Towards Developing a Fundamental Understanding of Laser-Plasma Interaction Physics

David Montgomery, LANL, P-24

Strong laser-plasma interaction (LPI) dynamics is a fundamental non-equilibrium physics problem. An unmagnetized plasma supports three natural modes: electromagnetic waves, electron plasma waves, and low-frequency ion acoustic waves. Using just these modes, up to seven resonant decay instabilities (3-wave) may exist, as well as modulational instabilities and self-focusing. In addition to wave-wave coupling, wave-particle coupling and collisional effects can be important in some regimes. Controlling LPI is of critical importance to achieving fusion ignition at the National Ignition Facility (NIF), where current ignition target designs require precise control of laser-illumination symmetry, high absorption of laser light, and low levels of hot-electron and x-ray preheat. LPI experiments over the past 30 years have in fact identified many of these phenomena, but due to poorly understood laser-plasma conditions, and the complex, nonlinear interactions, that can occur between various instabilities, a quantitative predictive capability for LPI is not yet in hand. Indeed, plasma inhomogeneity in large-scale LPI experiments often masks the subtle signatures of phenomena believed to control the nonlinear behavior of these instabilities. Using the Los Alamos Trident Laser Facility, we have developed a small-scale test-bed that allows us to perform experiments with well-characterized, extremely homogeneous plasma conditions, and allows us to observe the subtle signatures of many important nonlinear phenomena. These experiments have led to a more fundamental understanding of LPI, and are guiding the development of quantitative predictive models for LPI on NIF.

The P/T Colloquium is
typically held each
Thursday, 3:45–5:00 PM.
Refreshments are served
at 3:15 PM.