Conventional and Advanced ECE Diagnostic Techniques for NTM Mitigation on ITER*

A synthetic diagnostic for the electron cyclotron emission (ECE) system designed for ITER has shown low-latency detection of neoclassical tearing modes (NTM) and was used to explore radiometer design and optimization. For a full-field ITER scenario from the IMAS database, a 2/1 NTM was detected 430 ms after magnetic island seeding and before island locking. Island sizes as small as ~3cm are detectable at the 2/1 surface. The synthetic diagnostic incorporates recent physics models for island growth and rotation and high-temperature and density physics effects on ECE, including relativistic broadening which limits spatial resolution. The synthetic diagnostic predicts the location of magnetic surfaces such as the 2/1 where dangerous islands may seed, but prediction and detection could be improved by incorporating advanced NTM mitigation techniques. Resonant magnetic perturbation (RMP) coils may allow controlled island seeding. Islands could be seeded and tracked using ECE diagnostics to determine the NTM susceptibility of an ITER plasma scenario. Information on island behavior, including location of seeding, can be used to optimize detection and suppression methods. Additionally, RMP coils have been proposed to deliberately lock islands in front of EC launchers to avoid delays in aiming. If this technique is used on ITER, ECE diagnostics will need advanced methods to observe the magnetic island since conventional detection relies on island rotation. Potential observation methods will be discussed.