Magnetic Tower Outflows from a Radial Wire Array Z-pinch

We present the first results of high energy density laboratory astrophysics experiments which explore the evolution of collimated outflows and jets driven by a toroidal magnetic field. The experiments are scalable to astrophysical flows in that critical dimensionless numbers such as the Mach number, the plasma beta and the magnetic Reynolds number are all in the astrophysically appropriate ranges. Our experiments use the MAGPIE pulsed power machine and allow us to explore the role of magnetic pressure in creating and collimating the outflow as well as showing the creation of a central jet within the broader outflow cavity. We show that currents flow along this jet and we observe its collimation to be enhanced by the additional hoop stresses associated with the generated toroidal field. Although at later times the jet column is observed to go unstable, the jet retains its collimation. We also present simulations of the magnetic jet evolution using our two-dimensional resistive magneto-hydrodynamic (MHD) laboratory code. We conclude with a discussion of the astrophysical relevance of the experiments and of the stability properties of the jet.Comment: Accepted by MNRAS. 17 pages without figures. Full version with figures can be found at http://www.pas.rochester.edu/~afrank/labastro/MF230rv.pd

Review of experiments and calculations of the compressible richtmyer-meshkov instability from a single-mode, nonlinear initial perturbation

We review experiments and calculations of the compressible Richtmyer-Meshkov instability from a single-mode, nonlinear initial perturbation. These experiments were performed using the Nova laser. Measurements of the time-evolution of the mixing region were reported previously. We compared the experimental measurements with numerical simulations [1,2]. We found both experiment and simulation to be in good agreement with recent theories for the nonlinear evolution of the instability [3,4]. Experimental results beyond those previously presented provide additional support for the use of two phase flow models to describe the flow in the nonlinear regime. These experiments include measurement of the mixing region at additional times, including times earlier in the evolution of the instability than previously reported. We have also carried out experiments to examine the difference in the evolution of the instability from initial perturbations consisting of circular sawtooth grooves as well as rectilinear sawteeth. Our previous two-dimensional numerical simulations approximated the experimental linear grooves as circular grooves. We reasoned that the difference between the two cases would be small, based on scaling arguments, and limited to a very small region near the centerline. New experimental and numerical results confirm this. Finally, we discuss some additional issues in the derivation of the two-phase flow model used previously in describing the growth of the Richtmyer-Meshkov instability in the nonlinear phase relevant to other work presented at this meeting [5,6]

Experiments and simulations of a shocked right-cylinder perturbation

We have conducted a series of experiments using the Nova laser facility at LLNL and corresponding simulations using the two-dimensional, Arbitrary Lagrangian-Eulerian hydrodynamics code CALE. The purpose of this work was to study the shock-driven, hydrodynamic behavior of a right-cylinder perturbation. The accuracy of our simulations is examined by comparison with the experiments

Development and characterization of a CCD camera system for use on six-inch manipulator systems

The Lawrence Livermore National Laboratory has designed, constructed, and fielded a compact CCD camera system for use on the Six Inch Manipulator (SIM) at the Nova laser facility. The camera system has been designed to directly replace the 35 mm film packages on all active SIM-based diagnostics. The unit`s electronic package is constructed for small size and high thermal conductivity using proprietary printed circuit board technology, thus reducing the size of the overall camera and improving its performance when operated within the vacuum environment of the Nova laser target chamber. The camera has been calibrated and found to yield a linear response, with superior dynamic range and signal-to-noise levels as compared to T-Max 3200 optic film, while providing real-time access to the data. Limiting factors related to fielding such devices on Nova will be discussed, in addition to planned improvements of the current design

Experimental investigation of the compressible Richtmyer-Meshkov instability from a broad-spectrum, multimode initial perturbation

Experiments have been conducted using the Nova laser system to investigate the growth of the Richtmyer-Meshkov (RM) instability resuling from a strong shock wave (M{approximately}30) crossing a prescribed well-defined initial multimode perturbation. The perturbation was a 100 mode superposition of 1 {micro}m amplitude sine waves with randomly generated phases between 0 and 2{pi}. The two working fluids were fluidized brominated plastic and carbon resorcinol foam, giving a post-shock Atwood number of approximately 0.6. The present experimental results give a power-law coefficient of 0.87 {+-} 0.2 for the growth of the interface. This value is higher than results previously published

