Nonstandard Collapse of Strong Langmuir Turbulence: Constraints on Its Occurrence and Observation in the Solar Corona

We present fully kinetic simulations of strong Langmuir turbulence (SLT) excited by electron beams with solar coronal conditions. We study two different collapsing processes within the parameter regimes of classical modulational instability (MI) and electron MI (EMI). For the first time, we simulated the EMI-induced collapse of moving multiple packets that is referred to as the non-Zakharov (or nonstandard) process here. We also simulated the classical Zakharov collapse of SLT induced by MI. During the early stage of the nonstandard collapse, the propagating packets get localized to form density cavities with depths of less than 0.1 n0 (the background electron density) that are too shallow to trap the packets. As a result, a majority of the packet energy runs away, undergoes a secondary collapse, and generates stationary packets with cavities. During the damping stage, the packets accelerate the background electrons to form numerous bidirectional propagating jets that distribute asymmetrically. This study reveals novel features of SLT collapse under coronal conditions.