摘要:

A review of measurements of ion heat transport in Ohmic and beam‐heated plasmas is given. A study of ion heat transport in Ohmic TFTR plasma is also reported. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.44527

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Ion temperature profiles of neutral beam heated plasmas in JT‐60 have been simulated by using models of ion thermal diffusivity, &khgr;i, based on ion temperature gradient mode (&eegr;imode) turbulence and drift wave turbulence (trapped electron mode and circulating electron mode). Three different &khgr;imodels proposed by Dominguez and Waltz, Lee and Diamond, and Romanelli are adopted and the predictedTiprofiles are compared with those measured by CXRS (charge exchange recombination spectroscopy). All three &khgr;imodels can fit theTiprofile over wide range of plasma parameters of JT‐60L‐mode plasmas except for 1 MA limiter cases. However, in the high ion temperature (highTi) plasmas, the predictedTiprofiles are much broader than that of experiment.

ISSN:0094-243X    

DOI:10.1063/1.44529

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Validity of the ion temperature gradient mode (&eegr;imode) driven turbulent transport has been studied by comparing the nonlinear simulation results based on fluid‐type moment equations and profile data observed in JT‐60 experiments. Toroidal &eegr;imodes give the reasonable value of thermal diffusivity in the half‐way region of the plasma, while both toroidal and slab modes give the diffusivity strongly decreasing near the plasma periphery. Both the trapped electron effect and the neoclassical one have been also studied and tested in the edge region, but these effects are found to be not enough to explain experimental results.

ISSN:0094-243X    

DOI:10.1063/1.44531

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Measured profiles of the ion thermal diffusion coefficients &khgr;iexp(r) are compared with neoclassical predictions as well as with several predicted theoretical expressions that describe transport driven by the ion temperature gradient instability. While the multitude of &eegr;i‐models presently available makes a conclusive comparison between theory and experiment difficult, the overall magnitude of the predicted quantities, for some of the models, are reasonable. Steepening of the density profile by pellet injection did not reduce the anomaly in &khgr;iexp.

ISSN:0094-243X    

DOI:10.1063/1.44532

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Both the slab and toroidal branches of the ion temperature gradient (ITG) driven instabilities have been studied in the Columbia Linear Machine (CLM). The ITG instabilities are observed asm=2 modes when a sufficient parallel ion temperature gradient is reached by using either d.c. ion acceleration heating or rf‐transit time heating methods. The slab branch,m=2 mode, is identified as the ITG mode based on the four basic characteristics predicted by most theoretical work. The toroidal ITG mode is studied by starting with the slab ITG mode and gradually turning on the mirror current in CLM. The curvature effect is shown to further destabilize the mode and reduce the real frequency in the laboratory frame. The experimentally measured features in the presence of the ion temperature gradient and the mirror field also correspond closely to the theoretical predictions of a newly postulated hybrid ITG‐dissipative trapped electron drift mode. The anomalous local ion thermal conductivities due to the slab mode has been measured via a temperature relaxation method. Its average value of 0.5 m2/sec is about 3 orders of magnitude larger than the classical and 1 order of magnitude lower than the Bohm.

ISSN:0094-243X    

DOI:10.1063/1.44524

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

For high‐density ohmic discharges in the TEXT tokamak, a distinct ion mode (i.e., density fluctuations propagating in the ion diamagnetic drift direction) is observed in the microturbulence spectra. The magnitude and spectral characteristics of the mode are identified. Onset of the ion feature occurs at plasma densities where a clear saturation is evident in the global energy confinement time. By injecting pellets, a high‐density plasma is created in which the density profile is sharply peaked. Under these conditions the ion feature in the fluctuation spectra is suppressed. Possible connection between this experimentally observed ion mode and the theoretically predicted properties of the ion‐temperature‐gradient‐driven turbulence is explored. Experimental evidence from other devices is also discussed along with a critical evaluation of interpretation issues.

ISSN:0094-243X    

DOI:10.1063/1.44525

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Transport analysis for helical confinement systems are studied based on the electrostatic drift wave turbulence transport and the resistive interchange turbulence transport in addition to the neoclassical transport theory including the effect of radialelectric field and multi‐helicity magnetic components. The thermal conductivities predicted by the above theories are compared with CHS (compact helical system) experimental data for NBI‐heated plasmas. The experimental ion thermal conductivities in the central plasma region agree with the neoclassical value. And the electron thermal transport in the edge plasma region does not contradict the drift wave turbulence transport. For the plasma parameters in LHD (large helical device), 3‐D equilibrium/1‐D transport simulations including drift wave or empirical anomalous transport models are carried out, which suggests that the global confinement time of LHD is determined mainly by the electron anomalous transport near the plasma edge region rather than the helical ripple transport in the core region.

ISSN:0094-243X    

DOI:10.1063/1.44526

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A comprehensive program for the development and use of particle simulation techniques for solving the gyrokinetic Vlasov‐Maxwell equations on massively parallel computers has been carried out at Princeton Plasma Physics Laboratory. This is a key element of our ongoing theoretical efforts to systematically investigate physics issues vital to understanding tokamak plasmas. In this work, our focus is on the various aspects of spatial‐gradient‐driven microinstabilities. Although their presence is consistent with a number of significant confinement trends, results from high temperature tokamaks such as TFTR have highlighted the need for better insight into the linear and nonlinear properties of such instabilities in long‐mean‐free‐path plasmas. In addressing this general issue, we report important new results including (i) the first fully toroidal 3D gyrokinetic simulation of ITG modes and (ii) the comparisons of the fluctuation spectra in the simulation with those from the recent BES measurements of the TFTR core plasma for the supershot discharges. We also discuss (iii) the effects of ITG modes on the inward pinch of impurities in 3D slab geometry and (iv) the finite‐&bgr; stabilization of microinstabilities in 1D simulation. Finally, (v) the relationship between energy flux and entropy production in the simulation is explored.

ISSN:0094-243X    

DOI:10.1063/1.44530

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The ion temperature gradient‐driven mode, in three dimensional sheared‐slab geometry, is investigated using fully nonlinear and low noise, weighted‐particle gyrokinetic particle‐in‐cell models. Comparisons between the two models are made and in certain regimes the agreement is good. the adiabatic, Boltzman response model is used for the electron density but alternative treatments are discussed in relation to the development of equilibrium poloidal shear flows. Single and multiple rational surface results from nonlinear simulations are presented for parameters relevant to present experimental regimes. Quasilinear versus turbulent saturation dynamics is contrasted and the ion thermal diffusivity is enhanced by nonlinear interaction between modes with different rational surfaces. Kinetic mixing length diffusivities give good estimates of the radial ion thermal flux measured in the simulations.

ISSN:0094-243X    

DOI:10.1063/1.44508

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We investigate the anomalous heat conduction in a tokamak plasma analytically and computationally. Our toroidal particle simulation shows a new emerging physical picture that the toroidal plasma exhibits marked properties distinct from a cylindrical plasma: (i) the development of radially extended potential streamers localized to the outside of the torus, (ii) more robust ion temperature gradient instability, (iii) radially constant eigenfrequency, (iv) global temperature relaxation, and (v) radially increasing heat conductivity &khgr;i. These results are analyzed by linear and quasilinear kinetic theory. A relaxation theory based on the reductive perturbation theory in the quasilinear equation is developed. The theory constrains the thermal flux so that &khgr;iincreases radially. The Bohm‐like scaling is found in connection with the radially extended mode structure.

ISSN:0094-243X    

DOI:10.1063/1.44509

出版商:AIP    

年代:1994

数据来源: AIP