Measurements of an Ablator-Gas Atomic Mix in Indirectly Driven Implosions at the National Ignition Facility

Abstract

We present the first results from an experimental campaign to measure the atomic ablator-gas mix in the deceleration phase of gas-filled capsule implosions on the National Ignition Facility. Plastic capsules containing CD layers were filled with tritium gas; as the reactants are initially separated, DT fusion yield provides a direct measure of the atomic mix of ablator into the hot spot gas. Capsules were imploded with x rays generated in hohlraums with peak radiation temperatures of ∼294 eV. While the TT fusion reaction probes conditions in the central part (core) of the implosion hot spot, the DT reaction probes a mixed region on the outer part of the hot spot near the ablator-hot-spot interface. Experimental data were used to develop and validate the atomic-mix model used in two-dimensional simulations.

Self-Similar Structure and Experimental Signatures of Suprathermal Ion Distribution in Inertial Confinement Fusion Implosions

“…Until now, no simple solution to first-principles kinetic equation for the suprathermal ions has been found even in the one-dimensional (1D) planar case. The issue becomes particularly pressing in light of hydro-instabilities at the fuel-pusher interface [23][24][25][26][27][28][29][30]. It is near this interface that the suprather-mal ion distribution is modified most, so one should expect substantial interference between the instabilities and the fusion reactivity.…”

“…For the purpose of demonstration, here we consider a sample instability resulting in the interface perturbed as R = R h + ∆R cos (mϑ), where R and ϑ are the radial and polar angle coordinates of the hot-spot boundary and symmetry in the azimuthal angle ϕ is assumed. Experiments and simulations indicate that ∆R/R can be as large as 1/3 [25,26,28,30] and to imitate the spatial structure of the unstable region we take m = 20. Then, we evaluate the overall reactivity reduction as follows: for a point A inside the hot-spot the point B on the perturbed surface is found such that the distance AB is the shortest; the distribution function is evaluated from our solution with AB inserted for y; local reactivity reduction at each point A is calculated and averaged over the perturbed volume V .…”

Radiative ablation with two ionizing fronts when opacity displays a sharp absorption edge

“…But, this induction makes sense as long as a given effect cannot be produced by several different causes. Equations of state, opacities, NLTE model and many more data can be constrained through such type of indirect, inductive process : in [10], for instance, NLTE models are constrained in order to improve the agreement with the VISAR data, whereas in [14], eos for CH (LEOS 5370 and 5400) are constrained with the measured perturbation growth factors for optical-depth modulations as a function of the modulation mode number ( Fig.5 in [14]).…”

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

“…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]. In turn, describing these mix phenomena is often regarded as a crucial challenge faced by the ICF program.…”