Effect Of Finite Ion Temperature Research Articles

Ion temperature effects on plasma flow in the magnetic mirror configuration

Effects of finite ion temperature on the plasma flow in the converging–diverging magnetic field, the magnetic mirror, or equivalently, magnetic nozzle configuration are studied using a quasineutral paraxial two-fluid MHD model with isothermal electrons and warm magnetized ions. The ion acceleration was studied with an emphasis on the role of the singularity at the sonic point transition. It is shown that the regularity of the sonic point defines a global solution describing plasma acceleration from subsonic to supersonic velocity. Stationary accelerating solutions were obtained and compared with the time dependent dynamics, confirming that the solutions of the time-dependent equations converge to the stationary solutions and, therefore, are stable. The effects of the ion pressure anisotropy were analyzed using the Chew–Golberger–Low model and its generalization. It is shown that the mirror force (manifested by the perpendicular ion pressure) enhances plasma acceleration. The role of ionization and charge exchange on plasma flow acceleration have been investigated.

Nonlinear dynamics of laser-generated ion-plasma gratings: A unified description.

Laser-generated plasma gratings are dynamic optical elements for the manipulation of coherent light at high intensities, beyond the damage threshold of solid-state-based materials. Their formation, evolution, and final collapse require a detailed understanding. In this paper, we present a model to explain the nonlinear dynamics of high-amplitude plasma gratings in the spatially periodic ponderomotive potential generated by two identical counterpropagating lasers. Both fluid and kinetic aspects of the grating dynamics are analyzed. It is shown that the adiabatic electron compression plays a crucial role as the electron pressure may reflect the ions from the grating and induce the grating to break in an X-type manner. A single parameter is found to determine the behavior of the grating and distinguish three fundamentally different regimes for the ion dynamics: completely reflecting, partially reflecting or passing, and crossing. Criteria for saturation and lifetime of the grating as well as the effect of finite ion temperature are presented.

Finite ion temperature effects on scrape-off layer turbulence

Ion temperature has been measured to be of the same order, or higher, than the electron temperature in the scrape-off layer (SOL) of tokamak machines, questioning its importance in determining the SOL turbulent dynamics. Here, we present a detailed analysis of finite ion temperature effects on the linear SOL instabilities, such as the resistive and inertial branches of drift waves and ballooning modes, and a discussion of the properties of the ion temperature gradient (ITG) instability in the SOL, identifying the ηi=Ln/LTi threshold necessary to drive the mode unstable. The non-linear analysis of the SOL turbulent regimes by means of the gradient removal theory is performed, revealing that the ITG plays a negligible role in limited SOL discharges, since the ion temperature gradient is generally below the threshold for driving the mode unstable. It follows that the resistive ballooning mode is the prevailing turbulence regime for typical limited SOL parameters. The theoretical estimates are confirmed by non-linear flux-driven simulations of SOL plasma dynamics.

Role of finite ion temperature in the generation of field swelling instability

Field swelling instability is one of the most important instabilities in plasmas in which electrons are hotter than ions. In contrast to diamagnetic (mirror) instability belonging to the branch of slow magnetosonic waves, field swelling instability corresponds to the branch of fast magnetosonic waves. The theory of this instability was developed by (Basu and Coppi, 1982, 1984) in the early 1980s in the idealized zero ion temperature limit in the context of the magnetohydrodynamic model. To make the model more realistic, it is necessary to complete it with finite ion temperature effects. In addition, we consider the field swelling theory in the context of a more instructive quasihydrodynamic approach which showed a good performance on examination of the mirror instability. Here, it appears to be necessary to use only the transverse plasma pressure balance condition and Liouville theorem for calculating the transverse pressure variation. This consideration is simpler and clearer and makes it possible to understand in more detail the physical nature of the instability and to prepare the necessary basis for interpreting observational data.

