摘要:

A thermodynamic model is developed for plasma systems that are forced to carry an electrical current which prevents relaxation into global thermodynamic equilibrium. Complementary to earlier approaches in the framework of resistive magnetohydrodynamics, the role of nonresistive dissipation is analyzed by excluding momentum transfer between different particle species (electrons and ions). The general class of steady states compatible with the assumptions is found and their structures and symmetries are discussed. The second law of thermodynamics guarantees the existence of a generalized thermodynamic potential (including contributions of the electromagnetic field) which has a negative time derivate for all dynamical states subject to the equilibrium symmetry and boundary conditions. Applying Lyapunov’s theory, this functional provides a necessary and sufficient stability criterion. The linearized version of this criterion and the corresponding eigenvalue problem are also derived.

ISSN:0031-9171    

DOI:10.1063/1.866408

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A unified theory for the dynamics of thermally driven convective cell turbulence is presented. The cells are excited by the combined effects of radiative cooling and resistivity gradient drive. The model also includes impurity dynamics. Parallel thermal and impurity flows enhanced by turbulent radial diffusion regulate and saturate overlapping cells, even in regimes dominated by thermal instability. Transport coefficients and fluctuation levels characteristic of the saturated turbulence are calculated. It is found that the impurity radiation increases transport coefficients for high density plasmas, while the parallel conduction damping, elevated by radial diffusion, in turn quenches the thermal instability. The enhancement due to radiative cooling provides a resolution to the dilemma of explaining the experimental observation that potential fluctuations exceed density fluctuations in the edge plasma (e&Fgr;/Te>n/n0).

ISSN:0031-9171    

DOI:10.1063/1.866409

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A theory of anomalous electron heat transport, evolving from trapped‐particle‐induced resistive interchange modes, is proposed. The latter are a new branch of the resistive interchange‐ballooning family of instabilities, destabilized when the pressure carried by the unfavorably drifting trapped particles is sufficiently large to overcome stabilizing contributions coming from favorable average curvature. Expressions for the turbulent heat diffusivity and anomalous electron thermal conductivity at saturation are derived for two regimes of trapped‐particle energy: (i) a moderately energetic regime, which is ‘‘fluidlike’’ in the sense that the unstable mode grows faster than the time that it takes for particles in this energy range to precess once around the torus, and (ii) a highly energetic regime, where the trapped species has sufficiently high energy as to be able to interactresonantlywith the mode. Unlike previous theories of anomalous transport, the estimates of diffusion and transport obtained here are self‐consistent since the trapped particles do not ‘‘see’’ the magnetic flutter due to their rapid bounce motion. The theory is valid for moderate electron‐temperature, high ion‐temperature (auxiliary heated) plasmas and as such, is relevant for present‐ and future‐generation experimental fusion devices.

ISSN:0031-9171    

DOI:10.1063/1.866410

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The absorption of electron cyclotron waves in hot and dense plasmas is investigated by using the relativistic dispersion relation with finite Larmor radius (FLR) corrections. It is shown that the strong reduction caused by FLR effects on the damping of extraordinary waves propagating perpendicularly to the magnetic field becomes insignificant at large values of the parallel component of the refractive index. An application of these results to the auxiliary heating of dense plasmas of a compact ignition tokamak [PlasmaPhysicsandControlledNuclearFusion1986 (IAEA, Vienna, 1987), Vol. 3] is given. It is shown that the extraordinary mode with oblique propagation and frequency of 190 GHz can be strongly absorbed by dense plasmas with a toroidal magnetic field of 105 kG and a central electron density of 1×1015cm−3.

ISSN:0031-9171    

DOI:10.1063/1.866411

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

It is shown that toroidicity has stabilizing effects on the rippling mode in tokamaks. For typical tokamak edge parameters, the instability as predicted in slab geometry is unlikely to exist.

