Multi-ion Plasma Research Articles

Overview of Large Helical Device experiments of basic plasma physics for solving crucial issues in reaching burning plasma conditions

Abstract Recently, experiments on basic plasma physics issues for solving future problems in fusion energy have been performed on a Large Helical Device. There are several problems to be solved in future devices for fusion energy. Emerging issues in burning plasma are: alpha-channeling (ion heating by alpha particles), turbulence and transport in electron dominant heating helium ash exhaust, reduction of the divertor heat load. To solve these problems, understanding the basic plasma physics of (1) wave–particle interaction through (inverse) Landau damping, (2) characteristics of electron-scale (high-k) turbulence, (3) ion mixing and the isotope effect, and (4) turbulence spreading and detachment, is necessary. This overview discusses the experimental studies on these issues and turbulent transport in multi-ion plasma and other issues in the appendix.

Collision properties of overtaking magnetosonic solitary waves in the ionospheric multi-ion plasmas

Collision properties of overtaking magnetosonic solitary waves in the ionospheric multi-ion plasmas

Quadruple Beltrami field structures in electron–positron multi-ion plasma

Abstract A quadruple Beltrami (QB) equilibrium state for a four-component plasma that consists of inertial electrons, positrons, lighter positive (H +) ions and heavier negative ions O 2 − $\left({\mathrm{O}}_{2}^{-}\right)$ is derived and investigated. The QB relaxed state is a linear superposition of four distinct single Beltrami fields and provides the possibility of the formation of four self-organized vortices of different length scales. In addition, robust magnetofluid coupling characterizes this non-force-free state. The analysis of the QB state also shows that by adjusting the generalized helicities and densities of plasma species, the formation of multiscale structures as well as the paramagnetic and diamagnetic behavior of the relaxed state can be controlled.

Multi-ion magnetized sheath properties with non-extensive electron distribution

Magnetized plasma sheath plays an important role in semiconductor processing, material surface modification, film deposition, etc. In plasma experiments and discharge applications, multi-ion plasma consisting of more than two kinds of ions often exists. For a long range interacting plasma system, non-Maxwellian electrons can be described by the non-extensive distribution of Tsallis. In this work, a fluid model with one-dimensional spatial coordinates and three-dimensional velocity coordinates is established for the multi-ion plasma sheath. It is assumed that the electron velocity in the sheath follows a non-extensive distribution, and the background helium ions and different kinds of impurity ions are magnetized in a magnetic field with a certain tilt angle. The effects of non-extensive parameters, impurity ions and oblique magnetic field on the number density, velocity, wall potential and kinetic energy of ions in the multi-ion magnetic sheath are investigated by numerical simulation. The results show that in the helium-hydrogen or helium-argon mixed plasma sheath, the ionic velocity along the vertical wall direction decreases with the increase of the non-extensive parameters, the number density of ions and electrons in the sheath, the sheath thickness , and the kinetic energy of ions at the wall decrease. When the concentration of impurity ions increases, the kinetic energy of ions on the wall is independent of the type of ions. With the increase of magnetic field intensity, the number density of helium ions and the velocity along the vertical wall fluctuate along the sheath edge, and the fluctuation amplitude increases with the decrease of non-extensive parameters, while the heavy ions have no obvious fluctuation. In addition, the effects of the types and concentrations of impurity ions on the related properties of the sheath are also analyzed. With the increase of the magnetic field intensity, the number density and the velocity along the vertical wall direction fluctuate at the sheath edge, and the fluctuation amplitude increases with the decrease of the non-extensive parameter, whereas there are no significant fluctuations for heavy ions. In addition, when impurity ions are heavy ions, the absolute value of wall potential increases with the increase of impurity ion concentration and the decrease of non-extensibility parameters, and the kinetic energy of background ions increases at the wall surface. When the impurity ion is a light ion, the absolute value of the wall potential decreases with the increase of the impurity ion concentration and the decrease of the non-extensibility parameter, and the kinetic energy of the background ion at the wall decreases.

