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arXiv2009

Trinity: A Unified Treatment of Turbulence, Transport, and Heating in Magnetized Plasmas

To faithfully simulate ITER and other modern fusion devices, one must resolve electron and ion fluctuation scales in a five-dimensional phase space and time. Simultaneously, one must account for the interaction of this turbulence with the slow evolution of the large-scale plasma profiles. Because of the enormous range of scales involved and the high dimensionality of the problem, resolved first-principles global simulations are very challenging using conventional (brute force) techniques. In this thesis, the problem of resolving turbulence is addressed by developing velocity space resolution diagnostics and an adaptive collisionality that allow for the confident simulation of velocity space dynamics using the approximate minimal necessary dissipation. With regard to the wide range of scales, a new approach has been developed in which turbulence calculations from multiple gyrokinetic flux tube simulations are coupled together using transport equations to obtain self-consistent, steady-state background profiles and corresponding turbulent fluxes and heating. This approach is embodied in a new code, Trinity, which is capable of evolving equilibrium profiles for multiple species, including electromagnetic effects and realistic magnetic geometry, at a fraction of the cost of conventional global simulations. Furthermore, an advanced model physical collision operator for gyrokinetics has been derived and implemented, allowing for the study of collisional turbulent heating, which has not been extensively studied. To demonstrate the utility of the coupled flux tube approach, preliminary results from Trinity simulations of the core of an ITER plasma are presented.

physics.plasm-ph↗

arXiv2009

Focusing of light beyond the diffraction limit

Diffraction limits the behaviour of light in optical systems and sets the smallest achievable line width at half the wavelength. With a novel subwavelength plasmonic lens to reduce the diffraction via an asymmetry and to generate and squeeze the wave functions, an incident light is focused by the aperture to a single-line with its width beyond the limit outside the near zone. The fields focused are radiative and capable of propagating to the far zone. The light focusing process, besides being of academic interest, is expected to open up a wide range of application possibilities.

physics.optics↗

arXiv2009

Boosted high harmonics pulse from a double-sided relativistic mirror

An ultra-bright high-intensity X- and gamma-radiation source is proposed. A high-density thin plasma slab, accelerating in the radiation pressure dominant regime by a co-propagating ultra-intense electromagnetic wave, reflects a counter-propagating relativistically strong electromagnetic wave, producing strongly time-compressed and intensified radiation due to the double Doppler effect. The reflected light contains relativistic harmonics generated at the plasma slab, all upshifted with the same factor as the fundamental mode of the incident light.

physics.plasm-ph↗

arXiv2009

Integral equation for source of ionization in hollow cathode

To simulate the influence of pendulum effect in hollow cathode configuration on a current-voltage characteristic it is proposed to consider a plane glow discharge in one-dimensional space configuration with two plane parallel cathodes and one plane anode in the middle. A pendulum effect could be switched on or off, with consideration for the anode to be transparent or not for fast ionizing electrons. On the basis of a stationary kinetic equation for ionizing electrons an integral equation for a source of ionization is derived. This equation can be used as a component in self-consistent problem for field equations to calculate a current-voltage characteristic and to show how it changes in both cases - in presence or absence of anode transparency.

physics.plasm-ph↗

arXiv2009

The theory of gyrokinetic turbulence: A multiple-scales approach

Gyrokinetics is a rich and rewarding playground to study some of the mysteries of modern physics. In this thesis I present work, motivated by the quest for fusion energy, which seeks to uncover some of the inner workings of turbulence in magnetized plasmas. I begin with the fundamental theory of gyrokinetics, and a novel formulation of its extension to the equations for mean-scale transport -- the equations which must be solved to determine the performance of magnetically confined fusion devices. The second project presents gyrokinetic secondary instability theory as a mechanism to bring about saturation of the basic instabilities that drive gyrokinetic turbulence. Emphasis is put on the ability for this analytic theory to predict basic properties of the nonlinear state, which can be applied to a mixing length phenomenology of transport. The final project is an application of the methods from inertial range understanding of fluid turbulence, to describe the stationary state of fully developed two-dimensional gyrokinetic turbulence. This work explores the relatively new idea of a phase-space cascade, whereby fine scales are nonlinearly generated in both position space and velocity space, and ultimately smoothed by collisional entropy production. This process constitutes the thermodynamic balance which occurs in the true steady state of a turbulent plasma, including those found in fusion devices.

physics.plasm-ph↗

arXiv2009

An Explanation From First-Principle Equations For The Universality of Non-Gaussian Distributions in Edge Plasma Fluctuations