Propagation of shear Alvén waves in two-ion species plasmas confined by a nonuniform magnetic field

Ray tracing calculations are performed for shear Alfvén waves in two-ion species plasmas in which the magnetic field varies with position. Three different magnetic topologies of contemporary interest are explored: a linear magnetic mirror, a pure toroidal field, and a tokamak field. The wave frequency is chosen to lie in the upper propagation band, so that reflection at the ion-ion hybrid frequency can occur for waves originally propagating along the magnetic field direction. Calculations are performed for a magnetic well configuration used in recent experiments [S. T. Vincena et al., Geophys. Res. Lett. 38, L11101 (2011) and S. T. Vincena et al., Phys. Plasmas 20, 012111 (2013)] in the Large Plasma Device (LAPD) related to the ion-ion hybrid resonator. It is found that radial spreading cannot explain the relatively low values of the resonator quality factor (Q) measured in those experiments, even when finite ion temperature is considered. This identifies that a damping mechanism is present that is at least an order of magnitude larger than dissipation due to radial energy loss. Calculations are also performed for a magnetic field with pure toroidal geometry, without a poloidal field, as in experiments being planned for the Enormous Toroidal Plasma Device. In this case, the effects of field-line curvature cause radial reflections. A poloidal field is included to explore a tokamak geometry with plasma parameters expected in ITER. When ion temperature is ignored, it is found that the ion-ion hybrid resonator can exist and trap waves for multiples bounces. The effects of finite ion temperature combine with field line curvature to cause the reflection point to move towards the tritium cyclotron frequency when electron temperature is negligible. However, for ITER parameters, it is shown that the electrons must be treated in the adiabatic limit to properly describe resonator phenomena.

Magnetic island evolution in hot ion plasmas

Effects of finite ion temperature on magnetic island evolution are studied by means of numerical simulations of a reduced set of two-fluid equations which include ion as well as electron diamagnetism in slab geometry. The polarization current is found to be almost an order of magnitude larger in hot than in cold ion plasmas, due to the strong shear of ion velocity around the separatrix of the magnetic islands. As a function of the island width, the propagation speed decreases from the electron drift velocity (for islands thinner than the Larmor radius) to values close to the guiding-center velocity (for islands of order 10 times the Larmor radius). In the latter regime, the polarization current is destabilizing (i.e., it drives magnetic island growth). This is in contrast to cold ion plasmas, where the polarization current is generally found to have a healing effect on freely propagating magnetic island.

Effect of finite ion temperature on arbitrary amplitude dust ion acoustic solitary waves in quantum plasma

Effect of finite ion temperature on the formation of arbitrary amplitude dust ion acoustic solitary waves in unmagnetized quantum plasma is investigated using the Sagdeev’s potential approach. It is found that the ion temperature significantly affects the region of existence and formation of dust ion acoustic solitary waves in quantum plasma. The investigation shows that the solitary structure ceases to exist when the different parameters, viz., temperature, dust density and the soliton velocity cross certain critical values. It is also found that the presence of ion temperature increases the range of wave Mach number from subsonic to supersonic regime both in presence or absence of dust particle density in unmagnetized quantum plasma.

On blob generation mechanisms in tokamak edge plasma

The four-wave interaction technique is used to demonstrate the impact of primary electrostatic (drift wave) turbulence on the generation of large-scale electromagnetic structures (blobs). The analysis includes finite ion temperature effects and the associated diamagnetic contributions to the Reynolds stress. The impact of equilibrium plasma density variation on blob propagation is also discussed.

Generation of electromagnetic structures via modulational instability of drift waves

Generation mechanism for large scale electromagnetic structures (blobs) is considered by employing the technique of four-wave interactions (modulational instability). It is shown that primary electrostatic turbulence may generate elongated electromagnetic structures with poloidal modulations. Such structures are principally related to drift-Alfvén waves. The analysis fully takes into account finite ion temperature effects and associated diamagnetic contributions to Reynolds stress. The turbulent generation of blobs has instability growth rates which scale similar to the zonal flow instabilities, γ∼⟨qṼ⟩, where q is a characteristic wave vector of large scale modes, and Ṽ is a characteristic amplitude of the velocity of turbulent fluctuations. This analysis is shown to be fully consistent with results of an earlier analysis by using the wave kinetic equation.

