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Nakashima, Yosuke*; Takeda, Hisahito*; Ichimura, Kazuya*; Hosoi, Katsuhiro*; Oki, Kensuke*; Sakamoto, Mizuki*; Hirata, Mafumi*; Ichimura, Makoto*; Ikezoe, Ryuya*; Imai, Tsuyoshi*; et al.
Journal of Nuclear Materials, 463, p.537 - 540, 2015/08
Times Cited Count：19 Percentile：82.55(Materials Science, Multidisciplinary)Shimada, Michiya; Hirooka, Yoshihiko*
Nuclear Fusion, 54(12), p.122002_1 - 122002_7, 2014/12
Times Cited Count：37 Percentile：86.2(Physics, Fluids & Plasmas)Tungsten is considered to be the most promising material for divertor in a fusion reactor. Tungsten divertor can withstand the heat loads of ITER, but the heat loads of DEMO divertor is a challenge. Pulsive heat loads as those associated with disruption could melt tungsten targets. The surface would not be flat after subsequent resolidification, which would significantly deteriorate its heat handling capability. Furthermore, DBTT of tungsten is rather high: 
400
C, which would become even higher after neutron irradiation, possibly resulting in cracks in tungsten. Our proposal is to use liquid metal for the divertor target material and actively circulate it with 
force. A simplified analysis of mhd equation in a cylindrical geometry suggests that the engineering requirement is modest. This analysis suggests that this new divertor concept merits further investigation.
Nakashima, Yosuke*; Sakamoto, Mizuki*; Yoshikawa, Masayuki*; Oki, Kensuke*; Takeda, Hisahito*; Ichimura, Kazuya*; Hosoi, Katsuhiro*; Hirata, Mafumi*; Ichimura, Makoto*; Ikezoe, Ryuya*; et al.
Proceedings of 25th IAEA Fusion Energy Conference (FEC 2014) (CD-ROM), 8 Pages, 2014/10
Shimada, Michiya; Hirooka, Yoshihiko*; Zhou, H.*
Europhysics Conference Abstracts (Internet), 38F, p.O2.110_1 - O2.110_4, 2014/00
Tungsten is considered to be most promising candidate for divertor target material for fusion reactor. Although tungsten target can withstand the heat loads of ITER, the heat exhaust requirement for DEMO is much more demanding. Pulsive heat loads associated with disurption would melt the tungsten divertor target. Melting and subsequent resolidification will roughen the tungsten surface, significantly deteriorating the heat handling capability. Further, tungsten has a rather high DBTT (Ductile-Brittle-Transition temperature) of 400C. Neutron irradiation would further increase the DBTT, which could result in cracks. In view of these issues, liquid metal divertor is proposed, which is actively circulated with the Lorentz force introduced through the electrodes in the liquid metal. A modest flow speed of 0.3 m/s seems to be adequate for the heat load exhaust of DEMO. A simple treatment of MHD equation in a cylindrical geometry suggests that the requirements on the current and voltage are modest if the ramp-up of current is made slowly (e.g. in a minute), implying that the this concept is worth further study.
Shimada, Michiya; Hirooka, Yoshihiko*
no journal, ,
The use of circulating liquid metal is proposed to facilitate heat handling of the divertor, which is a very serious and challenging issue in fusion reactors. Two solid metal casings are placed where the separatrix magnetic surface hits. Each casing contains an electrode which can be biased positively or negatively with respect to the casing. The casing is filled with liquid metal like Ga, Sn or other metals with low melting point and low chemical activity. The j B force due to the radial current drives the poloidal motion of the liquid metal in such a way that the temperature rise at the separatrix hit point is kept at an acceptable level.
Shimada, Michiya; Miyazawa, Junichi*; Hirooka, Yoshihiko*
no journal, ,
Heat flux and plasma particle flux concentrate on the divertor. Therefore the divertor is the most difficult equipment of a fusion reactor. The feasibility of ITER divertor has been established and its construction is in progress. However, in a DEMO reactor the environment will be much more harsh than in ITER. The concept of DEMO divertor is yet to be developed. Liquid metal divertor could provide a feasible solution for DEMO divertor, if a good method of actively convect the liquid metal in magnetic field is established. Liquid metal divertor could also be resilient to disruptions, require less maintenance and contribute to a compact reactor. In this talk, the progress on the liquid metal plasma facing component will be reviewed and remaining issues will be discussed.
