Abstract
JET ITER-like wall (ILW) experiments show that the edge density evolution is strongly linked with the poloidal distribution of the ionization source. The fueling profile in the JET-ILW is more delocalized as compared to JET-C (JET with carbon-based plasma-facing components PFCs). Compared to JET-C the H-mode pedestal fueling cycle is dynamically influenced by a combination of plasma–wall interaction features, in particular: (1) edge-localized modes (ELMs) induced energetic particles are kinetically reflected on W divertor PFCs leading to distributed refueling away from the divertor depending on the divertor plasma configuration, (2) delayed molecular re-emission and outgassing of particles being trapped in W PFCs (bulk-W at the high field side and W-coated CFCs at the low field side) with different fuel content and (3) outgassing from Be co-deposits located on top of the high-field side baffle region shortly after the ELM. In view of the results of a set of well diagnosed series of JET-ILW type-I ELMy H-mode discharges with good statistics, the aforementioned effects are discussed in view of H-mode pedestal fueling capacity. The ongoing modelling activities with the focus on coupled core-edge plasma simulations and plasma–wall interaction are described and discussed also in view of possible code improvements required.
Highlights
The JET ITER-like wall (ILW) consists of a beryllium first-wall and tungsten armor in the divertor [1] and has demonstrated to perform very successfully for plasma–wall interaction (PWI) and plasma operation with the plasma-facing material selection foreseen in ITER [2]
Initial comparisons of JET-ILW with JET-C (JET with PFCs made of carbon-fiber composites) showed that the evolution of the edge density is strongly linked with the level of recycling [7] as with increasing density a delay is observed before the pedestal density recovers after an edgelocalized modes (ELMs)-crash
In this paper we present results from dedicated JET-ILW H-mode experiments in 2012 with Ip/Bt = 2.0 MA/2.0 T, low-triangularity, auxiliary neutral beam injection PNBI = 11 MW in semi-horizontal divertor configurations with typical thermal energy drops of 160 kJ per ELM
Summary
The JET ILW consists of a beryllium first-wall and tungsten armor in the divertor [1] and has demonstrated to perform very successfully for plasma–wall interaction (PWI) and plasma operation with the plasma-facing material selection foreseen in ITER [2]. The impact of the metallic wall on the fueling process has been recovered very early during the first JET-ILW campaigns as the poloidal distribution of the ionization source and the fueling profile have become more delocalized (i.e. away from the divertor). In H-mode this ratio can be even larger as energetic particles can enter deeper into the metallic bulk-W/W-coated CFC surface layers in the divertor so that for achieving a given pedestal density nped a throughput of one order of magnitude higher is required in JET-ILW than without carbon. The particle reflection coefficient for a D-particle with 1 keV impact energy increases from 0.1 to 0.5 when moving from C to W and likewise, the energy reflection coefficient increases by one order of magnitude [17] This induces the kinetic-geometric effect of reflected particles amending the poloidal ionization source profile (see figure 1). The impact of nitrogen on confinement is being dealt with in a separate contribution [26]
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