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Dec 1998

Volume 5, Issue 12, pp. 4117-4514

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Mode structure of turbulent electron temperature fluctuations in the Texas Experimental Tokamak Upgrade

B. H. Deng, D. L. Brower, G. Cima, C. W. Domier, N. C. Luhmann, and C. Watts

Phys. Plasmas 5, 4117 (1998); http://dx.doi.org/10.1063/1.873144 (4 pages) | Cited 17 times

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High spatial resolution electron cyclotron emission imaging (ECEI) has been employed on TEXT-U [Texas Experimental Tokamak Upgrade, G. Cima et al., Phys. Plasmas 2, 720 (1995)] to measure turbulent electron temperature fluctuations using an intensity interferometric technique. With the first dispersion relation measurements in the plasma confinement region, a broadband spectral feature is identified at poloidal wave numbers consistent with expectations for electron drift waves. © 1998 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.Kn Thermodynamics of plasmas
52.25.Gj Fluctuation and chaos phenomena
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Solitary radial electric field structure in tokamak plasmas

K. Itoh, S.-I. Itoh, M. Yagi, and A. Fukuyama

Phys. Plasmas 5, 4121 (1998); http://dx.doi.org/10.1063/1.873145 (3 pages) | Cited 29 times

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The solitary structure solution of the radial electric field Er in the tokamak plasmas is obtained. It is shown to be stable under an external power supply, like a biased electrode at the edge. The radial gradient is governed by the ion viscosity and the nonlinearlity of the perpendicular conductivity. The radial structure of Er and reduction of turbulent transport, which belong to key issues of the high confinement mode (H-Mode) [F. Wagner et al., Phys. Rev. Lett. 49, 1408 (1982)], are self-consistently determined. A bifurcation from a radially-uniform one to a solitary one occurs at a certain applied voltage, and a hysteresis is associated. © 1998 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Ra Plasma turbulence
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Landau damping and transit-time damping of localized plasma waves in general geometries

R. W. Short and A. Simon

Phys. Plasmas 5, 4124 (1998); http://dx.doi.org/10.1063/1.873146 (10 pages) | Cited 9 times

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Landau’s original derivation of the collisionless damping of small-amplitude Langmuir waves in an infinite homogeneous plasma relied on the introduction of complex velocities and was therefore somewhat difficult to interpret physically. This has inspired many subsequent derivations of Landau damping that involve only real physical quantities throughout. These “physical” derivations, however, have required the calculation of quantities to second order in the wave field, whereas Landau’s approach involved only first-order quantities. More recent generalizations of Landau damping to localized fields, often called “transit-time damping,” have followed the physical approach, and thus also required second-order calculations, which can be quite lengthy. In this paper it is shown that when the equilibrium distribution function depends solely on the energy, invoking the time-reversal invariance of the Vlasov equation allows transit-time damping to be analyzed using only first-order physical quantities. This greatly simplifies the calculation of the damping of localized plasma waves and, in the limit of an infinite plasma, provides a derivation of Landau damping that is both physical and linear in the wave field. This paper investigates the transit-time damping of plasma waves confined in slabs, cylinders, and spheres, analyzing the dependence on size, radius, and mode number, and demonstrating the approach to Landau damping as the systems become large. It is also shown that the same approach can be extended to more general geometries. A companion paper analyzes transit-time damping in a cylinder in more detail, with applications to the problem of stimulated Raman scattering in self-focused light filaments in laser-produced plasmas. © 1998 American Institute of Physics.
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52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Collisionless damping of localized plasma waves in laser-produced plasmas and application to stimulated Raman scattering in filaments

R. W. Short and A. Simon

Phys. Plasmas 5, 4134 (1998); http://dx.doi.org/10.1063/1.873147 (10 pages) | Cited 8 times

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Observations of stimulated Raman scattering (SRS) in laser-produced plasmas often yield results at odds with theoretical predictions. For example, SRS is commonly seen at incident laser intensities below the theoretical threshold, and the spectrum of SRS light often extends to much shorter wavelengths than models predict. To account for these anomalies it is often proposed that SRS is occurring in high-intensity, self-focused light filaments. A serious problem with this model is that plasma wave damping rates estimated on the basis of the usual Landau theory for homogeneous plasmas would seem to rule out this explanation for many cases of interest. Damping rates for plasma waves confined to small-radius filaments, however, could be significantly different than damping rates for plane waves. Using a novel method for calculating transit-time damping, this paper analyzes the collisionless damping of plasma waveguide modes in a cylinder. It is found that the actual damping rates for waveguide modes in a suitable filament model are much less than for the plane waves in a homogeneous plasma producing the same wavelength of SRS emission. Consequently, the filament model remains viable as an explanation of the anomalous SRS observations. © 1998 American Institute of Physics.
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52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Wave excitation in a modified double plasma device

