The potential role of electric fields and plasma barodiffusion on the inertial confinement fusion database

Abstract

The generation of strong, self-generated electric fields (GV/m) in direct-drive, inertial-confinement-fusion (ICF) capsules has been reported Rygg, Science 319, 1223 (2008); Li, Phys. Rev. Lett. 100, 225001 (2008). A candidate explanation for the origin of these fields based on charge separation across a plasma shock front was recently proposed Amendt, Plasma Phys. Controlled Fusion 51 124048 (2009). The question arises whether such electric fields in imploding capsules can have observable consequences on target performance. Two well-known anomalies come to mind: (1) an observed ≈2 greater-than-expected deficit of neutrons in an equimolar D3He fuel mixture compared with hydrodynamically equivalent D Rygg, Phys. Plasmas 13, 052702 (2006) and DT Herrmann, Phys. Plasmas 16, 056312 (2009) fuels, and (2) a similar shortfall of neutrons when trace amounts of argon are mixed with D in indirect-drive implosions Lindl, Phys. Plasmas 11, 339 (2004). A new mechanism based on barodiffusion (or pressure gradient-driven diffusion) in a plasma is proposed that incorporates the presence of shock-generated electric fields to explain the reported anomalies. For implosions performed at the Omega laser facility Boehly, Opt. Commun. 133, 495 (1997), the (low Mach number) return shock has an appreciable scale length over which the lighter D ions can diffuse away from fuel center. The depletion of D fuel is estimated and found to lead to a corresponding reduction in neutrons, consistent with the anomalies observed in experiments for both argon-doped D fuels and D3He equimolar mixtures. The reverse diffusional flux of the heavier ions toward fuel center also increases the pressure from a concomitant increase in electron number density, resulting in lower stagnation pressures and larger imploded cores in agreement with gated, self-emission, x-ray imaging data. © 2011 American Institute of Physics.