Deposition of carbon inside gaps of castellated tungsten blocks with intrinsic misalignment

When PFCs have castellated structure, co-deposition of fuel inside gaps between castellated blocks is an important issue. Four different shapes of castellated tungsten blocks were fabricated to study corresponding issues in KSTAR: Conventional “basic” rectangular shape, single chamfer leading edge, double-chamfer and rounded edge, with two different poloidal gap distances of 0.5mm and 1.0mm. These tungsten blocks were exposed plasma of L- and H-mode discharges during a whole campaign in 2014. The blocks were taken out from the vacuum vessel after the campaign. Gap deposition was analyzed by Electron Probe X-ray Micro Analyzer (EPMA) to obtain carbon surface density (atoms/cm2), and by Raman spectroscopy to identify chemical bonding structure of carbon deposits in gaps. The carbon surface density in toroidal and poloidal gaps was in a range from 0.5 × 1015 atom/cm2 up to 6.7 × 1015 atom/cm2. At the gap entrance, contribution of ions is 6.0–6.7 × 1015 atom/cm2, decreased down to 1.0 × 1015 atom/cm2 at a depth of 0.5mm, and remains constant afterwards. The contribution of charge exchange neutral is about 3.0 × 1015atom/cm2 at the gap entrance, and then gradually decreases as a function of distance from the entrance. Deposition in 1.0mm wide gaps show much larger deposition patterns and that particles have reached much deeper inside the gap. Raman spectra show that the intensity ratio I(D)/I(G) decreases from top to the depth of 5mm indicating the increase of hydrogen contents. Keywords: Plasma-facing components, Tungsten, Castellation, Gap geometry, Deposition, Retentio

Inter-ELM heat loads on tungsten leading edge in the KSTAR divertor

A series of leading edge heat load experiments are performed in KSTAR to study power balance and to support a divertor shaping decision on ITER. Tungsten blocks with leading edges of various heights were fabricated, adjusted and mounted to central divertor of KSTAR with extreme care to avoid the intrinsic misalignment caused by engineering limits. The results from IR measurements and COMSOL simulation are consistent with each other and the power discrepancy found at JET does not exist at KSTAR. A simple calculation with geometrical projection can be used to foreseen the heat load on divertor blocks with arbitrary shapes. Therefore, the results present in this paper are valuable for new design of divertor blocks. Keywords: Power handling, Leading edge, PFC shapin