摘要:

General plasma physics principles state that power flowQ(r) through a magnetic surface in a tokamak should scale asQ(r)= {32&pgr;2Rr3Te2c nea/[eB(a2−r2)2]}F(&rgr;*,&bgr;,&ngr;*,r/a,q,s,r/R,...) where the arguments ofFare local, nondimensional plasma parameters and nondimensional gradients. This paper reports an experimental determination of howFvaries with normalized gyroradius &rgr;*≡(2TeMi)1/2c/eBaand collisionality &ngr;*≡(R/r)3/2qR&ngr;e(me/ 2Te)1/2for discharges prepared so that other nondimensional parameters remain close to constant. Tokamak Fusion Test Reactor (TFTR) [D. M. Meadeetal., inPlasmaPhysicsandControlledNuclearFusionResearch, 1990, Proceedings of the 13th International Conference, Washington (International Atomic Energy Agency, Vienna, 1991), Vol. 1, p. 9] L‐mode data showFto be independent of &rgr;* and numerically small, corresponding to Bohm scaling with a small multiplicative constant. By contrast, most theories predict gyro‐Bohm scaling:F∝&rgr;*. Bohm scaling implies that the largest scale size for microinstability turbulence depends on machine size. Analysis of a collisionality scan finds Bohm‐normalized power flow to be independent of collisionality. Implications for future theory, experiment, and reactor extrapolations are discussed.  

ISSN:0899-8221    

DOI:10.1063/1.860534

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A boundary plasma fluid model that takes into account nonuniform magnetic fields in the previous study [T. Ohiraetal., Phys. Fluids B3, 2010 (1991)] is presented. From the numerical simulations based on the model, it was observed that cross‐field particle fluxes in a cylindrical scrape‐off layer (SOL) plasma are dramatically influenced by azimuthal (poloidal) changes in applied axial magnetic fields. In this study, experiments to confirm the numerical results and the phenomenon have been made. Two‐dimensional (r,&thgr;) distributions of plasma density, electron temperature, floating potential, and plasma potential in the cylindrical SOL plasma with and without nonuniform magnetic fields have been measured by 12 single probes located every 30° azimuthally. The nonuniform magnetic fields were produced by ferromagnetic amorphous shells. It was observed that the densities in the SOL plasma decrease where the axial magnetic fields have positive gradient azimuthally and increase where negative in the real experiment. In addition, the phenomenon could be simulated by the two‐dimensional SOL plasma code developed in the previous study. It is thought that this might be due to azimuthal mobility flows and cross‐fieldE×Bflows which are influenced by nonuniform magnetic fields.

ISSN:0899-8221    

DOI:10.1063/1.860535

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The three‐dimensional nonlinear kinetic equation for low collisionality tokamak plasmas with consistent consideration of neoclassical effects is obtained using an approach differing from the standard neoclassical theory technique. This allows treatment of large banana widths and large inverse aspect ratios. The equation is suitable for computer modeling of bootstrap currents and other phenomena arising from non‐Maxwellian distributions. The formalism described in this paper, which is for noncanonical variables, might also be of use for the consistent derivation of three‐dimensional kinetic equations that treat other effects, for example, additional heating.

ISSN:0899-8221    

DOI:10.1063/1.860536

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A comprehensive stability analysis of the ion‐temperature‐gradient‐driven mode in various parameter domains is presented. The effect of parallel ion dynamics on the threshold value in toroidal geometry is investigated for the short‐wavelength and finite‐shear limits. A general explicit expression for the threshold is given, which is in agreement with the results obtained by solving the full integrodifferential equation. The destabilizing effect of trapped electrons below the threshold is qualitatively similar to the results of local theory, but electron collisionality has to be sufficiently weak. In the long‐wavelength limit, two branches exist, respectively, toroidal and slablike in character. The toroidal branch has been investigated elsewhere [Romanellietal., Phys. Fluids B3, 2496 (1991)]. In this paper, the stability of the slablike branch is studied both analytically and numerically. The trapped‐ion effects on the threshold are discussed in detail.

