On the origin of the plasma current spike during a tokamak disruption and its relation with magnetic stochasticity

E. Nardon (1) , K. Särkimäki (2) , F. J. Artola (3) , S. Sadouni (1)

1 IRFM - Institut de Recherche sur la Fusion par confinement Magnétique
2 Max-Planck-Institut
3 ITER - ITER organization

A JOREK 3D non-linear MHD simulation of a disruption triggered by an argon massive gas injection in JET, which quantitatively reproduces the plasma current ($I_p$) spike, is analyzed in order to investigate the origin of the $I_p$ spike and its relation with magnetic stochasticity. The $I_p$ spike is associated to a current density ($j_ φ$) profile relaxation which appears to result from Shear Alfvén Wave (SAW) propagation along stochastic field lines, as proposed by Boozer, possibly complemented by a macroscopic E×B flow structure. Using axisymmetric JOREK simulations involving a mean field Ohm's law, we verify that the level of hyper-resistivity associated to SAWs is consistent with the prediction made in, which connects the $I_p$ spike with the level of stochasticity. The relaxation comprises two main phases, the first one corresponding to a fast (0.1 ms) and almost complete $j_φ$ flattening in the q < 2 region, while the second one is longer (0.5 ms) and corresponds to a more gradual, global and incomplete $j_φ$ flattening. During the first phase, strong E×B flows develop that play a key role in mixing impurities into the core.

Domains: Plasma Physics [physics.plasm-ph]

E. Nardon, K. Särkimäki, F. J. Artola, S. Sadouni. On the origin of the plasma current spike during a tokamak disruption and its relation with magnetic stochasticity. Nuclear Fusion, 2023, 63 (5), pp.056011. ⟨10.1088/1741-4326/acc417⟩. ⟨cea-04061073⟩