Experimental study of the richtmyer-meshkov instability, including amplitude and wavelength variations

We report on results of an experimental study of the Richtmyer- Meshkov instability. The growth of the mixing region in the nonlinear regime is measured for a set of cases in which the amplitude and wavelength of the initial perturbation are varied systematically. The experiments are conducted on the Nova laser facility, and use a Nova hohlraum as a driver source to launch a high-Mach-number shock into a miniature shock tube attached to the hohlraum. The shock tube contains brominated plastic and low-density carbon foam as the two working fluids, with a micro-machined, triangular sawtooth interface between them serving as the initial perturbation. The sawtooth perturbation waveform is dominated by a single mode, and the perturbation amplitudes are chosen to expedite transition into the nonlinear phase of the instability. The shock, upon crossing the perturbation at the interface, instigates the Richtmyer- Meshkov instability. The resulting growth of the mixing region is diagnosed radiographically. Quantitative measurements of the temporal growth of the width of the mixing region are made for six different combinations of amplitude and wavelength, building upon previous results which employed a single amplitude/wavelength combination. Data from both experiment and supporting simulations suggest that the nonlinear growth of the mix width admits a logarithmic time dependence. The results also suggest that, properly normalized, the total mixing width grows in a nearly self-similar fashion, with a weak shape dependence

An Experimental Study of the Richtmyer-Meshkov Instability, Including Amplitude and Wavelength V'ations An experimental study of the Richtmyer-Meshkov instability, including amplitude and wavelength variations

Abstract: We report on results of an experimental study of the Rlchtmyer-Meshkov instability. The growth of the mixing region in the nonlinear regime is measured for a set of cases in which the amplitude and wavelength of the initial perturbation are varied systematically. The experiments are conducted on the Nova laser facility, and use a Nova hohlraum as a driver source to launch a high-Mach-number shock into a miniature shock tube attached to the hohlraum. The shock tube contains brominated plastic and low-density carbon foam as the two working fluids, with a micr~machined, triangular sawtooth interface between them serving as the initial perturbation. The sawtooth perturbation waveform is dominated by a single mode, and the perturbation amplitudes are chosen to expedite transition into the nonlinear phase of the instability. The shock, upon crossing the perturbation at the interface, instigates the Richtmyer-Meshkov instability. The resulting growth of the mixing region is diagnosed radiographically. Quantitative measurements of the temporal growth of the width of the mixing region are made for six different combinations of amplitude and wavelength, building upon prṽ ious results which employed a single amplitude/wavelength combination ]. Data from both experiment and supporting simulations suggest that the nonlinear growth of the mix width admits a logarithmic time dependence. The results also suggest that, properly normalized, the tot al mixing width grows in a nearly self-similar fashion, with a weak shape dependence

An experimental study of the richtmyer-meshkov instability, including amplitude and wave length variations

We report on results of an experimental study of the Richtmyer- Meshkov instability. The growth of the mixing region in the nonlinear regime is measured for a set of cases in which the amplitude and wavelength of the initial perturbation are varied systematically. The experiments are conducted on the Nova laser facility, and use a Nova hohlraum as a driver source to launch a high-Mach number shock into a miniature shock tube attached to the hohlraum. The shock tube contains brominated plastic and low density carbon foam as the two working fluids, with a micro-machined, triangular sawtooth interface between them serving as the initial perturbation. The sawtooth perturbation waveform is dominated by a single mode, and the perturbation amplitudes are chosen to expedite transition into the nonlinear phase of the instability. The shock, upon crossing the perturbation at the interface, instigates the Richtmyer-Meshkov instability. The resulting growth of the mixing region is diagnosed radiographically. Quantitative measurements of the temporal growth of the width of the mixing region are made for six different combinations of amplitude and wavelength, building upon previous results which employed a single amplitude/wavelength combination. Data from both experimental and supporting simulations suggest that the nonlinear growth of the mix width admits a logarithmic time dependence. The results also suggest that, properly normalized, the total mixing width grows in a nearly self-similar fashion, with a weak shape dependence