(FT/P5-22) Concept of compact low aspect ratio demo reactor, SlimCS

K. Tobita1), S. Nishio1), M. Sato1), S. Sakurai1), T. Hayashi1), Y.K. Shibama1), T. Isono1), M. Enoeda1), H. Nakamura1), S. Sato1), K. Ezato1), T. Hayashi1), T. Hirose1), T. Inoue1), Y. Kawamura1), N. Koizumi1), Y. Nakamura1), K. Mouri1), Y. Nomoto1), J. Ohmori1), N. Oyama1), K. Sakamoto1), S. Suzuki1), T. Suzuki1), H. Tanigawa1), K. Tsuchiya1), D. Tsuru1)
1) Japan Atomic Energy Agency, Naka, Ibaraki, Japan

Abstract.  A new concept realizing a compact demonstration reactor is presented. The reactor design named ``SlimCS" adopts a reduced-size center solenoid (CS), which enables us to introduce a slender toroidal field (TF) coil system. Such a TF system decreases the reactor weight, eventually contributing to reducing the construction cost. The CS size (an outer radius of 0.7 m) is determined to have the capability of plasma shaping (triagularity of 0.4) enough to obtain high confinement in high density region and possibly to avoid giant edge-localized modes. The SlimCS concept expands the design window of fusion reactors to lower aspect ratio (A) of around 2.5 which facilitates higher elongation and higher beta access with reasonable design margins. As a result, SlimCS is as compact as advanced commercial reactor designs such as ARIES-RS and CREST, even with the assumption of relatively conservative plasma parameters. Another merit of low-A is that the first wall area on the low field side, where smaller electromagnetic (EM) force acts on disruptions, is wide compared with that of conventional-A. This means that tritium can be efficiently breeded with large blanket modules on the low field side. As a result, the demand for tritium breeding on the high field side is comparatively reduced so that small blanket modules, being robust to stronger EM force but less efficient for tritium breeding, can be arranged on the side. SlimCS is designed to produce 2.95 GW with a major radius of 5.5 m, aspect ratio of 2.6, normalized beta of 4.3, Greenwald-normalized density of 1.05, bootstrap current fraction of 0.77 and maximum field of 16.4 T. SlimCS uses technologies foreseeable in 2020's such as Nb3Al superconductor, water-cooled solid breeder blanket, and low activation ferritic steel F82H as the blanket structural material. Average neutron wall load is designed to be 3 MW/m2. A major technical issue on SlimCS is non-inductive plasma current ramp because the plasma current must be raised using an overdrive with a combination of bootstrap current and non-inductive external current drive. This technique is considered to be a continuation of the steady state operation of tokamak. Another issue is a physics basis on plasma around A=2.6, which can be resolved by the maximum use of a satellite tokamak NCT designed to cover A=2.6-3.1.

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