Overview of JET Results
Since the last IAEA, the scientific programme of JET has focussed on the qualification of the integrated operating scenarios for ITER and on physics issues essential for the consolidation of design choices and the efficient exploitation of ITER. Particular attention has been given to the characterisation of the edge plasma, pedestal energy and Edge Localised Modes (ELMs), and their impact on Plasma Facing Components (PFCs). Various ELM mitigation techniques have been assessed for all ITER operating scenarios using active methods such as resonant magnetic field perturbation, rapid variation of the radial field and pellet pacing. In particular, the amplitude and frequency of Type I ELMs have been actively controlled over a wide parameter range (q95 = 3-4.8, bN 3.0) by adjusting the amplitude of the n = 1 external perturbation field induced by Error Field Correction Coils. The study of disruption induced heat loads on PFCs has taken advantage of a new wide-angle viewing infra-red system and a fast bolometer to provide a detailed account of time, localisation and form of the energy deposition. Specific ITER-relevant studies have used the unique JET capability of varying the Toroidal Field (TF) ripple from its normal low value dBT = 0.08% up to dBT = 1% to study the effect of TF ripple on high confinement-mode plasmas. The results suggest that dBT < 0.5% is required on ITER to maintain adequate confinement to allow QDT=10 at full field. Physics issues of direct relevance to ITER include heat and toroidal momentum transport, with experiments using power modulation to decouple power input and torque to achieve first experimental evidence of inward momentum pinch and determine the threshold for ion temperature gradient driven modes. Within the longer term JET programme in support of ITER, activities aiming at the modification of the JET first wall and divertor and the upgrade of the neutral beam and plasma control systems are being conducted. The procurement of all components will be completed by 2009 with the shutdown for the installation of the beryllium wall and tungsten divertor extending from summer 2009 to summer 2010.