How solar eruptions generate X-rays and energetic particles

Models for solar eruptions are based on MHD and always start with a twisted magnetic field, i.e., an electric current flowing along a magnetic flux tube. Unfortunately, MHD cannot explain the most outstanding feature of eruptions, namely bursts of highly energetic particles and X-rays. Nevertheless MHD is obviously relevant, because it explains very well what happens before these bursts. Caltech lab experiments relevant to solar eruptions similarly demonstrate MHD dynamics followed by non-MHD bursts of X-rays and waves. Detailed examination of these experiments reveals a clear path from MHD dynamics to the non-MHD physics responsible for the X-ray and wave bursts. In this path a multi-step sequence of MHD instabilities chokes the flux tube cross-section at which point the electron drift velocity constituting the electric current becomes so large as to drive a kinetic instability which then greatly increases the local resistivity. The high local resistivity acts as an opening switch that nearly interrupts the electric current and so causes a large inductive voltage drop V= L dI/dt which accelerates charged particles to high energy. The experiments indicate that this behavior occurs when the current channel is choked by MHD instabilities to be of the order of the ion skin depth, the scale at which MHD fails. Since the ion skin depth is of the order of 10’s of meters in the solar corona, it is improbable that a nominal megameter solar flux tube could be squeezed to such a small scale. It is proposed that, instead, a megameter solar flux tube is actually composed of a rope-like braid of successively smaller filamentary current-carrying flux tubes having a fractal scaling, and that the smallest scale of these filaments become squeezed by MHD instabilities to the ion skin depth. The effect is like a rope breaking because its fine strands break.