摘要:

The central safety factor during a sawtooth oscillation in material limiter tokamak discharges (scrapeoff plates inserted to the separatrix) in the TOKAPOLE II poloidal divertor tokamak [Phys. Rev. Lett.49, 734 (1982)] is measured to be significantly less than 1 (approximately 0.7) during a sawtooth oscillation. This result is identical to that observed earlier in the same device in magnetic limiter discharges. Thus the presence of scrapeoff plasma beyond the divertor separatrix is not responsible for the absence of total reconnection.

ISSN:0899-8221    

DOI:10.1063/1.859078

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The evolution, through a toroidal magnetoactive plasma of the polarization of an electromagnetic wave and of the energy of the modes into which it splits, is analyzed here under the condition of negligible geometric refraction, also taking into account the possible wave absorption as a result of electron cyclotron resonances. The problem is reduced to the solution of a simple set of first‐order differential equations, avoiding both the complexity of the full Maxwell system and the limitations of a WKB treatment. This differential set is solved numerically, and its results are presented and discussed.

ISSN:0899-8221    

DOI:10.1063/1.859079

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The stabilizing effects of the addition of short‐range collisions to a partially ionized plasma are investigated through a recently developed numerical Laplace transform inversion algorithm. The technique is demonstrated using a two‐stream equilibrium distribution and double Maxwellian equilibrium distributions. The regions of plasma stability obtained in previous studies are verified.

ISSN:0899-8221    

DOI:10.1063/1.859080

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

In this paper the results of fully compressible, Fourier collocation, numerical simulations of the Orszag–Tang vortex system are presented. The initial conditions for this system consist of a nonrandom, periodic field in which the magnetic and velocity field contain X points but differ in modal structure along one spatial direction. The velocity field is initially solenoidal, with the total initial pressure field consisting of the superposition of the appropriate incompressible pressure distribution upon a flat pressure field corresponding to the initial, average Mach number of the flow. In these numerical simulations, this initial Mach number is varied from 0.2–0.6. These values correspond to average plasma beta values ranging from 30.0 to 3.3, respectively. It is found that compressible effects develop within one or two Alfve´n transit times, as manifested in the spectra of compressible quantities such as the mass density and the nonsolenoidal flow field. These effects include (1) a retardation of growth of correlation between the magnetic field and the velocity field, (2) the emergence of compressible small‐scale structure such as massive jets, and (3) bifurcation of eddies in the compressible flow field. Differences between the incompressible and compressible results tend to increase with increasing initial average Mach number.

ISSN:0899-8221    

DOI:10.1063/1.859081

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

It is shown that rippling instabilities can tap the density gradient expansion free‐energy source through the density dependence of the neoclassical resistivity. Linear analyses show that the region where neoclassical rippling modes are significantly excited extends from the edge of the plasma to the region where &ngr;@B|e≤1. Since these modes are nondispersive, diamagnetic effects are negligible in comparison to the nonlinear decorrelation rate at saturation. Thus the relevant regime is the ‘‘strong turbulence’’ regime. The turbulent radial diffusivities of the temperature and the density are obtained as eigenvalues of the renormalized eigenmode equations at steady state. The density gradient acts to enhance the level of turbulence, compared to that driven by the temperature gradient alone. The saturated turbulent state is characterized by current decoupling, the breakdown of Boltzmann relation, a radial mode scale of density fluctuations exceeding that of temperature fluctuations, implying that density diffusivity exceeds temperature diffusivity, and that density fluctuation levels exceed temperature fluctuation levels. Magnetic fluctuation levels are negligible.

ISSN:0899-8221    

DOI:10.1063/1.859030

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The collisionless electron temperature gradient‐driven instability is studied in the parameter regime relevant for field‐reversed configurations. Perturbations in the electrostatic potential and all three components of the vector potential are considered and fully magnetized models, which include finite beta orbit modifications, are used for electrons and ions. It is shown that the electron temperature gradient can drive unstable modes over a wide range of values of &bgr; and &eegr;e. These modes require a finite (but small)kzand propagate in the direction opposite to the lower hybrid drift.

ISSN:0899-8221    

DOI:10.1063/1.859031

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

In this paper numerical simulations are presented of the reversed field pinch (RFP) dynamo effect utilizing the resistive magnetohydrodynamic (MHD) equations in the quasilinear approximation. In addition, a mean field equilibrium magnetic field configuration is constructed in cylindrical geometry by dropping inertia on the symmetric radial component of the velocity field. Results are obtained for a variety of operating conditions: flat‐top current, current ramp‐up, and ramp‐down. It is found that the Alfve´n time, although present in the equations describing the perturbed quantities, is not important on the long resistive run time; the result is a three‐dimensional Ohmic equilibrium with symmetric mean toroidal magnetic field reversal. Using these results, and in view of recent RFP experimental data, a simple correspondence between global MHD behavior in the RFP and the tokamak is given.

ISSN:0899-8221    

DOI:10.1063/1.859032

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Toroidal calculations onm=2 magnetic feedback are presented. These calculations are performed using a coupled &Dgr;’formulation and show that the feedback can have a pronounced effect on the sideband (m=1 and 3) content.

ISSN:0899-8221    

DOI:10.1063/1.859033

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The magnetic configurations of two stellarators, ATF [Fusion Technol.10, 170 (1986)] and TJ‐II [Fusion Technol.13, 315 (1986)], are used as examples to study the influence that a superthermal component in the electron distribution function has upon the electron cyclotron resonance heating absorption process for microwaves propagating in the first and second harmonic of the electron cyclotron frequency. The non‐Maxwellian tail is simulated by adding a drifting Maxwellian to a bulk distribution function and an analytical form of the weakly relativistic dielectric tensor is obtained. The quantitative, and more importantly, the qualitative differences between nonrelativistic and relativistic models are also presented. A numerical analysis shows that an increase of up to 50% in the absorption power with respect to the pure Maxwellian models, can be obtained if sufficient superthermal populations are present in the plasma.

ISSN:0899-8221    

DOI:10.1063/1.859034

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A WKB theory is formulated for large‐nballooning modes in axisymmetric, toroidal plasmas with sheared equilibrium flows. The validity of the standard ballooning representation is severely restricted in the presence of sheared toroidal flow, despite the fact that to leading order in (1/n), wherenis the azimuthal number, the eigenmode equation contains only derivatives along a field line. Necessary and sufficient conditions for stability are obtained in a high‐beta ordering for rigid toroidal rotation as well as field‐aligned flows.

ISSN:0899-8221    

DOI:10.1063/1.859035

出版商:AIP    

年代:1989

数据来源: AIP