EFDA-JET-CP(04)07/35

Overview of JET Results

High density and high confinement operation in ELMy H-Mode is confirmed at or above the normalised parameters foreseen for the ITER operating point (H~1, n/nGW~1, bN>1.8 at q95~3). The scaling of the ELMy H-Mode with bN could be more favourable than predicted by the IPB98(y,2) scaling. In ELMy H-mode, ICCD control of large sawteeth stabilised by fast particle has been demonstrated and the underlying NTM and sawtooth physics is being refined. At high-density type-I ELMy H-modes show trends that would lead to marginally acceptable ELMs on ITER. Type II ELM regime has been produced, but under very restrictive conditions. Type III ELMy operation with radiation fractions up to 95% has been demonstrated by seeding of N2 in H-modes and could extrapolate to Q=10 ITER operation, albeit at high current (17MA). The mitigation of Type-I ELMs nevertheless remains a challenge. Considerable progress has been obtained in ITB plasmas, with operation at central densities close the Greenwald density or/and low toroidal rotation or/and high triangularity. Full CD demonstration and successful simultaneous real time control of safety factor and temperature profiles have been achieved in ITB plasmas. RWM physics have been compared with theory, showing favourable scaling to ITER. High bN~2.8 operation of hybrid modes (also called improved H-modes) has been obtained with dominant NB. Hybrid modes with dominant RF heating have also been achieved. Trace Tritium Experiments yielded valuable information on particle transport in H-mode, ITB and hybrid regimes. In Type I ELMy plasmas, successful tests of the conjugate-T ICRF scheme have been achieved as well as LHCD coupling at ITER-relevant 10-11cm distances. Reduced D and T fuel retention has been observed, which could relate to operation with vertical targets in the divertor and/or lower (ITER-like) vessel temperature. It is confirmed that erosion occurs predominantly on the main chamber surfaces, with possible benefits for T retention in ITER, although consequences for the metallic first wall lifetime need to be assessed. Disruption and ELM studies indicate that transient power deposition could be less constraining than expected for the ITER divertor, but more challenging for the metallic first wall. Alpha particle tomography and direct observation of alpha particle slowing down have made been possible by g-spectroscopy. Measurements of Alfvén cascades have been improved by a new interferometric technique. Promising tests of ITER relevant neutron counting detectors have been conducted.
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