Neoclassical Tearing Mode Stability at ITER-Like Parameters
New studies explore NTM scalings in the key parameters of extrapolation to ITER ­rotation and r*. Experiments show falls in both 3/2 and 2/1 NTM thresholds (denoting as poloidal/toroidal number) by about 1 unit in bN as momentum injection is withdrawn. Behaviour provides insight into the underlying physics mechanisms governing NTM behaviour, suggesting possible roles for rotation shear and/or ion polarisation currents in governing tearing stability. A new cross-machine study explores r* scaling for the performance limiting 2/1 NTM in the hybrid scenario, where high bN access is a crucial requirement. Results raise questions, with a general fall in NTM bN thresholds with r* on two devices, but JET indicating improved stability. Possible origins of this discrepancy are discussed, together with overall implications for ITER and plans for further work.