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arXiv2011

Direct observation of current in type I ELM filaments on Asdex Upgrade

Magnetically confined plasmas are often subject to relaxation oscillations accompanied by large transport events. This is particularly the case for the high confinement regime of tokamaks where these events are termed edge localized modes (ELMs). They result in the temporary breakdown of the high confinement and lead to high power loads on plasma facing components. Present theories of ELM generation rely on a combined effect of edge currents and the edge pressure gradient exceeding critical values which result in intermediate mode number ($n \cong 10-15$) structures (\emph{filaments}) localized in the perpendicular plane and extended along the field line. It is shown here by detailed localized measurements of the three components of the magnetic field perturbation carried by an individual type I ELM filament that these filaments carry a substantial current. The observations provide essential information for the understanding of ELM dynamics.

physics.plasm-ph↗
arXiv2009

From BBGKY Hierarchy to Non-Markovian Evolution Equations

The problem of description of the evolution of the microscopic phase density and its generalizations is discussed. With this purpose, the sequence of marginal microscopic phase densities is introduced, and the appropriate BBGKY hierarchy for these microscopic distributions and their average values is formulated. The microscopic derivation of the generalized evolution equation for average value of the microscopic phase density is given and the non-Markovian generalization of the Fokker-Planck collision integral is deduced.

physics.plasm-ph↗
arXiv2009

On shear flow stabilization concepts for the dense z pinch

Different ways to achieve the stabilization of a linear z-pinch by a superimposed shear flow are analyzed. They are: 1) Axial shear flow proposed by Arber and Howell with the pinch discharge in its center, and experimentally tested by Shumlak et al. 2) Spiral flow of a dense low temperature plasma surrounding a dense pinch discharge. 3) A thin metallic projectile shot at a high velocity through the center of the pinch discharge. 4) The replacement of the high velocity projectile by the shape charge effect jet in a conical implosion. 5) The replacement of the jet by a stationary wire inside the conical implosion.

physics.plasm-ph↗
arXiv2010

Hybrid modeling of plasmas

Here we present the mathematical and numerical details of a general hybrid model for plasmas. All grid quantities are stored at cell centers on the grid. The most common discretization of the fields in PIC solvers is to have the electric and magnetic fields staggered, introduced by Yee. This automatically ensures that div(B)=0, down to round-off errors. Here we instead present a cell centered discretization of the magnetic field. That the standard cell centered second order stencil for rot(E) in Faraday's law will preserve div(B)=0 was noted by Toth. The advantage of a cell centered discretization is ease of implementation, and the possibility to use available solvers that only handle cell centered variables. We also show that the proposed method has very good energy conservation for a simple test problem in three dimensions, when compared to a commonly used algorithm.

physics.space-ph↗
arXiv2009

Modeling of Perpendicularly Driven Dual-Frequency Capacitively Coupled Plasma

We proposed an altered configuration for dual-frequency (DF) capacitively coupled plasmas (CCP). In this configuration, two pairs of electrodes are arranged oppositely, and the discharging is perpendicularly driven by two rf sources. With Particle-in-cell/Monte Carlo method, we have demonstrated this configuration can remove the harmful electromagnetic and DF coupling effects in conventional DF-CCP.

physics.plasm-ph↗
arXiv2010

Ultradense Deuterium

An attempt is made to explain the recently reported occurrence of ultradense deuterium as an isothermal transition of Rydberg matter into a high density phase by quantum mechanical exchange forces. It is conjectured that the transition is made possible by the formation of vortices in a Cooper pair electron fluid, separating the electrons from the deuterons, with the deuterons undergoing Bose-Einstein condensation in the core of the vortices. If such a state of deuterium should exist at the reported density of about 100,000 g/cm3, it would greatly facility the ignition of a thermonuclear detonation wave in pure deuterium, by placing the deuterium in a thin disc, to be ignited by a pulsed ultrafast laser or particle beam of modest energy.

