Two-ion Plasma Research Articles

Observation of ion-beam instability in a two-ion species plasma

Observation of ion-beam instability in a two-ion species plasma

Wall Effects on the Propagation of Compressional Alfv�n Waves in a Cylindrical Plasma with Two-Ion Species

The dispersion relations for the compressional Alfven waves in a two-ion species plasma of deuterium and hydrogen are calculated for a configuration which includes a vacuum layer between the cylindrical plasma and the conducting wall. The presence of the vacuum layer strongly affects the propagation of the compressional Alfven wave, permitting some branches to propagate and penetrate the plasmacolumn over most frequencies in the ion-cyclotron range. Basic Alfven-wave propagation and heating experiments in two-ion species consequently should be possible using tokamak and mirror devces with minor radii smaller than the Alfven wavelength.

A numerical investigation of current-driven instabilities near the ion-ion hybrid frequency

A dispersion relation for electrostatic waves in a current-carrying, resistive, magnetized, two-ion plasma has been solved numerically for a range of parameter values. The behaviour of the resistive ion-ion hybrid instability is described and in addition a two-stream ion-ion hybrid instability is identified.

Numerical calculation of ICRF waves in tokamak plasmas

The ICRF (ion cyclotron range of frequency) wave in a two-ion component plasma in a tokamak is studied by solving the wave propagation equation based on a cold plasma model. The numerical solution for the three-dimensional structure is obtained by use of the finite difference method. The numerical method is described and its numerical accuracy is examined.

External excitation of ion cyclotron drift waves in a two-ion species plasma

Ion cyclotron drift waves propagating across a density gradient and a magnetic field have been excited externally in a two-ion species plasma, with its concentration ratio controlled. The measured dispersion relations agree with the theoretical predictions.

Development of a Plasma ion analyzer.

A Plasma ion analyzer for measuring mass, density and temperature of ions in a multi-ion species plasma has been developed. The analyzer is a simple and compact mass spectrometer where the magnetic field confining a plasma is used directly for the 180° magnetic deflection of accelerated ions. The numerical simulations of the analyzer characteristics provide the useful guiding principles for the data analysis as well as the optimum analyzer design. The test measurements of a two-ion species plasma has been made, and the results are in good agreement with the theoretical predictions and the spectroscopic measurements.

Ion acoustic turbulent resistivity of a two-ion plasma

A multicomponent plasma consisting of two-ion species having different mass and temperature is considered. Linear and non-linear dispersion relations have been derived. These are used to study the effect of turbulent fluctuations on the plasma resistivity. Results have been applied to the cases of a hydrogen-helium and a hydrogen-argon mixture. It is seen that the resistivity increases or decreases significantly with the addition of a light ion impurity depending upon temperature and mass ratio.

Ponderomotive force of an ion cyclotron wave in a two-ion species plasma

The ponderomotive force experienced by an ion in a left circularly polarized wave changes sign as the frequency increases from below to above the ion cyclotron frequency. If the wave frequency is chosen to lie between the ion cyclotron frequencies of two different isotopes, then the ponderomotive force tends to separate the two species in space. As a result, the index of refraction is modified. Self-consistent solutions of the nonlinear wave equation taking into account both effects are obtained analytically and numerically. The ratio of the densities of the two ions is proportional to exp[mE2(z)/4γ(1−γ)αB20kTi], where E(z) is the amplitude of the wave, B0 is the magnetic field, and Ti is the temperature of the ions, m=2m1m2/(m1+m2), α=(m1−m2)/(m1+m2), and γ=(ω−Ω2)/(Ω1−Ω2).

Fast-Wave Heating of Two-Ion Plasmas in the Princeton Large Torus through Minority-Cyclotron-Resonance Damping

Strong minority proton heating is produced in PLT through ion cyclotron resonance damping of fast waves at moderate rf power levels. In addition to demonstrating good proton confinement, the proton energy distribution is consistent with Fokker--Planck theory which provides the prescription for extrapolation of this heating regime to higher rf power levels.

Ion-acoustic resistivity of a multicomponent plasma

The expression for a general dispersion relation in the presence of ion-acoustic turbulence has been derived for a two-ion plasma and is used to study its effect on the turbulent resistivity. Results have been applied to the case of a hydrogen-helium plasma mixture. The effect of the addition of light ions on the variation of the drift velocity and resistivity of the plasma with T e T i is investigated for quasi-stationary fluctuation levels.

ICRF HEATING IN TOKAMAKS

The current status of ICRF heating of Tokamak plasmas is described. Two aspects of the subject are discussed: the physics of wave damping and the evaluation of ion heating. Recent experiments in several Tokamak devices at the second harmonic of the deuteron cyclotron frequency have exhibited large discrepancies between the observed and predicted wave damping. A possible explanation, based upon enhanced cyclotron harmonic damping due to the proximity of the two-ion hybrid and cyclotron resonance layers, is discussed. The boundary value problem for fast wave propagation in an inhomogeneous two-ion plasma has been solved explicitly to obtain the wave field structure. For modest proton concentrations (less than 5 percent) a steep gradient in the left-hand polarized electric field is found in the region between the hybrid and cyclotron resonant layers. This gradient appears to provide sufficient enhancement of the second harmonic damping strength to account for the observed discrepancies. However, a reliable measurement of the proton concentration is needed to choose between the two possibilities. Ion heating was examined in detail in recent experiments in the ATC device. It is shown that ICRF heating can heat the bulk of the ions in the core of a Tokamak plasma with efficienciesmore » ranging from 10 to 40 percent, without causing any significant change in the ion energy confinement.« less

