Fusion Engineering and Design 71 (2004) 175–181 Real-time motional Stark effect in jet D. Alves a,∗ , A. Stephen b , N. Hawkes b , S. Dalley b , A. Goodyear b , R. Felton b , E. Joffrin c , H. Fernandes a , EFDA-JET contributors a Associação EURATOM/IST, Centro de Fusão Nuclear, Instituto Superior Técnico, Av. Rovisco Pais 1049-001, Lisboa, Portugal b EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, UK c Association Euratom-CEA, CEA Cadarache, F-13108, St Paul lez Durance, France Available online 1 June 2004 Abstract The increasing importance of real-time measurements and control systems in JET experiments, regarding e.g. Internal Transport Barrier (ITB) and q-profile control, has motivated the development of a real-time motional Stark effect (MSE) system. The MSE diagnostic allows the measurement of local magnetic fields in different locations along the neutral beam path providing, therefore, local measurement of the current and q-profiles. Recently in JET, an upgrade of the MSE diagnostic has been implemented, incorporating a totally new system which allows the use of this diagnostic as a real-time control tool as well as an extended data source for off-line analysis. This paper will briefly describe the technical features of the real-time diagnostic with main focus on the system architecture, which consists of a VME crate hosting three PowerPC processor boards and a fast ADC, all connected via Front Panel Data Port (FPDP). The DSP algorithm implements a lockin-amplifier required to demodulate the JET MSE signals. Some applications for the system will be covered such as: feeding the real-time equilibrium reconstruction code (EQUINOX) and allowing the full coverage analysis of the Neutral Beam time window. A brief comparison between the real-time MSE analysis and the off-line analysis will also be presented. © 2004 Elsevier B.V. All rights reserved. Keywords: Real-time control; Motional Stark effect; Jet; Fusion 1. Introduction The MSE 1 diagnostic [1] explores the Stark split- ting of a spectral line produced by the electric field as- sociated with an atom’s motion across a magnetic field ∗ Corresponding author. Tel.: +351-21-8417693; fax: +351-21-8417819. E-mail address: dalves@cfn.ist.utl.pt (D. Alves). 1 Motional Stark effect. (Fig. 1). In fusion devices, neutral deuterium atoms are the source of the MSE measurement as they are injected into the plasma for heating, in the form of a high energy (∼120 keV) beam. This diagnostic is used to obtain information on the internal magnetic field structure which can then be used to calculate the safety factor (q) and current profiles. In JET, the MSE diagnostic provides a space resolution of ∼5 cm, a time resolution <10 ms and an accuracy of ∼0.1 ◦ over 25 different locations (chan- nels) along the neutral beam path. 0920-3796/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2004.04.030