Normal form for bifurcations of ion acoustic traveling waves in positive-negative ion species plasmas

The normal form for saddle-node and transcritical bifurcation of nonlinear ion-acoustic waves is derived in complex negative-positive plasmas. The physical parameters of four different kinds of multi-ion plasmas which mainly comprise of positive ions (i.e. Xe+ and Ar+) with a minority constituent of negative ions (i.e. and F −), inspired from the experimental studies, are examined on the types of bifurcations and nonlinear wave profiles. We find that such multi-ion plasmas admit transcritical bifurcation preceding the onset of saddle-node bifurcation. The fractional concentration of negative ions controls the dynamics of ion acoustic traveling waves and causes the appearance of solitary structures and supernonlinear periodic waves. When two nonlinear waves disappear via a saddle-node bifurcation on increasing the negative ion concentration, a nonlinear periodic wave is formed. Further, we reveal critical values of ion density marking the transition between nonlinear modes. Such critical points that can be detected analytically give rise to the propagation of new solitary structures. The results obtained here not only limited to laboratory plasmas, but can also be applied to explain wave excitations in space plasma environments.

Coexistence of positive and negative polarity solitons, double layers and supersolitons in electron-positron multi-ion plasmas

In order to analyze the nonlinear propagation of arbitrary amplitude ion-acoustic waves, the Sagdeev pseudopotential formalism is used to a four-component multi-ion plasma made up of inertial light positive ions, heavy negative ions, inertialess nonextensive electrons, and positrons. At first, we derived the expression of Sagdeev Pseudopotential for our plasma model and then numerically investigated the condition for the existence of several nonlinear structures such as solitons, double layers, supersolitons, etc. Based on numerical simulation, it is observed that within a certain range of parameters, our plasma model allows compressive as well as a rarefactive soliton, flat-top soliton, double layer, and supersoliton solutions. Great emphasis is placed on the determination of the existence regions for both solitons and supersolitons in the parameter space. Also, various nonlinear structures are explored to examine the effects of various plasma properties, such as the nonextensivity parameter, Mach number, etc. The findings of the current investigations may be helpful for comprehending significant features of ion-acoustic wave structures in space plasmas such as earth's ionosphere, cometary tails, etc., and laboratory plasmas like laser-plasma interaction research.

Closure theory for high-collisionality multi-ion plasmas

A general formalism is developed to construct and solve a system of linearized moment equations for parallel and perpendicular closures in high-collisionality plasmas. It is applicable for multiple ion species with arbitrary masses, temperatures, charges, and densities. The convergence of closure coefficients is evaluated by increasing the number of moments from 2 to 32 for scalar, vector, and rank-2 tensor moments. As an example, the complete set of closure coefficients for a deuterium-carbon plasma over the entire Hall parameter range is presented. The closure coefficients at various temperature ratios show that the one-temperature closure coefficients can differ significantly from the two-temperature coefficients.

Anomalous coupling in radiation mediated shocks

We summarize recent attempts to unravel the role of plasma kinetic effects in radiation mediated shocks. Such shocks form in all strong stellar explosions and are responsible for the early electromagnetic emission released from these events. A key issue that has been overlooked in all previous works is the nature of the coupling between the charged leptons, that mediate the radiation force, and the ions, which are the dominant carriers of the shock energy. Our preliminary investigation indicates that in the case of relativistic shocks, as well as Newtonian shocks in multi-ion plasma, this coupling is driven by either, transverse magnetic fields of a sufficiently magnetized upstream medium, or plasma microturbulence if strong enough magnetic fields are absent. We discuss the implications for the shock breakout signal, as well as abundance evolution and kilonova emission in binary neutron star mergers.

