@misc{oai:repo.qst.go.jp:00072208,
 author = {Tokunaga, Shinsuke and Hoshino, Kazuo and Asakura, Nobuyuki and Shimizu, Katsuhiro and Sakamoto, Yoshiteru and Homma, Yuuki and 徳永 晋介 and 星野 一生 and 朝倉 伸幸 and 清水 勝宏 and 坂本 宜照 and 本間 裕貴},
 month = {Jun},
 note = {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 Devices},
 title = {Neutral-neutral elastic scattering effect on 2D structure of full-detached divertor in DEMO},
 year = {2016}
}