Simulation of the electromagnetic wall response during Vertical Displacement Events (VDE) in ITER tokamak

TL;DR

This paper presents a finite element simulation method for analyzing electromagnetic wall responses during Vertical Displacement Events in ITER, incorporating Helmholtz decomposition and iron core effects for improved accuracy.

Contribution

It introduces a novel finite element approach using Helmholtz decomposition to model surface currents and accounts for iron core influence, enhancing disruption modeling accuracy in tokamaks.

Findings

Validated simulation with analytical solutions.

Improved evaluation of iron core effects on plasma equilibrium.

Reduced singularities using conformal transformation.

Abstract

The key basis for tokamak plasma disruption modeling is to understand how currents flow to the plasma facing surfaces during plasma disruption events. In ITER tokamak, the occurrence of a limited number of major disruptions will definitively damage the chamber with no possibility to restore the device. In the current exchange plasma-wall-plasma, according to the Helmholtz decomposition theorem, our surface current density in the conducting shell - the unknown of our problem - being a vector field twice continuously differentiable in 3D, has been splited into two components: an irrotational (curl-free) vector field and a solenoidal (divergence-free) vector field. Developing a weak formulation form and minimizing the correspondent energy functionals in a Finite Element approach, we have obtained the space and time distribution of the surface currents. We verified successfully our numerical simulation with an analytical solution with pure homogeneous Neumann B.C. and satisfying the necessary existence condition. By considering the iron core presence in JET tokamak, we have split the magnetization currents - the unknowns in some integral equations - into two components, the first producing a magnetic field in the iron region only and the second producing a magnetic field in the vacuum, obtaining thus a better evaluation of the influence of the iron core on the plasma equilibrium. To reduce the influence of the singularities appearing during the surface currents determination in multiply connected domains (L-shaped domains) we have used a conformal transformation method.