FWF - Stochastic Mapp T u N T - Stochastic Mapping Technique and Neoclassical Transport

The evaluation of neoclassical transport coefficients is an essential element in stellarator studies. It is needed for the optimization of magnetic configurations, and for the analysis and planning of experiments. It is also of relevance for stellarator specific issues of fusion reactors. In an arbitrary 3-dimensional magnetic field configuration of a stellarator this problem has to be solved numerically. At the present time methods which provide the most general solution are the conventional MC (Monte Carlo) method, which has been realized in numerous codes and the DKES (Drift Kinetic Equation Solver), a "regular" code which employs a variational principle where the solution is expressed using a series of Fourier-Legendre test functions. These two methods do not have principal limitation from the geometry of the device or from the confinement regime, however, as an adverse consequence of problem generality, these methods have low computational efficiency in certain collisionality regimes. This low efficiency becomes a substantial obstacle for optimization procedures where new, more effective methods are necessary. High computational speed is desirable also for the creation of neoclassical databases for a certain magnetic field configuration. Such databases are used for the analysis and the planning of experiments and are planned at the IPP Greifswald. Within the current proposal, the stochastic mapping technique (SMT) should be applied to compute transport coefficients, the bootstrap current, and supra-thermal particle fluxes. All the calculations will be done in the long mean free path regime, a regime where conventional MC methods have a very low efficiency. Up to now SMT works for magnetic fields given in real space coordinates and therefore a version of the code working directly with magnetic fields represented in Boozer coordinates (the most common representaion of magnetic fields) has to be developed. The procedure to calculate the bootstrap current, developed for the conventional MC method, has to be implemented in SMT. This includes the implementation of the proper orbitintegrated Coulomb collision operator into the code. Convective transport of supra-thermal electrons can play a significant role in the energy balance of stellarators in the presence of high power electron cyclotron heating. Here, together with neoclassical thermal particle fluxes, also the supra-thermal electron flux should be taken into account in the flux ambipolarity condition, which defines the self-consistent radial electric field. In this approach, SMT which is more effective than the conventional MC method, will be used.