8P03

早期発電実証炉設計を目指した
ヘリオトロン方式核融合炉コイル形状最適化
Optimization of coil geometry of heliotron type fusion reactor
for early power generation demonstration reactor design後藤拓也1,2)、山口裕之1,2)、市口勝治1,2)、佐竹真介1,2)、田村仁1,2)、
宮澤順一1,2)、柳長門1,2)
1,2)
Takuya Goto , Hiroyuki Yamaguchi1,2), Katsuji Ichiguchi1,2), Shinsuke Satake1,2),
Hitoshi Tamura1,2), Junichi Miyazawa1,2), Nagato Yanagi1,2)
1)

核融合研、2)総研大
1)
NIFS, 2)The Graduate University for Advanced Studies, SOKENDAI
A helical fusion reactor based on the heliotron
configuration with continuous helical coils has
several advantages in its engineering design: helicaldivertor field structure that enables flexible divert
design, coil shape with a small variance in its
curvature that enables flexible winding, large
apertures between coils for the maintenance of invessel components. On the other hand, there are two
major issues to realizing a fusion power plant with acompact size and high plant efficiency. One is aninsufficient plasma confinement performance. The
plasma performance of various magnetic
configurations has been examined in the LHDexperiment and it was found that there is a trade-off
between MHD stability and energy confinement
property. This trade-off limits the achievable fusion
gain of a fusion power plant. The other is a limit on
the distance between the helical coil and plasma at
the inboard side of the torus. This limit leads to theinsufficient performance of neutron shielding andtritium breeding of the blanket module.
Configuration optimization is expected to be asolution for these issues. In a previous study, it was
found that a slight change in the pitch modulation,
which is one parameter in the definition of the helicalcoil winding law, simultaneously improves MHD
stability and energy confinement property [1].
However, this change reduces the distance between
the helical coil and the plasma. It is not practical toscan all parameters of the winding law. Recently, thehelical coil optimization code OPTHECS has beendeveloped. OPTHECS can optimize the shape andthe current of the helical and vertical field coils byconsidering overall plasma performance, such asplasma volume, MHD equilibrium, rotationaltransform, neoclassical diffusion, alpha particle orbit,

and so on with a flexible change in the shape of thehelical coil beyond the conventional winding law.
Currently, optimization calculations are being
conducted to include the distance between theplasma and the coil in the optimization target. The
comparison of the Mercier parameter (index of MHDstability) and the neoclassical energy loss of theinitial candidate configuration with 4 cases of thevacuum magnetic axis positions and the two
reference configurations is shown in Fig. 1. The
comparable performance is obtained with ~10%
increase in the distance between the helical coil andthe plasma. In the presentation, the latest calculation
results and future prospects in the optimization study.

Figure 1. Comparison of Mercier parameter (left)
and neoclassical energy loss (right) of the initial
candidate configuration obtained by OPTHECS with
4 cases of the vacuum magnetic axis position Rax(solid curves, Rc is the major radius of the helicalcoil) and the reference configurations (broken curves
with Rax/Rc = 3.5/3.9).
[1] T. Goto et al., Plasma Fusion Res. 16 (2021)
1405085.