Tadao Honzawa

Phys. Plasmas 5, 4144 (1998); http://dx.doi.org/10.1063/1.873141 (5 pages) | Cited 2 times

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A modified double plasma (MDP) device is newly developed and shown to be useful for basic plasma wave experiments. Further, the mechanism of wave excitation in the MDP device is experimentally clarified. From the results the peculiarity of the device is found, that ion-acoustic waves can be excited in plasmas essentially freely from the effects of stationary beam ions and other modes, such as ion-beam modes as far as linear waves are concerned. For nonlinear waves, however, ion-acoustic solitons or shocks with reflected ions ahead and slower wave-like signals behind are possibly excited just as in a conventional DP device. © 1998 American Institute of Physics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Sb Solitons; BGK modes
52.35.Tc Shock waves and discontinuities
52.75.-d Plasma devices

Ion–neutral collision effects on Alfvén surface waves

C. Uberoi and Ajanta Datta

Phys. Plasmas 5, 4149 (1998); http://dx.doi.org/10.1063/1.873148 (7 pages) | Cited 4 times

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It is well established that in magnetized partially ionized plasmas, the dispersion of the shear Alfvén waves is strongly influenced by the ion–neutral collisions. In the case of inhomogeneous plasmas, the study of these collisions on Alfvén surface waves can become important, especially in understanding resonant absorption of Alfvén waves. In this paper, the dispersion equation for the surface waves in partially ionized plasma along a plasma–plasma interface is derived and it is shown that ion–neutral collisions can cause a drastic change in the Alfvén surface waves’ propagation characteristics. For the case when ion–neutral coupling is weak, the wave propagates along the interface with the natural frequency of Alfvén surface waves in the charged medium without friction. When coupling is strong, this frequency is determined by the mass densities of both ions and neutrals in both media. When the ionization fraction is low, these two frequencies can differ by several orders of magnitude. There also exists a range of frequencies, depending on the collisions, in which the surface waves do not propagate. The damping of surface waves due to ion–neutral collisions can be very small in the case of strong coupling. For weak coupling, this damping can become large due to large collision frequencies. The effect of this on the resonant absorption of surface waves is discussed briefly. The possibility of propagation of surface waves along thin plasma–plasma interfaces is also considered in the context of some astrophysical systems.© 1998 American Institute of Physics.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Modes localized to open magnetic field lines

Eliezer Hameiri

Phys. Plasmas 5, 4156 (1998); http://dx.doi.org/10.1063/1.873149 (4 pages) | Cited 7 times

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A constructive mathematical proof is given for the existence of modes localized to a single magnetic field line, which give rise to ballooning modes and to the Alfvén continuous spectrum. The unity of these two classes of modes is emphasized. © 1998 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Ion oscillation modes in inhomogeneous plasmas

Wen-shan Duan and Ke-pu Lu

Phys. Plasmas 5, 4160 (1998); http://dx.doi.org/10.1063/1.873150 (3 pages) | Cited 1 time

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Using the reductive perturbation method, the carrier wave modulation of ion acoustics waves in inhomogeneous plasma is investigated. It is shown that such a process can be described by a Nonlinear Schrödinger-type equation (NLS-type) equation. © 1998 American Institute of Physics.
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52.35.Dm Sound waves
52.35.Sb Solitons; BGK modes
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Surface waves in a magnetized plasma

M. Sita Janaki and Brahmananda Dasgupta

Phys. Plasmas 5, 4163 (1998); http://dx.doi.org/10.1063/1.873151 (6 pages) | Cited 2 times

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Electrostatic surface waves propagating along the interface between a warm magnetized plasma and vacuum are investigated by deriving the relevant dispersion relations using a fluid model. The general dispersion relation for arbitrary orientation of the magnetic field and the propagation vector is derived in a closed form and certain special cases (when the magnetic field is directed parallel and perpendicular to the boundary surfaces) are analyzed numerically. © 1998 American Institute of Physics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Generalized reduced magnetohydrodynamic equations

