Coalescence of two current loops with a kink instability simulated by a 3-D EM particle code

Abstract

We have studied the dynamics of a coalescence of current loops using a 3-D electromagnetic (EM) particle simulation code. Our focus is the investigation of kinetic processes such as energy transfer, heating of particles, and electromagnetic emissions associated with a current loop coalescence which cannot be studied by MHD simulations. First, the two loops undergo a pinching oscillation due to a pressure imbalance between the inside and outside of the current loop. During the pinching oscillation, a kinetic kink instability is excited and electrons in the loops are heated perpendicularly to an ambient magnetic field. Next, the two current loops collide and coalesce, while at the same time a helical structure grows further. Subsequently, the perturbed current, which is due to these helically bunched electrons, can drive a whistler instability. It should be noted in this case that the whistler wave is excited by the kinetic kink instability and not a beam instability. After two helical loop coalescence with tilting motions in the direction of left-hand rotation. the helical structure relaxes resulting in strong plasma heating mostly in the direction perpendicular to the ambient magnetic field.