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

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 (divergencefree) 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 currentsthe 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.

The JOREK non-linear extended MHD code and applications to large-scale instabilities and their control in magnetically confined fusion plasmas

“…For walls with a low poloidal path resistance, the usual JOREK BC for the electric potential (Φ = 0) gives the correct distribution of halo currents as demonstrated in [96]. The formalism derived in [93][94][95] has been implemented as a postprocessing tool to calculate wall forces and to visualize the source/sink currents (see figure 2). This tool has been validated as well for 3D walls with holes.…”

“…Via the derivation shown in references [93][94][95], plasma currents flowing directly into conducting structures or out of them (current sharing between plasma and wall), can be treated 35 Note, that the natural boundary condition, however, leads to a less sparse matrix structure for boundary degrees of freedom. Local interactions between neighbouring grid nodes are replaced by global interactions on the boundary.…”

The JOREK non-linear extended MHD code and applications to large-scale instabilities and their control in magnetically confined fusion plasmas

“…Via the derivation shown in Refs. [90][91][92], plasma currents flowing directly into conducting structures or out of them (current sharing between plasma and wall), can be treated consistently with the STARWALL formalism. The respective derivation for JOREK-STARWALL including the interaction of eddy and halo currents are shown Ref.…”

“…for the electric potential (Φ = 0) gives the correct distribution of halo currents as demonstrated in [93]. The formalism derived in [90][91][92] has been implemented as a post-processing tool to calculate wall forces and to visualize the source/sink currents (see Figure 2). This tool has been validated as well for 3D walls with holes.…”