Effects of momentum transport on error field threshold observed in KSTAR*

Resonant error field can lead to a disruptive mode locking when its strength is greater than a threshold. This mode locking process is often accompanied with the changes in the sawtooth activity, plasma rotation, and the reduction of energy confinement before terminating discharges in KSTAR. On the other hand, error field threshold against mode locking increases along with density but much weaker in KSTAR than expected, with the exponential scaling factor n_e^0.3. This might be related to the Linear Ohmic Confinement (LOC) to Saturated Ohmic Confinement (SOC) in the range of density for the studied KSTAR plasmas, as it implies weaker density correlation of momentum diffusion and viscous torque. Plasma rotation can also play a significant role to determine resonant error field thresholds. This supposition is clearly supported by an interesting example in KSTAR; A resonant field can accelerate rotation globally in some conditions and sustain plasma against mode locking beyond an expected error field threshold, as will be discussed in detail.