Modulated toroidal current suppression of MHD activity on the HT-7 superconducting tokamak

Abstract

Modulation of the plasma current has been used successfully to suppress MHD activity. This was achieved in discharges near the density limit where large MHD m = 2 tearing modes were suppressed by sufficiently large plasma current oscillations. The modulation of the plasma current must be large enough to move the resonance q = 2 surface outside the island width on a timescale faster than the growth time of the instability. These observations resemble those predicted in a previous study of non-linear effects on the m = 1 mode.

Hybrid simulation of energetic particle effects on tearing modes in tokamak plasmas

“…Then, dĴ h;r and dĴ h;h becomes large due to the coupling between curvature and perturbed pressure of energetic ions from Eqs. (2) and (3). Therefore, the return current dJ k;2 can become large and energetic ions can affect tearing modes significantly.…”

“…Hence, the control of tearing modes is an important issue for achieving steady-state and high confinement plasmas. 1 So far there are several methods under study for controlling tearing modes, such as electron cyclotron current drive (ECCD), 2 modulation of plasma current, 3 externally applied helical field, 4 and neutral beam injection (NBI). 5 Here, we will focus on the effects of energetic beam ions on tearing modes.…”

Impact of Micro-Scale Stochastic Zonal Flows on the Macro-Scale Visco-Resistive Magnetohydrodynamic Modes

“…Our aim in this paper is to consider the possibility of dynamic stabilisation of the MHD modes by the stochastic ZFs. We note that it is well-known theoretically and experimentally [20,21,49,50], that in principle, one can dynamically stabilise MHD modes using external applied electromagnetic perturbations with specific frequencies and amplitudes. We further extend this idea by including a spectrum of random perturbations on small-scales and show that in principle, their associated ZFs can result in stabilisation of the linear and non-linear unstable (1,1) and (2,1) visco-resistive MHD modes.…”

“…Control of the sawtooth crashes e.g. their amplitude and frequency, hence would be important for optimising plasma performance in a fusion device [17][18][19][20][21].…”

Design and Implementation of Magneto Hydrodynamics Control System on HT-7 Tokamak

“…Multi-pulse current addition on plasma current has been experimented on HT-6M and given effects of curbing MHD and avoiding or delaying the split of plasma, thus improved plasma confinement [2]. A set of lower hybrid wave (LHW) system based on modulated LHW control of MHD for HT-7 also produced good result of curbing MHD and avoid or alleviate large split [3][4][5][6]. Passive and active means have been tried and researched on main Tokamak device around the world, such as DIII-D, JET, NSTX, JT-60U, HEP-EP, and generated encouraging achievements [7][8][9][10].…”