Non-axisymmetric MHD simulations of the current quench phase of ITER mitigated disruptions

Abstract

Non-axisymmetric simulations of the current quench phase of ITER disruptions are key to predict asymmetric forces acting into the ITER wall. We present for the first time such simulations for ITER mitigated disruptions at realistic Lundquist numbers. For these strongly mitigated disruptions, we find that the edge safety factor remains above 2 and the maximal integral horizontal forces remain below 1 MN. The maximal integral vertical force is found to be 13 MN and arises in a time scale given by the resistive wall time as expected from theoretical considerations. In this respect, the vertical force arises after the plasma current has completely decayed, showing the importance of continuing the simulations also in the absence of plasma current. We conclude that the horizontal wall force rotation is not a concern for these strongly mitigated disruptions in ITER, since when the wall forces form, there are no remaining sources of rotation.

Runaway dynamics in tokamak disruptions with current relaxation

“…2021; Artola et al. 2022), the deep plasma core tends to be a region where flux surfaces are not completely destroyed, or are broken up only for a very short period within the thermal quench. This may be related to the typically low magnetic shear in the deep core, which does not favour island overlap.…”

Confinement of passing and trapped runaway electrons in the simulation of an ITER current quench

“…Initially there is no transport as the flux surfaces are intact, but between 10 -12 ms (when the mode energies peak, see Fig. 4 in [10]) the stochastic field region expands until it penetrates almost the whole plasma. This is the beginning of the stochastic phase; also here the confinement volume begins to shrink due to plasma moving vertically into the wall.…”

“…Because the Hamiltonian motion is dominant and the effect of the radiation reaction force is comparable to the Coulomb collisions, we resolve to use the Euler method for solving Eq. (10). For consistency the guiding-center radiation reaction force is also solved with the Euler method in this work.…”

“…In this work, we investigate the confinement of runaway electrons during a current quench in ITER by tracing particles in a recently completed JOREK MHD simulation [10]. The 3D simulation did not model thermal quench; instead, the initial conditions were assumed to be those of a mitigated disruption after the thermal quench.…”

“…The MHD simulation ("Case 1" in Ref. [10]) features a current quench lasting for ∼ 50 ms, during which there is an upward vertical displacement. Snapshots of magnetic field structure can be found in Fig.…”