Observation of interspecies ion separation in inertial-confinement-fusion implosions

Abstract

We report direct experimental evidence of interspecies ion separation in direct-drive, inertial-confinement-fusion experiments on the OMEGA laser facility. These experiments, which used plastic capsules with D2/Ar gas fill (1% Ar by atom), were designed specifically to reveal interspecies ion separation by exploiting the predicted, strong ion thermo-diffusion between ion species of large mass and charge difference. Via detailed analyses of imaging x-ray-spectroscopy data, we extract Ar-atom-fraction radial profiles at different times, and observe both enhancement and depletion compared to the initial 1%-Ar gas fill. The experimental results are interpreted with radiation-hydrodynamic simulations that include recently implemented, first-principles models of interspecies ion diffusion. The experimentally inferred Ar-atom-fraction profiles agree reasonably, but not exactly, with calculated profiles associated with the incoming and rebounding first shock. * * * We acknowledge R. Aragonez, T. Archuleta, J. Cobble, J. Fooks, V. Glebov, M. Schoff, T. Sedillo, C. Sorce, R. Staerker, N. Whiting, B. Yaakobi, and the OMEGA operations team for their support in experimental planning, execution, and providing processed x-ray and neutron data.

Progress on observations of interspecies ion separation in inertial-confinement-fusion implosions via imaging x-ray spectroscopy

“…Thus, we had four different types of targets based on the combinations of various pressures of D 2 /Ar gas. The core fuel pressures in the targets of this campaign were higher than those in the previous campaign 34,35 with a goal of observing slightly lowertemperature and more-symmetric implosions compared to the previous campaign. Higher fill pressure for otherwise the same target and laser drive increases collisionality and suppresses the interspecies ion separation (see Appendix B).…”

“…We chose Ar in particular because of its proven usefulness as an x-ray spectroscopic tracer in ICF implosions. The theory also predicts that the ion thermo-diffusion ratio maximizes, for a D/Ar plasma, with an Ar atomic concentration of around 1%, 34 thus motivating us to conduct experiments at and near this value. As in our previous publications, 34,35 we interpret observations of any deviation of the Ar ion number fraction from the spatially uniform target pre-fill value as proof of interspecies ion separation in the implosion core.…”

“…The theory also predicts that the ion thermo-diffusion ratio maximizes, for a D/Ar plasma, with an Ar atomic concentration of around 1%, 34 thus motivating us to conduct experiments at and near this value. As in our previous publications, 34,35 we interpret observations of any deviation of the Ar ion number fraction from the spatially uniform target pre-fill value as proof of interspecies ion separation in the implosion core. The main objectives of this campaign were to (a) confirm the observation of interspecies ion separation reported in our previous work, (b) investigate the effect of shell-fuel mixing on the experimental inference of interspecies ion separation, (c) compare experimental observations of interspecies ion separation with radiation hydrodynamic simulations that incorporate a multi-ion-species transport model, 16,29,[36][37][38] and (d) explore the dependence of interspecies ion separation on the relative concentration of the heavier species to further validate the theory.…”

“…Our earlier experimental campaign on interspecies ion separation in ICF implosions 34,35 provided direct experimental evidence for interspecies ion separation in an ICF implosion via detailed analysis of imaging x-ray spectroscopy data. In this paper, we provide the results from the analysis of imaging x-ray spectroscopy data from our second interspecies ion separation experimental campaign.…”

Observation of shock-front separation in multi-ion-species collisional plasma shocks

“…Prior experiments, simulations, and theoretical work explored multiion-species effects in the context of inertial confinement fusion (ICF), for which species separation in the fusion fuel potentially leads to neutron yield degradation [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Interspecies ion separation and velocity separation were experimentally observed [19][20][21][22][23]. Additional simulation and theoretical research on multi-ion-species plasmas examined how ion species diffusion causes species separation [24][25][26][27][28][29][30].…”