The experimental characteristics of divertor detachment in the JET tokamak with the Mark I pumped divertor are presented for Ohmic, L-mode and ELMy H-mode experiments with the main emphasis on discharges with deuterium fuelling only. The range over which divertor detachment is observed for the various regimes as well as the influence of divertor configuration, direction of the toroidal field, divertor target material and active pumping on detachment will be described. The observed detachment characteristics such as the existence of a considerable electron pressure drop along the field lines in the scrape-off layer, and the compatibility of the decrease in plasma flux to the divertor plate with the observed increase of neutral pressure and the D α emission from the divertor region will be examined in the light of existing results from analytical and numerical models for plasma detachment. Finally, a method to evaluate the degree and window of detachment is proposed and all the observations of the JET Mark I divertor experiments summarised in the light of this new quantitative definition of divertor detachment.

New experiments in 2013-2014 have investigated the physics responsible for the decrease in H-mode pedestal confinement observed in the initial phase of JET-ILW operation (2012 Experimental Campaigns). The effects of plasma triangularity, global beta and neutrals-both D and low-Z impurities-on pedestal confinement and stability have been investigated systematically. The stability of JET-ILW pedestals is analysed in the framework of the Peeling-Ballooning model and the pedestal predictive code EPED. Low D neutrals content in the plasma, achieved either by low D 2 gas injection rates or by divertor configurations with optimum pumping, and high beta are necessary conditions for good pedestal (and core) performance. In such conditions the pedestal stability is consistent with the Peeling-Ballooning paradigm. Moderate to high D 2 gas rates, required for W control and stable H-mode operation with the ILW, lead to increased D neutrals content in the plasma and additional physics in the pedestal models may be required to explain the onset of the ELM instability. The physics mechanism leading to the beneficial increase in pedestal temperature with N 2 seeding in high triangularity JET-ILW H-modes is not yet understood. The changes in H-mode performance associated with the change in JET wall composition from C to Be/W point to D neutrals and low-Z impurities playing a role in pedestal stability, elements which are not currently included in pedestal models. These aspects need to be addressed in order to progress towards full predictive capability of the pedestal height.

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As part of the ITER Design Review, the physics requirements were reviewed and as appropriate updated. The focus of this paper will be on recent work affecting the ITER design with special emphasis on topics affecting near-term procurement arrangements. This paper will describe results on: design sensitivity studies, poloidal field coil requirements, vertical stability, effect of toroidal field ripple on thermal confinement, heat load requirements for plasma-facing components, edge localized modes control, resistive wall mode control, disruptions and disruption mitigation.

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