ISSN:0031-9171    

DOI:10.1063/1.866412

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A new method for simulating gyromicrowave devices is suggested. The electron trajectories are represented in a Fourier series in initial gyrophases. Linear theory is reproduced by using three Fourier amplitudes. The nonlinear regime can be described by a relatively small number of amplitudes.

ISSN:0031-9171    

DOI:10.1063/1.866413

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The theory of kinetic instabilities in a plasma when the instabilities are driven by wave‐particle resonance is addressed. Recent progress on the linear theory of resonant oblique wave growth in plasmas is extended to plasmas modeled by three standard forms of distribution, a bi‐Maxwellian, a bi‐Lorenzian, and a loss cone, each incorporating a field‐aligned beam. The wave growth rates are shown to be functions of dimensionless integrals that can be expressed in terms of Bessel functions of argument equal to a normalized wave‐normal variable. A marginal stability criterion is obtained, and accordingly we identify a threshold beam velocity for unstable growth of the waves. The simple analytical results derived can be readily applied to a wide variety of problems on oblique wave growth in space plasmas that hitherto were amenable only to extensive computer calculations.

ISSN:0031-9171    

DOI:10.1063/1.866414

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A two‐dimensional, three‐fluid code based on the two‐fluid Potter code [MethodsinComputationalPhysics(Academic, New York, 1970), Vol. 9, p. 340] was developed for simulating the plasma focus discharge. With this code it is possible to treat the neutral gas in addition to the plasma components and to model the ionization and recombination phenomena. Thus the sheet dynamics in a plasma focus can be studied and effects investigated such as the occurrence of residual gas (or plasma) density behind the current sheet in the run‐down phase. This is a prerequisite to the occurrence of leak currents, which are one of the causes limiting the performance of large plasma focus devices. It is shown that fast operating foci with small dimensions behave favorably compared with the ‘‘classical’’ Mather focus [MethodsofExperimentalPhysics(Academic, New York, 1971), Vol. 9B, p. 187] with long coaxial electrodes.

ISSN:0031-9171    

DOI:10.1063/1.866524

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A one‐dimensional fluid theory of Langmuir probe operation in strong magnetic fields is presented. Cross‐field diffusion of ions both into and out of the the collection region is consistently accounted for, in effect taking momentum and particle diffusivity to be equal. The results differ by significant factors from previous analyses, which did not account for outward diffusion but in effect set momentum diffusivity to zero. The differences are especially large when parallel flow of the external plasma is present. It is thus clear that the value assumed for the momentum diffusivity strongly affects the interpretation of recent probe measurements. It is argued that the present results offer a more reliable basis for this interpretation.

ISSN:0031-9171    

DOI:10.1063/1.866415

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Alpha interactions with neutrals in the ablation cloud of a refueling pellet are considered as a fast alpha diagnostic through charge‐capture radiation (ACCR) by the alphas or their complete neutralization and escape. Calculations of pellet penetration into a reactor plasma indicate that regions ofr/a>0.61 could be reached by refueling pellets with initial radii of 4 mm, hence this would be an outer core diagnostic. A spherically symmetric neutral‐gas shielding model (SSMNGSM) in which ionization is treated self‐consistently and governed by local thermodynamic equilibrium is used in these calculations. Collisional processes are found to govern the alpha–cloud interactions and local equilibrium calculations were performed in which the charge exchange and ionization cross sections are used to obtain the state fractions of the alphas in the cloud. At 1640 A˚ the ratio of ACCR to cloud bremsstrahlung is found to be 10−5whereas at 304 A˚ this ratio ranges from 3×10−3to 0.5 for the cases considered; no neutralized alphas escape the cloud. Magnetic field effects are considered and they appear to reduce the bremsstrahlung from the cloud by a factor of 300 at 304 A˚ in regions perpendicular to the magnetic field from the pellet’s surface; escape of neutralized alphas may be possible in these directions. Alpha refueling pellet interactions are potentially useful as outer core fast alpha diagnostics and this could be tested in near term experiments.

ISSN:0031-9171    

DOI:10.1063/1.866416

出版商:AIP    

年代:1987

数据来源: AIP