It has been conjectured that the eruption of a solar prominence can be inhibited if a much larger scale, arched magnetic field straddles the prominence and effectively straps it down. We have demonstrated this effect in a laboratory experiment where a vacuum strapping field acts on a scaled simulation of a solar prominence. The required magnitude of the strapping field is in good agreement with a theoretical model that takes into account the full three-dimensional magnetic topology.
The laboratory experiments described in the present paper observe the blast-wave-driven RayleighTaylor instability with three-dimensional ͑3D͒ initial conditions. About 5 kJ of energy from the Omega laser creates conditions similar to those of the He-H interface during the explosion phase of a supernova. The experimental target is a 150 m thick plastic disk followed by a low-density foam. The plastic piece has an embedded, 3D perturbation. The basic structure of the pattern is two orthogonal sine waves where each sine wave has an amplitude of 2.5 m and a wavelength of 71 m. In some experiments, an additional wavelength is added to explore the interaction of modes. In experiments with 3D initial conditions the spike morphology differs from what has been observed in other Rayleigh-Taylor experiments and simulations. Under certain conditions, experimental radiographs show some mass extending from the interface to the shock front. Current simulations show neither the spike morphology nor the spike penetration observed in the experiments. The amount of mass reaching the shock front is analyzed and potential causes for the spike morphology and the spikes reaching the shock are discussed. One such hypothesis is that these phenomena may be caused by magnetic pressure, generated by an azimuthal magnetic field produced by the plasma dynamics.
Spheromak technology is exploited to create laboratory simulations of solar prominence eruptions. It is found that the initial simulated prominences are arched, but then bifurcate into twisted secondary structures which appear to follow fringing field lines. A simple model explains many of these topological features in terms of the trajectories of field lines associated with relaxed states, i.e., states satisfying ٌϫBϭ B. This model indicates that the field line concept is more fundamental than the flux tube concept because a field line can always be defined by specifying a starting point whereas attempting to define a flux tube by specifying a starting cross section typically works only if is small. The model also shows that, at least for plasma evolving through a sequence of force-free states, the oft-used line-tying concept is in error. Contrary to the predictions of line-tying, direct integration of field line trajectories shows explicitly that when is varied, both ends of field lines intersecting a flux-conserving plane do not remain anchored to fixed points in that plane. Finally, a simple explanation is provided for the S-shaped magnetic structures often seen on the sun; the S shape is shown to be an automatic consequence of field line arching and the parallelism between magnetic field and current density for force-free states.
Articles you may be interested inObservation and modeling of mixing-layer development in high-energy-density, blast-wave-driven shear flowa) Phys. Plasmas 21, 056306 (2014); 10.1063/1.4872223The high-energy-density counterpropagating shear experiment and turbulent self-heating Phys. Plasmas 20, 122704 (2013); 10.1063/1.4839115 Simulations of material mixing in laser-driven reshock experiments Phys. Plasmas 20, 022309 (2013); 10.1063/1.4793443 Experiment on the mass-stripping of an interstellar cloud in a high Mach number post-shock flowa)Radiographic data from a novel and highly successful high energy density Kelvin-Helmholtz ͑KH͒ instability experiment is presented along with synapses of the theory and simulation behind the target design. Data on instability growth are compared to predictions from simulation and theory. The key role played by baroclinic vorticity production in the functioning of the target and the key design parameters are also discussed. The data show the complete evolution of large distinct KH eddies, from formation to turbulent break-up. Unexpectedly, low density bubbles comparable to the vortex size are observed forming in the free-stream region above each vortex at late time. These bubbles have the appearance of localized shocks, possibly supporting a theoretical fluid dynamics conjecture about the existence of supersonic bubbles over the vortical structure ͓transonic convective Mach numbers, D. Papamoschou and A. Roshko, J. Fluid Mech. 197, 453 ͑1988͔͒ that support localized shocks ͑shocklets͒ not extending into the free stream ͑P. E. Dimotakis, Proceedings of the 22nd Fluid Dynamics, Plasma Dynamics and Lasers Conference, 1991, Paper No. AIAA 91-1724͒. However, it is also possible that these low density bubbles are the result of a cavitationlike effect. Hypothesis that may explain the appearance of low density bubbles will be discussed.
Shock-accelerated material interfaces are potentially unstable to both the Richtmyer-Meshkov and Rayleigh-Taylor (RT) instabilities. Shear that develops along with these instabilities in turn drives the Kelvin-Helmholtz instability. When driven by strong shocks, the evolution and interaction of these instabilities is further complicated by compressibility effects. This paper details a computational study of the formation of jets at strongly driven hydrodynamically unstable interfaces, and the interaction of these jets with one another and with developing spikes and bubbles. This provides a nonlinear spike-spike and spike-bubble interaction mechanism that can have a significant impact on the large-scale characteristics of the mixing layer. These interactions result in sensitivity to the initial perturbation spectrum, including the relative phases of the various modes, that persists long into the nonlinear phase of instability evolution. Implications for instability growth rates, the bubble merger process, and the degree of mix in the layer are described. Results from relevant deceleration RT experiments, performed on OMEGA [J. M. Soures et al., Phys. Plasmas 5, 2108 (1996)], are shown to demonstrate some of these effects.
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