A role for electron viscosity in plasma shock heating

Abstract

The contribution of electron viscosity to shock heating of high-Z plasmas is investigated. A classical shock profile calculation is employed to show that the electron viscosity substantially affects the structure of strong shock waves in a fully ionized plasma by reducing the overheating of the ions in the viscous subshock. This effect is present for an average ion charge Z above 10. Computer simulations of Z-pinch implosions are then employed to demonstrate that this effect of electron viscosity can also be accounted for in Lagrangian hydrodynamic simulations that use artificial viscosity. This is accomplished by dividing the corresponding viscous heat release between the ion and electron components of the plasma according to the ratio of their physical viscosities. When this is done in the time-varying, ionizing plasma environment of Z-pinch implosions that are theoretically designed to generate K-shell emission in titanium and krypton, it is found that electron viscous heating can be substantial, leading to sizable reductions in ion temperatures and 10%–20% increases in K-shell emission under certain implosion conditions.