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arXiv2013

Analysis of the Evolution of Hydrodynamic Instability at the Interface of Active and Passive Media

The evolution of an instability at the interface of active and passive media is considered. An asymptotic form of a collision integral is found and the limitations of hydrodynamic approach are determined. A growth increment of small perturbations of the interface is found using the potential flows theory. The obtained results were applied to estimation of the instability contribution to the development of some known physical processes.

physics.plasm-ph↗

arXiv2013

Features of Hypothetical Plasma Phase Transition in Interiors of Saturn and Jupiter

Anomalous features for hypothetical Plasma Phase Transitions (PPT), which is expected to occur in mixed hydrogen-helium plasma in interior of Jupiter and Saturn, are under discussion. The characteristics of the Coulomb and density corrections (the so-called non-ideality corrections) are reconstructed for hydrogen-helium plasma in the vicinity of phase coexistence boundary of this PPT in version of Saumon and Chabrier, using tabular data for hydrogen-helium EOS of Saumon, Chabrier and VanHorn and some general thermodynamic relations. Two previously unknown characteristics of the studied PPT have been estimated based on these results: (i) -- the jump of the electrostatic potential across the phase boundary of PPT (Galvani potential), and (ii) -- the scale of non-congruency for this PPT (the differences in chemical composition of the coexisting hydrogen-helium phases), which could be expected in H2/He mixture at typical parameters of plasma in interior of Jupiter and Saturn. While the first effect -- the potential of phase boundary -- turned out to be within the typical scale of contact electrochemical potentials, $Δφ$ ~ 1-2 eV, the second quantity -- the PPT non-congruency -- proved to be considerable under Saturn and Jupiter conditions.

physics.plasm-ph↗

arXiv2014

From Liouville's theorem to quasilinear, nonlinear stochastic, and fractional transport, a multi-scale kinetics of plasma turbulence

From Liouville's equation, a phase-space multi-scale transport equation is systematically derived. The proposed phase-space multi-scale transport equation based on the first principle indicates that the nonlinear stochastic transport is due to the micro-turbulence scattering while the familiar quasilinear transport is due to the long-range correlation of the meso-scale coherent modes; and more interestingly, it demonstrates a systematic derivation of the fractional transport equation that may provide a new view-angle to understand the anomalous transport observed in plasma turbulence. The multi-scale kinetics suggests a new approach to confinement improvement through the formation of nonlinearly self-organized stable large-scale structures.

physics.plasm-ph↗

arXiv2015

Warm dense matter conductivity including electron-electron collisions

The controversy with respect to the role of electron-electron collisions in the dynamic conductivity of dense plasmas is resolved. In particular, the dc conductivity is analyzed in the low-density, non-degenerate limit where the Spitzer theory is valid and electron-electron collisions lead to the well-known reduction of the result for a Lorentz plasma. With increasing degeneracy, the contribution of electron-electron collisions to the dc conductivity is decreasing and can be neglected for the liquid metal domain where the Ziman-Faber theory is applicable. We show how electron-electron collisions have to be implemented in calculations based on the Kubo-Greenwood formula which is prevalently applied in simulations for the frequency-dependent conductivity in the warm dense matter region, i.e. for arbitrary degeneracy.

physics.plasm-ph↗

arXiv2014

Exploring the nature of collisionless shocks under laboratory conditions

Collisionless shocks are pervasive in astrophysics and they are critical to understand cosmic ray acceleration. Laboratory experiments with intense lasers are now opening the way to explore and characterise the underlying microphysics, which determine the acceleration process of collisionless shocks. We determine the shock character - electrostatic or electromagnetic - based on the stability of electrostatic shocks to transverse electromagnetic fluctuations as a function of the electron temperature and flow velocity of the plasma components, and we compare the analytical model with particle-in-cell simulations. By making the connection with the laser parameters driving the plasma flows, we demonstrate that shocks with different and distinct underlying microphysics can be explored in the laboratory with state-of-the-art laser systems.

physics.plasm-ph↗

arXiv2014

Nonlinear interaction of electromagnetic field with quantum plasma

The analysis of nonlinear interaction of transversal electromagnetic field with quantum collisionless plasma is carried out. Formulas for calculation electric current in quantum collisionless plasma at any temperature are deduced. It has appeared, that the nonlinearity account leads to occurrence of the longitudinal electric current directed along a wave vector. This second current is orthogonal to the known transversal classical current, received at the classical linear analysis. The case of degenerate electronic plasma is considered. It is shown, that for degenerate plasmas the electric current is calculated under the formula, not containing quadratures. In this formula we have allocated known Kohn's singularities (W. Kohn, 1959).

physics.plasm-ph↗

arXiv2014

Proton-driven plasma wakefield acceleration: a path to the future of high-energy particle physics

