Gas propellant dependency of plasma structure and thrust performance of microwave rocket

Abstract

To identify the characteristics of a suitable gas propellant for a microwave rocket, the discharge physics induced by an intense microwave in nitrogen, hydrogen, and helium was numerically reproduced by coupling a plasma fluid model with an electromagnetic wave propagation model. A discrete plasma structure was induced in nitrogen and hydrogen, because the ionization region was smaller than the incident-beam quarter wavelength. However, a diffusive plasma pattern was generated in helium, because the electron temperature increased and the electron-impact ionization was maintained even in the low-electric-field region. The shock wave propagation inside the rocket nozzle was numerically reproduced to evaluate the thrust performance dependence on the propellant species; this was achieved by solving the two-dimensional axisymmetric Euler equation with an energy source term for the microwave heating. The simple shock-tube theory indicated that the momentum coupling coefficient is proportional to the energy stored inside the rocket nozzle and inversely proportional to the propellant sound speed. The smallest momentum coupling coefficient was obtained for the helium case, although the sound speed in helium is faster than that in hydrogen. This was because insufficient energy was stored inside the rocket nozzle when helium was used, owing to the faster plasma propagation and lower energy absorption rate. The findings of this work indicate that to obtain a large thrust for a microwave rocket, selection of a gas propellant with a high energy absorption rate, small electron diffusion coefficient, low sound speed, and low specific heat ratio are preferable.

Computational Analysis of Plasma Evolution during High Power Millimeter Wave Breakdown using Mesh Refinement based Fluid Simulations

“…The model can address any general problem involving HPM breakdown at high pressures and can accurately reproduce the experimental observations [3]- [5], [7], [17]- [21]. Accurate simulation of this complex phenomenon will further help to understand the underlying physics for various applications in aerospace research [5], [6], high-speed combustion [22], microwave rockets [17], [23], [24], to study plasma shields that hamper the high power microwave transmission through the air [11] and will also help to realize the safe operation of high power microwave devices such as airfilled waveguides by suppressing the breakdown phenomenon using an external DC magnetic field [13].…”

“…II. PHYSICAL AND COMPUTATIONAL MODEL The mmWave air breakdown at high pressure is highly collisional and nonlinear process [1], [4], [6], [8], [9], [11]- [13], [16], [23], [27], [28]. It can be captured by a plasma fluid model that follows a Maxwell-Boltzmann Probability Distribution Function (PDF) to define the plasma species, and various macroscopic quantities such as particle number density, mean velocity and mean energy are obtained by integrating the PDF over the momentum space of the Boltzmann equation [11].…”

Plasma propagation via radiation transfer in millimeter-wave discharge under subcritical condition

“…Experiments and numerical calculations have been carried out to study discharge phenomena caused by a high-power millimeter-wave irradiation [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. A millimeter-wave discharge can be applied to a microwave rocket (Fig.…”

Coupling Simulation on Two-dimensional Axisymmetric Beaming Propulsion System

“…On the beaming rocket, microwave rockets are especially attracting attention for achieving a drastic decrease of the launch cost because a construction cost of high-power microwave oscillator can be lower than that of laser beam [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The intense microwave beam is used to generate the propulsion force; however, a beam power per unit area tends to be lower than that in laser beam when a long-distance beam transmission of the microwave is conducted because of its larger divergence angle.…”