Modelling of the penetration process of externally applied helical magnetic perturbation of the DED on the TEXTOR tokamak

Abstract

The error-field penetration process of the dynamic ergodic divertor (DED) on the TEXTOR tokamak has been investigated analytically in terms of a single fluid MHD model with a finite plasma resistivity and viscosity in a cylindrical geometry. The linear model produces a localization of the induced current at the resonance surface and predicts a vortex structure of the velocity field near the resonance layer. Moreover, effects of the Alfvén resonance for the error-field penetration are identified by two peaks in the radial profiles of the perturbed toroidal current and the perturbed magnetic flux when the relative rotation velocity between the DED and the rotating tokamak plasma is set to large. Fine structures of the vorticity induced by the DED in the vicinity of the rational surface disappear by introducing a finite plasma perpendicular viscosity. In addition, it is shown that the two peaks of the perturbed toroidal current overlap by an anomalous plasma perpendicular viscosity. Likewise, a bifurcation of the penetration process from the suppressed to the excited state is obtained by a quasi-linear approach taking into account modifications of the radial profiles of the equilibrium current and the plasma rotation due to the DED. A comparison with real experimental results of the DED on the TEXTOR tokamak is shown.

Tearing mode physics studies applying the dynamic ergodic divertor on TEXTOR

“…The results are in good agreement with the experiment [15]. The calculated force transfer to the plasma is maximum when the resonance condition is fulfilled.…”

Role of singular layers in the plasma response to resonant magnetic perturbations

“…The above phenomenology of the LMO is in qualitative agreement with MHD theory, which shows that the suppression of the island is associated with singular currents flowing near the resonant surface [43,44,45,46,41,47,48]. The bifurcation occurs when the viscous force on the resonant layer, which acts to maintain the rotation, can no longer balance the electromagnetic braking force created by the RMP.…”

Magnetic Island Dynamics Under External Magnetic Perturbation in Rotating Resistive Iter Plasma

“…In general case, the stability index components C Δ and S Δ are found separately for both the cosine and sine space harmonics of the flux function similar to [2,3,5]. Without RMP, CS ΔΔ ,   one can obtain from (10), (13) - (16) In the model used for the TEAR code numerical calculations, we apply the factor  at the first terms in the right-hand side of equations (13), (14) in accordance with [2,9]. In this model we also supplement the equations (13), (14) with the neoclassical term and the term for the electron diamagnetic drift:…”