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Title: 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 (EM) emission mechanism, first studied in Tsiklauri, Phys. Plasmas 18, 052903 (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 {omega}{sub ce}/{gamma} are excited, mode converted and emitted at Almost-Equal-To {omega}{sub 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 phasemore » space shows harmonic oscillation in the perpendicular components at the relativistic gyrofrequency; (vi) The requirement for cyclotron maser emission, ({partial_derivative}f/{partial_derivative}v{sub Up-Tack })>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 Degree-Sign ; and (ix) The generated electromagnetic energy is of the order of 0.1% of the initial beam kinetic energy.« less

Authors:
;  [1]
  1. School of Physics and Astronomy, Queen Mary University of London, E1 4NS (United Kingdom)
Publication Date:
OSTI Identifier:
22068903
Resource Type:
Journal Article
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 19; Journal Issue: 11; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1070-664X
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BEAM INJECTION; DISTRIBUTION FUNCTIONS; ELECTROMAGNETIC RADIATION; ELECTRON BEAMS; ELECTRON DENSITY; ELECTRONS; GYROFREQUENCY; INCLINATION; KINETIC ENERGY; MAGNETIC FIELDS; MASERS; OSCILLATIONS; PHASE SPACE; PLASMA WAVES; POLARIZATION; RELATIVISTIC RANGE; SOLAR ACTIVITY

Citation Formats

Pechhacker, R., and Tsiklauri, D. The effect of electron beam pitch angle and density gradient on solar type III radio bursts. United States: N. p., 2012. Web. doi:10.1063/1.4768429.
Pechhacker, R., & Tsiklauri, D. The effect of electron beam pitch angle and density gradient on solar type III radio bursts. United States. doi:10.1063/1.4768429.
Pechhacker, R., and Tsiklauri, D. Thu . "The effect of electron beam pitch angle and density gradient on solar type III radio bursts". United States. doi:10.1063/1.4768429.
@article{osti_22068903,
title = {The effect of electron beam pitch angle and density gradient on solar type III radio bursts},
author = {Pechhacker, R. and Tsiklauri, D.},
abstractNote = {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 (EM) emission mechanism, first studied in Tsiklauri, Phys. Plasmas 18, 052903 (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 {omega}{sub ce}/{gamma} are excited, mode converted and emitted at Almost-Equal-To {omega}{sub 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, ({partial_derivative}f/{partial_derivative}v{sub Up-Tack })>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 Degree-Sign ; and (ix) The generated electromagnetic energy is of the order of 0.1% of the initial beam kinetic energy.},
doi = {10.1063/1.4768429},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 11,
volume = 19,
place = {United States},
year = {2012},
month = {11}
}