New acceleration technology is mandatory for the future elucidation of fundamental particles and their interactions. A promising approach is to exploit the properties of plasmas. Past research has focused on creating large-amplitude plasma waves by injecting an intense laser pulse or an electron bunch into the plasma. However, the maximum energy gain of electrons accelerated in a single plasma stage is limited by the energy of the driver. Proton bunches are the most promising drivers of wakefields to accelerate electrons to the TeV energy scale in a single stage. An experimental program at CERN -- the AWAKE experiment -- has been launched to study in detail the important physical processes and to demonstrate the power of proton-driven plasma wakefield acceleration. Here we review the physical principles and some experimental considerations for a future proton-driven plasma wakefield accelerator.

physics.acc-ph↗

arXiv2014

"Phase freezeout" in isentropically expanding matter

Features of isentropic expansion of warm dense matter (WDM) created by intense energy fluxes (strong shock compression or instant isochoric heating by laser or heavy ions) are under discussion in situation when ($i$) -- thermodynamic trajectory of such expansion crosses binodal of liquid-gas phase transition, and ($ii$) -- expansion within the two-phase region is going along equilibrium branch (not metastable one) of the two-phase mixture isentrope. It is known in the plane case that because of break in the expansion isentrope at binodal point (in $P-V$ plane) i.e. jump of sound velocity in this point, there appears extended zone ("boiling layer") of uniformity in expanding material with constant thermodynamic and kinematic parameters. It corresponds just to the state on this binodal of boiling liquid. The point is that because of self-similarity of such expansion (in plane case) this boiling layer contains finite and fixed part of whole expanding material. This property makes it possible (at least formally) to discuss this type of isentropic expansion of WDM as a tool for generation (and diagnostics) of extended uniform state of matter exactly on binodal (and even in critical point) when parameters of this binodal (and/or thermophysical properties on it) are not known. It is natural to use the term "phase freezeout" for this regime of expansion. It is similar to the terms "chemical freezeout" and "kinetic freezeout", which are widely used in interpretation of quark-hardon transformations during expansion of quark-gluon "fireball" in ultra-high energy ionic collisions in supercolliders. General hydrodynamic scheme of adiabatic movements for the case of ensemble of well positioned plates or foils (stack target) under instant isochoric heating (for example, by heavy ion beam) is considered as elaboration of simple idea of phase freeze-out ("reverberation" regime).

physics.plasm-ph↗

arXiv2014

The statistical mechanics of self-gravitating Keplerian disks

We describe the dynamics and thermodynamics of collisionless particle disks orbiting a massive central body, in the case where the disk mass is small compared to the central mass, the self-gravity of the disk dominates the non-Keplerian force, and the spread in semi-major axes is small. We show that with plausible approximations such disks have logarithmic two-body interactions and a compact phase space, and therefore exhibit thermodynamics that are simpler than most other gravitating systems, which require a confining box and artificial softening of the potential at small scales to be thermodynamically well-behaved. We solve for the microcanonical axisymmetric thermal equilibria and demonstrate the existence of a symmetry-breaking bifurcation into lopsided equilibria. We discuss the relation between thermal and dynamical instability in these systems and draw connections to astrophysical settings, as well as to the wider subject of the statistical mechanics of particles with logarithmic long-range interactions, such as point vortices in two-dimensional fluids.

astro-ph.GA↗

arXiv2014

Effects of the Second Harmonic on the GAM in Electron Scale Turbulence

The effects higher order harmonics have been self-consistently included in the derivation of the electron branch of the electron Geodesic Acoustic Mode (el-GAM) in an Electron-Temperature-Gradient (ETG) turbulence background. The work is based on a two-fluid model including finite $β$-effects while retaining non-adiabatic ions. In solving the linear dispersion relation, it is found that the due to the coupling to the $m=2$ mode the real frequency may be significantly altered and yield higher values.

physics.plasm-ph↗

arXiv2014

Measurements and modelling of fast-ion redistribution due to MHD instabilities in the Mega-Amp Spherical Tokamak

The results of a comprehensive investigation into the effects of various MHD modes on the NBI-generated fast-ion population in MAST plasmas are reported. Fast-ion redistribution due to low-frequency (20-50 kHz) chirping energetic particle modes known as fishbones, as well as the long-lived internal kink mode, is observed with the Fast-Ion Deuterium Alpha (FIDA) spectrometer and radially-scanning collimated neutron camera. In addition, strongly-driven chirping toroidicity-induced Alfven eigenmodes are observed to cause fast-ion redistribution, as are sawteeth and large edge-localised modes. In each case, the modes affect fast ions in a region of real space governed by the eigenmode structure and principal toroidal mode number. Modelling using the global transport analysis code TRANSP, with ad hoc anomalous diffusion introduced, reproduces the coarsest features of the affected fast-ion distribution in the presence of energetic-particle-driven modes, but the spectrally and spatially resolved FIDA measurements suggest that the distribution exhibits structure on a finer scale than is accounted for by this model.

physics.plasm-ph↗

arXiv2014

Remarks on the derivation and evaluation of the Stacey-Sigmar model for tokamak equilibrium

The Stacey-Sigmar model for tokamak equilibrium as presented in the literature relies heavily on the neoclassical theory of the electrostatic field. Its neglect of Gauss's law is inconsistent with the potential formulation of electrodynamics. Its treatment of the dynamic electric field generated by the central heating and poloidal field coils also is suspect. Its derivation of the viscosity term remains incomplete and does not account for the varying pitch angle of the magnetic field. A derivation of the viscosity term which respects the pitch angle can account for the radial force commonly ascribed to the radial electrostatic field, thereby obviating the desire to neglect Gauss's law.

physics.plasm-ph↗

arXiv2014

Perturbative transport experiments: to what extent do they really probe microscopic transport?

