摘要:

The hot plasma electrostatic dispersion relation for the lower hybrid frequency range has been cast into a form without any sums using the method of steepest descents. This new form of the dispersion relation with the exact resonance term, which is valid for general complex wavenumber and each term of which is identified according to its role of representing physical waves, is shown to be accurate and to be reducible to an expression obtained by Brambilla [Plasma Phys.18, 699 (1976)] when some approximations are taken. A very simple dispersion relation is also obtained without singular terms near the high ion cyclotron harmonics that are encountered by lower hybrid waves propagating in inhomogeneous magnetic fields. Finally, the damping rate in space is numerically calculated using the equation derived and compared with the result from the unmagnetized ion dispersion relation.

ISSN:0031-9171    

DOI:10.1063/1.866740

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An analysis of the mode conversion of an electrostatic Bernstein wave in a plasma near the upper‐hybrid resonance is developed. The conversion coefficients for the reflected extraordinary and electrostatic waves and for the transmitted electromagnetic wave are derived and calculated for various values of the inhomogeneity length and wave frequency.

ISSN:0031-9171    

DOI:10.1063/1.866741

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The theory of resistive evolution of plasmas is extended to include plasmas with imperfect magnetic surfaces, that is, plasmas having magnetic field lines that wander stochastically. In resistive evolution theory the plasma is assumed to be always in mechanical equilibrium and the evolution occurs by allowing the magnetic flux constraints determining the equilibrium to change, which happens on a resistive time scale. In this paper a formalism is created to describe magnetic field line structure in a general way in order to evaluate the field line integrals that are the magnetic flux constraints. The equations expressing evolution of these flux constraints, along with the plasma mechanical equilibrium equations, are a mathematical model that can be solved to determine the evolution of the plasma. An immediate result of this model is that, for plasmas with stochastic magnetic field lines, the current density has a filamentary structure, giving a self‐consistent source of the stochasticity. A simple two‐field‐line model of the reversed field pinch is discussed.

ISSN:0031-9171    

DOI:10.1063/1.866742

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A three‐dimensional self‐organization process of a compressible dissipative plasma with a velocity‐magnetic field correlation is investigated in detail by means of a variational method and a magnetohydrodynamic simulation. There are two types of relaxation, i.e., fast relaxation in which the cross helicity is not conserved and slow relaxation in which the cross helicity is conserved approximately. In the slow relaxation case the cross helicity consists of two components with opposite sign that have almost the same amplitude in the large wavenumber region. In both cases the system approaches a high correlation state, dependent on the initial condition. These results are consistent with observational data of the solar wind. Selective dissipation of magnetic energy, normal cascade of magnetic energy spectrum, and inverse cascade of magnetic helicity spectrum are observed for the sub‐Alfve´nic flow case, as was observed previously for the zero‐flow case. When the flow velocity is super‐Alfve´nic, the relaxation process is altered significantly from the zero‐flow case.

ISSN:0031-9171    

DOI:10.1063/1.866743

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Scaling laws for energy confinement in a turbulent plasma dominated by resistive pressure‐driven modes are revisited. New scaling laws are obtained under a consistent low‐beta approximation, and differ from earlier theories primarily in their dependence on the plasma pressure.

ISSN:0031-9171    

DOI:10.1063/1.866744

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The nonlinear growth for them/n≥2 resistive tearing mode is studied in the case when the rational surfaceq(r0)=m/nfalls in a regime of weak magnetic shear,q’(r0)&bartil;0. The island width is determined self‐consistently from the nonlinear, zero‐helicity component of the perturbed magnetic flux that provides the local shear. It is found that the magnetic perturbation keeps growing exponentially in the nonlinear regime on a hybrid resistive‐Alfve´nic time scale, while the island width and the vorticity grow on a much slower time scale. Accordingly, much faster release of magnetic energy results for modes growing near minima of hollowqprofiles.

ISSN:0031-9171    

DOI:10.1063/1.866745

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The results of investigations of nonlinear tearing‐mode dynamics in reversed field pinch plasmas are described. The linear instabilities have poloidal mode numberm=1 and toroidal mode numbers 10≲n≲20, and the resonant surfaces are therefore in the plasma core. The nonlinear dynamics result in dual cascade processes. The first process is a rapidm=1 spectral broadening toward highn, with a simultaneous spreading of magnetic turbulence radially outward toward the field‐reversal surface. Globalm=0 perturbations, which are driven to large amplitudes by them=1 instabilities, in turn trigger them=1 spectral broadening by back coupling to the highern. The second process is a cascade toward largemand is mediated bym=2 modes. Them=2 perturbations have the structure of localized, driven current sheets and nonlinearly stabilize them=1 modes by transferringm=1 energy to small‐scale dissipation. The calculated spectrum has many of the qualitative features observed in experiments.

ISSN:0031-9171    

DOI:10.1063/1.866746

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The relation between momentum and thermal transport in neutral‐beam‐heated tokamaks with subsonic toroidal rotation velocity has been investigated. A theory of diffusive momentum transport driven by ion‐temperature‐gradient‐driven turbulence (&eegr;iturbulence) is presented. In addition, the level of &eegr;iturbulence is enhanced by radially sheared toroidal rotation. The resulting ion shear viscosity is &khgr;&Jgr;=1.3{(1+&eegr;i)/&tgr;+[(Ln/2cs) (dV0/dr)]2}2(&rgr;2scs/Ls). The associated ion thermal diffusivity, &khgr;i, is identical to &khgr;&Jgr;. Thus a scenario based on velocity‐shear‐enhanced &eegr;iturbulence is consistent with the experimentally observed relationship between thermal and momentum confinement.

ISSN:0031-9171    

DOI:10.1063/1.866747

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Large ponderomotive forces can occur when waves in the ion cyclotron range of frequencies (ICRF) are employed in stabilization or high power heating schemes. It is shown that the magnetohydrodynamic (MHD) equilibrium of the plasma is modified when the rf antenna is localized poloidally and/or toroidally. In the two‐dimensional (2‐D) problem (toroidally uniform rf) a modified Grad–Shafranov equation describes ponderomotively driven magnetic surface distortions. At electric field strengths of interest for ICRF stabilization, the equilibrium distortions are small provided thatLrf≪aand the poloidal localization of the rf is not severe. The character of the 3‐D problem (toroidally and poloidally varying rf) depends on whether or not the ponderomotive force couples to rational surfaces within the plasma. For the case without rational surfaces, the 3‐D component of the distortions is found to be small by 1/q2arelative to the 2‐D component. In the case where rational surfaces are excited, magnetic islands result. A threshold condition for island overlap determines the rf electric field at which ergodicity may be expected. It is shown that ergodicity of the edge plasma may occur for some cases of interest for heating and stabilization, but should be controllable.

ISSN:0031-9171    

DOI:10.1063/1.866748

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The nonlinear evolution of the internal kink mode is studied in toroidal geometry for noncircular cross‐section tokamak plasmas. The study is focused on very low‐shear and hollowqprofiles, withq(&rgr;)≥1 for which the internal kink is unstable in the latter case, even at &bgr;=0. The nonlinear evolution is dominated by ideal magnetohydrodynamics (MHD), and the instability saturates, giving a quasihelical shift to the magnetic axis. The nonlinear saturation is caused by increased field line bending. Time scales of 103&tgr;Hpand axis shifts of 20% are reached when changes inqon the order of 3×10−3from the marginal profile are produced.

ISSN:0031-9171    

DOI:10.1063/1.866749

出版商:AIP    

年代:1988

数据来源: AIP