Effects of resonant magnetic perturbation on locked mode of neoclassical tearing modes

The effects of externally applied resonant magnetic perturbation (RMP) on the locked mode of the neoclassical tearing mode (NTM) are numerically investigated by means of a set of reduced magnetohydrodynamic equations.It is found that,for a small bootstrap current fraction,three regimes,namely the slight suppression regime,the small locked island (SLI) regime and the big locked island (BLI) regime,are discovered with the increase of RMP strength.For a much higher bootstrap current fraction,however,a new oscillation regime appears instead of the SLI regime,although the other regimes still remain.The physical process in each regime is analyzed in detail based on the phase difference between the NTM and the RMP.Moreover,the critical values of the RMP in both SLI and BLI regimes are obtained,and their dependence on key plasma parameters is discussed as well.

Screening effect of plasma flow on the resonant magnetic perturbation penetration in tokamaks based on two-fluid model

Numerical simulation on the resonant magnetic perturbation penetration is carried out by the newly-updated initial value code MDC(MHD@Dalian Code).Based on a set of two-fluid fourfield equations,the bootstrap current,parallel,and perpendicular transport effects are included appropriately.Taking into account the bootstrap current,a mode penetration-like phenomenon is found,which is essentially different from the classical tearing mode model.To reveal the influence of the plasma flow on the mode penetration process,E×B drift flow and diamagnetic drift flow are separately applied to compare their effects.Numerical results show that a sufficiently large diamagnetic drift flow can drive a strong stabilizing effect on the neoclassical tearing mode.Furthermore,an oscillation phenomenon of island width is discovered.By analyzing it in depth,it is found that this oscillation phenomenon is due to the negative feedback regulation of pressure on the magnetic island.This physical mechanism is verified again by key parameter scanning.

Effects of plasma radiation on the nonlinear evolution of neo-classical tearing modes in tokamak plasmas

The effects of plasma radiation on the nonlinear evolution of neo-classical tearing modes are investigated based on a set of reduced magnetohydrodynamic equations.It is found that the radiation can reduce the pressure near the rational surface.During the nonlinear evolution,the magnitude of perturbed bootstrap current is drastically enhanced in the presence of the radiation.Besides,the radiation can increase the growth rate of the magnetic islands by diminishing the pressure,such that the magnetic islands do not saturate compared with that without radiation.On the other hand,with the increase of the ratio of parallel to perpendicular transport coefficientχ‖/χ⊥,the reduction of pressure can further increase the growth rate of magnetic islands in the presence of plasma radiation.Finally,the mechanisms of the destabilizing effects driven by the radiation are discussed in detail as well.

A brief review:effects of resonant magnetic perturbation on classical and neoclassical tearing modes in tokamaks

This paper reviews the effects of resonant magnetic perturbation(RMP)on classical tearing modes(TMs)and neoclassical tearing modes(NTMs)from the theory,experimental discovery and numerical results with a focus on four major aspects:(i)mode mitigation,where the TM/NTM is totally suppressed or partly mitigated by the use of RMP;(ii)mode penetration,which means a linearly stable TM/NTM triggered by the externally applied RMP;(iii)mode locking,namely an existing rotating magnetic island braked and finally stopped by the RMP;(iv)mode unlocking,as the name suggests,it is the reverse of the mode locking process.The key mechanism and physical picture of above phenomena are revealed and summarized.

Intelligent control for predicting and mitigating major disruptions in magnetic confinement fusion

Magnetic confinement fusion is believed to be one of the promising paths that provides us with an infinite supply of an environment-friendly energy source,naturally contributing to a green economy and low-carbon development.Nevertheless,the major disruption of high temperature plasmas,a big threat to fusion devices,is still in the way of mankind accessing to fusion energy.Although a bunch of individual techniques have been proved to be feasible for the control,mitigation,and prediction of disruptions,complicated experimental environments make it hard to decide on specific control strategies.The traditional control approach,designing a series of independent controllers in a nested structure,cannot meet the needs of real-time complicated plasma control,which requires extended engineering expertise and complicated evaluation of system states referring to multiple plasma parameters.For-tunately,artificial intelligence(AI)offers potential solutions towards entirely resolving this troublesome issue.To simplify the control system,a radically novel idea for designing controllers via AI is brought forward in this work.Envisioned intelligent controllers should be developed to replace the traditional nested structure.The successful development of intelligent control is expected to effectively predict and mitigate major disruptions,which would definitely enhance fusion performance,and thus offers inspiring odds to improve the accessibility of sustainable fusion energy.