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 configurations 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 po-

sition 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 tran-

sition to a general coordinate formulation to expand the type of de-

vices/configurations to which it can be applied. A strategy has also

been devised to improve the iterative convergence to equilibrium solu-

tions, 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.