Capsule implosion experiments carried out on the Nova laser [E. M. Campbell et al., Rev. Sci. Instrum. 57, 2101 (1986)] are simulated with the three-dimensional HYDRA radiation hydrodynamics code [NTIS Document No. DE-96004569 (M. M. Marinak et al. in UCRL-LR-105821-95-3)]. Simulations of ordered, near single mode perturbations indicate that structures which evolve into round spikes can penetrate farthest into the hot spot. Bubble-shaped perturbations can burn through the capsule shell fastest, in which case they cause even more damage. A simulation of a capsule with a multimode perturbation of moderate amplitude shows spike amplitudes evolving in good agreement with a saturation model during the deceleration phase. The presence of sizable low mode asymmetry, caused either by drive asymmetry or perturbations in the capsule shell, can dramatically affect the manner in which spikes approach the center of the hot spot. Three-dimensional coupling between the low mode shell perturbations intrinsic to Nova capsules and the drive asymmetry is found to be important, bringing the simulated neutron yields into closer agreement with the experimental values.
Atomic force microscopy data reveal self-affine scaling of plasma polymer films. The rms surface roughness o. increases with film thickness 7. as o( f ( ( )rp, and with measurement length L as o(f ) . L ' ) g ') -L, where g is the surface roughness correlation length. At the deposition rate R = 2 p, m/h, the scaling exponents n and P are 0.9 and 0.7, both increasing to 1 at R = I pm/h. A competition between surface relaxation and deposition rate determine o. and (', which increase rapidly with R or inverse temperature. PACS numbers: 68.55.8d, 05.70.Ln, 68.55.Jk Comparison between self-affine surface structure data, computer simulations, and theoretical models is often made using scaling exponents for the rms surface roughness o(L, t) . [1 -3]: t~cL". a(Lr) = (h, (r, i) 2-1/2 h(r, t)(1) where t is the time, r is the position in the plane perpendicular to the growing direction, h(r, t) is the height of the surface at time t and position r, (h(r, t))" is the spatial average of h(r, t), L is the length of the surface measured, and c is a constant. Thus, cr initially scales with time as tP but shows a saturated scaling as I for thick layers [4]. Knowing the functional form of a and P in terms of process conditions allows the prediction of the surface roughness for any sample size.For simple random deposition with no spatial or temporal correlations between the deposited particles (the extreme kinetic limit), P = 0.5, since o. grows as a "random walk, " and n = 0, since there is no saturated scaling with L, For a real surface, relaxation processes such as in the Langevin type models couple the 2 degrees of freedom in the surface roughness, L and t, so as to change the scaling exponents. For example, Edwards and Wilkinson (EW) [5] use a Langevin equation [Eq. (2) with A = 0] to model the evolution of a surface, and find in d = 1 + 1 1 1 dimensions n = 2 and P = 4. In d = 2 + 1 the power law behavior in Eq. (1) changes to a logarithmic dependence. Kardar, Parisi, and Zhang (KPZ) [6] allowed for a component of interface growth parallel to the plane. They used the equation dh(r, t) 2 dt 2 = vV h(r, t) + -[Vh(r, t)] + rl(r, t), (2)where v is related to surface relaxation, g is the random fluctuation in the incoming flux, which is assumed to be Gaussian with delta function correlation (71(r, t) g(r', t')) = 2DB(rr', tt'), and A is the growth velocity perpendicular to the surface. In d = 1 + 1 dimensions they 1 1 obtained the exponents u = 2 and P = 3. In d = 2 + 1, Amar and Family [7] find that when 10~A2D/2v 25, P -0.25 and n -0.4, while for A2D/2v~-1, the effective value of P decreases. This connects the scaling exponent P to the surface relaxation process (v), and the deposition rate (-D). For the growth of plasma polymer films presented here we find 1 & a & 0.9 and 1 & P~0 .6. Of the experimental studies of the deposition of thin films, only a few have been analyzed in terms of both scaling laws of Eq. (1) [8]. For these studies 1~ct~0.2 and 0.56~P~0.22 [9]. The values of a overlap our own" but our values of P are si...
Several inertial confinement fusion (ICF) capsule designs have been proposed as possible candidates for achieving ignition by indirect drive on the National Ignition Facility (NIF) laser [Paisner et al., Laser Focus World 30, 75 (1994)]. This article reviews these designs, their predicted performance using one-, two-, and three-dimensional numerical simulations, and their fabricability. Recent design work at a peak x-ray drive temperature of 250 eV with either 900 or 1300 kJ total laser energy confirms earlier capsule performance estimates [Lindl, Phys. Plasmas 2, 3933 (1995)] that were based on hydrodynamic stability arguments. These simulations at 250 eV and others at the nominal 300 eV drive show that capsules having either copper doped beryllium (Be+Cu) or polyimide (C22H10N2O4) ablators have favorable implosion stability and material fabrication properties. Prototypes of capsules using these ablator materials are being constructed using several techniques: brazing together machined hemishells (Be+Cu), sputter deposition (Be+Cu), and monomer deposition followed by thermal processing (polyimide).
In this article we describe the design and simulated performance characteristics of an indirectly-driven inertial confinement fusion capsule which utilizes only 900 kJ of laser energy and 250 TW of laser power from the National Ignition Facility (NIF) [Paisner et al., Laser Focus World 30, 75 (1994)]. This intentional reduction in laser performance from the nominal NIF specifications of 1.8 MJ and 500 TW results in lowering the hohlraum x-ray drive temperature from 300 eV to 250 eV. These energy and radiation temperature reductions are believed to define a “lower bound” on the successful implosion of an ignition capsule. This reduced scale capsule has a beryllium ablator containing a radially varying copper dopant, and a cryogenic solid deuterium–tritium fuel layer surrounding a cavity filled with equilibrium vapor pressure gaseous deuterium and tritium. Two-dimensional simulations predict ignition and propagated burn from this capsule when either Rayleigh–Taylor instability or time-dependent drive asymmetry effects are included.
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