Neutral-neutral elastic scattering effect on 2D structure of full-detached divertor in DEMO

Conceptual design activity of economic rationality demonstrating reactor DEMO has been initiated. In contrast to the total performance prediction study of already manufactured ITER divertor, for the geometry optimization study of DEMO divertor against to larger heat/ neutron loads and He ash generation, the effect of each form-factor on fully detached plasma structure should be elucidated apart. Behavior of recycling neutral particles is main channel to reflect the divertor geometry to the detached plasma structure as well as magnetic field. In particular, turnover of dominant collisional process involving neutral is sensitive factor.In detached regime, the population of neutral is comparable to plasma particle so that neutral-neutral collision (NNC) plays significant role in profile formation. There were sophisticated preceding study to evaluate NNC rate based on BGK approximation, and have played leading role in ITER divertor design and prediction [1]. Today, estimation of particle exhaust by Direct Simulation Monte Carlo is also available [2]. There are however still a few important problems remaining in NNC treatment such as overestimation of heat conduction resulted from BGK approximation [3], difficulty of mutual diffusivity reproduction by Variable Hard Sphere model [4], and possible substantial over estimation of NNC rate in T>1eV region (it is relevant range in detached plasma region) [5].In the present study, NNC effect has been implemented to SONIC code [6] especially focusing on the validity in T>1eV range. We have developed collision rate database generator based on I-integral [7] to calculate NNC rate from elastic scattering cross-section data given by Krstic theoretically for atom-atom and atom-molecular collision [8] and Phelps for H2-H2 collision [9]. As a preliminary simulation result solving interaction with plasma and impurity, apparent localization of atom around strike point radially and poloidally was shown, as a natural consequence from shrink of mean-free-path. It suggests advantage of geometry to intentionally compress neutrals in SOL side to obtain full-detached plasma. Knudsen number of elastic scattering changes from molecular flow regime to viscous regime (~10^-3) over detach-front. Results of ongoing further analysis will be reported in the presentation.22nd International Conference on Plasma Surface Interactions in Controlled Fusion Device

Effect of dragged magnetic field lines into RAFM steel blanket modules on first wall heat load

The blanket modules in DEMO are made of reduced-activation ferritic martensitic (RAFM) steel F82H. This material is ferromagnetic and it drags the magnetic field lines into the first wall (FW). Because of this, the heat load by the plasma heat flux, which goes along the magnetic field line will become higher. In this research, the first analysis of such effect has been done. The extra magnetic field Bm made by RAFM wall becomes higher at inner midplane, and the heat load at the module front surface becomes 1.3 MW/m2 to 5 MW/m2. Additionally, near the toroidal gaps, BM becomes high. Thus, at the top of the FW, magnetic field lines are dragged into the toroidal gaps directly because, the magnetic flux surface is not closed. This makes high (about 10MW/m2) heat load concentration at the moduel edge. The effect of the NBI port is also analyzed. Also near the port, Bm becomes high and the orbit of the magnetic field lines are changed. The effect of this doesn\u27t occur near the port, but far region such as inner midplane or top of the FW. The heat load becomes 6 MW/m2 at inner midplane. These results indicate that the effect of RAFM steel on the FW heat load is not negligible, and more detailed analysis is necessary

Effect of dragged magnetic field lines into RAFM steel blanket modules on first wall heat load

The blanket modules in DEMO are made of reduced-activation ferritic martensitic (RAFM) steel F82H. This material is ferromagnetic and it drags the magnetic field lines into the FW. Because of this, the heat load by the plasma heat flux, which goes along the magnetic field line will become higher. In this research, the effect of this is analyzed. The extra magnetic field Bm made by RAFM wall becomes higher at inner midplane, and the heat load at the module front surface becomes 1.3 MW/m2 to 5 MW/m2. Additionally, near the toroidal gaps, BM becomes high. Thus, at the top of the FW, magnetic field lines are dragged into the toroidal gaps directly because, the magnetic flux surface is not closed. This makes high (about 10 MW/m2) heat load concentration at the moduel edge. The effect of the NBI port is also analyzed. Also near the port, Bm becomes high and the orbit of the magnetic field lines are changed. The effect of this doesn\u27t occur near the port, but far region such as inner midplane or top of the FW. The heat load becomes 6 MW/m2 at inner midplane.14th International Symposium on Fusion Nuclear Technolog