Rayleigh–Taylor Instability and Excitation of Super-Dreicer Electric Fields in the Solar Chromosphere

Abstract

Within the framework of the long-standing so-called “number problem” in the physics of solar flares, we consider the excitation of a super-Dreicer electric field at the leading edge of the electric current pulse that occurs at the chromospheric legs of a coronal magnetic loop as a result of the magnetic Rayleigh–Taylor instability. It is shown that for a sufficiently strong electric current, $I_{0} \ge 10^{10}~\mbox{A}$, the current pulse propagates in the non-linear mode and generates a strong longitudinal electric field $E_{z}$, which strongly depends on the current ($E_{z} \propto I_{0}^{3}$) and can exceed the Dreicer field ($E_{z} > E_{\mathrm{D}}$). In this case, the bulk of electrons in the site of the current pulse is in a runaway mode, and the energy release rate in the chromosphere increases significantly. Super-Dreicer electric fields also provide injection of protons into the regime of acceleration by Langmuir turbulence generated by fast electrons at the leading edge of the electric current pulse. The electric field at the pulse edge can exceed the Dreicer field starting from the chromosphere level with the number density $n \approx 10^{13}~\mbox{cm}^{-3}$. At a lower current $I_{0} < 10^{10}~\mbox{A}$, a super-Dreicer mode at the higher levels of the chromosphere with $n < 10^{12}~\mbox{cm}^{-3}$ occurs.