physics.gen-ph↗
arXiv2011

Unified Theory of Ghost and Quadratic-Flux-Minimizing Surfaces

A generalized Hamiltonian definition of ghost surfaces (surfaces defined by an action-gradient flow) is given and specialized to the usual Lagrangian definition. Numerical calculations show uncorrected quadratic-flux-minimizing (QFMin) and Lagrangian ghost surfaces give very similar results for a chaotic magnetic field weakly perturbed from an integrable case in action-angle coordinates, described by $L = L_0 + εL_1$, where $L_0(\dotθ)$ (with $\dotθ$ denoting $dθ/dζ$) is an integrable field-line Lagrangian and $ε$ is a perturbation parameter. This is explained using a perturbative construction of the auxiliary poloidal angle $Θ$ that corrects QFMin surfaces so they are also ghost surfaces. The difference between the corrected and uncorrected surfaces is $O(ε^2)$, explaining the observed smallness of this difference. An alternative definition of ghost surfaces is also introduced, based on an action-gradient flow in $Θ$, which appears to have superior properties when unified with QFMin surfaces.

physics.plasm-ph↗
arXiv2010

On the stability of a very dense deuterium-tritium plasma ball

General conditions of stability of a very dense deuterium-tritium plasma ball are discussed. It is shown that the decrease in the size of a plasma ball (increase in the plasma density) can be expected only when the temperature and the pressure in the plasma ball are kept high enough for all the particles, the nuclei and the delocalized electrons, to be described by classical statistics.

physics.plasm-ph↗
arXiv2010

Free magnetized knots of parity-violating deconfined matter in heavy-ion collisions

We show that the local parity violation in the quark-gluon plasma supports existence of free (meta)stable knots of deconfined hot quark matter stabilized by superstrong magnetic fields. The magnetic field in the knots resembles the spheromak plasma state of the magnetic confinement approach to nuclear fusion. The size of the knot is quantized, being inversely proportional to the chiral conductivity of the quark-gluon plasma. The parity symmetry is broken inside the knot. Particles produced in the decays of the knots have unusual azimuthal distribution and specific flavor content. We argue that these knots may be created in noncentral heavy-ion collisions.

nucl-th↗
arXiv2010

Time-Fractional KdV Equation for the plasma in auroral zone using Variational Methods

The reductive perturbation method has been employed to derive the Korteweg-de Vries (KdV) equation for small but finite amplitude electrostatic waves. The Lagrangian of the time fractional KdV equation is used in similar form to the Lagrangian of the regular KdV equation. The variation of the functional of this Lagrangian leads to the Euler-Lagrange equation that leads to the time fractional KdV equation. The Riemann-Liouvulle definition of the fractional derivative is used to describe the time fractional operator in the fractional KdV equation. The variational-iteration method given by He is used to solve the derived time fractional KdV equation. The calculations of the solution with initial condition A0*sech(cx)^2 are carried out. Numerical studies have been made using plasma parameters close to those values corresponding to the dayside auroral zone. The effects of the time fractional parameter on the electrostatic solitary structures are presented.

nlin.PS↗
arXiv2010

Theoretical Studies of Long Lived Plasma Structures

We construct the model of a long lived plasma structure based on spherically symmetric oscillations of electrons in plasma. Oscillations of electrons are studied in frames of both classical and quantum approaches. We obtain the density profile of electrons and the dispersion relations for these oscillations. The differences between classical and quantum approaches are discussed. Then we study the interaction between electrons participating in spherically symmetric oscillations. We find that this interaction can be attractive and electrons can form bound states. The applications of the obtained results to the theory of natural plasmoids are considered.

physics.plasm-ph↗
arXiv2010

Gyrokinetic simulation of entropy cascade in two-dimensional electrostatic turbulence