S. E. Kruger, C. C. Hegna, and J. D. Callen

Phys. Plasmas 5, 4169 (1998); http://dx.doi.org/10.1063/1.873152 (14 pages) | Cited 17 times

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A new derivation of reduced magnetohydrodynamic (MHD) equations is presented. A multiple-time-scale expansion is employed. It has the advantage of clearly separating the three time scales of the problem associated with (1) MHD equilibrium, (2) fluctuations whose wave vector is aligned perpendicular to the magnetic field, and (3) those aligned parallel to the magnetic field. The derivation is carried out without relying on a large aspect ratio assumption; therefore this model can be applied to any general toroidal configuration. By accounting for the MHD equilibrium and constraints to eliminate the fast perpendicular waves, equations are derived to evolve scalar potential quantities on a time scale associated with the parallel wave vector (shear-Alfven wave time scale), which is the time scale of interest for MHD instability studies. Careful attention is given in the derivation to satisfy energy conservation and to have manifestly divergence-free magnetic fields to all orders in the expansion parameter. Additionally, neoclassical closures and equilibrium shear flow effects are easily accounted for in this model. Equations for the inner resistive layer are derived which reproduce the linear ideal and resistive stability criterion of Glasser, Greene, and Johnson [Phys. Fluids 18, 875 (1975)]. © 1998 American Institute of Physics.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Gj Fluctuation and chaos phenomena
52.55.Fa Tokamaks, spherical tokamaks
52.55.Jd Magnetic mirrors, gas dynamic traps
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Computational investigation of single mode vs multimode Rayleigh–Taylor seeding in Z-pinch implosions

M. R. Douglas, C. Deeney, and N. F. Roderick

Phys. Plasmas 5, 4183 (1998); http://dx.doi.org/10.1063/1.873153 (16 pages) | Cited 17 times

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A series of two-dimensional magnetohydrodynamic calculations have been carried out to investigate single and multimode growth and mode coupling for magnetically-driven Rayleigh–Taylor instabilities in Z pinches. Wavelengths ranging from 5.0 mm down to 1.25 mm were considered. Such wavelengths are comparable to those observed at stagnation using a random density “seeding” method. The calculations show that wavelengths resolved by less than 10 cells exhibit an artificial decrease in initial Fourier spectrum amplitudes and a reduction in the corresponding amplitude growth. Single mode evolution exhibits linear exponential growth and the development of higher harmonics as the mode transitions into the nonlinear phase. The mode growth continues to exponentiate but at a slower rate than determined by linear hydrodynamic theory. In the two and three mode case, there is clear evidence of mode coupling and inverse cascade. In addition, distinct modal patterns are observed late in the implosion, resulting from finite shell thickness and magnetic field effects. © 1998 American Institute of Physics.  
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52.55.Ez Theta pinch
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.30.-q Plasma dynamics and flow

The three-dimensional stability of steady magnetohydrodynamic flows of an ideal fluid

V. A. Vladimirov and K. I. Ilin

Phys. Plasmas 5, 4199 (1998); http://dx.doi.org/10.1063/1.873154 (6 pages) | Cited 9 times

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The stability of steady magnetohydrodynamic flows of an ideal incompressible fluid to small three-dimensional perturbations is studied. Two new conditions sufficient for linear stability of steady magnetohydrodynamic flows are obtained by the energy method. © 1998 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
47.65.-d Magnetohydrodynamics and electrohydrodynamics

Wake potentials in nonuniform dusty magnetoplasmas

M. Salimullah and P. K. Shukla

Phys. Plasmas 5, 4205 (1998); http://dx.doi.org/10.1063/1.873155 (4 pages) | Cited 9 times

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It is shown that the presence of equilibrium density gradients in a magnetized dusty plasma can introduce new types of drift-like waves. These give rise to oscillatory wake-potentials, which can focus ions and attract dust grains of similar polarity. Using a test particle approach, typical profiles for wake-potentials are obtained in several interesting cases. It is found that the effective attraction length is independent of the magnetic field strength for high density dusty plasmas, whereas it is larger for larger magnetic fields in a low-density dusty plasma. Furthermore, the dust attraction takes place predominantly in the inhomogeneous region of the dusty plasma having smaller lattice periodicity for smaller scale length of the density inhomogeneity. © 1998 American Institute of Physics.
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52.25.Vy Impurities in plasmas
52.35.Kt Drift waves

