Electro-diffusion in a plasma with two ion species

Abstract

Electric field is a thermodynamic force that can drive collisional inter-ion-species transport in a multicomponent plasma. In an inertial confinement fusion (ICF) capsule, such transport causes fuel ion separation even with a target initially prepared to have equal number densities for the two fuel ion species. Unlike the baro-diffusion driven by ion pressure gradient and the thermo-diffusion driven by ion and electron temperature gradients, electro-diffusion has a critical dependence on the charge-to-mass ratio of the ion species. Specifically, it is shown here that electro-diffusion vanishes if the ion species have the same charge-to-mass ratio. An explicit expression for the electro-diffusion ratio is obtained and used to investigate the relative importance of electro- and baro-diffusion mechanisms. In particular, it is found that electro-diffusion reinforces baro-diffusion in the deuterium and tritium mix, but tends to cancel it in the deuterium and helium-3 mix.Comment: Submitted to Phys. Plasmas on 2012-03-06 (revised version 05/13/2012

Refractive Index Seen by a Probe Beam Interacting with a Laser-Plasma System

“…However, assessing this quantitatively requires multi-ion-fluid simulations and is considered outside the scope of this study. Species separation is an increasingly active field of research in the ICF community [28][29][30][31][32].…”

Response to “Comment on ‘Species separation in inertial confinement fusion fuels’” [Phys. Plasmas 20, 044701 (2013)]

“…8,9 One may observe that the leading edges of the two shock fronts in Fig. 4 of our manuscript 2 are very sharp.…”

Influence of coupling on thermal forces and dynamic friction in plasmas with multiple ion species

“…Then it can be shown that in order to recover the thermodynamic expression for the diffusive flux [39], the rate of the collisional momentum exchange between the two ion species must take the form [6] …”

“…In particular, it has been suggested that strong background gradients introduced during the implosion can separate fusion fuel constituents, resulting in yield degradation [1][2][3][4][5][6][7][8][9][10][11][12][13]. The same ion diffusion mechanisms that govern species separation in the fuel underlie mixing at the shell/fuel interface [14][15][16][17][18][19][20], as well as at the inner boundary of the hohlraum [21].…”