Conceptual design and prototyping of inductive magnetic sensors using photo-lithography processes: the JET DTE3 experience

Tokamak operation needs inductive magnetic sensors to monitor high frequency (HF) instabilities and as a back-up to the low-frequency (LF) inductive magnetic sensors used for the measurements leading to the equilibrium reconstruction. HF magnetic sensors need to minimize the self-inductance (L SELF) provided that the effective area (NAEFF) remains sufficiently large, while for the LF sensors the only physics-based design criteria is maximizing NAEFF independently of L SELF. Following up from our own 15-years long development of the Low-Temperature Co-fired Ceramic technology for producing inductive magnetic sensors for multiple tokamaks (most notably for ITER), in 2022 we started developing currently state-of-art and innovative photolithography (PL) processes for further miniaturising these sensors and improving their resilience to the harsh environmental conditions of thermonuclear fusion experiments in view of possible installation in DTT and DEMO. Starting from our previous work, in this paper we will present our recent advances in manufacturing inductive sensors using PL processes. In preparation for forthcoming DEMO and DTT irradiation testing activities (foreseen for 2027), some of these prototypes have been deployed at JET for the DTE3 experimental campaign, successfully surviving the harsh environmental conditions at the vessel boundary. In this contribution we will report on these recent achievements and the steps that still needed towards a full industrialization of the PL processes we have developed so far in-house.