| 1. |
- Dieckmann, Mark E, 1969-, et al.
(author)
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Emergence of MHD structures in a collisionless PIC simulation plasma
- 2017
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In: Physics of Plasmas. - Melville, NY, United States : A I P Publishing LLC. - 1070-664X .- 1089-7674. ; 24:9
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Journal article (peer-reviewed)abstract
- The expansion of a dense plasma into a dilute plasma across an initially uniform perpendicular magnetic field is followed with a one-dimensional particle-in-cell simulation over magnetohydrodynamics time scales. The dense plasma expands in the form of a fast rarefaction wave. The accelerated dilute plasma becomes separated from the dense plasma by a tangential discontinuity at its back. A fast magnetosonic shock with the Mach number 1.5 forms at its front. Our simulation demonstrates how wave dispersion widens the shock transition layer into a train of nonlinear fast magnetosonic waves.
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| 2. |
- Dieckmann, Mark E, 1969-, et al.
(author)
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Expansion of a radial plasma blast shell into an ambient plasma
- 2017
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In: Physics of Plasmas. - Melville, NY, United States : A I P Publishing LLC. - 1070-664X .- 1089-7674. ; 24:9
-
Journal article (peer-reviewed)abstract
- The expansion of a radial blast shell into an ambient plasma is modeled with a particle-in-cell simulation. The unmagnetized plasma consists of electrons and protons. The formation and evolution of an electrostatic shock is observed, which is trailed by ion-acoustic solitary waves that grow on the beam of the blast shell ions in the post-shock plasma. In spite of the initially radial symmetric outflow, the solitary waves become twisted and entangled and, hence, they break the radial symmetry of the flow. The waves and their interaction with the shocked ambient ions slow down the blast shell protons and bring the post-shock plasma closer to equilibrium.
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| 3. |
- Dieckmann, Mark Eric, et al.
(author)
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The interplay of the collisionless non-linear thin-shell instability with the ion acoustic instability
- 2017
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In: Monthly notices of the Royal Astronomical Society. - Oxford : Oxford University Press. - 0035-8711 .- 1365-2966. ; 465:4, s. 4240-4248
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Journal article (peer-reviewed)abstract
- The non-linear thin-shell instability (NTSI) may explain some of the turbulent hydrodynamic structures that are observed close to the collision boundary of energetic astrophysical outflows. It develops in non-planar shells that are bounded on either side by a hydrodynamic shock, provided that the amplitude of the seed oscillations is sufficiently large. The hydrodynamic NTSI has a microscopic counterpart in collisionless plasma. A sinusoidal displacement of a thin shell, which is formed by the collision of two clouds of unmagnetized electrons and protons, grows and saturates on time-scales of the order of the inverse proton plasma frequency. Here we increase the wavelength of the seed perturbation by a factor of 4 compared to that in a previous study. Like in the case of the hydrodynamic NTSI, the increase in the wavelength reduces the growth rate of the microscopic NTSI. The prolonged growth time of the microscopic NTSI allows the waves, which are driven by the competing ion acoustic instability, to grow to a large amplitude before the NTSI saturates and they disrupt the latter. The ion acoustic instability thus imposes a limit on the largest wavelength that can be destabilized by the NTSI in collisionless plasma. The limit can be overcome by binary collisions. We bring forward evidence for an overstability of the collisionless NTSI.
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