Modelling of magnetic field structure of the Ergodic Divertor of Tore Supra and comparison to the Dynamic Ergodic Divertor of TEXTOR

TL;DR

This paper applies an analytical magnetic field model to the Tore Supra tokamak's Ergodic Divertor, compares it with TEXTOR-DED, and analyzes the magnetic field structure, perturbations, and field line diffusion properties.

Contribution

It extends an existing model to Tore Supra's ED, providing detailed analysis and comparison with TEXTOR-DED, including asymptotic formulas and diffusion coefficient profiles.

Findings

Magnetic perturbation spectrum analyzed and compared with TEXTOR-DED.

Field line diffusion coefficients follow quasilinear formula at small perturbations.

Ergodic zone behavior varies with perturbation current, affecting diffusion coefficients.

Abstract

An analytical model previously developed to study the structure of the magnetic field for the TEXTOR-DED [S.S. Abdullaev et al. Phys. Plasmas, 6, 153 (1999)] is applied to the similar study of the Ergodic Divertor of Tore Supra tokamak [Ph. Ghendrih, Plasma Phys. Control. Fusion, 38, 1653 (1996)]. The coil configuration of ED Tore Supra consists of six modules equidistantly located along the toroidal direction on the low-field-side of the torus with given toroidal and poloidal extensions. The Hamiltonian formulation of field line equations in straight-field-line coordinates (Boozer coordinates) and the computationally efficient mapping method for integration of the Hamiltonian field line equations are used to study the magnetic field structure in the ED. Asymptotical formulas for the perturbation magnetic field created by the ED coils are obtained and the spectrum of magnetic perturbations is analyzed and compared with the one of the TEXTOR-DED. The structure of ergodic and laminar zones are studied by plotting Poincare sections, so-called laminar plots (contour plots of wall to wall connection lengths) and magnetic footprints. The radial profiles of field line diffusion coefficients are calculated for different perturbation currents and it is found that for the Tore Supra case in the ergodic zone the numerical field line diffusion coefficients perfectly follow the quasilinear formula for smaller perturbation currents although the situation is different for the maximum perturbation current.