Overview of the JET results (original) (raw)
Since the installation of an ITER-like wall, the JET programme has focused on the consolidation of ITER design choices and the preparation for ITER operation, with a specific emphasis given to the bulk tungsten melt experiment, which has been crucial for the final decision on the material choice for the day-one tungsten divertor in ITER. Integrated scenarios have been progressed with the re-establishment of long-pulse, high-confinement H-modes by optimizing the magnetic configuration and the use of ICRH to avoid tungsten impurity accumulation. Stationary discharges with detached divertor conditions and small edge localized modes have been demonstrated by nitrogen seeding. The differences in confinement and pedestal behaviour before and after the ITER-like wall installation have been better characterized towards the development of high fusion yield scenarios in DT. Post-mortem analyses of the plasma-facing components have confirmed the previously reported low fuel retention obtained by gas balance and shown that the pattern of deposition within the divertor has changed significantly with respect to the JET carbon wall campaigns due to the absence of thermally activated chemical erosion of beryllium in contrast to carbon. Transport to remote areas is almost absent and two orders of magnitude less material is found in the divertor.
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Overview of the JET results with the ITER-like wall
Nuclear Fusion, 2013
Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET Campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma facing materials. The large reduction of the carbon content (more than a factor ten) led to a much lower Z eff (1.2-1.4) during L-and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that fuel retention rates with the new wall are in line with the ITER needs. The re-establishment of high-confinement scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type I ELMy H-mode regimes with H 98,y2 close to 1 and b N~1 .6 have been achieved in high triangularity plasmas. The ELM frequency is the main factor for the control of the metallic impurities accumulation. Pedestal temperatures tend to be lower with the new wall, leading to somewhat reduced confinement, but nitrogen seeding restores high pedestal temperatures and high confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on plasma-facing components due to lower radiation, made the routine use of massive gas injection for disruption mitigation essential.
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