Stability regions and growth rates for a two-ion component plasma, unmagnetized

A uniform plasma, with a thermal core and a warm ring, in velocity space, is examined for instabilities. The parameters are the ratio of ring to core densities, the ratio of core thermal velocity to ring peak velocity, and the ring thermal velocity. The boundary between stable and unstable distributions is given, as dependent on these parameters, as obtained from the Penrose criterion. In addition, the upper and lower bounds on the wavenumbers (kmax, kmin) are found for typical distributions, as well as growth rates, ωi(k). For either dense ring or dense core distributions, the distributions are unstable for (vt/vr) ≲0.1, independent of the thermal spread of the ring, where vt is the core thermal spread, and vr is the ring peak speed. For more equal ring and core densities, the stability boundary moves to larger values, dependent on the thermal spread of the ring. Growth rates of ωi≈0.01 to 0.1 ωp are typical. Application of these results to magnetized plasmas is given.

Observation of Two Ion-Acoustic Waves in an Argon-Helium Plasma

The propagation of ion-acoustic waves in two-ion plasmas is investigated both experimentally and theoretically when the ratio of electron to ion temperature is 10 to 15. Although a single mode is observed in an argon-neon plasma, two modes are detected in an argon-helium plasma.

Eigenvalue formulation for linear modes in the homogeneous multiple-fluid plasma

The linearized equations of the multiple-fluid model, including an isotropic pressure law, of a plasma are cast into a concise form directly suited for the calculation of the full set of characteristic modes of the system. A fully ionized, homogeneous, drift-free, magnetized plasma having an arbitrary number of finite-temperature components is considered. For oscillations of the form exp[i (k⋅r−ωt)], the three separate problems of determining ω vs (k,ϑ), k vs (ω,ϑ), and kx vs (ω,kz) are treated by formulating the set of algebraic equations into matrix eigenvalue problems for which the eigenvalues are ω2, k2, and k2x, respectively. For each of the three cases, an example of the results of numerical evaluation of the eigenvalues is presented for an electron, two-ion species plasma. A method is described which may be used for calculating, directly within the eigensystem formulation, the group velocity of the characteristic modes.

Maximization in the damping rate of the ion acoustic wave in a two-ion plasma

The characteristics of dispersion and Landau damping of ion acoustic waves are experimentally investigated in an argon-helium plasma with varying ion composition ratio. The dispersion relations change continuously from the argon mode to the helium mode. The damping rate has a maximum when the ion number density ratio (r = nHe/nA + nHe) is about 0.08. This maximum is attributed to the resonance of helium ions with the argon mode ion acoustic wave and is consistent with theoretical predictions.

Multi-ion plasmas in astrophysics

The steady-state motion of a quasi-neutraln-ion plasma is investigated using a fluiddynamical model. The main results obtained are that there are only two distinct ways in which such a plasma can make a transition from a subsonic state to a supersonic one. There is one unique possibility for which there exists one critical point where all the ion gases have their Mach numbers exactly to unity and where the individual ion forcing functios (the inhomogeneous terms) are non-zero but linearly related to each other. The other possibility which we find is that at a critical point all inhomogeneous terms are identically equal to zero and there exist as many critical points as there exist simultianeous zeros of the ion forcing functions. These results are necessary and sufficient forn≥3. For one- and two-ion plasmas special results can be obtained, some of which fit into the above two classes and some of which do not.

Ion cyclotron wave generation in a two-ion plasma

Exact calculation of the dispersion relation of a cold plasma shows that the plasma behaviour is different from that predicted by the usual approximate theory which neglects electron inertia in the low-density limit. For example, the limiting value of Ω for optimum coupling is different from 1, where Ω is the wave frequency divided by the ion cyclotron frequency. This fact was ascertained experimentally in the QP-machine.Experimental observations of optimum coupling of the ion cyclotron wave in a two-ion plasma in the QP-machine are presented as functions of the plasma density. The plasma was produced by a PIG discharge with a density from 1010 to 2 × 1012 cm−3. The wave was generated by a Stix-type coil (coil wavelength 50 cm), which was fed by a 4.4-MHz, 20-kW oscillator. Experimental data lay within the band of H+ concentration between 10–90% of the dispersion relation of a homogeneous cold plasma column with a sharp boundary. However, the dependence of optimum loading on the diameter of the plasma column disagrees with the theoretical prediction.

Optimum Generation of Ion-Cyclotron Waves in a Cylindrical Two-Ion Plasma

Ion-cyclotron waves have been generated in a hydrogen-deuterium plasma (previously formed by Ohmic heating) contained in the Model C stellarator, using an induction coil of finite wavelength. The conditions for optimum generation of waves, found experimentally, were in good agreement with theoretical predictions.

Absorption of Ion Cyclotron Waves by One Component of a Two-Ion Plasma

Absorption of Ion Cyclotron Waves by One Component of a Two-Ion Plasma