1,721,218 research outputs found
Mechanism of growth reduction of the deceleration-phase Rayleigh-Taylor instability
No full textThe deceleration-phase (dp) ablative Rayleigh-Taylor instability (RTI) of igniting and nonigniting inertial fusion capsules is studied by high-resolution two-dimensional Lagrangian fluid simulations. It is found that growth reduction of the dp-RTI with respect to classical RTI results from the advection of perturbed fluid elements outside a thin unstable fluid layer. Within this layer, at fixed Lagrangian position, perturbations grow approximately classically
Three-dimensional study of radiation symmetrization in some indirectly driven heavy ion ICF targets
No full textSymmetrization of the radiation field inside hohlraum targets for indirectly driven heavy ion beam inertial confinement fusion (ICF) is investigated numerically. The targets considered consist of a casing, enclosing the spherical fuel capsule, and a few cylindrical radiators, schematically representing ion beam irradiated converters. Radiation absorption and re-emission are dealt with as in the paper by Murakami and Meyer-ter-Vehn (Nucl. Fusion 31 (1991) 1333), but with the geometry extended to three dimensions and with the finite size of the radiators taken into account. It is found that, for a practical casing to capsule area ratio (of the order of ten) and practical converter aspect ratios, two converters (allowing for two-side axisymmetric irradiation) cannot provide the uniformity required for ICF. However, with a spherical casing with six converters (placed in couples along the axes of a Cartesian co-ordinate system) it would be possible to illuminate a capsule with a non-uniformity well below 2%, which could satisfy the ICF requirements. The effects of changing the area ratio, the size and position of the converters and the geometry of the hohlraum are also discussed
Studies on Radiation Symmetrization in Heavy-Ion Driven Hohlraum Targets
No full textRadiation symmetrization within spherical, ellipsoidal and cylindrical hohlraum targets for heavy-ion inertial-confinement fusion (ICF) is studied by means of a 3D numerical static model, in which realistic assumptions are made concerning the geometry of the system and, particularly, of the radiation >. Among the systems so far studied, only spherical hohlraums with six converters achieve the illumination symmetry of the fusion capsule considered necessary for ICF applications. A parametric study of cylindrical hohlraums enlightens the effect of several parameter changes, and suggests directions for further studies, aiming at the design of two-converter targets
Proton-beam driven fast ignition of inertially confined fuels: Reduction of the ignition energy by the use of two proton beams with radially shaped profiles
No full textFast ignition of a spherical compressed deuterium-tritium assembly induced by the energy deposition of laser-accelerated proton beams is considered. An efficient way to reduce the ignition energy consists of using a two proton beams scheme [M. Temporal, Phys Plasmas 13, 122704 (2006)]. For a uniformly compressed fuel at 500 g/cm(3) irradiated by proton beams with Maxwellian energy distribution with a temperature of 4 MeV, the ignition energy is 10 kJ using only one proton beam and reduces to a total of 8 kJ with the two-beam scheme. Further reduction of the ignition energy is found by using a first beam with annular radial profile and a second beam with the uniform radial profile. It is found that the first beam causes some additional fuel compression and confinement that decrease the total beam energy required for the ignition to 6 kJ, which is 40% smaller than in the case of a single beam with uniform radial profile. (c) 2008 American Institute of Physics
Energetics and Symmetry of Hohlraum Targets Driven by Ion Beam Pulses with Simple Time Shape
No full textThe energetics of hohlraum targets for inertial fusion are studied by means of one-dimensional radiation hydrodynamics simulations, assuming that a pulse of thermal X-rays with a simple time shape is fed into the cavity. A fusion yield Efus = 160–250 MJ is released by a capsule with fuel mass mDT = 3.3 mg, driven by a two-step pulse. The required input energy is Ex ≈ 3.4 MJ for a hohlraum area ratio a = 9 and 6.6 MJ for a = 20, corresponding to gains of Gx = Efus/Ex = 50–73 and 25–35 respectively. Higher gains are obtained by three-step pulses. Targets with mDT = 0.4 mg require better-shaped pulses, with at least three steps. Driven by Ex = 0.85−1.7 MJ, they release Efus = 8–10 MJ. Symmetry aspects of axially symmetric hohlraums driven by heavy ion beams are studied by a viewfactor code, employing wall motion and re-emissivities provided by the one-dimensional hydro-simulations. The dependence of the capsule irradiation asymmetry on the hohlraum aspect ratio, area ratio and fill density is analyzed. Reductions of wall motion and converter expansion, and the use of shields appear necessary to allow for the use of a moderate area ratio a ≈ 10–15
A first analysis of fast ignition of precompressed ICF fuel by laser-accelerated protons
No full textThe main parameters of the beam required to ignite a precompressed DT fuel, as foreseen by the recently proposed scheme of fast ignition by laser-accelerated protons (Roth et al 2001 Phys. Rev. Lett. 86 436), are studied by 2-D numerical simulations and a simple model. For simplicity, instantaneous proton generation at distance d from the compressed fuel and exponential proton energy spectrum, dn/depsilon proportional to exp(-epsilon/T-p), are assumed. An analytical expression and parametric numerical results are then given for the dependence of the minimum required beam energy on d, T-p and on the fuel density rho. For the parameters of Roth et al (d approximate to 4 mm; rho approximate to 400 g/cm(3)) the minimum total proton energy for ignition is about 40 kJ
Converging geometry Rayleigh–Taylor instability and central ignition of inertial confinement fusion targets
No full textThe Rayleigh–Taylor instability (RTI) of the inner surface of an inertial confinement fusion shell is studied through high-resolution two-dimensional numerical simulations. The instability is seeded by a mass displacement introduced in the simulations at the end of the implosion coasting stage. Analysis of single-mode, small-amplitude perturbations confirms that ablation caused by electron conduction and fusion alpha-particles causes significant growth reduction of all modes and stabilization of high-l modes. Different measures of the instability are discussed and compared with modified Takabe-like expressions. Large-amplitude multi-mode simulations are performed to study the effects of RTI on ignition and burn. RTI perturbations reduce the size of the central hot spot and delay ignition. For a few different perturbation spectra the dependence of fusion yield on the initial perturbation root mean square amplitude is studied
Simmetria dell'implosione, ignizione e guadagno energetico nella fusione a confinamento inerziale
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