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The thermal shield system of ITER plays the role of reducing heat loads transferred by thermal radiation and conduction from warm components to the components and structures that operate at 4.5 K. In the design of thermal shields, it is of importance to ensure that they maintain thermal loads within the specified design criteria. In the present work, a study is conducted on thermal analyses in order to confirm that the thermal shield design can accommodate the thermal loads during the plasma operation state and the baking state of the ITER vacuum vessel. Design of the cooling tube layout of a vacuum vessel thermal shield is followed based on the results of thermal analyses. It is demonstrated that the present results can be applied to the detailed design of the ITER thermal shield system.

Based on the design done by the ITER international organization (ITER-O) and other participant teams, the more detail engineering design of the ITER vacuum vessel port and support is progressed by the Korea ITER project team. In this work, the recent design elaboration and manufacturing feasibility study from 2006 mainly focused on the equatorial and lower port are reported. The fabrication status and test plan of vacuum vessel support mock-up are also introduced.

The Korea superconducting tokamak advanced research (KSTAR), which is under construction at the National Fusion R&D Center, Korea Basic Science Institute, Daejeon, Korea, has the mission to develop a steady-state capable advanced superconducting tokamak to establish the scientific and technological bases for a fusion reactor. After an intensive R&D program, substantial progress of the KSTAR tokamak engineering had been made on major tokamak structures, superconducting magnets, in-vessel components, diagnostic system, heating system, and power supplies with industrial manufacturers by May 2002. The engineering design has been elaborated to the extent necessary to allow a realistic assessment of its feasibility, performance, and cost. Since May 2003, the project has been in the phase of procurement. The fabrication of main tokamak structure such as vacuum vessel, cryostat, and supporting structures is well progressed. The manufacturing work of superconducting coils is also proceeding favorably. The tokamak assembly started in July 2003 after site preparation and assembly jig. The start of commissioning is scheduled for June 2006. This paper describes the key features and engineering progress of the KSTAR tokamak and elaborates the work currently underway.

The current feeder system consisting of superconducting (SC) bus-lines, SC bus-line interface terminal, and current leads is used as the current transmission system for the KSTAR SC coils. The current lead system consists of 11 pairs of vapor-cooled leads for the PF coils and a pair of leads for the TF coils. The PF coils are operated at full currents only during a portion of the entire time. The heat loads of current leads in idle mode, when it carries no current, depend quite strongly on the using material. We have measured the heat load and temperature profile when the overload current was charged in 200 A optimum brass lead. Also, the current feeder system requires a long bus-line that must supply a large amount of current from a current lead to SC coils. We have designed a SC bus-line with NbTi cable-in-conduit conductor (CICC) to reduce Joule heating loss. The CICC is cooled with forced-flow supercritical helium (SHe). The bus-line requires higher reliability and safety than those of the SC coils of the KSTAR. The KSTAR bus-line has been designed to have an independent vacuum space and consist of SHe return and 60 K thermal shield line for shielding. To connect the bus-line with a cryostat of the KSTAR and current lead box, we have developed a prototype SC bus-line interface terminal.

The insulation system of the Korea Superconducting Tokamak Advanced Research (KSTAR) device plays a role of the structural element by binding the conductor jackets as well as breaking the current. The KSTAR Central Solenoid (CS) coils are stacked with four pairs of coils with up-down symmetry. The insulation of the CS coils experiences various stress states, such as tensile, normal compressive, and shear stresses due to applied preload at room temperature, thermal contraction difference during cool-down, and magnetic forces during operation. In particular, the normal tension and shear of the insulation has been a critical issue for magnet design. In this paper, a more detailed model in addition to electromagnetic and global structural analysis will be constructed and analyzed to evaluate the insulation stress. The results may suggest appropriate allowable stress criteria for insulation systems at cryogenic temperature.

The KSTAR vacuum vessel is designed as a racetrack-shaped double wall configuration with major ports, reinforcing ribs, bellows and a leaf spring style support structure. The vessel will be baked out by hot nitrogen gas and cooled with shielding water during normal operation. The baking/cooling medium will be fed into the double wall through the manifold to bake the vessel at 250 °C within 24 h. The heat-transfer mechanism used for the design is introduced. The heat loads on the non-symmetric vessel during the bakeout produce a non-symmetric thermal expansion that can create high thermal stresses on the support structure and the vacuum vessel interface area with the ports. The 3D temperature distribution and the resulting thermal loads in the vacuum vessel during bakeout are calculated. It is found that the vacuum vessel and its supports are structurally robust based on the thermal stress analyses.

The Korea Superconducting Tokamak Advanced Research (KSTAR) device is a steady-state-capable experimental fusion device with a fully superconducting magnet system, including toroidal field (TF) coils, central solenoid (CS) coils, and poloidal field (PF) coils. The major design consideration of the magnet system is to meet the KSTAR mission with plasma current of 2 MA and toroidal field of 3.5 T at the major radius 1.8 m and z=0. The preliminary analyses show that the magnet structure design has mechanical, electrical, and thermal stability during operation. The TF magnets have a wedged structure, including coil cases, inter-coil structures, and inter-octant joints. The CS and PF structures are designed to support the electromagnetic forces. To support the coil system against gravity and lateral loads, gravity support and lateral load structures are designed.

