摘要:

Fast wave flow drive in a two‐component plasma with low minority ion concentration is investigated. It is found that strongly sheared poloidal flow can be generated in a small region near the hybrid ion–ion resonance due the rapid spatial variation of the plasma velocity response to the fast wave electric field. The flow drive depends strongly on local plasma temperatures and is shown to be very effective in the edge region of a tokamak where the plasma temperature is low. The result is applied to a discussion of shear flow suppression of edge turbulence.

ISSN:0899-8221    

DOI:10.1063/1.860603

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A mean field Ohm’s law valid for collisionless plasmas is derived kinetically. It is shown that contrary to conventional thinking, the resulting hyperresistivity is significantly smaller than its fluid counterpart due to the fact that the turbulent decorrelation rate is linked to the rapid electron ballistic motion rather than the slower nonlinear mixing time. Moreover, the off‐diagonal contributions to the parallel electron momentum flux are shown to result in Ohm’s law renormalizations that dwarf the current diffusivity and break radial parity symmetry.

ISSN:0899-8221    

DOI:10.1063/1.860604

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The tokamak L–H (low‐mode–high mode) transition theory can be tested in stellarators in a controlled manner by making use of the two or more local maxima in poloidal viscosity in these devices. Depending on the relative magnitudes of the toroidal and helical components of the magnetic‐field spectrum, the local maxima, and thus transition, can occur either at a critical poloidalE×BMach numberMpof the order of unity, similar to that of a tokamak, or at anMpof the order of ‖m−nq‖/m, similar to that of a helically symmetric torus. Here,E(B) is the electric (magnetic) field strength,m(n) is the poloidal (toroidal) mode number of the helical component of the ‖B‖ spectrum, andqis the safety factor. Possible limitations on the test due to the effects of the charge‐exchange momentum loss are discussed.

ISSN:0899-8221    

DOI:10.1063/1.860605

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The nonlinear evolution of tearing modes with multiple rational surfaces is discussed. It is demonstrated that, in the presence of small differential rotation, the nonlinear growth might be faster than exponential. This growth occurs as the rotation frequencies of the plasma at the different rational surfaces equilibrate.

ISSN:0899-8221    

DOI:10.1063/1.860606

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The virial for a system of very long, parallel, charged rods is particularly simple. The virial equation (‘‘theorem’’) relates that quantity to the wall virial and to random and organized internal energies of the system. In the case of a long cylinder of pure‐electron plasma, the virial equation contains, as a special case, an equation derived recently by Davidson and Lund on the basis of mean‐field theory. The virial equation may be used to control the computation of thermodynamic functions for the plasma. It also gives insight into the more complicated motions which occur when the central axis of the column moves in a closed orbit.

ISSN:0899-8221    

DOI:10.1063/1.860607

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The exact Hamiltonian and the first‐order corrections to the standard drift Hamiltonian are given in magnetic coordinates for a full static electromagnetic field with magnetic surfaces. The exact Hamiltonian depends on both the field strength and the shape of the magnetic surfaces (the metric of the magnetic coordinates) while the standard drift Hamiltonian depends on the field strength only. The first‐order correction to the standard drift Hamiltonian, in gyroradius to system size, depends in a generic way on the metric of the magnetic coordinates, as does the exact Hamiltonian. The finite‐Larmor‐radius effect and the polarization drift are in the first‐order corrections.

ISSN:0899-8221    

DOI:10.1063/1.860608

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

It can be shown that whistler waves with low parallel phase velocity can be subject to strong cyclotron damping, even when the wave frequency is well below the cyclotron frequency. This resonance arises as a result of the Doppler effect which is proportional to the plasma density and increases the frequency experienced by electrons moving in the opposite direction to the wave. In this paper the dispersion relation of whistler waves in a cylindrically bounded plasma is obtained and then solved. This geometry is desirable for its relevance to experiment and also for comparison with theoretical results by other authors. In addition to cyclotron damping, Landau damping as well as electron–ion, electron–electron, and electron–neutral collisions are all included thus enabling the relative importance of these damping mechanisms to be evaluated. The dispersion relation that is obtained is used to explore the transition from Landau dominated damping to cyclotron dominated damping.

ISSN:0899-8221    

DOI:10.1063/1.860609

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A sheared slab magnetic field modelB=B0[zˆ+(x/Ls)yˆ], with inhomogeneous flows in theyˆandzˆdirections, is used to perform a fully kinetic stability analysis of the ion temperature gradient (ITG) and dissipative trapped electron (DTE) modes. The concomitant quasilinear stress components that couple to the local perpendicular (ycomponent) and parallel (zcomponent) momentum transport are also calculated and the anomalous perpendicular and parallel viscous stresses obtained. A breakdown of the ITG‐induced viscous stresses are generally observed at moderate values of the sheared perpendicular flow. Even in the absence of external momentum sources, ion diamagnetic effects can generate an inhomogeneous radial electric field which gives rise to a sheared perpendicular flow which can sustain a sheared parallel flow. The effect of the perpendicular stress component in the momentum balance equations is generally small while the parallel stress component, which is primarily determined by the perpendicular flow shear, can dominate the usual neoclassical viscous stress terms. The large anomalous effect suggests that the neoclassical explanation of poloidal flows in tokamaks may be incorrect. The present results are in general agreement with existing experimental observations on momentum transport in tokamaks.

ISSN:0899-8221    

DOI:10.1063/1.860610

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Electromagnetic wave scattering in a plasma half‐space from a propagating ion acoustic wave density perturbation with a transverse conducting boundary condition is analyzed. The analysis shows that there are two different types of scattered waves. One propagates only in the region where the plasma density is perturbed, its frequency and wave vector satisfies the conditions for a three‐wave interaction process. The other propagates as an unperturbed electron cyclotron mode with either an upshifted or downshifted frequency. Experiments are performed to examine electron cyclotron wave scattering by an ion acoustic wave excited by means of a grid along the magnetic field line in a mirror machine. The backscattered waves propagating away from the density perturbation region are measured and their dependence on the ion acoustic wavelength is examined. The scattered wave in the region of ion acoustic wave propagation is examined by measuring the scattered wave field pattern when the ion acoustic wave number is much larger than that of the incident wave. The measurements demonstrate that the scattered waves indeed propagate as two different modes.

ISSN:0899-8221    

DOI:10.1063/1.860611

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Numerical simulations of current sheet formation in a two‐dimensional ideal incompressible magnetohydrodynamic system reveal that sheets evolve self‐similarly with cross‐sheet profiles close toj(&psgr;)∝exp(−2&agr;&psgr;). This current profile has previously been derived by several authors as the most probable state in a current‐carrying plasma. A critical review of the different theoretical approaches is given.

ISSN:0899-8221    

DOI:10.1063/1.860612

出版商:AIP    

年代:1993

数据来源: AIP