Probability Distributions Functions (PDFs) of fluctuations of plasma edge parameters are skewed curves fairly different from normal distributions, whose shape appears almost independent of the plasma conditions and devices. We start from a minimal fluid model of edge turbulence and reformulate it in terms of uncoupled Langevin equations, admiting analytical solution for the PDFs of all the fields involved. We show that the supposed peculiarities of PDFs, and their universal character, are related to the generic properties of Langevin equations involving quadratic nonlinearities.

physics.plasm-ph↗

arXiv2014

Purely electrical nature of ball lightning (BL), its elementary equations, calculated parameters and conditions of BL possible experimental generation

The nature of ball lightning (BL) is pure electric and can be described by simple equations following to elementary considerations of equality of translational acceleration and velocity of the ions and electrons, a spherical-like dipole BL as a whole and balance of the energy influx of atmospheric electricity and radiation losses. From these equations follows a linear relationship between the size of BL and the tension of the atmospheric field E. A typical size of the fireball (FB) r ~ 5 cm corresponds to the calculated electron temperature T(e) ~ 8000K at a pressure p = 1 at with a horizontal component of the electric field E a few kV/cm. I estimate the energy of BL and characterize the conditions of its possible experimental generation. The estimation is given of the surface tension of BL. The possibility of the "hot" and the most realistic thermodynamic non-equilibrium "cold" BL is discussed. Here we presented preliminary evaluations preceding the more detailed work in Arxiv.org [11].

physics.plasm-ph↗

arXiv2009

Amortissement Landau

Dans cette note nous présentons les principaux résultats du récent travail hal-00376547/arXiv:0904.2760, où le phénomène d'amortissement Landau est pour la première fois établi dans un contexte non linéaire. ----- In this note we present the main results from the recent work hal-00376547 / arXiv:0904.2760, which for the first time establish Landau damping in a nonlinear context.

math.AP↗

arXiv2009

Statistical theory of intermittency in a multi-scale model of MHD and micro-turbulence

Traditionally the effects of MHD instabilities and micro-instabilities on plasma confinement are investigated separately. However, these two instabilities often occur simultaneously, with the overlap of the dynamics on a broad range of spatial scales. It is thus vital to incorporate these instabilities consistently by a proper multi-scale modeling. Furthermore, there has been an overwhelming evidence that the overall transport of heat and particles is significantly influenced by intermittency (or bursty events) caused by coherent structures. A crucial question in plasma confinement is thus the prediction of the probability distribution functions (PDFs) of the transport due to these structures and of their formation. In this paper, we investigate intermittent transport in a multi-scale model by consistently incorporating both tearing instabilities and micro-instability due to pressure gradient.

physics.plasm-ph↗

arXiv2009

Kinetic instability of ion acoustic mode in permeating plasmas

In plasmas with electron drift (current) relative to static ions, the ion acoustic wave is subject to the kinetic instability which takes place if the directed electron speed exceeds the ion acoustic speed. The instability threshold becomes different in the case of one quasi-neutral electron-ion plasma propagating through another static quasi-neutral (target) plasma. The threshold velocity of the propagating plasma may be well below the ion acoustic speed of the static plasma. Such a current-less instability may frequently be expected in space and astrophysical plasmas.

physics.plasm-ph↗

arXiv2009

Probing the sheat electric field using thermophoresis in dusty plasma. Part II: Experimental measurements

A two-dimensional dust crystal levitated in the sheath of a modified Gaseous Electronics Conference (GEC) reference cell is manipulated by heating or cooling the lower electrode. The dust charge is obtained from top-view pictures of the crystal using a previously developed analytical model. By assuming a simple force balance, and measuring the radial confining force, the vertical electric field profile in the sheath is reconstructed. The dust crystal is shown to levitate on the plasma side of the Bohm point. Finally, it is shown that the ion drag plays an important role in the vertical force balance, even for large dust grains.

physics.plasm-ph↗

arXiv2009

Solitary, explosive, rational and elliptic doubly periodic solutions for nonlinear electron-acoustic waves in the earth's magnetotail region

