This article describes the overall design of the Joint European Torus ͑JET͒ motional Stark effect ͑MSE͒ diagnostic. The principle of this diagnostic has been proven on other tokamaks ͑TFTR and DIII-D͒ but its implementation on JET involves specific difficulties associated with optical access and neutral beam geometry. The solutions adopted for the access problem include the use of a novel ''Air Amici'' prism for beam deviation and low Verdet coefficient glass for the relay optics. MSE signals from the different beam sources are distinguished by their Doppler shift; the diagnostic uses the ϩ components of the Stark spectrum to avoid contamination with signals from different beam sources. The optimum viewing location for good space resolution across the plasma profile is also one that allows good accuracy in the reconstruction of the q profile from the measurements. An assessment of the optical throughput predicts a measurement accuracy of the polarization angle of better than 0.15°with 1-10 ms time resolution.

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At JET, the Plasma Shape Control System (PPCC-SC) drives fast power amplifiers connected to the poloidal field coils. It determines the plasma boundary using the XLOC algorithm and data from the Magnetics Measurement System, KCID. The additional heating systems, NB (Neutral Beam), ICRH (Ion Cyclotron Resonance Heating), and LHCD (Lower Hybrid Current Drive) can be controlled by real-time algorithms on the RTSS (Real-Time Signal Server). The Wall Load Limit System limits the power applied to the vessel. Also, experimental systems analyze data in real-time, e.g. RT-BETA-LI calculates Wdia, Beta, Li, etc., and RT-EFIT calculates the current profiles and flux-surfaces. These systems are hosted on a variety of hardwardsoftware platforms, including -VMENxWorks, TMS320C40 DSPhative code, and PC/WindowsNT. They communicate using ethemet, fibre-optic point-to-point links, or with reflective memory. To improve reliability and flexibility, a new real-time data network (RTDN) is being developed, using standard ATM components. Simple tests on ATM connections indicate that, for packets of a fewhundred bytes, point-to-point transfers take less then 250 p, which is adequate. ATM links for the DSP systems have been developed, based on a PowerPC VME card. A simple message protocol, application programmer interface, and data presentation tools have also been developed.

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This paperpresents an overview of results of the 1994/95 experimental campaign on JET with the new pumped divertor and draws implications for ITERin the areas of detached and radiative divertorplasmas, theuseofberyllium as a divertor target tile malerial, the confmement properties of discharges with the same dimensionless parameters (exceptforthedimensionless Larmorradius) as lT!3R and the effect of varying the toroidal magnetic field ripple in the FTER relevant range.Discbarges withhigh fusionpe~ormance athighcurrentjn steadystate with ELMS and in the ELM-free hot -ion H-mode, are also reported. Limits to operations are discussed and projections to D-T performance are made.