At TEXTOR the dynamic ergodic divertor (DED) induces a stochastic edge layer by a resonant magnetic perturbation to control heat and particle exhaust. In this paper the characterization of its ...generic transport properties is described. The radial and poloidal distribution of electron density and temperature is analyzed accompanied by observations of the particle flux to the DED target. These experimental results are compared to the calculated magnetic topology and to results from EMC3/EIRENE modeling. Thereby, the existence of two poloidally separated transport domains is demonstrated: laminar flux tubes are dominated by parallel transport to the DED target – they act analogous to a classical scrape-off layer. In contrast, the adjacent ergodic domains show stochastic transport characteristics with enhanced radial transport.
Using the 3D SOL transport code EMC3/EIRENE, the paper presents a parameter study on CX-neutral transport and Fe-release from the wall due to physical sputtering in W7-AS diverted plasmas. The ...studies are restricted to the CX-neutrals induced by divertor and wall recycling processes. SOL plasma and divertor and wall recycling process are self-consistently calculated by the EMC3/EIRENE code. Island density is scanned across different confinement regimes. Cross-field transport coefficients are varied to cover an appropriate uncertainty range. Core plasma is prescribed, with the density profile, however, being switched between a peaked and a flat form typically measured for low and high density diverted plasmas. Studied are the sensitivities of the flux, energy spectrum and origin of the CX-neutrals to these parameters. In particular, it is aimed to identify under what condition and to what extent the edge islands can protect the wall from physical sputtering of the CX-neutrals.
The integrated model JINTRAC is employed to assess the dynamic density evolution of the ITER baseline scenario when fuelled by discrete pellets. The consequences on the core confinement properties, ...α-particle heating due to fusion and the effect on the ITER divertor operation, taking into account the material limitations on the target heat loads, are discussed within the integrated model. Using the model one can observe that stable but cyclical operational regimes can be achieved for a pellet-fuelled ITER ELMy H-mode scenario with Q = 10 maintaining partially detached conditions in the divertor. It is shown that the level of divertor detachment is inversely correlated with the core plasma density due to α-particle heating, and thus depends on the density evolution cycle imposed by pellet ablations. The power crossing the separatrix to be dissipated depends on the enhancement of the transport in the pedestal region being linked with the pressure gradient evolution after pellet injection. The fuelling efficacy of the deposited pellet material is strongly dependent on the E × B plasmoid drift. It is concluded that integrated models like JINTRAC, if validated and supported by realistic physics constraints, may help to establish suitable control schemes of particle and power exhaust in burning ITER DT-plasma scenarios.
Abstract
The influence of plasma beta effects on the edge plasma transport in the Wendelstein 7-X standard configuration is studied systematically by using EMC3-EIRENE combined with a 3D equilibrium ...code named HINT. The magnetic topology changes induced by plasma beta effects are significantly reflected in plasma transport behaviors and heat flux patterns on divertor targets. After validating the modeling strategy by comparisons with experimental data, the extended simulations for high performance plasmas show that the threshold separatrix density for accessing the power detachment is reduced in higher beta plasmas. Compared with the vacuum field case, the impurity radiation distributions with finite beta effects are modified in the magnetic island region. The divertor heat flux is distributed more evenly along the toroidal direction on the strike line at the vertical target. The strike line on the horizontal target moves towards the pumping gap with an increase in the plasma beta. In addition, the different pressure profiles with the same central beta also result in a modified heat flux pattern on the divertor targets.
The influence of the divertor geometry of the dynamic ergodic divertor (DED) in TEXTOR on particle recycling is discussed. The geometry can be varied by the choice of the base mode, the edge safety ...factor and the divertor coil current. The divertor volume is split into the upstream and the downstream area. Strong plasma flows in the downstream area, essential for high screening efficiency, are predicted. The source strength of deuterium and carbon in the downstream area is estimated by using the two-dimensional distribution of Dα and CIII emission in front of the target. The results are compared to EMC3 and ERO-code calculations.
Nitrogen seeded JET-ILW H-mode plasmas have been investigated with EDGE2D–EIRENE. The simulations reproduce the experimentally observed factor of 10 reduction in the outer target power deposition ...when the normalized divertor radiation, Praddiv/PSOL, increases from the unseeded levels of 15% up to the 50% levels required for detachment. At these radiation levels, nitrogen is predicted dominate the total radiation with a contribution of 85%, consistent with previous measurements in JET-C. Due to the low radiative potential of nitrogen at the electron temperatures above 100eV, more than 80% of the radiation is predicted to occur in the scrape-off layer, making nitrogen a suitable divertor radiator for typical JET divertor conditions with Te around 30eV. The simulations reproduce the experimentally observed particle flux reduction at the low-field side target without the need for strong recombination. This is due to strong impurity radiation reducing the power levels entering the deuterium ionization front.
Measurements of the plasma conditions at the low field side target plate in JET ITER-like wall ohmic and low confinement mode plasmas show minor differences in divertor plasma configurations with ...horizontally and vertically inclined targets. Both the reduction of the electron temperature in the vicinity of the strike points and the rollover of the ion current to the plates follow the same functional dependence on the density at the low field side midplane. Configurations with vertically inclined target plates, however, produce twice as high sub-divertor pressures for the same upstream density. Simulations with the EDGE2D-EIRENE code package predict significantly lower plasma temperatures at the low field side target in vertical than in horizontal target configurations. Including cross-field drifts and imposing a pumping by-pass leak at the low-field side plate can still not recover the experimental observations.
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