Toroidal rotation braking with low n external perturbation field on JET

The experimentally measured torque profile of the perturbation field induced by the n=1 EFCC field, T_EFCC, is determined by momentum transport analysis using the JETTO code. The NBI torque is calculated by the PENCIL code. The perpendicular diffusion coefficient and pinch velocity profile are determined by fitting the evolution of the velocity after the switch-off of EFCC current. The T_EFCC has a global profile. The maximum torque is in the plasma central region, which is different from the observations on NSTX and DIII-D with higher n perturbation field. This torque is not localized at a certain rational surface and the velocity evolution is obviously different from that in the mode locking phase as also observed on NSTX. With the vacuum field approximation, the NTV torque in the collisionless regime is calculated and compared with the observed T_EFCC. The calculated NTV torque profile in the 1/ν regime agrees with the profile of T_EFCC, although its absolute value is a factor of 2 larger. The NTV torque in the ν regime from the boundary layer contribution is comparable to the measured torque. Therefore, the NTV torque is in the same order as the observed T_EFCC. The NTV torque is a good candidate to explain the non-resonant magnetic braking observed on JET with n=1 perturbation field.