Pre-conceptual design of ECE Imaging for real time NTM control

The reduction or suppression of magneto-hydrodynamic instabilities, such as Neoclassical Tearing Modes (NTMs), can be performed through localized current driven by Electron Cyclotron Heating and Current Drive (ECH&CD). In this paper, we show that the proper aiming of a steerable antenna can be obtained using a suitable layout of an array of Electron Cyclotron Emission diagnostics (ECE imaging). The diagnostic principle leading to the adoption of ECE imaging is to exploit propagation reciprocity at electron cyclotron frequencies, which allows for the implementation of control strategies such as the In-Line (van den Brand et al., 2018) and the Quasi-In-Line (Sozzi et al., 2023) control schemes (I-L and Q-I-L schemes). However, these schemes require equipping a dedicated ECE diagnostic with at least a movable antenna. This contribution is based on simulations obtained for a DEMO-like reactor to demonstrate the feasibility of NTM control schemes based on information provided by an ECE imaging diagnostic, which uses a set of fixed Lines-of-Sight (LoS). Towards the design of a diagnostic layout suitable for the use in real machines, the following questions are here addressed: First, we evaluate the number of LoS required to satisfy the strict alignment precision necessary in a DEMO-like reactor and then provide a pre-conceptual design. Finally, the performance that could be obtained by a control system adopting such a diagnostic is evaluated and compared with the I-L and the Q-I-L schemes mentioned above. • Proposal of a new diagnostic to use for NTM control. • NTM tracking using a limited number of fixed ECE antennas. • Performance assessment and comparison with In-Line control strategy in EU-DEMO.