Charged-particle transport models for global models

This work analyses the influence of different charged-particle transport models on the global modeling of low-temperature plasmas. The simulations use the LisbOn KInetics simulation tool, calculating the charged-particle loss frequency due to transport with various formulations, categorized into two large groups: ambipolar-based and h-factor transport models. The models are applied to the description of (i) a DC discharge in oxygen (as example of an electronegative multi-ion plasma), at low to intermediate pressures, adopting a validated kinetic scheme as reference model; (ii) a microwave discharge in helium (as example of an electropositive multi-ion plasma), from low to atmospheric pressures, proposing and validating an updated kinetic scheme that bridges two previous models, adjusted separately for low to intermediate pressures and for atmospheric pressure. The analysis shows that using different charged-particle transport models can result in uncertainties of 20%–60% and 8%–115% in the discharge characteristics of oxygen and helium, respectively, with larger dispersion at low pressure and low electron density. The spreading in the results is observed also in the densities of the main plasma species, corresponding to uncertainties up to and within 50%–150% in oxygen and helium, respectively. Since transport accounts for more than of total charge losses, this mechanism should always be part of the quantitative sensitivity analysis of a kinetic scheme, considering several models with different validity domains, according to the electro-positive/-negative single-/multi-ion plasma under study and the low/high pressure conditions considered.

Transitional properties of nonlinear traveling waves at the transcritical bifurcation point in a plasma with positive–negative ions

The bifurcation types and transitional properties of nonlinear ion-acoustic traveling waves have been explored in detail for a complex plasma with positive-negative ions and nonthermal electrons. The existence domain of stationary points and bifurcation responses are investigated on the fixed points-negative ion density plane. It is shown that both mass ratio of the positive to negative ions and the negative ion concentration play a pivotal role in the occurrence of bifurcations and transition between nonlinear waves. Under certain circumstances, we show that multi-ion plasma system admits transcritical bifurcation preceding the onset of saddle-node bifurcation. It is found that a sudden emergence of spike-like wave and transition between solitary and periodic waves occur at the critical point of transcritical bifurcation. The effects of plasma parameters on the bifurcation regions and the onset of transition between solitary waves and nonlinear periodic waves are investigated. We also show a novel kind of solitary structure at the bifurcation point with fatter tails compared to regular solitons. The present model is used to investigate the dynamical behavior of ion-acoustic waves in the () and () plasmas which are found in the D- and F-regions of the Earth's ionosphere, and also in the () experimental plasma.

Impact of Heavy Ions on the Structure of Current Sheets in the Gravity Field of Exoplanets and Stars

Boundary current sheets (CSs) can be formed in collisionless space plasmas in the environment of exoplanets and cold stars. Usually they represent curved surfaces carrying the electric current analogous to the well-known planetary ionospheres, magnetopauses, or stellar coronas surrounding celestial bodies. At smaller local scales, some of them can be imagined as planar current layers of a finite scale located parallel to the surface of a celestial object and, correspondingly, perpendicular to the direction of the gravitational force. In some cases, this force crossed with magnetic field can influence the dynamics of charged particles in CSs and substantially change the structure of both the current layer and the magnetic field. We have generalized our prior model, taking into account a multi-ion plasma composition and a magnetic field configuration with a shear. It is shown that, due to the drift motion of plasma particles in the crossed gravitational and magnetic fields, the structure of CSs becomes more complex, accruing asymmetric and shifted profiles of the current and plasma densities that depend on dominating current carriers and the characteristics of the magnetic shear. We discuss possible applications of the results to the interpretation of observations of boundary layers in different space plasmas.

Existence and propagation characteristics of ion-acoustic Kadomtsev–Petviashvili (KP) solitons in nonthermal multi-ion plasmas with kappa distributed electrons

The dynamics of two dimensional Kadomtsev–Petviashvili (KP) electrostatic solitary waves (ESWs) propagating in multi-ion unmagnetized plasma is investigated, in the presence of energetic (nonthermal) electrons. Two distinct ion components are considered as inertial fluids, while inertialess electrons are characterized by an excess superthermal population described by a kappa distribution. The primary (heavier and cold) ion population is assumed to be positively charged, while the charge and sign of the (lighter and warm) ions is left arbitrary in the model. A linear analysis reveals the existence of two harmonic modes propagating with different phase speeds, identified as slow and fast ion-acoustic waves i.e., SIAW, FIAW respectively. Nonlinear analysis, based on a multiscale (reductive perturbation) technique, leads to a two-dimensional Kadomtsev–Petviashvili (KP) equation for the electrostatic potential. Pulse-shaped electrostatic potential solitary wave solutions and associated bipolar electric field structures are obtained analytically as well numerically. A parametric investigation reveals that, if both ion species are positively charged, then either negative or positive polarity electrostatic potential solitary waves structures may occur for the slow (SIAW) mode case (only), depending on the light ion density and temperature. On the other hand, considering a negatively charged light (warm) ion fluid case, then solitary structures of SIAW are formed of positive polarity (only), while their fast counterpart FIAW is of opposite (negative) polarity. The (O, H) multi-ion plasma is considered and parametric dependence of nonlinear electrostatic solitary wave characteristics (amplitude, width) on the intrinsic plasma configurational parameters i.e., light-to-heavy ion density and light ion to electron temperature ratios and nonthermal electrons spectral index kappa is investigated.

