Effect of the Temperature of Background Plasma and the Energy of Energetic Electrons on Z-Mode Excitation

Abstract

It has been suggested that the Z-mode instability driven by energetic electrons with a loss-cone type velocity distribution is one candidate process behind the continuum and zebra pattern of solar type-IV radio bursts. Both the temperature of background plasma ($T_0$) and the energy of energetic electrons ($v_e$) are considered to be important to the variation of the maximum growth rate (${\gamma }_{max}$). Here we present a detailed parameter study on the effect of $T_0$ and $v_e$, within a regime of the frequency ratio ($10\le \frac{{\omega }_{pe}}{{\Omega }_{ce}}\le 30$). In addition to ${\gamma }_{max}$, we also analyze the effect on the corresponding wave frequency (${\omega }_{max}^r$) and propagation angle (${\theta }_{max}$). We find that (1) ${\gamma }_{max}$ in-general decreases with increasing $v_e$, while its variation with $T_0$ is more complex depending on the exact value of $v_e$; (2) with increasing $T_0$ and $v_e$, ${\omega }_{max}^r$ presents step-wise profiles with jumps separated by gradual or very-weak variations, and due to the warm-plasma effect on the wave dispersion relation ${\omega }_{max}^r$ can vary within the hybrid band (the harmonic band containing the upper hybrid frequency) and the band higher; (3) the propagation is either perpendicular or quasi-perpendicular, and ${\theta }_{max}$ presents variations in line with those of ${\omega }_{max}^r$, as constrained by the resonance condition. We also examine the profiles of ${\gamma }_{max}$ with $\frac{{\omega }_{pe}}{{\Omega }_{ce}}$ for different combinations of $T_0$ and $v_e$ to clarify some earlier calculations which show inconsistent results.

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Cited by in corpus (1)

• PIC Simulation of Double Plasma Resonance and Zebra Pattern of Solar Radio Bursts