Computational Edge Plasma Models

Integrated computational models comprising the physics of the plasma flow near boundaries, the atomic and molecular processes and the particle-surface 

These models are limited, because at least one important ingredient, the (turbulent) plasma transport across the B-field, is not understood and this is likely to remain so in the future. 

The goal of present numerical code development is, therefore, to treat all the other, predictable, physical components of the model accurately. This applies, in particular, for the atomic, molecular and surface processes, which largely control the plasma flow and plasma energy content in the important near target region. If that can be achieved, then the unknown anomalous cross field transport can be separated and isolated computationally, and can then perhaps be determined experimentally even in the edge region. 

The peculiarities of plasma flow in the edge region of magnetic confinement fusion machines result from the strong stiffness of the equations (very different timescales within one problem), the inherently (at least) two-dimensional nature of the flow (on multiple connected domains), the extreme anisotropy (by a factor 106) in the flow, the strongly nonlinear dependence of the transport coefficients on the flow parameters, the large number of species (equations) to be considered simultaneously, and the nonlocal nature 

Currently only Monte Carlo approaches can handle the wide range of surface geometries, reflection models and support complex atomic and molecular processes that occur in real fusion edge plasmas. Therefore the neutral particle transport (ionization, dissociation, etc.) as well as impurity ion transport in the edge region of fusion plasmas is often treated by Monte Carlo simulation on a kinetic level. 

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Fig. 2.6. Top section of computational domain for TEXTOR model, showing also the cross-section of the toroidal ALT-II limiter 45 degrees underneath the outer mid-plane. Bottom computed Balmer-alpha emission profile (photons/s/cm3, logarithmic colour scale) in the TEXTOR edge plasma, as used for interpretation of visible spectroscopy [26] and determination of plasma particle confinement...

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