Moment-Fourier approach to ion parallel fluid closures and transport for a toroidally confined plasma

A general method of solving the drift kinetic equation is developed for an axisymmetric magnetic field. Expanding a distribution function in general moments, a set of ordinary differential equations is obtained. Successively expanding the moments and magnetic-field involved quantities in Fourier series, a set of linear algebraic equations is obtained. The set of full (Maxwellian and non-Maxwellian) moment equations is solved to express the first-order density, temperature, and flow velocity in terms of radial gradients of the zeroth-order pressure and temperature. Closure relations that connect parallel heat flux density and viscosity to the radial gradients and parallel gradients of temperature and flow velocity are also obtained by solving the non-Maxwellian moment equations. The closure relations combined with the linearized fluid equations reproduce the same solution obtained directly from the full moment equations. The method can be generalized to derive closures and transport for an electron-ion plasma and a multi-ion plasma in a general magnetic field.

How to evaluate neoclassical transport coefficients by a single δf simulation

The δf method is extended to calculate all possible components of neoclassical transport matrices, including non-diagonal components and interspecies components of any species combinations in an arbitrary magnetic field configuration, by a single simulation. The method is implemented in a global neoclassical code FORTEC-3D and applied to cases of multi-ion species plasmas in a tokamak and a helical configuration, respectively. The results are benchmarked against analytic solutions and local simulation results. It is found that the results obtained with the newly developed method provide reliable solutions that satisfy the Onsager symmetry relation as well as the intrinsic ambipolarity in a tokamak configuration.

Proton and Helium Heating by Cascading Turbulence in a Low-beta Plasma

How ions are energized and heated is a fundamental problem in the study of energy dissipation in magnetized plasmas. In particular, the heating of heavy ions (including 4He2+, 3He2+, and others) has been a constant concern for understanding the microphysics of impulsive solar flares. In this article, via two-dimensional hybrid-kinetic particle-in-cell simulations, we study the heating of helium ions (4He2+) by turbulence driven by cascading waves launched at large scales from the left-handed polarized helium ion cyclotron wave branch of a multi-ion plasma composed of electrons, protons, and helium ions. We find significant parallel (to the background magnetic field) heating for both helium ions and protons due to the formation of beams and plateaus in their velocity distribution functions along the background magnetic field. The heating of helium ions in the direction perpendicular to the magnetic field starts with a lower rate than that in the parallel direction, but overtakes the parallel heating after a few hundreds of the proton gyro-periods due to cyclotron resonances with mainly obliquely propagating waves induced by the cascade of injected helium ion cyclotron waves at large scales. There is, however, little evidence for proton heating in the perpendicular direction due to the absence of left-handed polarized cyclotron waves near the proton cyclotron frequency. Our results are useful for understanding the preferential heating of 3He and other heavy ions in the 3He-rich solar energetic particle events, in which helium ions play a crucial role as a species of background ions regulating the kinetic plasma behavior.

