Developing a 2D Analytic Description of Laser Propagation in Unmagnetized Gaspipes

We present a simple 2D model describing the evolution of a laser absorption wave in a cylindrical gaspipe. Laser propagation distance and velocity are important diagnostics to assess how much laser energy is delivered to a gas target. This work extends the Denavit¹ laser propagation and absorption model by also including radial heat conduction in the electron energy equation. Diffusing heat away from the laser-irradiated region decreases the laser front propagation speed due to the increase in laser absorption via inverse bremsstrahlung. We compare to simulations with the radiation-MHD code Hydra² to verify our model's assumptions. We consider systems typical of NIF experiments that study laser preheat for the MagLIF fusion scheme³. Our previous simulation work has shown reduced thermal conductivity due to nonlocal kinetic effects moderately impacts the laser propagation⁴. The simple model offers analytic insights into how thermal conductivity affects laser propagation via plasma parameters, nonlocal effects and magnetic fields.