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Plasma Physics

New submissions

[ total of 11 entries: 1-11 ]
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New submissions for Tue, 20 Mar 18

[1]  arXiv:1803.06358 [pdf, ps, other]
Title: Scaling of ion trapping in laser-driven relativistically transparent plasma
Subjects: Plasma Physics (physics.plasm-ph)

Ion trapping by ion wave breaking is investigated for laser-driven near-critical relativistically transparent plasma. Guided by three-dimensional particle-in-cell simulations, we study ion motion along the laser propagation direction within a 1D fluid model. The threshold for ion trapping is found, and the singular behaviour of longitudinal electric field, ion velocity, and ion density in the vicinity of the ion wave breaking point is derived analytically showing power-law distributions. The important result is that only a fraction of ions is trapped, different from the regime of hole boring. The number of trapped particles is determined and how it depends on target density for fixed laser intensity. Results are confirmed by the simulations.

[2]  arXiv:1803.06452 [pdf, ps, other]
Title: Spectral Estimation of Plasma Fluctuations II: Nonstationary Analysis of ELM Spectra
Comments: Figures missing
Journal-ref: Physics of Plasmas, Volume 1, Issue 3, March 1994, pp.501-514
Subjects: Plasma Physics (physics.plasm-ph)

Several analysis methods for nonstationary fluctuations are described and applied to the edge localized mode (ELM) instabilities of limiter H-mode plasmas. The microwave scattering diagnostic observes poloidal $k_{\theta}$ values of 3.3 cm$^{-1}$, averaged over a 20 cm region at the plasma edge.A short autoregressive filter enhances the nonstationary component of the plasma fluctuations by removing much of the background level of stationary fluctuations. Between ELMs, the spectrum predominantly consists of broad-banded 300-700 kHz fluctuations propagating in the electron diamagnetic drift direction, indicating the presence of a negative electric field near the plasma edge. The time-frequency spectrogram is computed with the multiple taper technique. By using the singular value decomposition of the spectrogram, it is shown that the spectrum during the ELM is broader and more symmetric than that of the stationary spectrum. The ELM period and the evolution of the spectrum between ELMs varies from discharge to discharge. For the discharge under consideration which has distinct ELMs with a 1 msec period, the spectrum has a maximum in the electron drift direction which relaxes to a near constant value %its characteristic shape in the first half millisecond after the end of the ELM and then grows slowly. In contrast, the level of the fluctuations in the ion drift direction increases exponentially by a factor of eight in the five milliseconds~after the ELM. High frequency precursors are found which occur one millisecond before the ELMs and propagate in the ion drift direction. These precursors are very short ($\sim 10 \mu$secs), coherent bursts, and they predict the occurrence of an ELM with a high success rate.

[3]  arXiv:1803.06509 [pdf, ps, other]
Title: Explosive shock tube of xenon non-ideal plasma for proton radiography
Comments: 7 pages, 6 figures. To appear in the proceedings of XXXIII International Conference on Equations of State for Matter, 1-6, 2018, Elbrus, Kabardino-Balkaria, Russia
Subjects: Plasma Physics (physics.plasm-ph)

A high explosive shock tube of non-ideal gaseous plasma for proton radiography is described. The gas dynamic flow in the shock compressed xenon at initial pressure of 7 bar was investigated in the tube. The velocity of the shock wave in xenon and the associated particle velocity were measured by a high-speed rotating mirror streak camera. Experimental time-distance data was used for approximation of the velocities by exponential decay functions. The shock tube is intended for generation of non-ideal plasma of xenon at the pressure of 5-12 kbar, the density of 0.24-0.3 g/cm3 when the initial pressure is about 7 bar.

[4]  arXiv:1803.06868 [pdf, other]
Title: Generation of ten kilotesla longitudinal magnetic fields in ultraintense laser-solenoid target interactions
Comments: 5 pages, 4 figures
Subjects: Plasma Physics (physics.plasm-ph); Optics (physics.optics)

Production of the huge longitudinal magnetic fields by using an ultraintense laser pulse irradiating a solenoid target is considered. Through three-dimensional particle-in-cell simulations, it is shown that the longitudinal magnetic field up to ten kilotesla can be observed in the ultraintense laser-solenoid target interactions. The finding is associated with both fast and return electron currents in the solenoid target. The huge longitudinal magnetic field is of interest for a number of important applications, which include controlling the divergence of laser-driven energetic particles for medical treatment, fast-ignition in inertial fusion, etc., as an example, the well focused and confined directional electron beams are realized by using the solenoid target.

Cross-lists for Tue, 20 Mar 18

[5]  arXiv:1803.06338 (cross-list from cond-mat.quant-gas) [pdf, other]
Title: Elliptic flow in a strongly-interacting normal Bose gas
Comments: 4 pages, 3 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Atomic Physics (physics.atom-ph); Plasma Physics (physics.plasm-ph); Quantum Physics (quant-ph)

We study the anisotropic, elliptic expansion of a thermal atomic Bose gas released from an anisotropic trapping potential, for a wide range of interaction strengths across a Feshbach resonance. We show that in our system this hydrodynamic phenomenon is for all interaction strengths fully described by a microscopic kinetic model with no free parameters. The success of this description crucially relies on taking into account the reduced thermalising power of elastic collisions in a strongly interacting gas, for which we derive an analytical theory. We also perform time-resolved measurements that directly reveal the dynamics of the energy transfer between the different expansion axes.