A new quasilinear saturation rule for tokamak turbulence with application to the isotope scaling of transport

A new quasilinear saturation model SAT3 has been developed for the purpose of calculating radial turbulent fluxes in the core of tokamak plasmas. The new model is shown to be able to better recreate the isotope mass dependence of nonlinear gyrokinetic fluxes compared to contemporary quasilinear models, including SAT2 (Staebler et al 2021 Nucl. Fusion 61 116007), while performing at least as well in other key equilibrium parameters. By first quantifying the isotope scaling of gyrokinetic flux spectra, it is shown that the deviation from the gyroBohm scaling of fluxes originates primarily in the magnitude of the saturated potentials. Using this result SAT3 was formulated using observations made from gyrokinetic data, including a novel and robust relation between the 1D potential spectrum and the radial spectral widths. This serves to define the underlying functional forms of SAT3 before then connecting to the linear dynamics, including a difference in saturation level between ITG- and TEM-dominated turbulence, with the resulting free parameters having been fit to a database of high-resolution nonlinear CGYRO simulations. Additional features outside of the database are included, including E × B shear and multi-ion plasma capability. The methodology used in the development of SAT3 represents an algorithm which can be used in the improvement and generation of future saturation models.

Multiscale structures in three species magnetoplasmas with two positive ions

The self-organization in a multi-ion plasma composed of electrons and two species of positively charged ions is investigated. It is shown that when canonical vorticities and velocities of all the plasma fluids are aligned, the magnetic field self-organizes to Quadruple Beltrami state (superposition of four Beltrami fields). The self-organized magnetic and velocity fields strongly depend on the relative strengths of the generalized vorticities, flows, inertia and densities of the plasma species. Thus, it is possible to generate a wide variety of multiscale magnetic field and flow structures. It is also shown that relaxed magnetic fields and velocities can vary on vastly different length scales simultaneously and are coupled together through singular perturbation generated by Hall effect. In this multi Beltrami self-organized states, then, the dynamo mechanism emerges naturally. The scale separation also suggests the heating of the plasma through a dissipative process. The work could be useful to study the dynamics and morphology of the multiscale magnetic field configurations in laboratory and astrophysical plasmas.

Characteristics of plasma sheath in multi-component plasmas with three-ion species

The plasma sheath of a three ion species plasma is studied numerically, relying on the results of the experiment by Yip et al. (Phys. Plasmas 23:050703 (2016) to measure the positive ion velocities at the sheath edge. The positive ion species (Ar^+, Kr^+, and Xe^+) are assumed to be singly charged and to be characterized by the same temperature. It is shown that the sheath characteristics, viz. the particle number densities, the electrostatic potential and the space charge density profile in the sheath all depend on the Kr^+ concentration that is gradually added to the argon-xenon plasma as the third positive ion species. Also, the effect of ion-neutral collisions on the sheath properties is investigated numerically. Our results may be extended to a multi-ion plasma with more than two species of positive ions.

Relaxation of multi-ion plasmas in an internal conductor

The possibility of the formation and characteristics of the relaxed structures in the multi-ion magnetized plasmas consisting of heavy ions, light ions, and inertia-less electrons have been explored. Using the vortex dynamic equations with the current density, the system is relaxed to triple Beltrami states. Solutions of the relaxed states are determined in two different cases: (i) simple slab geometry and (ii) slab geometry with an internal conductor. The impact of Beltrami parameters and density ratios of the plasma components on the formation of equilibrium structures in both geometries has been studied. Moreover, we also highlight the equivalences of both geometries (simple slab geometry and a slab geometry with an internal conductor). This investigation will be useful for studying and understanding the relaxed structures in different astrophysical objects such as solar wind, Earth’s ionosphere, near-Earth plasmasheet, upper ionosphere, and Saturn and in the laboratory plasmas having two positively charged ions of different masses. Moreover, this work will be helpful in describing the underlying physics of the relaxed structures. These structures are developed in different astrophysical bodies that revolve around the planet such as Jupiter magnetosphere.

Two-Dimensional Electrostatic Solitary Waves in Multi-Ion Plasmas in the Presence of Suprathermal (Kappa Distributed) Electrons – Existence, Propagation Characteristics and Application to the Ionosphere

Two-Dimensional Electrostatic Solitary Waves in Multi-Ion Plasmas in the Presence of Suprathermal (Kappa Distributed) Electrons – Existence, Propagation Characteristics and Application to the Ionosphere