A magnet-supporting post installed between the lower TF coil cooled by 4.5 K supercritical helium and the cryostat base is one of the most important components of the superconducting magnet-supporting structure for KSTAR Tokamak. This structure should be flexible to absorb thermal shrink of the magnet and should also be rigid to support the magnet weight and the plasma disruption load. The post was designed with stainless steel (SS) 316 LN and carbon fiber reinforced plastic (CFRP) that has low thermal conductivity and high structural strength at low temperature. In order to verify the fabricability and the structural safety, a whole scale prototype of the KSTAR magnet-supporting post was manufactured and tested. Both static and compressive cyclic load tests under the maximum plasma vertical disruption load and the magnet dead weight were performed. The test results showed that the magnet-supporting post of KSTAR Tokamak was fabricable and structurally rigid.

The construction of ITER is an extremely important project, not only within the fusion society but also for mankind: By solving critical energy and environmental problems, another major step in human history will be taken. Design, construction, and assembly of an ultra large scale machine such as ITER require thoroughly well defined plans, strategies, and predictions of potential problems and solutions. It is believed that preceding devices and projects may provide useful references for the several important considerations noted above. The KSTAR (Korea Superconducting Tokamak Advanced Research), a representative superconducting tokamak, has the most similar characteristics to the design concept of the ITER. Therefore, the lessons learned from KSTAR can be categorized according to the following engineering aspects: 1) policies to prioritize decisions, 2) catch-up plans for delayed schedules, 3) strategies in site assembly, 4) troubleshooting, 5) standard indexes or guides for tests and acceptance of individual systems and of site assemblies, and 6) interfaces that can be easily omitted in view of the system integration. This paper will summarize the lessons we have learned from the KSTAR project, focusing on engineering related points that can be considered to suggest guidelines for the ITER construction.

The vacuum vessel of the KSTAR (Korea Superconducting Tokamak Advanced Research) tokamak has 72 ports for diagnostics, plasma heating, vacuum pumping, baking, and cooling. The design and fabrication of the bellows at each port need special care in order to compensate relative displacement between the vacuum vessel and the cryostat. S-type welded bellows were designed based on the port shape, the maximum displacement, and the life cycle. Fatigue strength evaluation using Minor's rule was performed. Rectangular-shaped prototype bellows with outer dimension of 1370 mmtimes1610 mm was fabricated and tested. We confirmed that the bellows had sufficient fatigue strength and vacuum reliability. VALQUA fabricated the bellows including one prototype bellows and 72 main bellows. The fabricated bellows were assembled with the vacuum vessel ports. The assembled port devices are going to be welded on the vacuum vessel body in accordance with the KSTAR tokamak assembly scenario

The KSTAR cryostat is a 8.8 m diameter vacuum vessel that provides the necessary thermal barrier between the ambient temperature test cell and the supercritical helium cooled superconducting magnet providing the base pressure of 1/spl times/10/sup -5/ torr. The cryostat is a single walled vessel consisting of central cylindrical section and two end closures, a flat base structure with external reinforcements and a dome-shaped lid structure. The base structure has 8 equally spaced support legs anchored on the concrete base. The cryostat vessel design was executed to satisfy the performance and operation requirements. The mechanical penetration components with bellows were designed to restrict the displacements of all kinds of ports due to EM loads and thermal loads within the allowable limits. The major loads considered in this paper for the design of cryostat vessel are the vacuum pressure, the dead weight of vacuum vessel, PFC, and magnet which are total about 400 tons, the electromagnetic load driven by plasma disruption, and seismic loads. Based on these loads, structural analyses were performed. It was found that the maximum stress intensity was below the allowable limit, and that the cryostat vessel had buckling safety of over 5. Based on the results, structural robustness of the cryostat vessel has been proved.

The KSTAR Vacuum vessel thermal shield is composed of multilayer insulation (MLI), cryopanel and supports. One of the major design parameters for the design of thermal shield cryopanel and supports is the eddy current induced during plasma disruption. The eddy current creates joule heating as well as electromagnetic (EM) loads combining with magnetic fields. Since the cryopanel should be maintained at a cryogenic temperature lower than 80 K, even a small amount of joule heating may play an important role in increasing the cyropanel temperature. Also the EM loads are very critical mechanical forces for the design of structure of the thermal shield, especially for the supports. Joule heating and EM loads on the vacuum vessel thermal shield during plasma disruption were calculated to provide the design requirement of the thermal shield. Based on the joule heating and EM loads, the structural and thermal stress analyses were performed for the assessment of the structural robustness of the vacuum vessel thermal shield. It was found that the effect of joule heating on the thermal shield design is minimal, but the EM loads are important for the design of cryopanel as well as supports. The optimal number and size of supports were determined.