Parametric instability on an annular beam induced by a periodic beam-channel boundary

A. Lazaros and J. L. Vomvoridis

Phys. Plasmas 5, 4209 (1998); http://dx.doi.org/10.1063/1.873156 (5 pages)

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In the framework of the general Nishikawa formalism for parametric instabilities the coupling is examined of the plasma oscillations to the density modulations of an annular electron beam, modulated by an axially periodic beam-channel boundary commonly used in microwave sources. It is found that the instability is present when the distance between the beam and the channel boundary is larger than the periodic length of the boundary. It is also found that the growth rate of the instability is independent of the beam current and depends only on the beam velocity and the periodic length of the beam-channel boundary. © 1998 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.40.Mj Particle beam interactions in plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Intermittent particle transport in two-dimensional edge turbulence

Y. Sarazin and Ph. Ghendrih

Phys. Plasmas 5, 4214 (1998); http://dx.doi.org/10.1063/1.873157 (15 pages) | Cited 115 times

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Interchange turbulence in two dimensions is investigated in the scrape-off layer (SOL) of fusion devices, when driven by a constant core particle influx. Contrary to the standard gradient-driven approach, density is allowed to fluctuate around its average profile. Transverse transport exhibits some of the features of self-organized critical systems, namely inward and outward avalanches, together with a frequency spectrum decrease in 1/f and f−2 at intermediate and high frequencies, respectively. An avalanche occurs when the local radial density gradient exceeds the critical one. A self-sustained particle flux then follows the large radial structures of the electric potential. As observed experimentally, the radial profile of density relative fluctuations decreases from the wall into the core plasma, while that of electric potential relative fluctuations peaks inside the SOL. Equilibrium density exhibits the experimental exponential decrease. An analytical expression of the SOL width ΔSOL is obtained, which maximizes the linear growth rate, when the poloidal modulation of electric potential equilibrium is taken into account. The parametric dependencies of ΔSOL are compared to experimental data. © 1998 American Institute of Physics.
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52.25.Fi Transport properties
52.35.Ra Plasma turbulence
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Gj Fluctuation and chaos phenomena

Solitary Alfvén wave in an electron positron ion plasma

H. Kakati and K. S. Goswami

Phys. Plasmas 5, 4229 (1998); http://dx.doi.org/10.1063/1.873158 (6 pages) | Cited 14 times

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Solitary Alfvén waves in electron positron ion plasmas are investigated. The Alfvén wave is shown to have an exact solitary wave solution for a small but finite value of β. It is shown that the existence regions are different if the value of β is changed; however, the change in Kx simply changes the soliton width. © 1998 American Institute of Physics.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Sb Solitons; BGK modes

Scaling of spectral anisotropy with magnetic field strength in decaying magnetohydrodynamic turbulence

Sean Oughton, William H. Matthaeus, and Sanjoy Ghosh

Phys. Plasmas 5, 4235 (1998); http://dx.doi.org/10.1063/1.873159 (8 pages) | Cited 39 times

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Space plasma measurements, laboratory experiments, and simulations have shown that magnetohydrodynamic (MHD) turbulence exhibits a dynamical tendency towards spectral anisotropy given a sufficiently strong background magnetic field. Here the undriven decaying initial-value problem for homogeneous MHD turbulence is examined with the purpose of characterizing the variation of spectral anisotropy of the turbulent fluctuations with magnetic field strength. Numerical results for both incompressible and compressible MHD are presented. A simple model for the scaling of this spectral anisotropy as a function of the fluctuating magnetic field over total magnetic field is offered. The arguments are based on ideas from reduced MHD (RMHD) dynamics and resonant driving of certain non-RMHD modes. The results suggest physical bases for explaining variations of the anisotropy with compressibility, Reynolds numbers, and spectral width of the (isotropic) initial conditions. © 1998 American Institute of Physics.
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52.35.Ra Plasma turbulence
52.30.-q Plasma dynamics and flow

