Time-Dependent Boundary Conditions During ELMs in ITER Plasma

Abstract

The boundary conditions (BCs) involving a plasma-wall transition (PWT) are crucial when estimating the particle and heat fluxes at the wall, and when simulating the edge plasma with fluid, gyro-kinetic and gyro-fluid codes. The aim of this work was to derive time-dependent BCs at the PWT for ELM-free, Type-I ELM and post-ELM states based on a kinetic test simulation in the ITER tokamak without neutrals, so as to obtain the steady state. This contribution describes the first results of attempts to address this issue for ITER simulations under high-performance conditions using the 1D3V electrostatic parallel Particle-in-Cell code BIT1 (Tskhakaya in Plasma Phys Control Fusion 59(11401):19pp, 2017). The burning plasma conditions correspond to the ITER Q = 10, 15 MA baseline at $q_{95}$ = 3, for which the poloidal length of the 1D SOL is $\sim$ 20 m from the inner to the outer target, assuming typical upstream separatrix parameters of $n_e$ $\sim$ 3 to 5 $\cdot 10^{19}$ m$^{-3}$, $T_e$ $\sim$ 100 to 150 eV and $T_i$ $\sim$ 200 to 300 eV. Inclined magnetic fields at targets of ($\sim 5^{\circ }$) are included, as are the particle collisions, with a total of 3.4 $\cdot 10^{5}$ poloidal grid cells, giving shortening factors of 20. The results show that for the ELM-free state the BCs relate to the classic one; in the phase of the Type-I ELM, the BCs are increasing; and in the post-ELM, the BCs are decreasing, reaching the classic values. Taking into account this kind of BC dependence, we can provide realistic ITER plasma profiles for subsequent investigations. As this is a time-consuming process, the simulations are first conducted without neutrals, while in order to obtain realistic values for the BCs, the neutrals are added to the system. At a later stage, these will be used as BCs for the calculations of the ELM target heat loads using the SOLPS-ITER (Bonnin in Plasma Fusion Res 11:1403102, 2016; Wiesen in J Nucl Mater 463:480–484, 2015) code.