Song Yuntao

Design, Analysis and R&D of the EAST In-Vessel Components

In-vessel components are important parts of the EAST superconducting tokamak. They include the plasma facing components, passive plates, cryo-pumps, in-vessel coils, etc. The structural design, analysis and related R&D have been completed. The divertor is designed in an up-down symmetric configuration to accommodate both double null and single null plasma operation. Passive plates are used for plasma movement control. In-vessel coils are used for the active control of plasma vertical movements. Each cryo-pump can provide an approximately 45 m3/s pumping rate at a pressure of 10−1 Pa for particle exhaust. Analysis shows that, when a plasma current of 1 MA disrupts in 3 ms, the EM loads caused by the eddy current and the halo current in a vertical displacement event (VDE) will not generate an unacceptable stress on the divertor structure. The bolted divertor thermal structure with an active cooling system can sustain a load of 2 MW/m2 up to a 60 s operation if the plasma facing surface temperature is limited to 1500 °C. Thermal testing and structural optimization testing were conducted to demonstrate the analysis results.

Static and Dynamic Mechanical Analyses for the Vacuum Vessel of EAST Superconducting Tokamak Device

EAST (experimental advanced superconducting tokamak) is an advanced steady-state plasma physics experimental device, which is being constructed as the Chinese National Nuclear Fusion Research Project. During the plasma operation the vacuum vessel as one of the key component will withstand the electromagnetic force due to the plasma disruption, the Halo current and the toroidal field coil quench, the pressure of boride water and the thermal load due to 250 oC baking by pressurized nitrogen gas. In this paper a report of the static and dynamic mechanical analyses of the vacuum vessel is made. Firstly the applied loads on the vacuum vessel were given and the static stress distribution under the gravitational loads, the pressure loads, the electromagnetic loads and thermal loads were investigated. Then a series of primary dynamic, buckling and fatigue life analyses were performed to predict the structures dynamic behavior. A seismic analysis was also conducted.

Current Status of ICRF Heating Experiments on EAST

Radio frequency (RF) heating in the ion cyclotron range of frequencies (ICRF) is one of the primary auxiliary heating methods for EAST. The ICRF system provides 6 MW power in primary phase and will be capable of 10 MW later. Three 1.5 MW ICRF systems in a frequency range of 25 MHz to 70 MHz have already been in operation. The ICRF heating launchers are designed to have two current straps with each driven by a RF power source of 1.5 MW. In this paper a brief introduction of the ICRF heating system capability in EAST and the preliminary results in EAST are presented.

Primary Design and Analysis of Feeder for ITER Poloidal Field

An electromagnetic (EM) analytic model for the PF feeder, applied to ITER and needed to convey the cryogenic supply and electrical power to the PF magnets, was built up. The magnetic flux density and the EM force under the worst conditions with the maximum working current in each coil were then calculated. Based on the EM analysis and theoretical calculation, the relationship between the busbar stress and the distance of neighbouring busbar supports was obtained, which provides an approach to optimize the design of the busbar supports. In order to check the feasibility of the PF feeder structure, a finite element model was built up and the ANSYS code was applied to analyze the stress and displacement. The numerical results show that the stress of the PF feeder is within the allowable limits and the structure is feasible.

Optimization and Update of EAST In-Vessel Components in 2011

For safe operation with active water cooling plasma facing components (PFCs) to handle a large input power over a long pulse discharge, some design optimization, R&D and maintenance were accomplished to improve the in-vessel components. For the purpose of large plasma current (1 MA) operation, the previous separated top and bottom passive stabilizers in the low field were electrical connected to stabilize plasma in the case of vertical displace events (VDEs). The design and experiments are described in this paper

Preload Analysis of Screw Bolt Joints on the First Wall Graphite Tiles in EAST

The first wall in the Experimental Advanced Superconducting Tokamak (EAST) used graphite tiles to withstand high thermal energy.The graphite tiles are mounted on the heat sink using screw bolts which have been preloaded to produce a clamp force.The clamp force is very important to keep the graphite tiles tightly on the surface of the heat sink so that the heat flux crosses this contacting surface in a small thermal resistor.Without the clamp force,the small gap between the graphite tiles and the heat sink will make it impossible for thermal power to be carried away by cooling water.Some bolts may even fall off with the loss of clamp force.From the mathematical models,the loss process of the clamp force has been studied.Research results explain how the different thermal expansions of three members of the screw joint makes the clamp force decrease to zero under temperature rise and external force,and how the stiffness affects the relation between the clamp force and temperature.The research also gives the critical temperature at which the clamp force can remain above zero.Analysis results indicate that the current screw joints are almost destined to lose their clamp force during the running time of EAST,so the bolt joints should be redesigned in order to improve its reliability.

