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(EX8/5) Error Field Mode Studies on JET, COMPASS-D and DIII-D, and Implications for ITER

R. Buttery¹, M. de Benedetti⁴, D. Gates^1*, Y. Gribov⁵, T. Hender¹, R. J. La Haye³, P. Leahy¹, J. A. Leuer³, A. W. Morris¹, A. Santagiustina², J. T. Scoville³, B. Tubbing^2**, and the JET², COMPASS-D¹ and DIII-D³ Teams

¹ EURATOM/UKAEA Fusion Association, Culham Science Centre, Oxon, UK
² JET Joint Undertaking, Oxon, UK
³ General Atomics, San Diego, USA
⁴ Imperial College, London, UK
⁵ ITER-Naka Joint Working Site, JAPAN
^* now at Princeton University, NJ 08543, USA
^** now at European Commission, Brussels

Abstract.  New experiments on COMPASS-D, DIII-D and JET have identified the critical scalings of error field sensitivity and harmonic content effects, enabling predictions of the requirements for larger devices such as ITER. Thresholds are lowest at low density, a regime proposed for H mode access on ITER. Results suggest a moderate error field sensitivity ( $\delta$B/B $\sim$ 10^-4) for ITER, comparable with the size of its intrinsic error, although there are uncertainties in scaling behaviour. Other studies on COMPASS-D and DIII-D show that sideband harmonics to the (2,1) component play an important role. Thus a correction system for ITER will be important, with flexibility to correct sidebands desirable, possibly assisted by beam rotation. Such a system has been designed and is capable of reducing multiple harmonic error levels to $\sim$ 2×10^-5.

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