(TH/P3-18) Kinetic Simulation of Heating and Collisional Transport in a 3D Tokamak

A. Bustos Molina1), F. Castejón1)4), L. A. Fernández2)4), V. Martin-Mayor2)4), A. Tarancón3)4), J.L. Velasco3)4)
1) Laboratorio Nacional de Fusion Asociacion EURATOM/CIEMAT para Fusion, Madrid, Spain
2) Dep. de Fısica Teórica I. Universidad Complutense, 28040-Madrid, Spain.
3) Dep. de Fısica Teórica. Universidad de Zaragoza, 50009-Zaragoza, Spain.
4) BIFI: Instituto de Biocomputación y Fısica de Sistemas Complejos, 50009-Zaragoza, Spain

Abstract.  The microwave plasma heating has a strong influence on collisional transport, experimentally observed both in stellarators and tokamaks. The estimate of the interplay between heating and collisional transport implies solving a 5D kinetic equation (2D in momentum space and 3D in real space), which is a difficult task. We attempt to solve this problem using a recently developed code (ISDEP: Integrator of Stochastic Differential Equations for Plasmas) in a tokamak with ripple as a test device. Previously, ISDEP has been successfully applied to the TJII stellarator [1]. Our Monte Carlo method is based on the equivalence between the linear Fokker-Planck and Langevin equations. This allows us to describe the system by taking average values over many independent test particle trajectories. The dynamics of these ions are determined by the guiding center approximation, ion-ion collision [2] and the interaction with microwaves (Ion Cyclotron Heating, ICH, since we are dealing with ion transport). We also have developed a selfconsistent method to update the background temperature in order to introduce nonlinear terms. Thus, we have modified ISDEP to include the geometry of a tokamak with ripple and the Langevin equations for ICH [3]. The European Computer Grid (EGEE) has been used to perform the calculations. The main results of this work are the calculation of transport quantities and the velocity probability distribution function. We have compared these results in the cases with and without heating, and investigated the differences between them. There are three main conclusions: i) the increment of the kinetic energy, with a consequent increment of the temperature, and an increase of the outward fluxes, which implies a reduction of the particle confinement. ii) The deviations of the distribution function from the Maxwellian, both in the bulk and in the wings in the presence of ICH. iii) The included ripple is not enough to generate toroidal asymmetries. This computer code can be adapted to other geometries and allows to consider other features that can be taken into account in the ion dynamics (NTM, ee collisions and Alfvén instabilities).

[1] F. Castejón et al, Nucl. Fusion 42, 271 (2002); [2] Z. A. Pietrzyk et al. Physical Review Letters 86, 1530 (2001); [3] S. Murakami, Nucl. Fusion 45, 221 (2003)

Full paper available (PDF)