Speaker
Description
SONIC divertor code has simulated the divertor performance of power exhaust by seeding impurity (Ar) and He exhaust in the detached divertor for JA DEMO design (1.5 GW-level fusion power), where exhaust power, fuel and He particles at the core-edge boundary of 250 MW, 1x$10^{22}$ D/s and 5.3x$10^{20}$ He/s, respectively, were given [1]. Recently, NEUT2D and IMPMC codes (kinetic MC modellings for neutral and impurity transport, respectively) incorporated (i) neutral-neutral elastic collision (NNC) database [2], where collision rates and momentum exchange rates are evaluated from differential cross-section database for $D_{0}$-$D_{0}$, $D_{0}$-$D_{2}$, and $D_{2}$-$D_{2}$, and it is rather theoretical expression compared to those in EIRENE, and (ii) an extended kinetic thermal force (TF) model for the impurity transport, including a collisionality parameter and heat flux limiter in the conventional formula as a collisionality-dependent term, which expects reduction in TF in the high $T_{i,e}$ SOL and edge [3]. Effects on the divertor detachment and impurity concentrations in SOL and edge were investigated in the reference series of the JA DEMO design with similar total radiation fraction of $f_{rad}$ = $P_{rad}/P_{sep}$ ~0.8.
NNC affected distributions of neutral and molecular pressures ($P_{D0}$, $P_{D2}$) in the private and sub-divertor regions. Outer peak heat load at the divertor target ($q_{target}^{out}$, produced in attach plasma region) was reduced from 6.5 to ~4 $MW/m^{2}$ with increasing $P_{D0}$+$P_{D2}$ from 2.1 to 3.5 Pa and reducing the local $T_{e,i}^{div}$ from 35 to 10 eV. These peak-$q_{target}^{out}$ values were systematically smaller than those without NNC model since $P_{D0}$+$P_{D2}$ became larger. At the same time, comparing to result without NNC model, $D_{0}$ penetration in the sub-divertor was reduced, and $P_{D2}$ was increased by the factor of two. Extended TF-model also affected detachment in the outer divertor, which was extended to the upstream and radial directions. As a result, Ar concentration in the SOL ($c_{Ar}^{sol}$) was increased and $c_{Ar}$ inside the separatrix ($c_{Ar}^{edge}$) was increased from 0.6-0.8% to ~1%. The latter value was larger than the design reference (0.6%). $c_{He}^{sol}$ was also increased, but $c_{He}^{edge}$ was similar than the design reference (0.7%). Operation window of $f_{rad}$, $D$-gas puff rate will be investigated to satisfy requirements of the JA DEMO divertor design such as $q_{target}^{out}$, $c_{Ar}^{edge}$ and $c_{He}^{edge}$ values.
[1] N. Asakura, et al., Nucl. Mater. Energy 26 (2021), 100864.
[2] S. Tokunaga, et al., PSI22, P.3.105, May 2016, Rome, Italy.
[3] Y. Homma, et al. Nucl. Fusion 60 (2020) 046031.