Experiments featuring fast heat propagation, or so called "non-local" transport, were a puzzle for almost two decades. However recently it was shown, and it is recalled here, that a collective ideal MHD response of the plasma provides a quantitative agreement with these experiments, whereas transport plays just a secondary role. Then this work reviews the algebraic approach to transport data inversion that provides a formally exact solution, as well as a quantitative assessment of error bars, limited to periodic signals. Conversely, standard transport reconstructions are shown to sometimes fail to match the exact solution. The adoption of automated global search algorithms based upon Genetic Algorithms is bound to greatly increase the probability of finding optimal solutions. Finally, the standard methods of reconstruction infer the diffusivity D and pinch V by matching experimental data against those simulated by transport codes. These methods do not warrant the validity neither of the underlying models of transport, nor of the reconstructed D(r) and V(r), even when the results look reasonable.

physics.plasm-ph↗

arXiv2014

Accurate numerical simulation of radiation reaction effects in strong electromagnetic fields

The Landau-Lifshitz equation provides an efficient way to account for the effects of radiation reaction without acquiring the non-physical solutions typical for the Lorentz-Abraham-Dirac equation. We solve the Landau-Lifshitz equation in its covariant four-vector form in order to control both the energy and momentum of radiating particle. Our study reveals that implicit time-symmetric collocation methods of the Runge-Kutta-Nyström type are superior in both accuracy and better maintaining the mass-shell condition than their explicit counterparts. We carry out an extensive study of numerical accuracy by comparing the analytical and numerical solutions of the Landau-Lifshitz equation. Finally, we present the results of simulation of particles scattering by a focused laser pulse. Due to radiation reaction, particles are less capable for penetration into the focal region, as compared to the case of radiation reaction neglected. Our results are important for designing the forthcoming experiments with high intensity laser fields.

physics.plasm-ph↗

arXiv2014

Using k-alpha emission to determine fast electron spectra using the Hybrid code ZEPHYROS

A high intensity laser-solid interaction invariably drives a non-thermal fast electron current through the target, however characterizing these fast electron distributions can prove difficult. An understanding of how these electrons propagate through dense materials is of fundamental interest and has applications relevant to fast ignition schemes and ion acceleration. Here, we utilize an upgraded version of the Hybrid code ZEPHYROS to demonstrate how the resulting k-alpha emission from such an interaction can be used as a diagnostic to obtain the characteristic temperature, divergence and total energy of the fast electron population.

physics.plasm-ph↗

arXiv2014

Longitudinal forces in pinched electric currents

It is shown that the theory of Mbelek and Lachièze-Rey predicts longitudinal forces of gravitational origin in pinched current distributions, with magnitudes large enough to have noticeable effects.

gr-qc↗

arXiv2014

Relativistic plasma optics enabled by near-critical density nanostructured material

The nonlinear optical properties of a plasma due to the relativistic electron motion in an intense laser field are of fundamental importance for current research and the generation of brilliant laser-driven sources of particles and photons1-15. Yet, one of the most interesting regimes, where the frequency of the laser becomes resonant with the plasma, has remained experimentally hard to access. We overcome this limitation by utilizing ultrathin carbon nanotube foam16 (CNF) targets allowing the strong relativistic nonlinearities at near- critical density (NCD) to be exploited for the first time. We report on the experimental realization of relativistic plasma optics to spatio-temporally compress the laser pulse within a few micrometers of propagation, while maintaining about half its energy. We also apply the enhanced laser pulses to substantially improve the properties of an ion bunch accelerated from a secondary target. Our results provide first insights into the rich physics of NCD plasmas and the opportunities waiting to be harvested for applications.

physics.plasm-ph↗

arXiv2014

On differences between the B- and E-approaches and the implications for the Solar atmosphere

A simple collisional three-component plasma model consisting of electrons, ions, and neutrals with arbitrary collision frequencies and dynamic time scales is considered. It is shown that the usual MHD-approach dealing with magnetic field perturbations can give other results than the approach in which all perturbations are expressed via the perturbed electric field. For the partially ionized plasma with strong collisional coupling of neutrals with ions, magnetosonic (nondamping) and Alfvén (weakly damping) waves modified by the presence of neutrals are obtained. It is shown that the magnetic diffusivity for Alfvén waves appears only due to the longitudinal current connected with the field $E_{1z}$ at the angular propagation of perturbations relatively to the background magnetic field. The model can be applied to different parts of a solar atmosphere and prominences.

astro-ph.SR↗