Effect of the relative shift between the electron density and temperature pedestal position on the pedestal stability in JET-ILW and comparison with JET-C

The electron temperature and density pedestals tend to vary in their relative radial positions, as observed in DIII-D (Beurskens et al 2011 Phys. Plasmas 18 056120) and ASDEX Upgrade (Dunne et al 2017 Plasma Phys. Control. Fusion 59 14017). This so-called relative shift has an impact on the pedestal magnetohydrodynamic (MHD) stability and hence on the pedestal height (Osborne et al 2015 Nucl. Fusion 55 063018). The present work studies the effect of the relative shift on pedestal stability of JET ITER-like wall (JET-ILW) baseline low triangularity (\u3b4) unseeded plasmas, and similar JET-C discharges. As shown in this paper, the increase of the pedestal relative shift is correlated with the reduction of the normalized pressure gradient, therefore playing a strong role in pedestal stability. Furthermore, JET-ILW tends to have a larger relative shift compared to JET carbon wall (JET-C), suggesting a possible role of the plasma facing materials in affecting the density profile location. Experimental results are then compared with stability analysis performed in terms of the peeling-ballooning model and with pedestal predictive model EUROPED (Saarelma et al 2017 Plasma Phys. Control. Fusion). Stability analysis is consistent with the experimental findings, showing an improvement of the pedestal stability, when the relative shift is reduced. This has been ascribed mainly to the increase of the edge bootstrap current, and to minor effects related to the increase of the pedestal pressure gradient and narrowing of the pedestal pressure width. Pedestal predictive model EUROPED shows a qualitative agreement with experiment, especially for low values of the relative shift

Correlation of the tokamak H-mode density limit with ballooning stability at the separatrix

We show for JET and ASDEX Upgrade, based on Thomson-scattering measurements, a clear correlation of the density limit of the tokamak H-mode high-confinement regime with the approach to the ideal ballooning instability threshold at the periphery of the plasma. It is shown that the MHD ballooning parameter at the separatrix position\u3b1sep ncreases about linearly with the separatrix density normalized to Greenwald density, ne,sep/nGW for a wide range of discharge parameters in both devices. The observed operational space is found to reach at maximum ne,sep/nGW 48 0.4-0.5 at values for \u3b1sep 4822.5, in the range of theoretical predictions for ballooning instability. This work supports the hypothesis that the H-mode density limit may be set by ballooning stability at the separatrix

Overview of fuel inventory in JET with the ITER-like wall

Post mortem analyses of JET ITER-Like-Wall tiles and passive diagnostics have been completed after each of the first two campaigns (ILW-1 and ILW-2). They show that the global fuel inventory is still dominated by co-deposition; hence plasma parameters and sputtering processes affecting material migration influence the distribution of retained fuel. In particular, differences between results from the two campaigns may be attributed to a greater proportion of pulses run with strike points in the divertor corners, and having about 300 discharges in hydrogen at the end of ILW-2. Recessed and remote areas can contribute to fuel retention due to the larger areas involved, e.g. recessed main chamber walls, gaps in castellated Be main chamber tiles and material migration to remote divertor areas. The fuel retention and material migration due to the bulk W Tile 5 during ILW-1 are presented. Overall these tiles account for only a small percentage of the global accountancy for ILW-1

MeV-range velocity-space tomography from gamma-ray and neutron emission spectrometry measurements at JET

We demonstrate the measurement of a 2D MeV-range ion velocity distribution function by velocity-space tomography at JET. Deuterium ions were accelerated into the MeV-range by third harmonic ion cyclotron resonance heating. We made measurements with three neutron emission spectrometers and a high-resolution \u3b3-ray spectrometer detecting the \u3b3-rays released in two reactions. The tomographic inversion based on these five spectra is in excellent agreement with numerical simulations with the ASCOT-RFOF and the SPOT-RFOF codes. The length of the measured fast-ion tail corroborates the prediction that very few particles are accelerated above 2 MeV due to the weak wave-particle interaction at higher energies

Experimentelle Bestimmung von städtischen Emissionen anhand von Konzentrationsmessungen im Lee einer Stadt - Untersuchungen zum Beitrag verschiedener Quelltypen und Vergleich mit einem Emissionsberechnungsmodell

For the evaluation of an emission inventory measurements of specific trace gases downwind of the city of Augsburg were performed during two field campaigns in March and October 1998 . These long-term ground based measurements were part of an integrated experiment (EVA-Experiment) which also included airborne measurements and tracer experiments on some selected days (intensive phases) . From the long-term measurements the composition of the urban emissions was determined taking into account mixing with background air masses and chemical degradation during transport from the emission source to the measurement site. The data were analysed with respect to differences between the two campaigns and between weekdays and weekends. The composition of emission sources was investigated . The results were compared with the results of an emission inventory with the aim to assess the correctness and to determine the uncertainties of the inventory. The composition of the hydrocarbon mixture varies significantly between weekdays and weekends resulting in a higher mean reactivity with respect to ozone formation on weekdays than on weekends. In October the contribution of aromatics is higher than in March whereas the contribution of C2-C4-alkanes is lower. ;H/NOC,- and HC;/CO-ratios are lower in March than in October which is mainly due to higher CO- and NOxemissions in March. The comparison of the measured hydrocarbon mixture with clearly traffic dominated measurements shows that the prevailing source of hydrocarbon emissions is traffic. In contrast the contribution of solvent emissions is small. For the intensive phases in October calculated and measured absolute CO-emissions agree within the uncertainty ranges. For March the model tends to underestimate both parameters . Considering only hydrocarbons, which can be specified by the emission model, calculated and measured composition of hydrocarbon mixtures as well as ;H/NO,,-Cratios agree rather well. These specified compounds are mainly due to traffic emissions . However, the differences in the composition of hydrocarbon mixtures between March and October are not found by the emission model. The percentage of hydrocarbons specified by the emission model is only between 50 and 60 °Io of the hydrocarbons which are detectable by the used GC-System and included in the results . Considering these additional hydrocarbon emissions, which are exclusively due to solvent use, calculated ;.H/N-CO and HC;/CO-ratios (ppbC/ppb) are up to a factor of 3 higher than measured ones. The most important result from the evaluation of the emission model by the measurements is that the model overpredicts the contribution of solvent emissions by far whereas traffic emissions are underestimated. The effects of the discrepancies between experimentally determined and calculated emissions were investigated with a photochemical boxmodel. The ozone production in the case of modelled emissions was almost a factor of two higher than in the case of measured emissions . This shows that shortcomings in emission inventories lead to incorrect predictions of ozone concentrations . Since it was shown that Augsburg is a typical German city with respect to its emissions the results obtained within this work can be generalise