Mechanical Design and First Engineering Commissioning of ICRF Antenna for EAST

A new loop and fold wave-guide ion cyclotron resonance frequency (ICRF) antenna with a power output of 3 MW, which can operate at a frequency in the range of 30 MHz to 110 MHz, was designed. The design of key components of the new ICRF antenna and the characters of the new prototype ICRF antenna are presented. The thermo-mechanical analysis of both the Faraday shield and the current straps was conducted, and the stresses due to heat loads are studied in detail with different cooling-water velocities considered. In addition, the movability of prototype ICRF antenna under vacuum condition by the driving system was tested. An engineering commissioning was successfully performed on the prototype ICRF antenna using the original transmitter. The results are close to the expected.

Temperature Field and Thermal Stress Analysis of the HT-7U Vacuum Vessel

The HT-7U vacuum vessel is an all-metal-welded double-wall interconnected with toroidal and poloidal stiffening ribs. The channels formed between the ribs and walls are filled with boride water as a nuclear shielding. On the vessel surface facing the plasma are installed cable-based Ohmic heaters. Prior to plasma operation the vessel is to be baked out and discharge cleaned at about 250°C. During baking out the non-uniformity of temperature distribution on the vacuum vessel will bring about serious thermal stress that can damage the vessel. In order to determine and optimize the design of the HT-7U vacuum vessel, a three-dimensional finite element model was performed to analyse its temperature field and thermal stress. The maximal thermal stress appeared on the round of lower vertical port and maximal deformation located just on the region between the upper vertical port and the horizontal port. The results show that the reinforced structure has a good capability of withstanding the thermal loads.

Experimental study of hypervapotron under conditions of high heat flux

In the light of the needs to develop high-performance heat transfer component for nation-level large-scale scientific projects of China, a hypervapotron experimental platform with supply of heat flux 1–10 MW m−2 was established. With this platform, the multiphase flow and heat transfer phenomena on the surface of triangular fin when the subcooled water flowed through were observed and measured with the planar laser induced fluorescence (PLIF) and high-speed photography techniques. The temperature contour on the slice plane of fin symmetry was measured and the heat flux contour was processed based on gradient computation. It is confirmed that: 1) PLIF with high-speed photography is very powerful technique to investigate the multiphase flow of hypervapotron quantitatively; 2) evaporation is the primary way in heat transfer mechanism of hypervapotron flow under the condition of high heat flux. The techniques and results obtained will provide useful reference in the R&D of hypervapotron technology in China.

Evolution of the Design of Cold Mass Support for the ITER Magnet Feeder System

This paper presents the evolution of the design of cold mass support for the ITER magnet feeder system. The glass fibers in the cylinder and the flanges of the normal G10 support are discontinuous in the preliminary design. The heat load of this support from the analysis is only 4.86 W. However, the mechanical test of the prototype showed that it can only endure 9 kN lateral force, which is significantly less than the required 20 kN. So, the configuration of the glass fibers in the cylinders and flanges of this G10 support are modified by changing it to a continuous and knitted type to reinforce the support, and then a new improved prototype is manufactured and tested. It could endure 15 kN lateral forces this time, but still not meet the required 20 kN. Finally, the SS316LN material is chosen for the cold mass supports. The analysis results show that it is safe under 20 kN lateral forces with the heat load increased to 14.8 W. Considering the practical application, the requirements of strength is of primary importance. So, this SS316LN cold mass support is acceptable for the ITER magnet feeder system. On the other hand, the design idea of using continuous and knitted glass fibers to reinforce the strength of a G10 support is a good reference for the case with a lower heat load and not too high Lorentz force.