摘要:

The theoretical calculation of electron transport properties in partially ionized gases using a Laguerre (or Sonine) polynomial expansion has met with convergence difficulties in certain cases, in particular, when there is a Ramsauer minimum in the electron‐neutral momentum transfer cross section. In this work, which deals specifically with electrical conductivity, it is shown that the difficulties can be avoided by choosing a (nonorthogonal) expansion that includes a limiting‐case analytical solution. With some simplifications, the approach leads to a practical formula for the conductivity involving generalized collision integrals. A formula based on a BGK‐type approximation to the electron–electron collision operator is also given. Calculated conductivities are found to agree well with the more sophisticated expansion method.

ISSN:0031-9171    

DOI:10.1063/1.865970

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The class of isodynamic magnetohydrodynamic (MHD) equilibria in three dimensions is studied. A reduction of the problem to that of finding a force‐free equilibrium is carried out, and the resulting force‐free problem transformed, by means of a three‐dimensional hodograph technique, to a simple and elegant form. The flux surface equation in a potentially very useful form is split off in a further representation.

ISSN:0031-9171    

DOI:10.1063/1.865972

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Solutions of the Alfve´n wave continuum equation for a pressureless, magnetohydrodynamic plasma in nonaxisymmetric, toroidal geometry are presented. The analysis is based on the Hamiltonian form of the continuum equation along lines of force of the equilibrium magnetic field. Canonical transformation methods are invoked to determine approximate solutions of the continuum equation. The approximate solutions are used to identify the conditions that govern the Alfve´n continuous spectrum in nonaxisymmetric toroidal geometry.

ISSN:0031-9171    

DOI:10.1063/1.865973

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A plasma in contact with an external source of power, especially a source that interacts specifically with highvelocity electrons, exhibits transport properties, such as conductivity, different from those of an isolated plasma near thermal equilibrium. This is true even when the bulk of the particles in the driven plasma is near thermal equilibrium. To describe the driven plasma, we derive an adjoint equation to the inhomogeneous, linearized, dynamic Boltzmann equation. The Green’s functions for a variety of plasma responses can then be generated. It is possible to modify the Chapman–Enskog [MathematicalTheoryofNonuniformGases, 3rd ed., (Cambridge U.P., Cambridge, MA, 1970)] expansion in order to incorporate the response functions derived here.

ISSN:0031-9171    

DOI:10.1063/1.865974

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A theory for the generation of current in a toroidal plasma by radio‐frequency waves is presented. The effect of an opposing electric field is included, allowing the case of time varying currents to be studied. The key quantities that characterize this regime are identified and numerically calculated. Circuit equations suitable for use in ray‐tracing and transport codes are given.

ISSN:0031-9171    

DOI:10.1063/1.865975

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The poloidal potential is calculated numerically in the low‐collisionality regime for nonaxisymmetric tori such as stellarators and bumpy tori. It is found that even fairly deep into the superbanana regime, the poloidal potential retains the simple azimuthal dependence of the plateau regime.

ISSN:0031-9171    

DOI:10.1063/1.865976

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The effect of turbulent electron diffusion from stochastic electron orbits on the stability of low‐beta fluctuations is considered through the use of the normal stochastic approximation. A set of coupled, self‐adjoint equations is derived for the fluctuation potentials &fgr;˜ andA˜∥. Solutions to this set of equations describe both unstable finite‐&bgr; drift waves when analyzed for high‐mmodes and the tearing mode when analyzed for low‐mmodes. For the tearing mode, it is shown that stability is obtained for sufficiently large values of the diffusion coefficient. ProvidedDe∼1/n, this implies that a density threshold must be surpassed before the tearing mode is observed. Physically, turbulent electron diffusion prohibits the formation of a perturbed current within a finite region about the rational surface. At higher densities, the inclusion of a finite electrostatic potential &fgr;˜ gives an additional stabilizing term to the dispersion relation, which physically represents ion inertial effects. This ion inertial effect implies that, in the absence of diffusion, the tearing mode is stabilized for ion betas &bgr;iabove some critical value.

ISSN:0031-9171    

DOI:10.1063/1.865977

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The effects of nonadiabaticity and electromagnetic fluctuations on the steady‐state properties of the ELMO Bumpy Torus (EBT) [Nucl. Fusion20, 403 (1980); Phys. Fluids27, 1759 (1984)] hot electron annulus are calculated using a multifluid approach. These effects are added to those previously included to form a comprehensive picture of EBT ring properties, scaling, and spatial location.

ISSN:0031-9171    

DOI:10.1063/1.865978

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Turbulence associated with sheared radial electric fields such as those arising in tokamak edge plasmas is investigated analytically. Two driving mechanisms are considered: in the region of maximum vorticity (maximum electric field shear), the electric field is the dominant driving mechanism. Away from the maximum, turbulence is driven by the density gradient. In the latter case, previous work is extended to include the effects of the electric field on the spatial scales of density correlation in the frequency‐Doppler‐shifted, density‐gradient‐driven turbulence. For radial‐electric‐field‐driven turbulence, the effects of magnetic shear on linear instability and on fully developed turbulence are examined. In the case of weak magnetic shear, saturation occurs through an enstrophy cascade process which couples regions of driving and dissipation in wavenumber space. For stronger magnetic shear, such that the width of the dissipation region resulting from parallel resistivity is comparable to the radial electric field scale length, saturation occurs through nonlinear broadening of the mode structure, which pushes enstrophy into the region of dissipation. Estimates of mode widths, fluctuation levels, and scalings are obtained for both mechanisms. Comparison is made with the results of fluctuation measurements in the TEXT tokamak [Phys. Fluids27, 2956 (1984)].

ISSN:0031-9171    

DOI:10.1063/1.865979

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Equilibria with minimum energy are constructed from a variational principle in which the potential energy of a plasma is minimized, subject to a small set of global invariants. These invariants are preserved exactly, by ideal motions of the plasma, and approximately, by a tearing mode of them=1,n=1 type. Estimates of decay rates for the energy and the invariants are given. A tokamak window with lowqand zero current on the boundary is found and shown to be ideally and resistively stable. The reversed‐field pinch (RFP) window and the transition region between the two windows is found to be unstable to high‐nmodes.

ISSN:0031-9171    

DOI:10.1063/1.865981

出版商:AIP    

年代:1986

数据来源: AIP