Electron Density Depletion in Re-Entry Plasma Flows Using Pulsed Electric Fields

TL;DR

This paper tackles the radio-frequency communication blackout encountered during atmospheric re-entry by evaluating a mitigation strategy based on pulsed electric fields. It introduces the first fully-coupled simulation of high-voltage pulsed discharges interacting with a Mach 24 flowfield, revealing the formation of a large cathode-near non-neutral plasma sheath that depletes electron density by orders of magnitude. The depletion reduces 4 GHz signal attenuation from approximately $60\%$ to $4\%$ at a power deposition of about $66$ W cm$^{-2}$, with ion kinetics identified as the primary control on sheath topology; electron mobility has limited influence, and the drift-diffusion model provides a conservative lower bound, whereas a kinetic treatment with ballistic transport and non-local ionization would predict thicker sheaths and greater mitigation. The work offers a quantitative pathway toward mitigation of telemetry blackout for re-entry vehicles and informs model choice by highlighting the role of ion kinetics and the potential benefits of kinetic approaches.

Abstract

Communication blackout due to the plasma layer creates a critical telemetry gap for re-entry vehicles. To mitigate this, we present the first fully-coupled simulation of high-voltage pulsed discharges interacting with a Mach 24 flowfield. The results demonstrate that the applied electric field generates a large, non-neutral plasma sheath near the cathode, depleting electron density by several orders of magnitude over a distance commensurate with the height of the shock layer. This depletion window effectively reduces the attenuation of a 4 GHz signal from 60% to 4% with a manageable power requirement of 66 W per cm$^2$ of exposed cathode surface. A sensitivity analysis reveals that the sheath topology is governed principally by ion kinetics; specifically, corrections to ion mobility at high reduced electric fields lead to enhanced space-charge shielding and a subsequent contraction of the sheath. Conversely, the sheath structure is largely insensitive to the electron mobility model. Finally, we argue that the present drift-diffusion model likely yields a conservative lower bound for mitigation performance. A kinetic approach accounting for ballistic ion transport and non-local ionization would likely predict thicker sheaths and lower attenuation for equivalent power deposition.