A. Mutzke

Modeling of localized neutral particle sources in 3D edge plasmas

A 3D fluid neutral model is added to the 3D plasma transport code BoRiS. The neutral model includes equations for parallel momentum and collisional perpendicular diffusion. This makes BoRiS an integrated plasma-neutral model suitable for a variety of applications. Results are presented for the distribution of neutrals from a localized gas source in the National Compact Stellarator Experiment geometry.

Hierarchy tests of edge transport models (BoRiS, UEDGE)

Abstract BoRiS is a 3D scrape-off layer (SOL) transport code under development to solve a system of plasma fluid equations. Using a simplified SOL model including particle continuity, parallel momentum and energy equations for both electrons and ions, BoRiS is tested in different geometries. To verify its proper operation in 1D and 2D cases, BoRiS solutions are compared to the results obtained with the established UEDGE code. In addition to these benchmarks some results for 3D problems are obtained.

Concept and Status of a 3D SOL Fluid Code

A new 3D scrape-off layer transport code is under development using the same plasma fluid approach as the well-known B2 code. The equations are solved in magnetic coordinates in order to deal with the complex 3D geometry. Starting from a simple temperature equation the code is successively extended towards a full physics model as in B2. Results for the solution of the coupled anisotropic Laplace equations for both electron and ion temperatures in a single magnetic island flux tube of W7-X are given.

Calculation of magnetic coordinates for stellarator fields including islands and the Scrape-Off Layer

We present an extension of the Nemov algorithm (Nemov V.V. 1988 Nucl. Fusion 28 1727) to compute the magnetic coordinates in stellarators and their associated metric coefficients, requiring only a knowledge of the magnetic field and field line tracing techniques. The method is not limited to the core of the plasma, but also applies to island chains and Scrape-Off Layer regions. The procedure allows the computation of the Clebsch components of the magnetic field by transforming the magnetic differential equations for the radial and angular coordinates into initial-value problems involving field line tracing. Moreover, it has been optimized for numerical accuracy by minimizing recourse to derivatives of derived quantities. Illustrative applications of the algorithm, as applied to W7-X, including a numerical benchmark for the core region, are presented.

Highly accurate nuclear and electronic stopping cross sections derived using Monte Carlo simulations to reproduce measured range data

We have examined and confirmed the previously unexplored concept of using Monte Carlo calculations in combination with measured projected ranges of ions implanted in solids to derive a quantitative description of nuclear interaction and electronic stopping. The study involved 98 ranges of 11B in Si between 1 keV and 8 MeV, contained in 12 sets of 10 different groups. Systematic errors by up to ±8% were removed to establish a refined data base with 93 ranges featuring only statistical uncertainties (±1.8%). The Monte Carlo calculations could be set up to reproduce the refined ranges with a mean ratio 1.002 ± 1.7%. The input parameters required for this very high level of agreement are as follows. Nuclear interaction is best described by the Kr-C potential, but in obligatory combination with the Lindhard-Scharff (LS) screening length. Up to 300 keV, the electronic stopping cross section is proportional to the projectile velocity, Se = kSe,LS, with k = 1.46 ± 0.01. At higher energies, Se falls progressively ...

Comprehensive suite of codes for plasma-edge modelling

The various aspects of plasma-edge physics are included in a comprehensive suite of codes having applications from industrial plasmas to fusion devices. Here the basic ideas, status, and relationship of the codes are summarized: Plasma-wall interaction effects on a microscopic length-scale (e.g., chemical sputtering effects) are studied with molecular dynamics. Mesoscale effects (e.g., sputtering and diffusion in amorphous materials) are analysed with Monte Carlo methods (kinetic Monte Carlo with input from molecular dynamics or experiment or binary collision approximation). A full kinetic description (including ions, electrons, neutrals and their collisions) is possible for some low-temperature plasmas (e.g., electron cyclotron resonance heated methane plasmas) and for qualitative studies of edge plasma effects in fusion edge plasmas. Fluid transport codes for the edge of magnetically confined plasmas (2D tokamaks, tokamaks with ergodic perturbations, 3D stellarators) are necessary for understanding better the complex physics in such devices. The different code levels provide physics which is embodied in simplified models for those above and below it in the hierarchy or for those linked across various boundary regions.