Multiphysics Model of Hypervelocity Impact and Impact Induced Plasma Formation

Abstract

Previous studies on hypervelocity impact (HVI) have primarily focused on the mechanical response of solids, namely the projectile and the target. While several experiments have observed plasma formation and associated electromagnetic (EM) emissions, key questions remain unresolved — including the source of ionization (projectile, target, or ambient medium), the plasma composition, and the spectral radiance of emitted EM waves. Addressing these questions requires expanding current models to incorporate extreme thermodynamics, ionization, and chemical reactions. Most research in HVI has focused on exoatmospheric applications, where the ambient environment is typically assumed to be vacuum. For example, satellite-chondrite collisions often exceed impact velocities of 7 km/s, justifying this assumption. However, such simplifications are no longer valid for terrestrial or atmospheric applications of HVI. Developing a complete physical model requires expanding the analysis to include the surrounding fluid and its interaction with the solid materials. This dissertation presents a novel computational framework to simulate hypervelocity impacts and the resulting plasma formation within the projectile, target, and ambient fluid. A fully coupled fluid-solid simulation platform has been developed and applied to study metallic rods impacting soda-lime glass (SLG) in a chemically inert environment at hypersonic velocities. The framework addresses challenges such as interface tracking under large deformation and discontinuities in state variables and material models. Each of the three material subdomains — metallic projectile, silicate target, and gaseous environment — is modeled using a distinct equation of state (EOS) to accurately capture their thermodynamic behavior. In particular, SLG is modeled using an extended Noble-Abel stiffened gas EOS that supports a nonlinear relationship between the Grüneisen parameter and specific volume. Its parameters are calibrated using shock compression experiments conducted in the Lindhurst Laboratory at Caltech with a two-stage light-gas gun, which measured pressures up to 110 GPa and temperatures up to 5300 K. Plasma formation is modeled using the non-ideal Saha equation, solved under constraints of conservation of charge and nuclei. This allows for quantification of plasma temperature, charge density, Debye length, and elemental composition. An extended level-set method with dual signed distance functions is employed to track interfaces, accommodating large deformation, contact, and separation between materials. The Euler equations are solved using a high-resolution finite volume method. Interfacial fluxes are computed using the FInite Volume method with Exact multi-material Riemann solvers (FIVER). All modular components of the framework have been independently verified or validated against analytical solutions, published numerical results, or experimental data. A series of parametric studies were performed to investigate the effect of impact velocity, projectile radius, and material type on plasma characteristics and thermal response in the solid and fluid domains. Across velocities ranging from 2 to 7 km/s, the results show that ionization in the ambient gas becomes significant above 4 km/s. Under these conditions, plasma density in the fluid is found to be two orders of magnitude greater than in the solids. These results confirm that at moderate impact velocities, the ambient gas is the dominant source of impact-induced plasma. It was also found that within the SLG target, ionization is primarily driven by metallic constituents such as sodium, magnesium, and calcium, which contribute over 99% of free electrons despite comprising less than 15% of the total mass. This work assumes local thermodynamic equilibrium (LTE), a valid approximation in the early stages of impact when hydrodynamic forces dominate. Electromagnetic forces and plasma self consistency are not resolved in the present model but can be incorporated by extending the solver to include the Vlasov–Maxwell equations. This would enable modeling of electrodynamic forces and the propagation of EM waves as the plasma expands and transitions into a non-collisional regime.