Capsule design for the National Ignition Facility

Abstract

Abstract.Several choices exist in the design and production of capsules intended to ignite and propagate fusion burn of the DT fuel when imploded by indirect drive at the National Ignition Facility. These choices include ablator material, ablator dopant concentration and distribution, capsule dimensions, and x-ray drive profile (shock timings and strengths). The choice of ablator material must also include fabrication and material characteristics, such as attainable surface finishes, permeability, strength, transparency to radio frequency and infrared radiation, thermal conductivity, and material homogeneity. Understanding the advantages and/or limitations of these choices is an ongoing effort for LLNL and LANL designers. At this time, simulations in one-two-and three-dimensions show that capsules with either a copper doped beryllium or a polyimide (C,,H,,N,O,) ablator material have both the least sensitivity to initial surface roughnesses and favorable fabrication qualities. Simulations also indicate the existence of capsule designs based on these ablator materials which ignite and burn when imploded by less than nominal laser performance (900 kJ energy, 250 TW power, producing 250 eV peak radiation temperature). We will describe and compare these reduced scale capsules, in addition to several designs which use the expected 300 eV peak x-ray drive obtained from the nominal NIF laser (1.3 MJ, 500 TW). Introduction.National Ignition Facility (NIF) (Paisner et al. 1994) capsule designs cover a range of x-ray drive temperatures, ablator materials, and total laser energies. Ablator materials studied to date include polystyrene (CH) doped with bromine (Br) or germanium (Ge), beryllium (Be) doped with copper (Cu), and polyimide (C,,H,,N,O,). Numerical simulations show that a capsule design using a CH ablator requires a dopant material such as Br or Ge to achieve optimum performance when imploded by a 300 eV peak temperature x-ray source obtained from a 1.3 MJ total energy laser. According to simulations, capsule designs using a Be ablator also require doping (e.g., with Cu) in order to achieve optimum performance. Currently, these Be ablator capsule designs span several peak x-ray drive temperatures and total laser energies: 330 eV

Converging geometry Rayleigh–Taylor instability and central ignition of inertial confinement fusion targets

“…When the initial perturbation is evaluated only on modes with l > 10 (modes with smaller l are weakly affected by RTI) we see (frame (b)) that the 50% degradation threshold decreases to σ rms 1-1.5 µm. These results are qualitatively analogous to those published by several other groups [2,3,[13][14][15]21]. Frames (c) and (d) show that decreased yield for increased initial perturbation is associated with delayed ignition, lower fusion power, and longer (but less effective) burn.…”

Rayleigh-Taylor and Richtmyer-Meshkov instabilities and mixing in stratified cylindrical shells

“…The above gelatin ring experiments help shed light on feedthrough and subsequent growth at the inner surface of single-shell capsules like the ones planned for NIF 8,41 . Another class of capsules involves double-shell designs 8,42 where an inner capsule containing the fuel gas is imploded after colliding with an outer shell.…”

The k-L turbulence model for describing buoyancy-driven fluid instabilities

“…Lagrangian, radiation-hydrodynamics codes that are widely used to design ICF target capsules Haan et al, 1995;Dittrich et al, 1999;Peterson et al, 2002! numerical simulations~Marinak et al, 1996!…”