The Langdon effect in laser plasmas: absorption, conduction, and beyond

It is now well-established that the plasmas produced in the coronae of direct-drive inertial confinement fusion (ICF), the hohlraum blowoff of indirect-drive ICF, as well as fundamental laser-plasma physics platforms all develop non-Maxwellian electron distribution functions due to the Langdon effect. This occurs when the rate of inverse bremsstrahlung (IB) absorption is competitive with the electron thermalization rate. The result is electron distribution functions with persistent depleted populations at both small and large energies. This impacts all aspects of electron kinetics in laser plasmas, including IB absorption, electrical and thermal conduction, and atomic kinetics. It also affects the interpretation of diagnostics based on photon scattering or plasma self-emission. I will present a variety of recent theoretical calculations and kinetic simulations illustrating the origin and the wide-ranging impact of the Langdon effect in laser plasmas. I hope to convey that the Langdon effect is no longer an "exotic" phenomenon, but is rather sufficiently well understood to become a standard part of modeling laser-produced plasmas.