Simulation Studies of Short Pulse High Intensity Laser-Matter Interactions

Summary form only given. Intense short-pulse laser-matter interactions are under study for use in the fast ignitor approach to inertial confinement fusion and for fast high energy radiography. The modeling of this phenomenology is challenged by the difficulties of using traditional explicit particle-in-cell codes for electron transport in high-density plasmas. Implicit simulation avoids such limitation, but can require careful application to assure accuracy. We describe results from the use of the relativistic ANTHEM implicit model to laser foil interactions at intensities exceeding 10¹⁹ W/cm² and target densities exceeding 150n_crit (1.5times10²³ cm^-3 electrons). Our studies show that for steep foils (micron scale lengths) intense thermoelectric magnetic fields laterally spread rapidly from diffraction limited laser spots. Significant hot electron surface transport moves on the surface with the spreading B-fields. Directly below the spot electrons enter the foil in a beam that spreads in cone-like fashion with depth. In thick aluminum foils, modeled with a Spitzer resistance capped at 100 eV values, the penetrating electron streams break into filaments. When the density gradient in front of such foils is milder (10 s of micron scales), the intense B-fields and the hot electrons remain more localized near the laser spot. This behavior is examined in a convergence study that systematically reduces the mesh dimensions. Thus, we work to extract major skin depth related effects, such as traditional collisionless Weibel instability, and connect these effects to the larger scale phenomenology only accessible through implicit simulation