24P100-P
Design and Manufacturing Status of JT-60SA Vacuum Vessel and Cryostat
JT-60SA真空容器とクライオスタットの設計、製作の現状
Yusuke K. Shibama, Kei Masaki, Shigetoshi Nakamura, Atsushi Kaminaga, Yasuhiko Miyo,Sinji Sakurai, Kiyoshi Shibanuma and Akira Sakasai
芝間祐介, 正木 圭, 中村誠俊, 神永敦嗣, 三代康彦, 櫻井真治, 柴沼 清, 逆井 章
Japan Atomic Energy Agency
801-1, Mukoyama, Naka-shi, Ibaraki-ken 319-0193, Japan
日本原子力研究開発機構 〒319-0193 茨城県那珂市向山801-1
JT-60SA is a fully superconducting coil tokamak upgraded from the JT-60U. This paper focuses on thevacuum vessel (VV, 150 tons) and cryostat (610 tons), whose structural concepts are developed from theASME BPVC Section VIII Division 2. The VV is a stainless steel torus double-walled, which achieves
high electrical resistivity in the toroidal and high stiffness in the light structure. The cryostat is large size
vacuum thermal insulation vessel. The present status of both vessels is reported.

1. Introduction
JT-60SA is a combined Japan (JA) - theEuropean Union (EU) satellite tokamak program,aiming at the ITER program supports and thesupplements toward the DEMO, under both
broader approach agreement and the JA domestic
program [1]. This machine is upgraded to alarge volume vacuum space for core plasma and afully superconducting coil magnet system.
These results in larger size of vacuum vessel(VV) construction by JA, and cryostat as anextensive thermal insulation structure by the EU,especially, in Spain. The entire tokamak systemof JT-60SA is as shown in figure 1. Recent
design and its manufacturing status of the eachcomponent are discussed in the following sections.
2. Design
The VV and cryostat are basically designed bythe ASME BPVC Section VIII division 2, andsome unique design descriptions to the fusion
machine are explained. The each component issplit in pieces of parts limited by the JA domestictransport and assembled in the JA Naka-site [2].
2.1 Vacuum Vessel
The VV is a vessel to ensure sufficient
ultrahigh vacuum and one turn toroidal electricalresistance for plasma breakdown. The VV torus
is outside diameter of 10 m and its height of 6.6m, and consists of 18 sectors with 73 port
penetrations.
A double wall structure is selected to secure thevessel’s higher stiffness, to resist the operationalloads and also to support various in-vessel
components such as divertor [3] and plasma
control coils [4]. The space between these walls

is utilized for the neutron shielding by 323 K
boron water circulation, and for baking at 473 K
by nitrogen gas flow to achieve the vacuum lessthan 10-5 Pa. The total weight amounts to 400
tons which includes the VV of 150 tons, thein-vessel component of 195 tons, and theshielding water of 55 tons. The dead weight is
supported from the bottom of every odd numbersector, and these 9 support legs have radialleaf-springs to absorb the thermal displacement.
The material is selected as type 316L stainlesssteel (SS316L) additionally restricted in thecobalt contents less than 0.05wt%.
The VV electromagnetic (EM) response ischaracterized by the toroidal one turn resistance of15 μΩ and the toroidal eddy current decay time
constant of 110 ms [5]. The seismic event isdesigned by the design response spectrum (DRS),
which is based on the geological survey forprevious JT-60 construction, and for the ITER
design activity [6]. The mechanical response is
Cryostat Vessel Body

Vacuum Vessel

PlasmaN-NBI

Cryostat BaseFig. 1 Tokamak Machine of JT-60SA

2 sectors

Fig. 2 First two sectors (40 deg.) of Vacuum Vessel wasin the final inspection, and completed in May 2011 (left).

characterized by the horizontal stiffness of 6.46 x
102 MN/m and the design damping ratio of 5.0% at
the plasma operational state.
The welding
technical elements are selected to validate its
weldability and mechanical performance before
product VV fabrication [7]. The product VVmanufacturing is validated by these fundamentalsurveillance and several mock-up trials [5, 8].
2.2 Cryostat
Cryostat [9] is also a vessel to provide thevacuum thermal insulation for cryogenic device,
and a base to support tokamak machine dead weight.
The vessel is of 14 m diameter and of 16 m height,
and the structural material type 304 is selected assame cobalt restriction as the VV.
This
component is split in mainly two; the upper part as
the cryostat-vessel-body (CVB) and the other lower
part as the cryostat-base (CB).
The CVB
structural design condition is substantially governedby difference in pressure; the operational negative
pressure of 10-3 Pa inside, with various operationalloads, as discussed in the VV. The CB is designedby those reaction loads from the tokamak devices.
The EM force is very small because the cryostat isDouble Ring

Cryostat Base

Lower Structure

Fig. 3 CB consists of double ring and lower structure[9], whose radial beam is a first part fabricated .

located away from core plasma. Toroidal one turnresistance is higher than 25 μΩ, and the decay timeof toroidal currents is over 250 ms [10].
The CVB consists of two major part; lateral partand top lid. The CVB is made of 34 mm thicksingle-walled with poloidal rib reinforcement.
The lateral part has the corresponding port bores tothe VV and supports the dead weight of diagnostics
port plugs and the other ports for various in-cryostat
systems [2]. Bellows are attached between themto absorb difference in operational movements, andrupture disks are also prepared for overpressure
protection.
The CB is designed to bear the load of the entire
tokamak machine and to transfer the loads to thefloor and lower pillars of the tokamak torus hall.
The CB is designed as bolt fastened structure,
which forms double ring and lower structure asshown in figure 3 [9]. Both structures consist ofmajor three parts split and are assembled as one
ring support base. The fabrication of the CB has
been started in August.
The each part of the cryostat is connected bybolts and vacuum-sealed by inside conventionalwelding. Major surrounding facilities in the torus
hall; such as the Neutral Beam Injector (NBI),Electron Cyclotron Resonance Heating (ECRH) areconnected after assembly. Auxiliary systems suchas 80K thermal shield and vacuum exhaust areincluded as its component.
3. Manufacturing Status and Conclusions
The first 40 degree part of the VV (2 sectors) iscompleted in May 2011, as shown in figure 2.
Other sectors and related ports and gravity supports
are under constructions.
The CB has been fabricated since August 2011
(Fig. 3). The CVB and its design in detail areunder constructions.
References[1] S.Ishida et al., Fusion Eng. Des. 85, 2070 (2010).
[2] K.Shibanuma et al, J. Plasma Fusion Res. SERIES,Vol. 9 276 (2010)[3] S.Sakurai et al., Proceeding of the 23rd IAEA
Fusion Energy Conference, Daejeon Korea (2010).
[4] M.Takechi et al., ibid.
[5] Y.K.Shibama et al., Proceeding of 2011 ASME PVP
Conference, Baltimore, Maryland (2011).
[6] S.Tado et al., Seismic, Shock, and Vibration
Isolation -1998, ASME 1998 PVP-Vol.379, 197 (1998).
[7] S.Asano et al, Fusion Eng. Des. 86 1816 (2011)[8] K.Masaki et al, Fusion Eng. Des. 86 1872 (2011)[9] E.Rincóna et al., Fusion Eng. Des. 86 623 (2011)[10] Y.K.Shibama et al., Fusion Eng. Des. 83 1605
(2008)