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A computationally efficient method for transporting radiation in multidimensional plasmas has been developed and evaluated. The basis of this method is a uniform plasma approximation that allows one to utilize existing escape probability techniques that are successfully used in one-dimensional (1D) calculations to approximately solve the multidimensional radiation transport problem. This method is superior to diffusion methods because (1) the probability of escape technique insures that the plasma goes to the correct optically thin and thick limits, (2) the effects of line absorption due to photoexcitations are modeled, and (3) this method uses source functions that are based on a self-consistent nonlocal thermodynamic equilibrium calculation, not an ad hoc assumption that the source functions are Planckian. This method is highly efficient because equation of state information from 1D calculations is tabulated as a function of plasma internal energy, ion density, and the line probability of escape from a ...

The classical Richtmyer‐Meshkov ~RM! instability develops when a planar shock wave interacts with a corrugated interface between two different fluids. A larger family of so-called RM-like hydrodynamic interfacial instabilities is discussed. All of these feature a perturbation growth at an interface, which is driven mainly by vorticity, either initially deposited at the interface or supplied by external sources. The inertial confinement fusion relevant physical conditions that give rise to the RM-like instabilities range from the early-time phase of conventional ablative laser acceleration to collisions of plasma shells ~like components of nested-wire-arrays, double-gas-puff Z-pinch loads, supernovae ejecta and interstellar gas!. In the laser ablation case, numerous additional factors are involved: the mass flow through the front, thermal conduction in the corona, and an external perturbation drive ~laser imprint!, which leads to a full stabilization of perturbation growth. In contrast with the classical RM case, mass perturbations can exhibit decaying oscillations rather than a linear growth. It is shown how the early-time perturbation behavior could be controlled by tailoring the density profile of a laser target or a Z-pinch load, to diminish the total mass perturbation seed for the Rayleigh‐Taylor instability development. © 2000 American Institute of Physics. @S1070-664X~00!93305-6#

Mitigation of the Rayleigh–Taylor (RT) instability of Z-pinch loads imploded from large initial radii through tailoring initial load density profiles in radial and axial directions is studied numerically. These methods could be helpful for a variety of applications of high-power Z-pinches, from producing large amounts of K-shell radiation to imploding inertial confinement fusion pellets. Radial density tailoring is demonstrated to delay the onset of the RT instability development at the expense of reducing the energy available for conversion into radiation. Axial density tailoring can fully stabilize acceleration of a fraction of the initial load mass. For a better tradeoff between stability and radiative performance of the loads, the density profiles could be tailored in two dimensions, combining the advantages of both methods. Post-processing of the radiation-magnetohydrodynamic simulation results demonstrates that an appreciable K-shell argon radiation power could be generated with a stabilized argon load imploded by a 5 MA current from a ∼10 cm initial radius in about 0.5 μs.

The stability and radiative performance of structured Z‐pinch plasma loads heated by high‐current (≳20 MA) pulsed power generators are investigated. A limited mapping of parameter space is made for the regions of stability for loads configured as thin shells, uniform fills, and multiple shells. Although large diameter thin shell loads are shown to be the most efficient radiators of K‐shell x rays, they are susceptible to disruption by the Rayleigh–Taylor instability. Large diameter uniform fill loads are shown to be more stable and very good radiators.

A two‐dimensional magnetohydrodynamic code that includes resistivity and viscosity has been used to study the growth of m=0 perturbations of a Z pinch in which the current increases with time. Stability for all wave numbers was found when the product SR was less than about 1000, where S is the Lundquist number and R is the Alfven–Reynolds number. Since SR depends only on the line density N, the stability criterion translates as N

The evolution of a dynamic X‐pinch plasma, formed by two or more intersecting crossed copper wires, is investigated theoretically and numerically in two dimensions to determine the behavior at the point of intersection. An X‐pinch plasma for conditions corresponding to (a) pure hydrodynamic and (b) nonlocal thermodynamic equilibrium radiation hydrodynamic simulations are considered when driven by an externally applied current.

The stability of a Z pinch carrying the Pease–Braginskii current is examined using a two‐dimensional compressible magnetohydrodynamic (MHD) code that includes resistivity and bremsstrahlung. It is found that the growth rate of m=0 perturbations depends upon the Lundquist number S and that the pinch is stable when S is less than about 6 for ka= (1)/(3) and less than about 1 for ka=1, where k is the wave number and a is the pinch radius.

An investigation has been conducted to determine the feasibility of generating conditions favorable to population inversion, gain, and x‐ray lasing in a two‐component plasma consisting of sodium and neon. An intense laser beam is assumed incident on both sides of a Na/Ne slab target separated by a carbon thermal buffer. Temperature and density profiles of the laser target interaction are calculated using a Lagrangian hydrodynamics model. Level populations and radiative emissions are evaluated using a collisional‐radiative equilibrium model including opacity effects. It appears possible to achieve measurable gain at 82, 58 and 230 A from the 3‐2, 4‐2, and 4‐3 transitions of heliumlike neon, respectively. Additionally, by pulse tailoring and target design, it should be possible to enhance the Na pumping power. off

The implosion dynamics of a hollow cylindrical neon gas‐puff plasma are investigated using a 1‐D non‐local thermodynamic equilibrium radiation hydrodynamic model. Two cases are considered: the implosion of the gas puff with and without a low‐density central core plasma. It is shown that the implosion efficiently converts the kinetic energy of runin into radiation and that the radiation plays a significant role in the implosion energetics. For each case, the history of the implosion dynamics and emission spectra are presented as well as the distribution of radiative energy in the L and K shells. Finally, a comparison is made with purely hydrodynamic calculations.