Material migration studies with an ITER first wall panel proxy on EAST

Abstract

The ITER beryllium (Be) first wall (FW) panels are shaped to protect leading edges between neighbouring panels arising from assembly tolerances. This departure from a perfectly cylindrical surface automatically leads to magnetically shadowed regions where eroded Be can be re-deposited, together with co-deposition of tritium fuel. To provide a benchmark for a series of erosion/re-deposition simulation studies performed for the ITER FW panels, dedicated experiments have been performed on the EAST tokamak using a specially designed, instrumented test limiter acting as a proxy for the FW panel geometry. Carbon coated molybdenum plates forming the limiter front surface were exposed to the outer midplane boundary plasma of helium discharges using the new Material and Plasma Evaluation System (MAPES). Net erosion and deposition patterns are estimated using ion beam analysis to measure the carbon layer thickness variation across the surface after exposure. The highest erosion of about 0.8 µm is found near the midplane, where the surface is closest to the plasma separatrix. No net deposition above the measurement detection limit was found on the proxy wall element, even in shadowed regions. The measured 2D surface erosion distribution has been modelled with the 3D Monte Carlo code ERO, using the local plasma parameter measurements together with a diffusive transport assumption. Excellent agreement between the experimentally observed net erosion and the modelled erosion profile has been obtained.

ERO modeling and sensitivity analysis of locally enhanced beryllium erosion by magnetically connected antennas

“…Indeed, in comparison to values used earlier in ERO or other models for D ⊥ (see paragraphs below), this value is in agreement with that used by the EDGE2D-Eirene simulations that provided the background plasma: 0.5 m 2 /s at the separatrix and 1.0 m 2 /s elsewhere [16]. It is also consistent with values suggested in the literature [11,25], and calculated and used by other ERO studies [27,28,29].…”

“…Given that background plasma flux reaching a given surface cell may cross neighboring regions with different connection lengths, 'shadowing by L C zones' has also been implemented. In this model, similar to that used by Ding et al [27], the surface is divided into zones, defined by all cells with a L C within a given range and the mean L C value is assigned to the entire zone (Table 1, 'mean'). The difference in erosion or emission between the local implementation of shadowing and that by zones is negligible.…”

Nonlinear reversed shear Alfvén eigenmode saturation due to spontaneous zonal current generation

“…the ITER; Tomabechi et al 1991) are expected to operate at steady state with a substantial non-inductive current fraction (Gormezano et al 2007), which generally renders a reversed shear scenario (Huang et al 2020). In this circumstance, the reversed shear Alfvén eigenmode (RSAE; also known as Alfvén cascade) is frequently observed (Sharapov et al 2001) as driven unstable by energetic particles (EPs) (Zonca et al 2002;Fasoli et al 2007;Chen et al 2014;Chen & Zonca 2016) in present-day tokamaks, and is expected to play significant roles in future reactors (Wang et al 2018), in transporting fusion alpha particles to the tokamak edge (Wang et al 2019), which has deleterious effects on plasma self-heating, and may damage the plasma-facing components (Ding et al 2015). The RSAE is a branch of the shear Alfvén wave (SAW) eigenmode localized radially near the minimum of the safety factor q-profile (Sharapov et al 2002), which is denoted as q min .…”

Fast-ion velocity-space tomography using slowing-down regularization in EAST plasmas with co- and counter-current neutral beam injection

“…Fast ions play a key role in present-day tokamak operation. Loss of fast ions can lead to reduced heating efficiency and can damage plasma-facing components [1,2]. In addition, fast ions will be vital for the next generation tokamaks such as ITER and CFETR which will strongly rely on continuous plasma heating through collisions with highly energetic fusion-born alpha particles [3][4][5][6].…”