Diagnostics, simulations and advanced facilities drive breakthroughs in plasma technology

By Carmen Guerra-Garcia and Andrey Starikovskiy|December 2023

The Plasmadynamics and Lasers Technical Committee works to apply the physical properties and dynamic behavior of plasmas to aeronautics, astronautics and energy.

This year saw significant advances in laser diagnostics for various plasma applications. Researchers at Colorado State University and Sandia National Laboratory pioneered the use of Thomson scattering to measure electron temperature and density in high-power, laser-triggered switches, with applications to pulsed power. In February, researchers at Texas A&M University and Georgia Tech introduced a novel Thomson scattering method with Bragg notch filters. This approach enables one-dimensional electron temperature and density measurements, opening new avenues for exploring the spatiotemporal dynamics of low- temperature plasmas. In March, researchers at Purdue University demonstrated resonance enhanced multiphoton ionization-Thomson microwave scattering for diagnostics of electric propulsion devices, specifically targeting the measurement of krypton neutrals and ions in the exhaust plume of an ion engine. In May, researchers at Princeton University, in collaboration with the Princeton Collaborative Low Temperature Plasma Research Facility, developed a new method for calibrating two-photon absorption laser-induced fluorescence measurements of hydrogen atoms. The method is based on the complete dissociation of molecular hydrogen in hydrogen-xenon plasma and enables fast and reliable calibration for femtosecond, picosecond and nanosecond lasers. In June, researchers from Texas A&M and the University of Michigan conducted experiments in the Hypervelocity Expansion Tunnel at Texas A&M’s National Aerothermochemistry and Hypersonics Laboratory, measuring nitric oxide formation behind a normal shock with planar laser-induced fluorescence. The measurements validated computational fluid dynamics simulations over a total enthalpy range of 7 to 10 megajoules per kilogram.

There were also advances in computational plasma simulations, with researchers utilizing a range of methods from fluid models to solutions of the Boltzmann equation. In January, researchers at the University of Minnesota performed large-eddy simulations of plasma-assisted ignition in static and flowing mixtures. They examined the effects of discharge pulse frequency on the probability of ignition, and the results largely lined up with the outcomes of previous experiments performed by colleagues at the U.S. Air Force Research Laboratory in Ohio. Also in January, MIT researchers developed a fluid model to explain experimental observations of both the increase and decrease in flame speed when influenced by nanosecond pulsed plasmas. The simulations revealed that the plasma accelerates the flame through kinetic effects and decelerates the flame through pressure perturbations. In June, scientists at Princeton University, in collaboration with FAA, modeled the effectiveness of a surface nanosecond dielectric barrier discharge for de-icing aerodynamic surfaces. The main effect of the plasma was volumetric gas heating in the boundary layer. Researchers at Texas A&M and the Air Force Research Laboratory at Wright-Patterson Air Force Base in Ohio led advances in modeling rarefied flows, where traditional fluid approximations can fall short. With the direct simulation Monte Carlo method, the team reproduced the standoff distance and geometry of a Mach 15 bow shock, matching wind tunnel measurements via the Michelson interferometry technique.

Researchers advanced science and technology leveraging facilities that replicate extreme conditions. In February, a team from Princeton University and Combustion Science and Engineering Inc. of Baltimore developed a prototype ignition system for scramjet engines based on nanosecond aperiodic discharge. The ignition system demonstrated efficient nonequilibrium plasma generation in large discharge gaps that mirror scramjet engine combustion chamber conditions. In August, scientists at Princeton University introduced a technique for studying pulsed nanosecond discharges in liquid via sub-nanosecond laser schlieren photography, revealing nano-void formation under the action of ponderomotive forces and discharge evolution in inhomogeneous media. Also this year, researchers at the University of Stuttgart in Germany operated their PWK4 arc jet facility with a hydrogen and helium mixture for the first time, simulating atmospheric entry conditions for giant planets.

Contributors: Christopher M. Limbach, Stefan Loehle, Alexey Shashurin, Albina Tropina, Azer Yalin and Suo Yang