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"Dedicated experiments have been performed in KSTAR Ohmic plasmas to investigate the detailed physics of the rotation reversal phenomena  Here we adapt the more general definition of rotation reversal  a large change of the intrinsic toroidal rotation gradient produced by minor changes in the control parameters  Camenen et al 2017 Plasma Phys  Control  Fusion 59 034001   which is commonly observed in KSTAR regardless of the operating conditions  The two main phenomenological features of the rotation reversal are the normalized toroidal rotation gradient  u   change in the gradient region and the existence of an anchor point  For the KSTAR Ohmic plasma database including the experiment results up to the 2016 experimental campaign  both features were investigated  First  the observations show that the locations of the gradient and the anchor point region are dependent on q 95   Second  a strong dependence of u  on nu eff  is clearly observed in the gradient region  whereas the dependence on R L-Ti  R L-Te  and R L-ne is unclear considering the usual variation of the normalized gradient length in KSTAR  The experimental observations were compared against several theoretical models  The rotation reversal might not occur due to the transition of the dominant turbulence from the trapped electron mode to the ion temperature gradient mode or the neoclassical equilibrium effect in KSTAR  Instead  it seems that the profile shearing effects associated with a finite ballooning tilting well reproduce the experimental observations of both the gradient region and the anchor point  the difference seems to be related to the magnetic shear and the q value  Further analysis implies that the increase of u  in the gradient region with the increase of the collisionality would occur when the reduction of the momentum diffusivity is comparatively larger than the reduction of the residual stress  It is supported by the perturbative analysis of the experiments and the nonlinear gyrokinetic simulations  The absence of the sign change of u  even when a much lower collisionality is produced by additional electron cyclotron heating brings further experimental support to this interpretation "
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