ISSN:0899-8221    

DOI:10.1063/1.860537

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The toroidal field in the translated field‐reversed configuration (FRC) plasma has been measured, although the FRC plasma has sometimes been described as having only the poloidal field. Measurements of the toroidal field distribution during the plasma translation clarify the location where the toroidal field originates. The experimental results show that the flux of poloidal and toroidal components decays monotonically in time after the beginning of the translation. This indicates that the toroidal field occurs just after the FRC formation without further production during the translation.

ISSN:0899-8221    

DOI:10.1063/1.860538

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Current drive via nonresonant interaction between radio‐frequency (rf) waves and plasma is studied. The averaged force of rf waves acting on each species of a plasma can be divided into a resonant force and a nonresonant one. A part of the nonresonant force cannot be expressed by a gradient of a scalar potential and remains after integrating along the direction of the force. This force mainly acts as an internal force among plasma species and the net momentum input from the wave to the plasma is usually small. This process is not included in the conventional current drive schemes but is associated with the rf wave helicity injection. Quantitative analysis using a one‐dimensional kinetic wave code is applied to waves in the ion cyclotron range of frequencies and low‐frequency Alfve´n waves in a large tokamak. The driven current is estimated taking account of the effect of the toroidally trapped particles. The spatial profile of the forces acting on electrons and ions as well as the driven current are obtained. The parameter dependence of the current drive efficiency on the wave number, the plasma density, the temperature, and the toroidal magnetic field is compared with the estimate based on a local analysis.

ISSN:0899-8221    

DOI:10.1063/1.860539

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Experiments have been performed on the Reversatron II [IEEE Trans. Plasma Sci.PS‐16, 667 (1988)] reversed‐field pinch to study phase locking of kink modes in discharges with thick and thin shells. In the thick shell discharges, internal modes which are resonant or nearly resonant on axis are found to phase lock at random locations in toroidal angle. Externally nonresonant modes which lock tend to do so at the shell gap. In the thin shell discharges, the internally resonant modes and the externally nonresonant modes both tend to lock at the shell gap. Phase locking is not observed in every shot and the duration of the locking varies. The position of locking does not rotate.

ISSN:0899-8221    

DOI:10.1063/1.860540

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The Reversatron II [IEEE Trans. Plasma Sci.PS‐16, 667 (1988)] reversed‐field pinch has been operated with shells having magnetic penetration time comparable to and shorter than the discharge duration. The spectra and growth rates of the resistive wall modes have been measured and compared for the two cases. The growth rates of modes are typically in the expected range &ggr;&tgr;s=0.5–2 where &ggr; is the growth rate and &tgr;sis the magnetic penetration time of the shell. The spectra, however, are broader than expected from linear theory and there are indications that both the growth rates and the mode spectra are affected by nonlinearities.

ISSN:0899-8221    

DOI:10.1063/1.860541

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The nonlinear interaction of an ultrashort‐pulse laser with a solid target is investigated by using a newly developed particle simulation code, which enables the analysis of laser–plasma interaction in the very steep density gradient in which the laser light penetrates into an overdense plasma. For an ultrashort laser pulse, the plasma density scale lengthLdsatisfiesLd≤r0for an electron excursion lengthr0. Laser absorption and electron acceleration processes are proposed for the above situation. It is found that the wave breaking is the main mechanism of the electron acceleration and laser absorption, as is discussed in Brunel’s paper [Phys. Rev. Lett.59, 52 (1987)].

ISSN:0899-8221    

DOI:10.1063/1.860542

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The nonlinear saturation amplitudes attained by Rayleigh–Taylor perturbations growing on ablatively stabilized laser fusion targets are crucial in determining the survival time of those targets. For a given set of baseline simulation parameters, the peak amplitude is found to be a progressive function of cross‐sectional perturbation shape as well as of wave number, with three‐dimensional (3‐D) square modes and two‐dimensional (2‐D) axisymmetric bubbles saturating later, and at higher amplitudes than two‐dimensional planar modes. In late nonlinear times hydrodynamic evolution diverges; the 3‐D square mode bubble continues to widen, while the 2‐D axisymmetric bubble fills in.

ISSN:0899-8221    

DOI:10.1063/1.860543

出版商:AIP    

年代:1993

数据来源: AIP