Eighth Annual Richard K. Osborn Lecture

Abstract: Laboratory thermonuclear fusion experiments with z-pinches, tokamaks, stellarators, and mirror machines began in the early 1950’s, but achieving the Holy Grail of energy breakeven has remained a Quixotic quest. The first laser was built in 1960 and by 1974, KMS fusion in Ann Arbor reported the first thermonuclear neutrons from a laser-driven inertial confinement fusion (ICF) implosion (Chroma laser: 0.8kJ). The optimism of producing net energy with modest lasers based on 1-D simulations with limited physics proved unfounded. In the succeeding 45 years, a series of larger lasers has been built, but NIF (1.8 MJ) @ LLNL has yet to achieve ignition. All the approaches in the NNSA ICF program, laser indirect and direct drive, as well as magnetic direct drive on Z at Sandia will require a major new facility to produce significant yield. Can modern computing models, validated by new data on critical physics issues, help cut the Gordian Knot and establish a credible path for a high yield facility? Until recently, computational constraints limited the physical adequacy of our ICF design tools. In particular, thermal conduction flux limiters are still used in direct and indirect drive laser ICF target design, rather than accounting for the kinetic and non-local nature of electron heat transport. My 1978 dissertation on Fokker-Planck modeling was motivated by this problem, but the development of practical models for use in 3-D rad-hydro codes is ongoing. Excitingly, recent measurements on Omega of nonlocal heat flux in laser-produced coronal plasmas using a novel Thomson scattering technique [1] are finally providing the missing validation data for these models, and Vlasov-Fokker-Planck simulations are in progress to determine the self-consistent electron distribution functions and heat flux. Improvements in this and related laser-plasma interaction models will provide a firmer foundation for future extrapolations. My talk concludes with a roadmap for achieving ignition and yield from direct drive ICF with excimer lasers.

Bio: Dr. Tom Mehlhorn, heads the Plasma Physics Division at the Naval Research Laboratory where he oversees a broad spectrum of research, including fusion, pulsed power, laser wakefield acceleration, space plasmas, and plasma processing. He has a B.S., M.S. and Ph.D. in Nuclear Engineering from the University of Michigan. Dr. Mehlhorn has received several scientific awards, including the 2004 U of M Alumni Society Award in NERS. He is a Fellow of the APS Division of Plasma Physics, the AAAS in Physics, and the IEEE. He is an author on over 160 peer-reviewed papers.

This annual lecture series has been made possible by a generous endowment by MIT Professor Emeritus Sidney Yip, a former student of Professor Osborn. These annual lectures are a tribute to Professor Osborn's unwavering dedication to education of students in fundamental science. It is the goal of these lectures to inspire future generations of students in nuclear theory and simulation.