Study Of Magnetic Braking Effect By Neoclassical Toroidal Viscosity In The EAST Tokamak

In order to achieve safe and stable operation of burning plasma in fusion devices,dedicated experiments aiming to MagnetoHydroDynamics(MHD)instabilities control by Resonant Magnetic Perturbation(RMP)have been carried out in the EAST tokamak,at which the obvious plasma toroidal rotation braking was observed.It is also referred as magnetic braking,which is studied systematically based on experimental data analysis and simulation with Neoclassical Toroidal Viscosity(NTV)theory for comparison for further understanding the physical mechanism of rotation braking induced by magnetic perturbation,and finally solve the problems of MHD instabilities that restrict the development of future devices seriously.The experimental braking torque,which can reproduce the evolution of plasma rotation,is calculated by momentum transport analysis and compared with the torque predicted by NTV theory.The NTV torque shows good agreement with the observed torque in general.The NTV torque is modeled by NTVTOK code which included the contributions from both resonant and non-resonant NTV regimes.In the case of toroidal mode n=1 static RMP,the total NTV torque is reasonably consistent to the total observed torque.It is found that bounce-drift resonance from ions contributes significantly to the NTV torque in the plasma core in EAST,while the toroidal precession resonance of ions is dominant near the edge.Hence there are two peaks located near the plasma core and the edge in torque density profile,respectively.And the observed torque profile also has a similar shape.In the plasma edge,the peak value of observed torque has a good agreement in amplitude with that of NTV torque,but there is still order of magnitude difference between them near the core region,which may due to the underestimate of radial magnetic displacement in plasma response modeling in the plasma core.And there is similar phenomenon in the case of n=4 static RMP.We also study the impact of RMP spectrum change for rotation braking base on RMP phase difference scan,i.e.phasing RMP.It is found that plasma toroidal rotation shows periodic change,which is consistent with the periodic evolution of experimental torque calculated by momentum balance and the modeled NTV torque.This is due to the strength of magnetic perturbation on the equilibrium magnetic flux surface changes periodically in phasing RMP.Therefore the radial displacement of magnetic flux surface will also show a periodic change,which induces a periodic NTV torque evolution corresponding to that of observed torque.In addition the value of q95 can alter the resonant condition in RMP spectrum,which will change the dependence between braking torque and phase difference of RMP.