Resonant magnetic perturbation effect on tearing mode dynamics

Abstract

The effect of a resonant magnetic perturbation (RMP) on the tearing mode (TM) dynamics is experimentally studied in the EXTRAP T2R device. EXTRAP T2R is equipped with a set of sensor coils and active coils connected by a digital controller allowing a feedback control of the magnetic instabilities. The recently upgraded feedback algorithm allows the suppression of all the error field harmonics but keeping a selected harmonic to the desired amplitude, therefore opening the possibility of a clear study of the RMP effect on the corresponding TM. The paper shows that the RMP produces two typical effects: (1) a weak oscillation in the TM amplitude and a modulation in the TM velocity or (2) a strong modulation in the TM amplitude and phase jumps. Moreover, the locking mechanism of a TM to a RMP is studied in detail. It is shown that before the locking, the TM dynamics is characterized by velocity modulation followed by phase jumps. Experimental results are reasonably explained by simulations obtained with a model.

Understanding the effect of resonant magnetic perturbations on tearing mode dynamics

“…Besides, we find that as long as the 2/1 TM can be completely suppressed by RMPs, higher RMP amplitude or a longer duration at the flattop of I c can result in locked mode. On EXTRAP TAR, 7 the suppression or locking of m/n = 1/-12 TM by RMPs is observed, the high RMP amplitude case is likely to be that described in Fig. 3.…”

“…In Ref. 7, a full rotation of (1, -12) mode is managed to rotate in the deceleration region and then locked by applied RMPs. The time evolution of TM phase and amplitude are similar to that shown in Fig.…”

“…3 Since the first RMPs experiment on PULSATOR, 4 many experiments related to RMPs have been carried out. 1,[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The RMPs related experiments covers a broad spectrum of physics issues including the effect of RMPs on tearing mode (TM) dynamics, 1, 4-10 error field, 11,12 particle transport, 13,14 and mitigation or suppression of edge localized modes (ELMs). [15][16][17][18] One of the results is that RMPs with moderate amplitude can suppress Mirnov oscillations effectively.…”

“…8,9 The RMPs effect on TM dynamics associated with mode stabilization has been investigated experimentally. 7 It is believed that there should exist some mechanisms which are responsible for the suppression of magnetic island by RMPs. On the other hand, when the applied RMPs is relatively strong, mode locking can always be observed, 9 and the shape of Mirnov signals turn to be strongly deviated from sinusoidal.…”

Simulation and Control of Turbulence at Tokamaks with Artificial Intelligence Methods

“…Many of the proposed solutions are related to the employment of resonant magnetic perturbations (RMPs). A RMP is a magnetic perturbation characterized by a helical resonant inside the plasma and typically produced by a dedicated set of active coils [4]. Recently, RMPs have been utilized to produce stochasticity at the plasma edge.…”