Magnetized Viscosity Effects in MagLIF-like Plasmas

Pulser ICF concepts, such as magnetized liner inertial fusion (MagLIF), represent a promising pathway toward controlled thermonuclear fusion. In MagLIF, a cylindrical liner implodes onto a magnetized fuel column, compressing both plasma and magnetic field to fusion-relevant conditions. Viscosity, often disregarded as a transport term, may play a crucial role by damping hydrodynamic instabilities, dissipating fuel kinetic energy in vortical structures into thermal energy, and influencing compression symmetry. Near stagnation, strong velocity gradients develop where viscous heating contributes significantly to the energy budget. Strong magnetic fields fundamentally alter the viscous stress tensor through charged particle gyro-motion, suppressing perpendicular viscosity while leaving parallel viscosity unaffected, creating preferential momentum transport along field lines.

This work presents the implementation of Braginskii's magnetized viscosity formulation for an arbitrary magnetic field into the Pacfic Fusion branch of FLASH to enable high-fidelity simulations of MagLIF-like plasmas with accurate treatment of anisotropic transport phenomena [1]. Verification against analytical solutions and validation through benchmark problems will be presented to demonstrate the accuracy of the implementation. We expect that magnetized viscosity could reveal several important effects on implosion dynamics and fusion performance. The perpendicular viscosity acts to suppress velocity shear along magnetic field lines, potentially stabilizing certain modes of the magneto-Rayleigh-Taylor instability that develop during the liner implosion phase. This stabilization could lead to more symmetric compression of the fuel column and improved magnetic flux conservation. Additionally, the viscous heating associated with strong velocity gradients in the converging flow provides an additional energy source that may improve the fuel preheat and reduce the compression requirements for ignition. This work represents an essential step toward the predictive modeling of magnetized high-energy-density plasmas.

[1] Braginskii, S. I. ``Transport processes in a plasma.'' Reviews of Plasma Physics 1, 205 (1965).