Nonlinear interaction of whistler waves with a modulated thin electron beam

C. Krafft and A. Volokitin

Phys. Plasmas 5, 4243 (1998); http://dx.doi.org/10.1063/1.873160 (10 pages) | Cited 17 times

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The nonlinear theory of a thin modulated electron beam interaction with a monochromatic whistler wave is considered. The self-consistent set of differential equations describing the wave amplitude evolution and the beam particle motion has been solved by a computer code. Results issued from the numerical solution of the differential system are discussed, namely the physical features of the nonlinear beam–wave interaction (trapping, slowing down of the beam, wave damping, multiple bunching, beam focusing), as well as the influence of the physical parameters on the wave emission: beam energy and density, initial beam velocity distribution, and beam current modulation. It has been shown that the trapped particles are the source of the emission; they are decelerated in phase with the wave and remain in Cherenkov resonance with it owing to a nonlinear shift of the parallel wave number. No quasiperiodic exchange of energy between the wave and the particles has been observed. Time evolution of the wave amplitude and the particle energy has been explained by a simple model, as well as the multibunched structures appearing in the particle dynamics for certain physical parameters. © 1998 American Institute of Physics.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.40.Mj Particle beam interactions in plasmas

Wave propagation and absorption simulations for helicon sources

Y. Mouzouris and J. E. Scharer

Phys. Plasmas 5, 4253 (1998); http://dx.doi.org/10.1063/1.873161 (9 pages) | Cited 24 times

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A two-dimensional (2-D), finite-difference computer code is developed to examine helicon antenna coupling, wave propagation, collisionless Landau, and collisional heating mechanisms. The code calculates the electromagnetic wave fields and power absorption in an inhomogeneous, cold, collisional plasma. The current distribution of the launching antenna, which provides the full antenna spectra, is included in the model. An iterative solution that incorporates warm plasma thermal effects has been added to the code to examine the contribution of collisionless (Landau) wave absorption by electrons. Detailed studies of the wave fields and electron heating profiles at low magnetic fields (B0<100 G), where both Trivelpiece–Gould (TG) and helicon (H) modes are present, are discussed. The effects of the applied uniform magnetic field (B0 = 10–1000 G), 2-D (r,z) density profiles (ne0 = 1011–1013 cm−3), neutral gas pressures of 1–10 mTorr and the antenna spectrum on collisional and collisionless wave field solutions and power absorption are investigated. Cases in which the primarily electrostatic (TG) surface wave dominates the heating and the power is absorbed near the edge region and cases in which the propagating helicon wave transports and deposits its energy in the core plasma region are examined. © 1998 American Institute of Physics.
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52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.65.-y Plasma simulation
52.25.Kn Thermodynamics of plasmas

Observation of collisionless thermalization of a plasmoid with a field-reversed configuration in a magnetic mirror

H. Himura, S. Ueoka, M. Hase, R. Yoshida, S. Okada, and S. Goto

Phys. Plasmas 5, 4262 (1998); http://dx.doi.org/10.1063/1.873162 (9 pages) | Cited 7 times

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A systematic translation study of field-reversed configurations (FRCs) has been conducted on the FRC Injection Experiment (FIX) machine [Okada et al., in Fusion Energy 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 2, p. 229]. Plasma density and temperature of a translated FRC moving at supersonic speed are measured in the downstream magnetic mirror of FIX to verify a shock jump there when the FRC is reflected. A significant jump is observed. Moreover, the time evolution of the Carbon V Doppler profile is measured both quasi-parallel and perpendicular to the direction of FRC motion. Distinct transitions from Gaussian to non-Gaussian shapes are clearly seen in both profiles before and after the shock jump. Also, the ion mean-free path in the downstream magnetic mirror is calculated to be much longer than the characteristic width of the shock jump. These results indicate that the thermalization of flow energy in the translated FRC in the mirror is produced by a collisionless process, implying that this heating mechanism can be realized even in a reactor regime. © 1998 American Institute of Physics.
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28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.55.Ez Theta pinch
52.25.-b Plasma properties
52.30.-q Plasma dynamics and flow

Tokamak turbulence with stochastic field lines

P. Beyer, X. Garbet, and P. Ghendrih

Phys. Plasmas 5, 4271 (1998); http://dx.doi.org/10.1063/1.873163 (9 pages) | Cited 29 times

