Effects of propagation distance and half angle on the merging of hypervelocity plasma jets

Abstract

We investigate the effects of the half angle on the intersection and merger of two plasma jets and verify the observation of the density drop and undulations at the merger interface seen in recent experiments. To perform this analysis, we employed a Smooth Particle Hydrodynamic code to model the jets and their merger. We validate the code against well-known test cases, Sod shock tube, Noh-Cylindrical implosion, and Kelvin-Helmholtz instability. These cases stress and quantify the Smoothed Particle Hydrodynamic code's ability to handle the expected physics of two jet merging. The half angle influences the shock region of the jets, but all jets merge and demonstrate density undulations along their centerline. The merged jet has velocity and density profiles consistent with experimental observations. The density drop was observed in the simulation and can be attributed to the sequence of thermal expansion of the free jets prior to the merge and subsequent density jump across the shock, where the centerline jump would be at the lowest density. A potential cause of the undulations along the centerline can be attributed to Kelvin-Helmholtz instability as it was the culprit in the simulation, although perturbations in the experiments or other causes cannot be ruled out.