Speaker
Description
SONIC divertor code enables simultaneous calculations of seeding impurity (Ar) and fusion product (He ash) transport. He exhaust has been investigated in JA DEMO, where exhaust power ($P_{out}$ = 250 MW), ion flux ($\Gamma_{out}^{D}$ = $\rm 1x10^{22} s^{-1}$) and He ion flux ($\Gamma_{out}^{He}$ =$\rm 5.3x10^{20} s^{-1}$, corresponding to 1.5 GW fusion power) were given at the core-edge boundary. Plasma diffusion coefficients of $\chi$ = 1 $\rm m^{2}s^{-1}$ and $D$ (plasma and impurity ions) = 0.3 $\rm m^{2}s^{-1}$ were the same as “standard” values in the ITER simulation. Peak heat loads at the inner and outer divertor targets were reduced less than 10 $\rm MWm^{-2}$ for a reference series of the radiation fraction in the SOL and divertor, i.e. $f_{rad}^{div}$ = $(P_{rad}^{sol}+P_{rad}^{div})/P_{sep}$ $\sim$0.8. He concentration ($c_{He}^{edge}$ = $n_{He}/n_{i}$) averaged at the plasma edge near the midplane ($r^{mid}/a_{p}$ = 0.96-0.98) was evaluated in the detached divertor condition; fully and partially detachment in the inner and outer divertors, respectively. $c_{He}^{edge}$ was reduced from 6 $\%$ to 4 $\%$ with increasing $n_{e}^{sep}$ from $\rm 1.8x10^{19}$ to $\rm 2.3x10^{19} m^{-3}$ by $\rm D_{2}$ gas puff (keeping the same $f_{rad}^{div}$ $\sim$0.8 by reducing Ar seeding rate), while the partial detachment was extended. In the divertor, in-out asymmetry of $c_{He}^{div}$ was seen (2-3 times); $c_{He}^{div}$ in the upstream of the inner divertor was enhanced to larger than 10 $\%$, maybe caused by large thermal force (parallel ion temperature gradient) on He ions in the fully detached condition.The in-out asymmetry were reduced near the separatrix of the main SOL.
Influences of reducing $\chi$ and $D$ on the He exhaust were investigated ($\chi$ = 0.5, $D$ = 0.15 $\rm m^{2}s^{-1}$), compared to above “standard” case. Radial gradient of the plasma density profile was increased particularly in SOL, and both $n_{i}^{sep}$ and $n_{e}^{sep}$ were increased from $\rm 1.6x10^{19}$ and $\rm 2.1x10^{19} m^{-3}$ to $\rm 2.4x10^{19}$ and $\rm 2.9x10^{19} m^{-3}$, respectively. Since $n_{He}^{sep}$ $\rm \sim 1x10^{18} m^{-3}$ and $n_{Ar}^{sep}$ $\rm \sim 2x10^{17} m^{-3}$ near the separatrix, $n_{e}^{sep}$ was $\sim$25$\%$ larger than $n_{i}^{sep}$. Radial gradient of the temperature profile was increased near and inside the separatrixa. $c_{He}^{div}$ was increased to $\sim$15$\%$ and $\sim$10$\%$ in the inner and outer divertors, respectively. On the other hand, $c_{He}^{edge}$ = 7-9$\%$ was slightly increased. Since plasma performance such as $P_{fus}$ and $HH_{98y2}$ for the JA DEMO is based on system code results with $c_{He}$ = 7$\%$ in the main plasma, the plasma design is consistent with above simulation results, but it is necessary to avoid higher $c_{He}^{edge}$.
For the fuel particle exhaust, neutral and gas pressures ($P_{D0}$, $P_{D2}$) in the divertor were evaluated at exhaust slots of the dome and in the sub-divertor. For the “standard” case (without include neutral-neutral collisions, NNC), total neutral pressure ($P_{D}$ = $P_{D0}$ + $P_{D2}$) was increased from $\sim$2 to $\sim$3 Pa at the exhaust slots, and from $\sim$1 to $\sim$1.8 Pa in the sub-divertor, with increasing $\rm D_{2}$ puff rate from $\rm 4.8x10^{22}$ to $\rm 9.6x10^{22} D/s^{-1}$. Effects of NNC on the particle exhaust and detachment are shown.
| Speaker's Affiliation | National Institutes for Quantum, Science and Technology (QST), Naka Institute |
|---|---|
| Member State or IGO | Japan |
