Mikhail M. Basko

Dynamics of volumetrically heated matter passing through the liquid-vapor metastable states ✩

Abstract Remaining within the pure hydrodynamic approach, we formulate a self-consistent model for simulating the dynamic behavior of matter passing through metastable states in the two-phase liquid–vapor region of the phase diagram. The model is based on the local criterion of explosive boiling, derived by applying the theory of homogeneous bubble nucleation in superheated liquids. Practical application of the proposed model is illustrated with hydrodynamic simulations of a volumetrically uniformly heated planar layer of fused silica SiO 2 . Implications for experimentally measurable quantities are briefly discussed. A newly developed equation of state, based on the well known QEOS model and capable of handling homogeneous mixtures of elements, was used in the numerical simulations.

On possible target design for a heavy ion ignition facility

Abstract We investigate minimum energy requirements for ignition of indirect drive targets driven by beams of heavy ions. Two types of hohlraums containing an NIF-scale fusion capsule [J. Lindl, Phys. Plasmas 2 (1995) 3933] are considered. The required ion beam energy is evaluated by combining two and three-dimensional view factor simulations of the radiation transport with one-dimensional hydrodynamic simulations of the converter dynamics. It is found that an ignition facility based on the HIDIF driver concept (I. Hofmann, Nucl. Instr. and Meth. 1998) would require about 4xa0MJ of the ion beam energy. The impact of the ion-range shortening on target performance is discussed in some detail.

On the symmetry of cylindrical implosions driven by a rotating beam of fast ions

Cylindrical implosions driven by intense beams of heavy ions are one of the promising ways to create high energy density states in matter. To ensure the needed azimuthal symmetry of the beam energy deposition, it was proposed [Sharkov et al., Nucl. Instrum. Methods Phys. Res. A 464, 1 (2001)] to rotate the ion beam around the target axis. Combining analytical calculations with two-dimensional hydrodynamic simulations, a lower limit is established on the frequency ν of the beam rotation dictated by the target hydrodynamics. This limit is shown to be directly proportional to the desired radial convergence ratio Cr for stepwise beam power profiles, and to Cr1/2 for smooth pulses. With a smooth pulse, 6–10 beam revolutions per pulse should be sufficient to reach Cr≃30, while a stepwise pulse requires ≃100 revolutions. Also, the upper bound on the asymmetry of the elliptical focal spot of a rotating ion beam is calculated.

Kinetic theory of alpha particles production in a dense and strongly magnetized plasma

In connection with fundamental issues relevant to magnetized target fusion, the distribution function of thermonuclear alpha particles produced in situ in a dense, hot, and strongly magnetized hydrogenic plasma considered fully ionized in a cylindrical geometry is investigated. The latter is assumed in local thermodynamic equilibrium with Maxwellian charged particles. The approach is based on the Fokker–Planck equation with isotropic source S and loss s terms, which may be taken arbitrarily under the proviso that they remain compatible with a steady state. A novel and general expression is then proposed for the isotropic and stationary distribution f(v). Its time-dependent extension is worked out numerically. The solutions are valid for any particle velocity v and plasma temperature T. Higher order magnetic and collisional corrections are also obtained for electron gyroradius larger than Debye length. f(v) moments provide particle diffusion coefficient and heat thermal conductivity. Their scaling on colli...

A hybrid model of laser energy deposition for multi-dimensional simulations of plasmas and metals

Abstract The hybrid model of laser energy deposition is a combination of the geometrical-optics ray-tracing method with the one-dimensional (1D) solution of the Helmholtz wave equation in regions where the geometrical optics becomes inapplicable. We propose an improved version of this model, where a new physically consistent criterion for transition to the 1D wave optics is derived, and a special rescaling procedure of the wave-optics deposition profile is introduced. The model is intended for applications in large-scale two- and three-dimensional hydrodynamic codes. Comparison with exact 1D solutions demonstrates that it can fairly accurately reproduce the absorption fraction in both the s - and p -polarizations on arbitrarily steep density gradients, provided that a sufficiently accurate algorithm for gradient evaluation is used. The accuracy of the model becomes questionable for long laser pulses simulated on too fine grids, where the hydrodynamic self-focusing instability strongly manifests itself.

