Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh13b1975p&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH13B-1975
Astronomy and Astrophysics
Astrophysics
[2772] Magnetospheric Physics / Plasma Waves And Instabilities, [7514] Solar Physics, Astrophysics, And Astronomy / Energetic Particles, [7519] Solar Physics, Astrophysics, And Astronomy / Flares, [7534] Solar Physics, Astrophysics, And Astronomy / Radio Emissions
Scientific paper
A recent work by Tsiklauri, Physics of Plasmas 18, 052903 (2011), presented the first attempt to produce synthetic (simulated) dynamical spectrum of the solar type III radio bursts in the fully kinetic plasma model. The latter was based on 1.5D non-zero pitch angle (non-gyrotropic) electron beam, that is an alternative to the plasma emission classical mechanism for which two spatial dimensions are needed. High-resolution, 1.5D Particle-in-Cell, relativistic, fully electromagnetic simulations were used to model electromagnetic wave emission generation in the context of solar type III radio bursts. The model studied generation of electromagnetic waves by a super-thermal, hot beam of electrons injected into a plasma thread that contains uniform longitudinal magnetic field and a parabolic density gradient. In effect, a single magnetic line connecting Sun to earth was considered, for which several cases were studied. Tsiklauri (2011) established the following: (i) The physical system without a beam is stable and only low amplitude level electromagnetic drift waves (noise) are excited. (ii) The beam injection direction is controlled by setting either longitudinal or oblique electron initial drift speed, i.e. by setting the beam pitch angle (the angle between the beam velocity vector and the direction of background magnetic field). In the case of zero pitch angle i.e. when ěc vb \cdot ěc E⊥=0, the beam excites only electrostatic, standing waves, oscillating at local plasma frequency, in the beam injection spatial location, and only low level electromagnetic drift wave noise is also generated. (iii) In the case of oblique beam pitch angles, i.e. when ěc vb \cdot ěc E⊥ ¬ =0, again electrostatic waves with same properties are excited. However, now the beam also generates the electromagnetic waves with the properties commensurate to type III radio bursts. The latter is evidenced by the wavelet analysis of transverse electric field component, which shows that as the beam moves to the regions of lower density and hence lower plasma frequency, frequency of the electromagnetic waves drops accordingly. (iv) When the density gradient is removed, an electron beam with an oblique pitch angle still generates the electromagnetic radiation. However, in the latter case no frequency decrease is seen. Here we extend the previous analysis of Tsiklauri (2011) by presenting a full parameter space investigation and the beam's long-term time evolution. We study how the generated radio burst emission varies as a function of beam pitch angle and its temperature (which is normally different from the background plasma temperature). We established that: (i) there is an optimal angle for which the maximal radio emission occurs and (ii) in the plausible range of beam temperatures, their variation does not produce a significant effect on the generated radio emission.
Pechhacker R.
Tsiklauri David
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