Scientific workflows for MHD stability chain analysis of tokamak plasmas

Conference poster, 2015

The onset of MHD activity in present tokamak plasmas plays a detrimental role in the discharge performance and operational limits. A comprehensive characterisation of the modes observed and stability boundaries often call for the comparison of the experimentally measured toroidal/poloidal mode spectra and propagating frequencies against the predictions from linear MHD codes. In addition, predicting the MHD stability boundaries in operational plasma scenarios foreseen for ITER and under investigation for future devices such as DEMO plays an essential role in fusion research. Thus, the benchmark of high-resolution MHD equilibrium and stability solvers is an important step in the verification and validation of the involved numerical codes. Such benchmarks are greatly facilitated when all codes share the same physics and machine data ontology and methods for reading and writing the data, as in the European Integrated Modelling framework [1], presently maintained by the EUROfusion Code Development Work Package. Under its auspices, a scientific workflow, coded in Kepler [2] and dedicated to the analysis of MHD activity in tokamak plasmas, has been developed, that can be coupled to equilibrium reconstruction codes or discharge simulator scientific workflows. The workflow presently includes HELENA [3], CHEASE [4] and CAXE [5] equilibrium codes and ILSA [6], MARS [7], MARS-F [8] and KINX [5] linear MHD stability codes. This paper presents the benchmark of the codes integrated therein on custom-made circular and elongated plasma equilibria as well as JET and AUG plasma equilibria derived from experimental data. The study involved internal kink and global modes extending to the vacuum region. Radial and poloidal convergence analysis and growth rate dependence of global modes on the distance of the ideal conducting wall to the plasma boundary are addressed. Examples of interchangeability between some of the involved codes, an added value of the workflow user interface, are also included.