Double plasma resonance instability as a source of solar zebra emission
Abstract
Context. The double plasma resonance (DPR) instability plays a basic role in the generation of solar radio zebras. In the plasma, consisting of the losscone type distribution of hot electrons and much denser and colder background plasma, this instability generates the upperhybrid waves, which are then transformed into the electromagnetic waves and observed as radio zebras.
Aims: In the present paper we numerically study the double plasma resonance instability from the point of view of the zebra interpretation.
Methods: We use a 3dimensional electromagnetic particleincell (3D PIC) relativistic model. We use this model in two versions: (a) a spatially extended "multimode" model and (b) a spatially limited "specificmode" model. While the multimode model is used for detailed computations and verifications of the results obtained by the "specificmode" model, the specificmode model is used for computations in a broad range of model parameters, which considerably save computational time. For an analysis of the computational results, we developed software tools in Python.
Results: First using the multimode model, we study details of the double plasma resonance instability. We show how the distribution function of hot electrons changes during this instability. Then we show that there is a very good agreement between results obtained by the multimode and specificmode models, which is caused by a dominance of the wave with the maximal growth rate. Therefore, for computations in a broad range of model parameters, we use the specificmode model. We compute the maximal growth rates of the double plasma resonance instability with a dependence on the ratio between the upperhybrid ω_{UH} and electroncyclotron ω_{ce} frequency. We vary temperatures of both the hot and background plasma components and study their effects on the resulting growth rates. The results are compared with the analytical ones. We find a very good agreement between numerical and analytical growth rates. We also compute saturation energies of the upperhybrid waves in a very broad range of parameters. We find that the saturation energies of the upperhybrid waves show maxima and minima at almost the same values of ω_{UH}/ω_{ce} as the growth rates, but with a higher contrast between them than the growth rate maxima and minima. The contrast between saturation energy maxima and minima increases when the temperature of hot electrons increases. Furthermore, we find that the saturation energy of the upperhybrid waves is proportional to the density of hot electrons. The maximum saturated energy can be up to one percent of the kinetic energy of hot electrons. Finally we find that the saturation energy maxima in the interval of ω_{UH}/ω_{ce} = 318 decrease according to the exponential function. All these findings can be used in the interpretation of solar radio zebras.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 March 2018
 DOI:
 10.1051/00046361/201731424
 arXiv:
 arXiv:1711.04281
 Bibcode:
 2018A&A...611A..60B
 Keywords:

 instabilities;
 methods: numerical;
 Sun: radio radiation;
 Physics  Plasma Physics;
 Astrophysics  Solar and Stellar Astrophysics;
 Physics  Space Physics
 EPrint:
 8 pages, 12 figures