Gyrokinetic turbulent transport simulation of a high ion temperature plasma in large helical device experiment

Abstract

Ion temperature gradient turbulent transport in the large helical device (LHD) is investigated by means of gyrokinetic simulations in comparison with the experimental density fluctuation measurements of ion-scale turbulence. The local gyrokinetic Vlasov simulations are carried out incorporating full geometrical effects of the LHD configuration, and reproduce the turbulent transport levels comparable to the experimental results. Reasonable agreements are also found in the poloidal wavenumber spectra of the density fluctuations obtained from the simulation and the experiment. Numerical analysis of the spectra of the turbulent potential fluctuations on the two-dimensional wavenumber space perpendicular to the magnetic field clarifies the spectral transfer into a high radial wavenumber region which correlates with the regulation of the turbulent transport due to the zonal flows. The resultant transport levels at different flux surfaces are expressed in terms of a simple linear relation between the transport coefficient and the ratio of the squared turbulent potential fluctuation to the averaged zonal flow amplitude. V C 2012 American Institute of Physics. [http://dx

A reduced model for ion temperature gradient turbulent transport in helical plasmas

“…Using GKV-X, various nonlinear local simulations of the ITG turbulent transport in LHD plasmas with high ion temperature are performed at several radial positions, q r=a with the minor radius a, in two different field configurations with the major radius R 0 ¼ 3.75 m and 3.6 m. The field configuration with R 0 ¼ 3.75 m corresponds to the LHD plasma #88343 investigated in Ref. 3, and the configuration with R 0 ¼ 3.6 m, which has a more inward-shifted magnetic axis position, is one of the optimized configurations to reduce the neoclassical transport. 25 Based on the temperature and density profiles and field configurations obtained from the high ion temperature LHD experiments, the ion temperature gradient R 0 /L Ti , density gradient R 0 /L n , safety factor q, magnetic shear s ðr=qÞdq=dr, and other parameters are varied in a realistic region of parameter space covered by high ion temperature LHD plasmas.…”

“…Indeed, comparisons between gyrokinetic turbulence simulations and experiments have been made not only for tokamaks 2 but also for helical plasmas. 3 Since the turbulence simulations require expensive computational costs, it is not practical to perform nonlinear gyrokinetic simulations a large number of times for the purpose of surveying the transport levels in a wide space of multiple parameters corresponding to various experimental conditions. Especially, gyrokinetic simulations for helical systems such as stellarators and heliotrons [4][5][6][7] tend to consume much larger computational resources than for tokamaks because of the higher spatial resolutions required by the complicated helical field structure.…”

“…In our previous papers, 3,16 we performed gyrokinetic Vlasov simulations for ITG turbulent transport in the Large Helical Device 17 (LHD) plasma with the high ion temperature 18 by using the local flux-tube code, GKV-X. 19 In the GKV-X simulations, the nonlinear gyrokinetic equation for the perturbed ion gyrocenter distribution function 20,21 in the low-b electrostatic limit…”

Relation among ITG Turbulence, Zonal Flows, and Transport in Helical Plasmas

“…In addition to the physical clarification and validation, it is also necessary to construct a reduced transport model for integrated simulations [4]. Therefore, we should clarify the intermediate relation bridging the turbulence simulation and transport modeling.In our previous paper [5], nonlinear local flux-tube gyrokinetic Vlasov simulations of ITG turbulent transport were carried out by using the GKV-X code [6] for the high ion temperature (high-T i ) LHD plasma in shot number 88343 [7]. The simulation results reproduced the turbulent ion heat transport level and the wavenumber spectra of the density fluctuations observed in the experiment.…”

“…In our previous paper [5], nonlinear local flux-tube gyrokinetic Vlasov simulations of ITG turbulent transport were carried out by using the GKV-X code [6] for the high ion temperature (high-T i ) LHD plasma in shot number 88343 [7]. The simulation results reproduced the turbulent ion heat transport level and the wavenumber spectra of the density fluctuations observed in the experiment.…”