Two-dimensional electrostatic turbulence in magnetized weakly-collisional plasmas exhibits a cascade of entropy in phase space [Phys. Rev. Lett. 103, 015003 (2009)]. At scales smaller than the gyroradius, this cascade is characterized by the dimensionless ratio D of the collision time to the eddy turnover time measured at the scale of the thermal Larmor radius. When D >> 1, a broad spectrum of fluctuations at sub-Larmor scales is found in both position and velocity space. The distribution function develops structure as a function of v_{perp}, the velocity coordinate perpendicular to the local magnetic field. The cascade shows a local-scale nonlinear interaction in both position and velocity spaces, and Kolmogorov's scaling theory can be extended into phase space.

physics.plasm-ph↗
arXiv2010

A microscopic instability in neutral magnetized plasmas

We show that in a neutral magnetized plasma there exist microscopic oscillatory modes, with wavelengths of the order of magnitude of the mean interparticle distance, which become unstable when the electron density exceeds a limit proportional to the square of the magnetic field. The model we consider is just a linearization of the classical one for neutral plasmas, namely a system of electrons subjected to Coulomb interactions among themselves and with a uniform positive neutralizing background. This model is here dealt with as an actual many-body problem, without introducing any averaging over the individual particles. The expression of the density limit coincides, apart possibly from a numerical factor of order one, with the well-known Brillouin density limit for a nonneutral plasma, which has however a macroscopic origin. The density limit here found has the same order of magnitude as the operational density limit observed in several conventional tokamak devices. We finally show that, when the full electromagnetic interactions are taken into account, dispersion relations are obtained which for short wavelengths reduce to those obtained here in the purely Coulomb case, and for long wavelengths reproduce the familiar ones of MHD.

physics.plasm-ph↗
arXiv2013

Minimization of an energy error functional to solve a Cauchy problem arising in plasma physics: the reconstruction of the magnetic flux in the vacuum surrounding the plasma in a Tokamak

A numerical method for the computation of the magnetic flux in the vacuum surrounding the plasma in a Tokamak is investigated. It is based on the formulation of a Cauchy problem which is solved through the minimization of an energy error functional. Several numerical experiments are conducted which show the efficiency of the method.

math.NA↗
arXiv2010

Effects of the neutral point of dust charge in plasma sheath

We numerically investigate the dust charging in the sheath, by using the usual fluid approximation, it is extended to include self consistently the dust charge variation. The grain charge becomes a new self consistent dynamic variable, it is found that dust grains are first charged negatively at the sheath edge and then begin to be charged positively in the sheath. The numerical results show that the initial velocity of dust charged grains, sized grains and the density ratio of ion to electron at the sheath edge have affected the neutral point of dust charge. Moreover, the neutral point of dust charge affects the spatial distribution of dust density.

physics.plasm-ph↗
arXiv2011

Plasma bremsstrahlung emission at electron energy from low up to extreme relativistic values

We consider the bremsstrahlung of electrons of fully ionized plasma. Electron energy range extends from a few hundred electron volts before the extreme relativistic energies of several MeV. The results of calculations of effective slow-down rate of a single electron and the power emission from a volume of the plasma with Maxwellian electrons. At relativistic energies, the Born approximation yields highly accurate results. Correction to the Born approximation are considered for low-energy regimes. In the high-energy regimes numerical results are close to extreme relativistic analytic results. The formulas are suggested that approximate the results of numerical calculations.

physics.plasm-ph↗
arXiv2010

The Procedure Of Examination Of The Stability Of Boundary Between Plasma And The Magnetic Field In Electroneutral Approach

A procedure that allows study of unstable stability of a boundary layer between plasma and a magnetic field has been developed. Layer equilibrium for one reason or another is not set but follows from strict solution of kinetic equation with self-consistent electromagnetic field. Nicolson's solution was used as equilibrium solution. The non-equilibrium component to the distribution function was found and on this basis tensor of dielectric permeability simulating the medium was (boundary layer) is calculated. This tensor essentially differs from the known tensor for magnetoactive plasma. Equations for electric field perturbation were obtained from the Maxwell's equations completed with the derived constitutive equation. The technique of determination of dispersion characteristics of perturbations of a boundary layer was proposed. The theory is applicable to thermal nonrelativistic plasma.

physics.plasm-ph↗