摘要:

High spatial resolution electron cyclotron emission imaging (ECEI) has been employed on TEXT-U [Texas Experimental Tokamak Upgrade, G. Cima &etal;, Phys. Plasmas2, 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.

ISSN:1070-664X    

DOI:10.1063/1.873144

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The solitary structure solution of the radial electric fieldErin 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 ofErand reduction of turbulent transport, which belong to key issues of the high confinement mode (H-Mode) [F. Wagner &etal;, 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.

ISSN:1070-664X    

DOI:10.1063/1.873145

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

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.

ISSN:1070-664X    

DOI:10.1063/1.873146

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

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.

ISSN:1070-664X    

DOI:10.1063/1.873147

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

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.

ISSN:1070-664X    

DOI:10.1063/1.873141

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

It is well established that in magnetized partially ionized plasmas, the dispersion of the shear Alfve´n waves is strongly influenced by the ion–neutral collisions. In the case of inhomogeneous plasmas, the study of these collisions on Alfve´n surface waves can become important, especially in understanding resonant absorption of Alfve´n 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 Alfve´n surface waves’ propagation characteristics. For the case when ion–neutral coupling is weak, the wave propagates along the interface with the natural frequency of Alfve´n 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.

ISSN:1070-664X    

DOI:10.1063/1.873148

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

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 Alfve´n continuous spectrum. The unity of these two classes of modes is emphasized. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.873149

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

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 Schro¨dinger-type equation (NLS-type) equation. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.873150

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

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.

ISSN:1070-664X    

DOI:10.1063/1.873151

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

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. Fluids18, 875 (1975)]. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.873152

出版商:AIP    

年代:1998

数据来源: AIP