摘要:

The marginal stability of the ion temperature profiles for bothL‐mode and supershots is analyzed using a fully implicit &dgr;fgyrokinetic code including most relevant kinetic and collisional effects. The stability results tend to indicate that theL‐mode discharges are in agreement with the marginal stability hypothesis in the core while the pellet shot is rather well above the critical temperature gradient. The linear stability results are highly inconsistent with the experimentally inferred transport, which implies that effects beyond lowest order ballooning theory must be important.

ISSN:0094-243X    

DOI:10.1063/1.44510

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Transport due to toroidal &eegr;iand collisionless trapped electron modes is studied using an advanced reactive fluid model. Transport code simulations of DIII‐D and JET discharges are analyzed. The recent experimental results with off‐axis electron cyclotron heating in the DIII‐D tokamak [Phys. Rev. Lett.68, 52 (1992)] are recovered with inward flow of electron energy and peaked electron temperature profile. For the JET equilibria the model gives heat diffusivities of the correct order of magnitude which grow with radius up tor/a=0.8.

ISSN:0094-243X    

DOI:10.1063/1.44511

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The method of Hammett and Perkins [Phys. Rev. Lett.64, 3019 (1990)] to model Landau damping has been recently applied to the moments of the gyro‐kinetic equation with curvature drift by Waltz, Dominguez, and Hammett [Phys. Fluids B4, 3138 (1992)]. The higher moments are truncated in terms of the lower moments (density, parallel velocity, and parallel and perpendicular pressure) by modeling the deviation from a perturbed Maxwellian to fit the kinetic response function at all values of the kinetic parameters:k∥vth/&ohgr;,b=(k⊥&rgr;)2/2, and &ohgr;D/&ohgr;. Here the resulting gyro‐Landau fluid equations are applied to the simulation of ion temperature gradient (ITG) mode turbulence in toroidal geometry using a novel 3D nonlinear ballooning mode representation. The representation is a Fourier transform of the Cowleyetal. [Phys. Fluids B3, 2767 (1991)] field line following twisted eddy basis (kx’,ky’,z’) with periodicity in toroidal and poloidal angles. Particular emphasis is given to the role of nonlinearly generatedn=0 (ky’=0,kx’≠0) ‘‘radial modes’’ in stabilizing the transport from the finite‐nITG ballooning modes.

ISSN:0094-243X    

DOI:10.1063/1.44512

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Early results from nonlinear simulations and analysis based on a recently derived nonlinear gyrofluid model [W. Dorland and G. W. Hammett, Phys. Fluids B, 812 (1993)] of electrostatic ion‐temperature‐gradient driven turbulence are presented. Comparisons with gyrokinetic particle simulations reveal a few important simulation requirements (such as enforcing radial periodicity), and indicate that the gyrofluid description is probably adequate to describe three‐dimensional, low‐frequency drift‐type turbulence. Results from a detailed weak‐turbulence analysis of drift wave turbulence are presented which support this conclusion. The importance of keeping the proper adiabatic electron response is also discussed. In particular, perpendicular velocity shear is greatly enhanced when the magnetic shear is weak if the nonphysical radial transport of electrons is disallowed.

ISSN:0094-243X    

DOI:10.1063/1.44513

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Low frequency drift‐type microinstabilities driven by trapped‐electron and ion temperature gradient dynamics continue to be among the more strongly supported candidates to account for the anomalous transport observed in tokamak plasmas. The possible relevance of these instabilities is addressed by applications of realistic kinetic stability calculations in toroidal geometry using parameters specific to TFTR confinement experiments of interest. With regard to examining the basic question of how sensitive transport might be to spatial gradient variations, representativeL‐mode cases have been analyzed by artificially varying the local density and temperature gradients for each species.

ISSN:0094-243X    

DOI:10.1063/1.44514

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An analysis of the radial structure of the ion temperature gradient driven mode is presented and the dependence of the radial correlation lengthLron parameters such as magnetic shear is discussed. It is found thatLrdecreases algebraically with increasing shear for moderate shear values, and it decreases exponentially with decreasing shear for low shear values. These results seem in qualitative agreement with several experiment which observe strong reduction of the transport coefficients close to the magnetic axis.

ISSN:0094-243X    

DOI:10.1063/1.44515

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The radial profile problem of the anomalous ion thermal conductivity &khgr;iwhich is observed to increase with the minor radius, unlike the expectation from the usual drift wave turbulence transport model, is reconsidered in terms of the toroidal ion temperature gradient mode transport model. First, we discuss several stabilizing factors which may be closely related to the decrease of &khgr;iin the core region, Secondly, we present some possible models to explain the large &khgr;inear the edge region.

ISSN:0094-243X    

DOI:10.1063/1.44516

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Cross‐field energy flux which is consistently related to the dispersion relation has been evaluated in a tokamak. Resultant ion heat conductivity profile shows similar behavior as the simple one derived under many assumptions. The effect of continuous eigenvalue spectrum given by the toroidal ion drift resonance on the thermal flux, which may be considered as the free streaming ion effect, is also evaluated. It is found that the continuum contribution to heat conductivity increases sharply near the edge, which may have correlation with experimentally observed behavior.

ISSN:0094-243X    

DOI:10.1063/1.44517

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Interest in plasma pinches has recently increased due to the observation in electron cyclotron heated (ECH) plasmas in the Doublet III‐D (DIII‐D) tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] of an electron energy pinch. Previous work on drift wave‐induced particle and electron energy pinches concluded that they were only possible in strictly collisionless plasmas, &ngr;*=0, an assumption not applicable to electron cyclotron heating experiments. In the present work it is shown that a more detailed quasilinear analysis predicts a particle pinch at moderate collisionality, &ngr;*=0.2 to 1.0, when the electron temperature gradient parameter &eegr;eis in the range &eegr;e=2 to 3. Further, the quasilinear analysis is expanded to include the effects of turbulent resonance broadening on the circulating electrons. It is then found that, in addition to a particle pinch (qualitatively the same as the quasilinear prediction), a simultaneous particle and electron energy pinch at moderate collisionality can occur at &eegr;e&bartil;1, which is lower than in ECH experiments where &eegr;e=2 to 3.

ISSN:0094-243X    

DOI:10.1063/1.44518

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The combined effects of collisions, an ion temperature gradient, and the presence of an impurity are studied in the context of a sheared slab magnetic configuration. Unstable electrostatic modes, that propagate in the electron diamagnetic direction, are found to exist for a wide range of parameters and to be unstable for both strong and weak magnetic shear. The linear eigenfunctions have extended structure in the radial direction.

ISSN:0094-243X    

DOI:10.1063/1.44519

出版商:AIP    

年代:1994

数据来源: AIP