ITER steady-state magnetic sensors: design status and performance

Full text of publication follows. Tokamak magnetic diagnostics provide information of key plasma parameters that are crucial for machine protection, real time plasma control, and physics studies. Traditionally, these measurements are performed by inductive sensors, such as pick-up coils or Rogowski coils. However, these techniques meet a challenge when implemented on ITER, as considerable signal drifts are foreseen during ITER's long-pulse, high-radiation burning plasma operation. Therefore, alternative technologies, such as the non-inductive micro-mechanical magnetometers (MEMS) have been investigated [1]. Arrays of MEMS, complementary to the inductive sensors [2], will be deployed on the outer surface of the ITER vacuum vessel to measure the slowly-varying component of local magnetic field both tangential and normal to the vessel surface, including the regions near the ferromagnetic inserts. Preliminary design of the electronics system for the MEMS detectors has been done [3], with capacitance excitation and second harmonic coil voltage detection implemented to reduce the crosstalk induced errors. The use of these sensors for equilibrium magnetic reconstruction of ITER plasmas is under consideration. A preliminary examination of the likely performance [2] yielded encouraging results. Additional analysis is planned [4] [5]. This work is partly supported by EFDA under Task TW6-TPDS-DIASUP3, and by F4E under grants F4E-GRT-156 and F4E-GRT-047. Disclaimer: the views expressed in this publication are the sole responsibility of the authors and do not necessarily reflect the views of the Fusion for Energy and the ITER Organization. Neither Fusion for Energy nor any person acting on behalf of Fusion for Energy is responsible for the use, which might be made of the information in this publication. References: [1] Kyynaeraeinen, J., Kuisma, E., Magnetometer for ITER Magnetic Diagnostics. Final report of EFDA Task TW6-TPDS-DIASUP3 p 26 ITER reference: ITER_D3MBAWH (private communication); [2] P. Moreau et al, Fusion Engineering and Design 84 (2009) 1344-1350; [3] ITER Design Description Document 55.A5,A6 Outer Vessel Steady State Sensors (private communication); [4] GRT047 Technical Report on Equilibrium reconstruction in ITER using external pick-up and steady state sensors, in preparation (private communication); [5] GRT047 Technical Report on Total toroidal current reconstruction in ITER using external pick-up and steady state sensors, in preparation (private communication). (authors)