Predictions of toroidal rotation and torque sources arising in non-axisymmetric perturbed magnetic fields in tokamaks

Abstract

Capabilities of the integrated framework consisting of TOPICS, OFMC, VMEC and FORTEC-3D, have been extended to calculate toroidal rotation in fully non-axisymmetric perturbed magnetic fields for demonstrating operation scenarios in actual tokamak geometry and conditions. The toroidally localized perturbed fields due to the test blanket modules and the tangential neutral beam ports in ITER augment the neoclassical toroidal viscosity (NTV) substantially, while do not significantly influence losses of beam ions and alpha particles in an ITER L-mode discharge. The NTV takes up a large portion of total torque in ITER and fairly decelerates toroidal rotation, but the change in toroidal rotation may have limited effectiveness against turbulent heat transport. The error field correction coils installed in JT-60SA can externally apply the perturbed fields, which may alter the NTV and the resultant toroidal rotation profiles. However, the non-resonant components of the magnetic fields arising from the toroidal field ripple mainly contribute to the NTV, regardless of the presence of the applied field by the coil current of , where n is the toroidal mode number. The theoretical model of the intrinsic torque due to the fluctuation-induced residual stress is calibrated by the JT-60U data. For five JT-60U discharges, the sign of the calibration factor conformed to the gyrokinetic linear stability analysis and a range of the amplitude thereof was revealed. This semi-empirical approach opens up access to an attempt on predicting toroidal rotation in H-mode plasmas.

Effects of the applied magnetic fields with various toroidal phase differences on the neoclassical toroidal viscosity in JT-60SA

“…This observation and its analysis were first reported in NSTX experiments [5,6], subsequently DIII-D [7,8] and in many devices [9][10][11][12][13][14][15][16][17][18]. Also, an estimate of the NTV in future devices was performed in ITER [19] and JT-60SA [20], in which the NTV is expected to play a more crucial role in regulating toroidal rotation due to a larger volume and relatively small external torque input. In view of importance of toroidal rotation effects on confinement, transport and stability, an accurate estimation of the NTV, as an indispensable piece for predicting toroidal rotation, under the external MPs is a compelling need.…”

“…In common with the previous work [20], a plasma for the #3 scenario [23] is considered in this section: a high-density H-mode plasma with the plasma current I p = 5.5 MA, the toroidal magnetic field B T = 2.25 T. The kinetic profiles and the safety factor q profiles are the same as those shown in figure 10 of [20] and fixed throughout the following simulations. The plasma is heated by the balanced-injected positive-ion-source NBs of 20 MW and the co-injected negative-ion-source NBs of 10 MW.…”

“…Also, several tools required to mediate between the codes are adjunctively used. The integrated model as a whole and the detailed calculation procedure are described in [20,22].…”

“…Especially for the cases with the resonant magnetic perturbations (RMPs) applied, the plasma response is of critical importance [2]. VMEC has been widely used to compute the ideal, nonlinear 3D plasma response by MPs [20][21][22]36] and RMPs [36][37][38][39][40] for the actual and/or future devices. In terms of the use of VMEC for the cases with RMPs, a resonant response has been verified with the theoretical work under the zero-beta assumption [41] and soon it has been qualitatively assured for a finitepressure equilibrium by comparison with the numerical code that allows for discontinuities at rational surfaces [42].…”

“…EFCCs can also be utilized for ELM mitigation and n = 3 MPs with around 10 kA are planned to be applied [43]. This is because we have previously studied the NTV for such a case [20]. However, as seen from the specification of EFCCs, applying MPs with other type of Fourier harmonics is feasible.…”