Observation of the Generalized Neoclassical Toroidal Viscosity Offset Rotation Profile and Implications for ITER

摘要

Neoclassical Toroidal Viscosity (NTV) due to non-ambipolar particle diffusion that occurs in tokamaks due to low magnitude (δB/B_0~ 0(10~(-3))) 3D applied fields [1,2] is often used for positive purposes including modification of the plasma toroidal rotation profile, V?, to stabilize MHD modes and for ELM suppression at plasma rotation speeds characteristic of unbalanced neutral beam injection. However, tokamak devices aiming to produce high fusion power output, including ITER, are expected to rotate much more slowly due to relatively small levels of momentum injection and larger plasma mass compared to present machines. Therefore methods of producing and altering plasma rotation on these devices are highly desired. Understanding how plasmas intrinsically rotate is of primary interest to confidently extrapolate this effect to ITER-scale plasmas as it may provide significant rotation. A potentially beneficial NTV effect that may be important in slowly rotating plasmas such as envisioned in ITER is the NTV offset rotation [1,3]. Past experimental research has only considered that the NTV offset rotation can occur in the direction opposite to the plasma current (counter-I_p). In the experiments described in this paper, the NTV offset rotation profile, V_0~(NTV), was directly measured and studied in the KSTAR superconducting tokamak in a parameter regime that has shown for the first time controlled rotation in the co-I_p direction at high electron temperature, T_e. This result is expected when considering generalized NTV theory allowing for torques generated by both electron and ion channels, the balance of which yields the V_0~(NTV) profile (electron/ion NTV torque scales as (m_i/m_e)~(0.5)(T_e/T_i)~(3.5) indicating that the electron channel can be dominant) [1,4]. Co-I_p plasma rotation and shear in the plasma outer region has significantly exceeded ITER projections [5].