Dynamics of a high-power aluminum-wire array Z-pinch implosion

Abstract

Annular Al-wire Z-pinch implosions on the Saturn accelerator ͓D. D. Bloomquist et al., Proceedings, 6th Pulsed Power Conference ͑Institute of Electrical and Electronics Engineers, New York, 1987͒, p. 310͔ that have high azimuthal symmetry exhibit both a strong first and weaker second x-ray burst that correlate with strong and weaker radial compressions, respectively. Measurements suggest that the observed magnetic Rayleigh-Taylor ͑RT͒ instability prior to the first compression seeds an mϭ0 instability observed later. Analyses of axially averaged spectral data imply that, during the first compression, the plasma is composed of a hot core surrounded by a cooler plasma halo. Two-dimensional ͑2-D͒ radiation magnetohydrodynamic computer simulations show that a RT instability grows to the classic bubble and spike structure during the course of the implosion. The main radiation pulse begins when the bubble reaches the axis and ends when the spike finishes stagnating on axis and the first compression ends. These simulations agree qualitatively with the measured characteristics of the first x-ray pulse and the overall energetics, and they provide a 2-D view into the plasma hydrodynamics of the implosion.

Numerical simulations of annular wire-array z-pinches in (x,y), (r,{theta}), and (r,z) geometries

“…If it retains this spread, hits the center near the experimentally observed 50 cm /psec, and if radiation is produced as plasma thermalizes on axis, a pulse duration of some 4 ns (2 mm/(0.5 mm/ns)) would be expected. This duration is close to the observed value for our highly symmetric 90-wire shots [4], and is the mechanism believed responsible for the observed pulse width.…”

“…The perturbation is typically an initial random density variation. With an appropriate choice for the magnitude of this random density perturbation, Jim Hammer [SI showed that the growth of the RT instability, and the resultant increase in the thickness of the plasma sheath at the time of stagnation, can account for the width of the radiation pulse measured for our 90-wire implosions [4]. The dependence of such RT growth on a wide range of initial sheath densities and radii has been studied by Darrell…”

“…The parameters, used here and throughout the report, are: The initial sheath profile is a Gaussian with a millimeter FWHM. The series circuit consists of a voltage source (tabular Saturn voltage as a function of time), an external resistor and inductor, and a plasma load [4].…”

Wire array Z-pinch insights for enhanced x-ray production

“…IOC), and higher and then lower ion velocities of the emitting plasma (Fig. 10D), as expected for a double implosion q ' [25]. Images of the x-ray emission from the imploding shell a few nanoseconds prior to the first implosion exhibit the classic bubble and spike structure associated with the RT instability.…”

Fast Fission Assisted Ignition of Thermonuclear Microexplosions

“…Estimates indicated a drastic reduction of the total energy needed for compression and ignition to perhaps as little as ∼ 100 kJ. The compression could be done as in other ICF concepts by laser or particle beams [2 -5] or even by soft X-rays from electric pulse powered imploded arrays of thin wires [6]. For the fast ignitor, two petawatt lasers were originally proposed.…”