Fast simulation of gas heating effects during high power mmWave breakdown*

The high frequency high power microwave/millimeter (HPM) wave discharge continues to be an important research domain since decades due to its numerous applications in aerospace research, propulsion, high-speed combustion etc [1].  Several microwave discharges have been reported such as streamer, overcritical, subcritical and initiator based. The simulation of this highly nonlinear phenomena involves multiscale and multiphysics modeling. Most of the existing computational studies suggest the use of the plasma fluid model coupled with the Maxwell’s equations to study the EM-plasma interaction (hundreds of nanoseconds timescale). But the multi-scale nature of the problem as well as the stringent numerical requirements for capturing the sharp electric fields and plasma gradients present in the system makes it a computationally very expensive problem. Therefore, very few computational works have discussed the gas heating phenomenon involving longer timescales (>100 ns) for bigger problem sizes. We have proposed the application of a mesh refinement (MR) based selective gridding technique along with a MPI based parallelization which allows to accurately simulate the problem with significantly less simulation time [1]. The proposed algorithm has enabled to achieve an overall speedup of 30-80 times compared to a uniform fine mesh based finite difference algorithm. The fast MR based algorithm has enabled the investigation of large problem sizes involving plasma formation, subsequent energy exchange between EM wave and plasma, and afterwards between the gas and the plasma. In this work, we present the physics and the role of gas heating during HPM breakdown using 2D simulations.

[1]. P. Ghosh and B. Chaudhury, "Computational Analysis of Plasma Evolution during High Power Millimeter Wave Breakdown using Mesh Refinement based Fluid Simulations". arXiv e-prints. (2021): arXiv:2105.13276.