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Three-dimensional numerical simulations of ballooning turbulence in a tokamak plasma with stochastic magnetic field lines are presented. Three main features are observed. First, the level of pressure fluctuations decreases in the ergodic layer. Second, this is essentially due to a suppression of large scale structures. Finally, the turbulent heat diffusivity does not decrease in the stochastic layer due to an increase of electric field fluctuations. These observations are in agreement with turbulence measurements on Tore Supra [Equipe Tore Supra, Proceedings, 13th International Conference on Plasma Physics and Controlled Nuclear Fusion, Washington, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 1, p. 549]. © 1998 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Suppression of drift-type instabilities by radio frequency waves

S. Sen and R. A. Cairns

Phys. Plasmas 5, 4280 (1998); http://dx.doi.org/10.1063/1.873164 (4 pages) | Cited 5 times

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The use of radio frequency waves is shown to stabilize drift-type waves in a tokamak if the radial profile of the radio frequency field energy is properly chosen. The estimate of the radio frequency power required for this stabilization is found to be rather modest. This result might have important implications as regards whether the use of the radio frequency waves can create a transport barrier to reduce the loss of particle and energy from the plasma. © 1998 American Institute of Physics.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Alpha particle-driven toroidal Alfvén eigenmodes in Tokamak Fusion Test Reactor deuterium–tritium plasmas: Theory and experiments

G. Y. Fu, R. Nazikian, R. Budny, and Z. Chang

Phys. Plasmas 5, 4284 (1998); http://dx.doi.org/10.1063/1.873165 (8 pages) | Cited 10 times

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The toroidal Alfvén eigenmodes (TAE) in the Tokamak Fusion Test Reactor [K. Young et al., Plasma Phys. Controlled Fusion 26, 11 (1984)] deuterium–tritium plasmas are analyzed using the NOVA-K code [C. Z. Cheng, Phys. Rep. 211, 1 (1992)]. The theoretical results are compared with the experimental measurements in detail. In most cases, the theory agrees with the observations in terms of mode frequency, mode structure and mode stability. However, one mode with toroidal mode number n = 2 is observed to be poloidally localized on the high field side of the magnetic axis with a mode frequency substantially below the TAE frequency. © 1998 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Fi Transport properties

Tearing mode analysis in tokamaks, revisited

Y. Nishimura, J. D. Callen, and C. C. Hegna

Phys. Plasmas 5, 4292 (1998); http://dx.doi.org/10.1063/1.873166 (8 pages) | Cited 6 times

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A new Δ′ shooting code has been developed to investigate tokamak plasma tearing mode stability in a cylinder and large aspect ratio (ϵ ⩽ 0.25) toroidal geometries, neglecting toroidal mode coupling. A different computational algorithm is used (shooting out from the singular surface instead of into it) to resolve the strong singularities at the mode rational surface, particularly in the presence of the finite pressure term. Numerical results compare favorably with Furth et al. [H. P. Furth et al., Phys. Fluids 16, 1054 (1973)] results. The effects of finite pressure, which are shown to decrease Δ′, are discussed. It is shown that the distortion of the flux surfaces by the Shafranov shift, which modifies the geometry metric elements, stabilizes the tearing mode significantly, even in a low-β regime before the toroidal magnetic curvature effects come into play. © 1998 American Institute of Physics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa Tokamaks, spherical tokamaks
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
02.60.-x Numerical approximation and analysis

Drift waves in plasmas with sheared flows

J. Vranješ, D. Jovanović, and P. K. Shukla

Phys. Plasmas 5, 4300 (1998); http://dx.doi.org/10.1063/1.873167 (5 pages) | Cited 10 times

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In the standard approach to the problem of shear stabilization of drift waves the diamagnetic drift velocity v∗ is regarded as a constant, which is usually not satisfied at the edge of a tokamak plasma. In configurations of this type, with a steep density gradient and radially sheared transverse velocity field, the magnetic shear stabilization criteria are severely restricted, and the velocity profile curvature v0″(x) is found to play a crucial role. In the strongly nonlinear regime, unstable drift waves may saturate into stationary coherent vortex-type structures. The latter include a tripolar vortex. © 1998 American Institute of Physics.
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52.35.Kt Drift waves
52.30.-q Plasma dynamics and flow
52.55.Fa Tokamaks, spherical tokamaks
52.40.Hf Plasma-material interactions; boundary layer effects
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