar type III radio bursts
• Electron cyclotron maser emission mode coupling to the z-mode on a longitudinal density gradient in the context of solar type III bursts

Cited by in corpus (7)

• Highly efficient electromagnetic emission during 100 keV electron beam relaxation in a thin magnetized plasma
• The effect of initial conditions on the electromagnetic radiation generation in type III solar radio bursts
• The effects of density inhomogeneities on the radio wave emission in electron beam plasmas
• The effect of electron beam pitch angle and density gradient on solar type III radio bursts
• Electron cyclotron maser emission mode coupling to the z-mode on a longitudinal density gradient in the context of solar type III bursts
• Numerical simulations of a continuously injected relativistic electron beam relaxation into a plasma with large-scale density gradients
• Whistler wave generation by non-gyrotropic, relativistic, electron beams