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Villard, L.*; Angelino, P.*; Bottino, A.*; Allfrey, S. J.*; Hatzky, R.*; Idomura, Yasuhiro; Sauter, O.*; Tran, T. M.*
Plasma Physics and Controlled Fusion, 46(12B), p.B51 - B62, 2004/12
Times Cited Count：29 Percentile：67.01(Physics, Fluids & Plasmas)This paper reviews the present status of recent first principles based plasma turbulence simulations, and gives quantitative discussions on influences of the v// nonlinearlity and the geometry effects in the gyrokinetic Poisson equaiton, which are ignored in the conventional approximations, on simulations results. Careful treatments of these effects enable turbulence simulations satisfying the conservation of the energy and the particle number. The new simulation disclosed new phenomena, and it is found that (1) turbulence spreading is induced by avalanche like phnemena consisting of bursty heat transport and local flattening of pressure profiles, and (2) nonlinearly driven E
B flows become global shear flows with scale lengths of about 30 ion gyro radii.
Obrejan, K.; Idomura, Yasuhiro; Honda, Mitsuru*
no journal, ,
The use of tungsten to coat divertors or other plasma facing components, inevitably leads to the pollution of the fusion plasma by heavy and highly charged (high-Z) impurities. This kind of neoclassical and turbulent transport of high-Z impurities is not yet fully understood. To study high-Z impurity transport, the gyrokinetic full-f Eulerian simulation code GT5D was upgraded with an implicit collision solver based on a multi-species linear Fokker-Plank collision operator. The commonly employed low order approximation of the standard neoclassical theory showed good agreement for low-Z impurities, but large differences were observed for high-Z impurities in the presence of temperature gradients. We tested an improved form of the neoclassical transport theory, that takes into account higher order flows to more accurately recover the friction coefficients in a high collisionality regime, showing good agreement with GT5D. An important consequence of this improved method is the weakening of thermal screening effect of bulk ions on impurity transport.
Obrejan, K.; Idomura, Yasuhiro; Honda, Mitsuru*
no journal, ,
The numerical accuracy of the gyrokinetic full-f Eulerian code GT5D is studied with respect to collisional or neoclassical transport of heavy impurity ions such as tungsten. Collisional transport of tungsten is determined by its collisional interaction with fuel ions such as deuterium and tritium. Because of the extreme mass ratio between deuterium and tungsten, the collision operator becomes a multi-scale problem in velocity space. In this work, numerical convergence of the collision operator is examined by estimating friction matrix elements, and numerical resolution needed for recovering collisional transport theory of heavy impurity ions clarified.
Obrejan, K.; Idomura, Yasuhiro; Honda, Mitsuru*
no journal, ,
The use of tungsten in plasma facing components inevitably leads to the pollution of the fusion plasma by heavy impurities and their accumulation at the core. Although heavy impurity transport has been estimated by the neoclassical transport theory, recent studies exhibited differences between global gyrokinetic simulations and the Hirshman-Sigmar (HS) moment approach, a commonly employed local theory. We performed a thorough benchmark for neoclassical particle transport of various impurities using the newly upgraded multi-species linear Fokker-Plank collision operator of our gyrokinetic full-f Eulerian simulation code GT5D. While good agreement was obtained in the case of flat temperature profiles, the dependence on the temperature gradient was found to be much weaker than the H-S theory in small machine sizes. Good agreement between GT5D and the H-S theory was recovered only for the case of large machine sizes, similar to ITER but beyond that of most current fusion devices.
Obrejan, K.; Idomura, Yasuhiro; Honda, Mitsuru*
no journal, ,
The use of tungsten in plasma facing components inevitably leads to the pollution of the fusion plasma by heavy impurities and their accumulation at the core, and this phenomenon is not yet fully understood. In this study, we performed a thorough comparison of the impurity particle fluxes between the global gyrokinetic full-f Eulerian code GT5D and local collisional transport theory called as the Hirshman-Sigmar moment approach. It is found that the simulation and the theory agree only in flat temperature profile cases or in large device sizes comparable to ITER. The cause of their discrepancy at the current device sizes is investigated in detail by comparing flows, which drive collisional impurity transport.