Consequences of finite ion temperature effects on parametric instabilities of circularly polarized Alfvén waves

Parametric instabilities of finite amplitude, circularly polarized, parallel propagating Alfvén waves in a homogeneous plasma is discussed analytically, taking into account the ion Landau damping and the ion finite Larmor radius (FLR) effects. A hybrid kinetic fluid model is systematically derived from one‐dimensional Vlasov equation for longitudinal ion motion and the FLR‐Hall magnetohydrodynamic (MHD) equations for transverse directions. The longitudinal kinetic effects are retained in the model, whereas transverse kinetic effects such as ion cyclotron damping is neglected. Validity of the model is justified as far as the collisionless damping is concerned, since the ion cyclotron damping for typical quasi‐parallel Alfvén waves in the solar wind is considered to be negligibly small. As already shown in a number of past studies, inclusion of the kinetic effects let some new instabilities emerge, while that reduces the growth rates of fluid instabilities in general. Damping rates computed by a model using collision‐like (local) damping terms deviate from results of the present model, suggesting the importance of using the exact Landau‐type interactions. Furthermore, as a consequence of the FLR effects, the growth rates of the fluid decay and beat instabilities of the left‐hand (right‐hand) polarized mode are reduced more strongly (weakly) in the FLR‐Hall‐MHD model (FHM model) than in the Hall‐MHD model (HM model). A hybrid simulation is carried out to confirm that the FHM model is in better agreement than the HM model with the simulation results. When the initial parent wave amplitude is relatively small, the simulation results quantitatively agree with the linear analysis. Furthermore, some arguments are given to the observed ion relaxation and the energy oscillation of the parent waves observed in the hybrid simulations. Here again, quantitatively better explanation is obtained by using the FHM model rather than the HM model, suggesting that it is important to include the FLR effects for correctly describing the Alfvén wave parametric instabilities in finite ion beta plasmas, such as the solar wind near the Earth and the foreshock plasma.

Zonal flow and field generation by finite β drift waves: Finite ion temperature effects

The generation of zonal flows and zonal fields by finite β drift waves in plasmas with finite ion temperature Ti is investigated. This work extends our earlier work with zero ion temperature. The growth rate of the zonal flow and field is enhanced by finite Ti effects. This leads to a reduction in the critical electron temperature derived earlier for triggering low to high transitions in tokamak plasmas.

511 サーマルプローブを用いたイオン温度計測の新しいアプローチ(GS-6 液滴・計測)

Plasma is generally in the non-thermal equibilium, and its components, ion and electron, have different temperatures. Though Langmuir probe method is widely used to measure electorn temperature, ion temperature is difficult to deduce with it. In this paper, we propose the thermal probe as a new tool for ion temperature measurement. Firstly the effect of finite ion temperature onto analytical heat flux formula in the sheath theory. Then the procedure to deduce the ion temperature from heat flux data is presented. Finally we make a prototype of the thermal probe and test it with the glow discharge plasma.

Finite ion temperature effects on oblique modulational stability and envelope excitations of dust-ion acoustic waves

Theoretical and numerical investigations are carried out for the amplitude modulation of dust-ion acoustic waves (DIAW) propagating in an unmagnetized weakly coupled collisionless fully ionized plasma consisting of isothermal electrons, warm ions and charged dust grains. Modulation oblique (by an angle $\theta$ ) to the carrier wave propagation direction is considered. The stability analysis, based on a nonlinear Schrodinger-type equation (NLSE), exhibits a sensitivity of the instability region to the modulation angle $\theta$ , the dust concentration and the ion temperature. It is found that the ion temperature may strongly modify the wave’s stability profile, in qualitative agreement with previous results, obtained for an electron-ion plasma. The effect of the ion temperature on the formation of DIAW envelope excitations (envelope solitons) is also discussed.