A theoretical investigation has been made of electron acoustic wave propagating in unmagnetized collisionless plasma consisting of a cold electron fluid and isothermal ions with two different temperatures obeying Boltzmann type distributions. Based on the pseudo-potential approach, large amplitude potential structures and the existence of Solitary waves are discussed. The reductive perturbation method has been employed to derive the Korteweg-de Vries (KdV) equation for small but finite amplitude electrostatic waves. An algebraic method with computerized symbolic computation, which greatly exceeds the applicability of the existing tanh, extended tanh methods in obtaining a series of exact solutions of the KdV equation, is used here. Numerical studies have been made using plasma parameters close to those values corresponding to Earth's plasma sheet boundary layer region reveals different solutions i.e., bell-shaped solitary pulses and singularity solutions at a finite point which called "blowup" solutions, Jacobi elliptic doubly periodic wave, a Weierstrass elliptic doubly periodic type solutions, in addition to the propagation of an explosive pulses. The result of the present investigation may be applicable to some plasma environments, such as earth's magnetotail region and terrestrial magnetosphere.

nlin.PS↗

arXiv2009

Nonlinear dynamics experiments in plasmas

The study of nonlinear dynamics or chaos theory has emerged in the last three decades or so as an important interdisciplinary area of research encompassing a wide range of fields like: fluids, plasmas, biomedical sciences, finance, turbulence, astronomy, material sciences, etc. In plasma chaos was first experimentally observed by Boswell. Different other nonlinear dynamics related phenomena like, the intermittency route to a chaos, Homoclinic chaos, Period adding route to chaos and period subtracting, mode locking, period pulling, etc., had been observed by several researchers. In this thesis, we have presented (a) anode glow related observation of chaos to order transition and homoclinic bifurcation; (b) coherence resonance and stochastic resonance; and self organized criticality behavior in glow discharge plasma.

physics.plasm-ph↗

arXiv2009

An Overview of Plasma Confinement in Toroidal Systems

This overview presents a tutorial introduction to the theory of magnetic plasma confinement in toroidal confinement systems with particular emphasis on axisymmetric equilibrium geometries, and tokamaks. The discussion covers three important aspects of plasma physics: Equilibrium, Stability, and Transport. The section on equilibrium will go through an introduction to ideal magnetohydrodynamics, curvilinear system of coordinates, flux coordinates, extensions to axisymmetric equilibrium, Grad-Shafranov Equation (GSE), Green's function formalism, as well as analytical and numerical solutions to GSE. The section on stability will address topics including Lyapunov Stability in nonlinear systems, energy principle, modal analysis, and simplifications for axisymmetric machines. The final section will consider transport in toroidal systems. We present the flux-surface-averaged system of equations describing classical and non-classical transport phenomena. Applications to the small-sized high-aspect-ratio Damavand tokamak will be described.

physics.plasm-ph↗

arXiv2009

Analytic, quasineutral, two-dimensional Maxwell-Vlasov equilibria

Two-dimensional Maxwell-Vlasov equilibria with finite electric fields, axial ("toroidal") plasma flow and isotropic pressure are constructed in plane geometry by using the quasineutrality condition to express the electrostatic potential in terms of the vector potential. Then for Harris-type distribution functions, Ampere's equation becomes of Liouville type and can be solved analytically. As an example, a periodic "cat-eyes" steady state consisting of a row of magnetic islands is presented. The method can be extended to (toroidal) axisymmetric equilibria.

physics.plasm-ph↗

arXiv2010

Vorticity Flow Stabilization of Magnetized Plasmas

Exact solutions of a magnetized plasma in a vorticity containing shear flow for constant temperature are presented. This is followed by the modification of these solutions by thermomagnetic currents in the presence of temperature gradients. It is shown that solutions which are unstable for a subsonic flow, are stable if the flow is supersonic. The results are applied to the problem of vorticity shear flow stabilization of a linear z-pinch discharge.

physics.plasm-ph↗

arXiv2010

Single-Species Weibel Instability of Radiationless Plasma

A Particle-in-Cell (PIC) numerical simulation of the electron Weibel instability is applied in a frame of Darwin (radiationless) approximation of the self-consistent fields of sparse plasma. As a result, we were able to supplement the classical picture of the instability and, in particular, to obtain the dependency of the basic characteristics (the time of development and the maximum field energy) of the thermal anisotropy parameter, to trace the dynamic restructuring of current filaments accompanying the nonlinear stage of the instability and to trace in detail the evolution of the initial anisotropy of the electron component of plasma.

physics.plasm-ph↗

arXiv2010

Shear Flow Stabilization of a z-Pinch Plasma in the Presence of a Radial Temperature Gradient

The previous study regarding the stabilization of a magnetized constant temperature plasma by shear flow with vorticity is extended to a plasma of non-constant temperature, where in the presence of heat source or sinks the thermomagnetic Nernst effect becomes important. Of special interest is what this effect has on the stabilization of a linear z-pinch discharge for which exact solutions are given. Solutions which are unstable for subsonic shear flow become stable if the flow is supersonic.

physics.plasm-ph↗