On the maximum conversion efficiency into the 13.5-nm extreme ultraviolet emission under a steady-state laser ablation of tin microspheres

Theoretical investigation has been performed on the conversion efficiency (CE) into the 13.5-nm extreme ultraviolet (EUV) radiation in a scheme where spherical microspheres of tin (Sn) are simultaneously irradiated by two laser pulses with substantially different wavelengths. The low-intensity short-wavelength pulse is used to control the rate of mass ablation and the size of the EUV source, while the high-intensity long-wavelength pulse provides efficient generation of the EUV light at λ=13.5 nm. The problem of full optimization for maximizing the CE is formulated and solved numerically by performing two-dimensional radiation-hydrodynamics simulations with the RALEF-2D code under the conditions of steady-state laser illumination. It is shown that, within the implemented theoretical model, steady-state CE values approaching 9% are feasible; in a transient peak, the maximum instantaneous CE of 11.5% was calculated for the optimized laser-target configuration. The physical factors, bringing down the fully o...

Hydrodynamic instability of shells accelerated by direct ion beam heating

The Rayleigh–Taylor (RT) instability of planar shells accelerated by direct heating of an underlying absorber layer is analyzed. A specific feature of the problem considered is a fixed in space energy deposition region, which allows the unstable transition layer to develop only gradually as the heated matter is pushed out of the deposition region. The linear growth spectrum ω(k) is investigated by relating a simple analytic estimate for a stationary exponential transition layer with the results of two-dimensional hydrodynamic simulations. For the unperturbed motion, an analytic solution is used which describes a uniform acceleration of the payload driven by a time-dependent uniform heating of the absorber with a fixed spatial extension. It is shown that an enhancement factor of 1.5(h/d), where h is the effective half-thickness of the heated region and d is the in-flight thickness of the payload, can be achieved for the distance-moved-over-thickness ratio as compared to the classical RT case of a strong de...

Power-law scaling of plasma pressure on laser-ablated tin microdroplets

The measurement of the propulsion of metallic microdroplets exposed to nanosecond laser pulses provides an elegant method for probing the ablation pressure in dense laser-produced plasma. We present the measurements of the propulsion velocity over three decades in the driving Nd:YAG laser pulse energy, and observe a near-perfect power law dependence. Simulations performed with the RALEF-2D radiation-hydrodynamic code are shown to be in good agreement with the power law above a specific threshold energy. The simulations highlight the importance of radiative losses which significantly modify the power of the pressure scaling. Having found a good agreement between the experiment and the simulations, we investigate the analytic origins of the obtained power law. Interestingly, we conclude that none of the available analytic theories agree with the observed power.

Creation of a homogeneous plasma column by means of hohlraum radiation for ion-stopping measurements

Abstract In this work, we present the results of two-dimensional radiation-hydrodynamics simulations of a hohlraum target whose outgoing radiation is used to produce a homogeneously ionized carbon plasma for ion-beam stopping measurements. The cylindrical hohlraum with gold walls is heated by a frequency-doubled (λlxa0=xa0526.5xa0μm) 1.4xa0ns long laser pulse with the total energy of Elxa0=xa0180u2009xa0J. At the laser spot, the peak matter and radiation temperatures of, respectively, Txa0≈xa0380xa0eV and Trxa0≈xa0120xa0eV are observed. X-rays from the hohlraum heat the attached carbon foam with a mean density of ρCxa0=xa02xa0mg/cm3 to a temperature of Txa0≈xa025xa0eV. The simulation shows that the carbon ionization degree (Zxa0≈xa03.75) and its column density stay relatively stable (within variations of about ±7%) long enough to conduct the ion-stopping measurements. Also, it is found that a special attention should be paid to the shock wave, emerging from the X-ray heated copper support plate, which at later times may significantly distort the carbon column density traversed by the fast ions.

3D MHD simulation of wire-array Z-pinch implosion under the action of high current pulse

The 3D radiative-magnetohydrodynamic code MARPLE (KIAM RAS) was applied to simulations of wire-array Z-pinch experiments on ANGARA-5-1 pulsed power facility (TRINITI, Russia). Different configurations of wire arrays accelerated by the current up to 3.5 MA (pulse rise time 100 ns) were investigated as soft X-ray sources.