Effect of finite ion temperature on large-amplitude solitary kinetic Alfvén waves

By using the Sagdeev pseudopotential method, solitary kinetic Alfvén waves (SKAW) are studied in a low-β plasma, taking into account the electron inertia and ion temperature. Solitary wave solutions, and the electric and magnetic fields, are obtained using the knowledge of the pseudopotential analysis in plasma dynamics. It is found that both hump and dip solitons exist for SKAWs, conforming to the results of Freja scientific satellite observations in space.

Effect of finite ion temperature on ion acoustic solitary waves in a two-temperature electron-plasma system

The pseudopotential for a plasma with two electron temperatures is derived without neglecting electron inertia and ion temperature. For the zero-temperature case our analytical results agree with the published numerical results. The conditions for existence of solitary waves are discussed. It is found that the effect of ion temperature is to increase the amplitude of the soliton, and also to reduce the region of existence of solitary waves. Resume : Sans negliger les effets de la masse electronique ni de la temperature ionique, nous obtenons le pseudopotentiel pour un plasma a deux temperatures. A temperature nulle, notre expression analytique agree avec les resultats numeriques deja publies. Nous etudions les condition d’existence d’ondes solitaires. Notre theorie predit que l’augmentation de la temperature ionique accroit l’amplitude du soliton mais reduit la region ou peuvent exister des ondes solitaires. [Traduit par la redaction]

Effect of finite ion temperature on ion acoustic solitary waves in a two-temperature electron-plasma system

Effect of finite ion temperature on ion acoustic solitary waves in a two-temperature electron-plasma system

Ion acoustic solitons in a weakly relativistic magnetized warm plasma.

The oblique propagation of nonlinear ion acoustic solitary waves (solitons) in a magnetized low-\ensuremath{\beta}, weakly relativistic warm plasma is examined by the Korteweg--de Vries equation. Two types of modes (fast and slow ion acoustic modes) exist in the plasma. The fast mode corresponds to the propagation of compressive solitons, whereas the rarefactive solitons exist for the slow mode. The amplitude and energy of both types of solitons increase with the angle between the wave vector and magnetic field and also with the relativistic ion drift velocity. The effect of finite ion temperature is to decrease the amplitude of the soliton and to increase its width. The strength of the magnetic field weakens the soliton energy and the width becomes smaller. \textcopyright{} 1996 The American Physical Society.

The effect of finite ion temperature on solitary waves in a plasma with an ion beam

The effect of finite ion and beam ion temperature on the conditions for existence of solitary waves in a beam plasma system is investigated. It is found that a finite ion temperature drastically reduces the region in which solitary waves can exist. This work can be considered as an extension of the work done by Zhang and Kuehl [Phys. Fluids B 4, 2517 (1992)].

Neutral plasma solution in a beam generated plasma using a one dimensional fluid model

A steady state plasma is generated between two electrodes by an energetic electron beam, which is emitted from the cathode. The beam-generated plasma is studied using one-dimensional fluid equations for both the plasma electrons and ions, and the beam electrons. The singularities in the three-fluid equations are discussed, and removed by the assumption of neutrality. The neutral approximation, which contains equations for the plasma electrons and ions plus the beam electrons are solved by an analytic approach. Effects of finite ion temperature, collisons between plasma particles and neutrals, and Coulomb collisions are included, and we also discuss the use of velocity dependent collisions between ions and neutrals. The effect of momentum transfer from the high energetic electron beam to the bulk-plasma is included.

Obliquely propagating ion-acoustic double layers in a multicomponent magnetized plasma

Considering the appropriate coordinate transformation and charge separation effect, the reductive perturbation method is used to derive a mKdV equation for a multi-component magnetized plasma having two Maxwellian electron distributions and two warm adiabatic ion distributions. The double layer solution of the mKdV equation is discussed in detail. It is found that the width of the double layer increases as we increase the obliqueness θ, where θ is the angle between wave vector and magnetic field, while the effect of obliqueness on the amplitude of the double layer is negligible. The effect of finite ion temperature is to increase (decrease) the amplitude of compressive (rarefactive) double layer and decrease (increase) its width. The effect of the concentration of second ion impurity, concentration and the temperature ratios of two electron species on the amplitude and width of the double layer is also studied.