[6]  arXiv:1803.06350 (cross-list from physics.flu-dyn) [pdf, other]
Title: Magnetic Prandtl number dependence of turbulence generated by chiral MHD dynamos
Comments: 18 pages, 10 figures, submitted to GAFD for the special issue "Recent Developments in Natural Dynamos"
Subjects: Fluid Dynamics (physics.flu-dyn); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); Plasma Physics (physics.plasm-ph)

An asymmetry in the number density of left- and right-handed fermions is known to give rise to a new term in the induction equation that can result in a small-scale instability. This is a microphysical effect characterised by a chiral chemical potential and is mathematically similar to the alpha effect, which is a turbulent or macrophysical effect. At high temperatures, when a chiral asymmetry can survive for long enough, these chiral MHD dynamos can amplify magnetic fields efficiently, which in turn drive turbulence via the Lorentz force. While it has been demonstrated in numerical simulations that chiral magnetically driven turbulence exists and modifies the evolution of the plasma, the details of this process remain unclear. The goal of this paper is to shed new light on the properties of chiral magnetically driven turbulence using numerical simulations with the Pencil Code. We explore the generation of turbulence for different initial conditions, including a variation of the initial chiral chemical potential and the magnetic Prandtl number, Pm. In particular, we determine the ratio of kinetic to magnetic energy, Upsilon^2, that can be reached in chiral magnetically driven turbulence. Within the parameter space explored in this study, Upsilon reaches a value of approximately 0.24-0.29 - independently of the initial chiral asymmetry and for Pm=1. Our simulations suggest, that Upsilon decreases as a power law when increasing Pm. While the exact scaling depends on the details of the fitting criteria and the Reynolds number regime, an approximate result of Upsilon(Pm)=0.3*Pm^{-0.2} is reported. Using the findings from our numerical simulations, we estimate the properties of chiral magnetically driven turbulence in the early Universe.

[7]  arXiv:1803.06378 (cross-list from physics.space-ph) [pdf, ps, other]
Title: Characterizing Ion Flows Across a Dipolarization Jet
Subjects: Space Physics (physics.space-ph); Plasma Physics (physics.plasm-ph)

The structure of dipolarization jets with finite width in the dawn-dusk direction relevant to magnetic reconnection in the Earth's magnetotail is explored with particle-in-cell simulations. We carry out Riemann simulations of the evolution of the jet in the dawn-dusk, north-south plane to investigate the dependence of the jet structure on the jet width in the dawn-dusk direction. We find that the magnetic field and Earth-directed ion flow structure depend on the dawn-dusk width. A reversal in the usual Hall magnetic field near the center of the current sheet on the dusk side of larger jets is observed. For small widths, the maximum velocity of the Earthward flow is significantly reduced below the theoretical limit of the upstream Alfv\'en speed. However, the ion flow speed approaches this limit once the width exceeds the ion Larmor radius based on the normal magnetic field, $B_z$.

[8]  arXiv:1803.06889 (cross-list from physics.optics) [pdf, other]
Title: Terahertz emission from laser-driven gas-plasmas: a plasmonic point of view
Subjects: Optics (physics.optics); Plasma Physics (physics.plasm-ph)

We investigate terahertz generation in two-color laser-induced gas plasmas. Resonances attributed to plasmonic effects are shown to broaden the emission spectra significantly, when electrons are excited along a direction where the plasma size is smaller than the plasma wavelength. We demonstrate that such resonances can be turned on and off by changing the polarization properties of elliptically-shaped driving laser-pulses. Both 3D Maxwell consistent simulations and experimental results confirm that a significant THz pulse shortening and spectral broadening can be achieved by exploiting the transverse driving laser-beam shape as an additional degree of freedom.

Replacements for Tue, 20 Mar 18

[9]  arXiv:1711.04009 (replaced) [src]
Title: Numerical investigation into the effects of non-equilibrium plasma discharge on two-stage ignition and LTC of DME/O2/Ar Mixtures
Authors: Yao Zhang
Comments: Authorship disputes, withdrawing the paper to resolve conflicts
Subjects: Plasma Physics (physics.plasm-ph)
[10]  arXiv:1802.02174 (replaced) [pdf, other]
Title: A fluid-kinetic framework for self-consistent runaway-electron simulations
Comments: 7 pages, 1 figure
Subjects: Plasma Physics (physics.plasm-ph)
[11]  arXiv:1710.03879 (replaced) [pdf, other]
Title: Improving particle beam acceleration in plasmas
Comments: Submitted for publication
Subjects: Accelerator Physics (physics.acc-ph); Plasma Physics (physics.plasm-ph)
[ total of 11 entries: 1-11 ]
[ showing up to 2000 entries per page: fewer | more ]

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