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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.

A load structure with tailored density profile which delays the onset of the Rayleigh-Taylor instability development in imploding {ital Z} pinches by inverting acceleration of the magnetic field/plasma interface is proposed and studied numerically. This approach makes it possible to start gas-puff implosions from large radii (say, 8cm) and produce significant {ital K}-shell yield with current pulse duration of 250ns and longer. It could also be used to mitigate imprinting of initial perturbations into laser fusion targets. {copyright} {ital 1996 The American Physical Society.}

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.

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.

The performance of plasma radiation source (PRS) loads imploded by a long current pulse machine is investigated theoretically. The emission tolerant (with oil) Decade Quad design of Pulse Sciences Incorporated is an example of such a long current rise time machine. It has a peak short circuit current of 9 MA that is reached in 300 nanoseconds. Large radius loads must be employed for this type of machine in order to insure that high implosion velocities are reached and that the available energy is utilized. However, large radius implosions are known to be susceptible to the Rayleigh Taylor instability. The extent to which this instability affects the ability of an argon load to radiate K-shell photons is not known and is the subject of this model investigation.

We discuss the design of structured Z-pinch loads capable of mitigating the detrimental effect of Rayleigh-Taylor (RT) instability on the performance of fast Z-pinch devices used as plasma radiation sources. The stabilizing effects of density tailoring in both the radial and the axial directions are considered. Our 2-D numerical simulations demonstrate that using a structured gaseous load with a radial density profile specifically tailored for a given current wave form, it is possible to delay the onset of the RT instability development while a shock wave propagates through the load. Once the acceleration of the magnetic field/plasma interface is inverted, perturbations are shown to oscillate rather than to grow exponentially. Our simulation results indicate the possibility of high-quality implosions producing significant Ar K-shell yield from initial radii in the range between 4 and 8 cm, with current pulse duration of 250 ns and longer. Axial density tailoring can actually mitigate the RT instability, or even suppress it completely, at the expense of decreased hydrodynamic efficiency of acceleration. Seeking the best trade-off between stability and performance, it would be natural to combine the two approaches.

The dependence of the growth rate of the n = 1(lambda = 2..pi..R/sub 0/) kink instability on plasma ..beta.. has been investigated experimentally in a rectangular-cross-section high-toroidal-..beta.. (..beta../sub t/ (axis) approximately-greater-than 10%) device and compared with theoretical predictions. The ..beta../sub t/ for the onset of instability as well as the estimated values of the growth rates observed experimentally are in good agreement with predictions from a numerical ideal magnetohydrodynamic model.

A two‐dimensional resistive MHD code is used to examine the stability of a z‐pinch to m=0 perturbations under conditions of rising current. The current waveform is chosen to rise according to the one‐third power of time in order to keep the unperturbed radius of the pinch constant. One‐dimensional calculations show that regardless of the initial shape of the current density profile, the plasma column recovers the self‐similar profile dictated by this current rise. In two‐dimensions, initial perturbations corresponding to m=0 instability modes oscillate without growing or grow weakly at low values of the current in apparent contradiction to ideal MHD theory. At high current, the pinch is unstable with a growth rate predicted by ideal MHD. This is put forward as a possible explanation of experimental results which shown anomalously stable Z‐pinches. Enhanced stability is also seen for low values of the Lundquist number when the current is set to the Pease‐Braginskii value where the ohmic heating and radiati...