Gonzalo Fernandez-Torija Daza (University Carlos III de Madrid, Spain)

"FLIPEC: A free-boundary equilibrium solver in the context of Ideal MHD for toroidally axisymmetric plasmas in the presence of flows"

Abstract: The ability of calculating ideal MHD equilibria is needed not only during the design of a magnetic fusion device, but also in its normal operation. In the case of tokamak axisymmetric configu- rations with significant plasma flow, the majority of codes consist of a fixed-boundary solver for the Grad-Shafranov-Bernoulli system of equations in which the plasma edge is maintained fixed as the code iteratively searches for the equilibrium. However, plasma flows may induce changes in the configuration such as displacements of the position of the X-point, the magnetic axis or the shape of the plasma boundary, to name a few, that cannot be quantified properly in a fixed- boundary setup. In this contribution we present a new code that can iteratively obtain free-boundary axisymmetric ideal MHD equilibria for arbitrary plasma flows. The code employs a mesh discretization that combines pseudo-spectral and finite differences together with a free- plasma-boundary scheme previously proved for 3D, non-axisymmetric configurations in the absence of flow within the SIESTA equilibrium code.

Three developments has been recently implemented, such as the transition to a general coordinate formulation to expand the type of devices/configurations to which it can be applied. A strategy has also been devised to improve the iterative convergence to equilibrium solutions, avoiding the onset of vertical instabilities. Additionally, a current targeting scheme has been developed in response to the observed loss of plasma current in some specifics configuration throughout the itera- tions of the code

Examples of application of the code to ITER and NSTX configurations will be presented to showcase the capabilities of the code.