SEMINAR: Physics Seminar

Laser Fusion was first proposed in the early 70s as a means for the extraction of energy from the burn of thermonuclear hydrogen fuels in the laboratory. Long-pulse (nanosecond,) time-shaped laser beams would be used for the adiabatic compression of micrograms deuterium-tritium microspheres, and for the subsequent shock-heating of the central fuel in these targets to kilovolt temperatures. The earliest predicted required laser energies were in the kilojoule range, from which 10-fold breakeven fusion yields were expected. In the four decades intervening, experimental experience has shifted the required input laser energy to the megajoule range, culminating most recently in the completion of the NIF facility in Livermore, CA, which will soon test this approach to fusion energy.

In the mid-90s the new availability of picosecond lasers suggested that, as a second possibility, the final heating of compressed target fuel might be accomplished with independent short-pulses at extreme intensities. The energy from such lasers makes copious relativistic “hot” electrons, which stream for the absorbing surface to the compressed core of a target. The timing and spectrum of these “hots” must be adjusted to optimize the heating in time and space for maximum thermonuclear yield production. Also alternatively, the short-pulses might be used to first generate focused fast ions to initiate the thermonuclear “burn.”

Aspects of such Fast Ignition (FI) by hot electron and/or fast ions are now receiving vigorous worldwide study. This approach may prove crucial to success in Inertial Confinement Fusion. Modeling of the underlying hot electron and ion transport for FI presents particular challenges, which will be emphasized in this talk. Sample applications from our code ePLAS (which has Los Alamos roots) will be discussed. The focus will be on the novel code features, such as the implicit treatment of active self-consistent electromagnetic fields and hybrid particle and fluid treatments for the background plasma. We will show that useful intuition can be gained through calculations on a simple portable PC, and aided by copious graphical output.

The special implicit/hybrid features of ePLAS permit diverse application to other pressing plasma physics issues, such as plasma jet formation for Magnetically Insulated Fusion, and lightning studies. The talk will outline these capabilities as well.