摘要:

The conditions are obtained for confining a plasma of arbitrary asymmetry, plasma beta, and collisionality, in an equilibrium configuration free of neoclassical transport. Such omnigeneous scalar pressure equilibria are shown to exist if, and only if, the divergence of the parallel current density vanishes, while for an anisotropic pressure other mild restrictions are needed. Explicit constraints are derived for axisymmetric tori and long‐thin, low‐beta conventional and tandem mirrors.

ISSN:0031-9171    

DOI:10.1063/1.863577

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Rayleigh–Taylor instabilities of an accelerating plasma sheet are studied by application of normal mode analysis to the one‐fluid magnetohydrodynamic equations. The equilibrium unperturbed states are determined by specifying the resistivity law of the current carrying plasma, although resistivity effects are neglected in the developing instabilities. The dispersion curves for the current filamentation and interchange type instabilities are given.

ISSN:0031-9171    

DOI:10.1063/1.863578

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The stability of a low‐beta spheromak with a perfectly conducting cylindrical boundary of lengthLand radiusRis analyzed in terms of force‐free fields with J = &lgr;B(&lgr; = const). The axisymmetric equilibrium is found unstable to tilting when the elongationL/Ris larger than about 1.67. Numerical solutions of the time‐dependent ideal magnetohydrodynamic equations confirm this result.

ISSN:0031-9171    

DOI:10.1063/1.863579

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Radiation from relativistic runaway electrons is considered as a source for plasma frequency radiation in tokamaks. Two specific mechanisms, Cerenkov emission and radiation produced by nonlinear coupling of plasma and acoustic waves, are studied. In many cases the Cerenkov emission provides a reasonable spectral fit. It can also be used to measure the runaway current, and to estimate the runaway cutoff velocity. The nonlinear emission is found to be negligible unless the acoustic waves are enhanced by about two orders of magnitude above the thermal level (or the plasma waves correspondingly enhanced above their superthermal level). Some observations, though, indicate the need for significant nonlinear (or other) emission in addition to the Cerenkov emission. For some typical Alcator data, the Cerenkov model gives a runaway current of 2.5% of the Ohmic current, and a cutoff energy of 1.5 MeV.

ISSN:0031-9171    

DOI:10.1063/1.863589

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The fluid stability of laser‐fusion targets is considered as a stability problem of a pseudo‐planetary atmosphere. Three atmospheric type modes are studied; acoustic, gravity, and Lamb modes. The changing character (i.e., growing, oscillatory, or growing‐oscillatory) of each is investigated as a function of the density‐gradient scale lengthHof the fluid. A growing class of modes is found which is distinct from the gravity (i.e., Taylor) mode if a gradient in entropy exists in the fluid. These modes are shown to be overstable Lamb modes. Also, the gravity mode is only stable for a distinct band of values ofH. These values, at which the density and Lamb modes change character, are derived from the dispersion relation for the modes. Finally, the consequences for laser targets are discussed.

ISSN:0031-9171    

DOI:10.1063/1.863590

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A model for microwave heating of electron rings in the ELMO Bumpy Torus configuration is analyzed using a relativistically correct quasi‐linear formulation. The spatial locations of heating by the different electron‐cyclotron harmonics are calculated. The steady‐state ring energy and the microwave power required to sustain the rings are determined by balancing the line‐averaged heating rate against classical collisional and radiative energy loss processes. Although ring formation is generally attributed to the second harmonic electron‐cyclotron resonance, the calculations show that fundamental heating also plays a critical role in ring start‐up and steady state. The model predicts ring power requirements for EBT which are consistent with previous estimates.

ISSN:0031-9171    

DOI:10.1063/1.863591

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Singular perturbation theory is used to construct a class of stationary solutions to the resistive plasma equilibrium equations in a plane slab geometry. These are nonlinearly saturated magnetic island structures which bifurcate from the basic Ohmic state when &Dgr;′(k) is positive and small in some sense. The relationship between the nondimensional wavenumberkand the size of the islands is obtained by a self‐consistent, matched asymptotic expansion. The assumed resisitivity profile is found to determine the relationship uniquely. It is found that either two bifurcating branches exist or none at all depending upon the profile chosen. The structure of the plasma current due to the islands is evaluated in terms of two functions which are independent of the resistivity profile. It is found that for sufficiently large &Dgr;′(k) and suitable resistivity, a self‐consistent, steady magnetic island state cannot be found. A possible connection between this phenomenon and disruptive instabilities observed in experimental plasmas is discussed very briefly. The proposed model complements the work done on magnetic islands by various groups using powerful numerical codes. In contrast to such codes, the current distributions due to a wide class of resistivity profiles have been calculated using the model. The solutions constructed shed some light on how nonlinear saturation in the island states can occur.

ISSN:0031-9171    

DOI:10.1063/1.863592

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Some nonlinear optical phenomena are investigated, especially stimulated scattering, from the point of view of the kinetic theory of radiation (i.e., photon transport theory). Kinetic theory provides a perspective, different from Maxwell’s wave theory, from which an examination of these complex matters may proceed with some advantages: (i) considerable mathematical simplication in some instances, (ii) clear and natural separation of microscopic versus macroscopic nonlinearities, (iii) kinetic theory couples the radition field nonlinearly to a formally exact description of the matter field, and (iv) it is believed that the mathematical model provided by kinetic theory is perhaps better suited for numerical studies of the effect of diverse nonlinear optical phenomena upon laser‐fusion implosion dynamics than Maxwell’s wave theory. Although the main emphasis is upon stimulated scattering, the incorporation of other nonlinearities into the kinetic model is discussed briefly.

ISSN:0031-9171    

DOI:10.1063/1.863593

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A Hamiltonian theory of guiding center motion which uses rectangular coordinates in physical space and noncanonical coordinates in phase space is presented. The averaging methods preserve two important features of Hamiltonian systems, viz., conservation of energy (for time‐independent fields) and Liouville’s theorem. These features are sacrificed by the traditional averaging methods. The methods also relieve much of the burden of higher order perturbation calculations, and the drift equations for fully electromagnetic fields are extended to one higher order than they have been known in the past. The first correction to the relativistic magnetic moment is also calculated. Many applications are anticipated, both to single particle motion and to kinetic theory.

ISSN:0031-9171    

DOI:10.1063/1.863594

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A general stability boundary is determined which establishes the minimum Reynolds numberRiand percent area ratio for the onset of flow instabilities. Both nonaxisymmetrix and axisymmetric disturbances were observed. The existance of a finite extent turbulence region is also described.

ISSN:0031-9171    

DOI:10.1063/1.863595

出版商:AIP    

年代:1981

数据来源: AIP