Jing Wei

Microstructure and Mechanical Properties of ITER Correction Coil Case Material

The modified 316LN austenitic stainless steel was selected as ITER correction coils case material to provide structural reinforcement to the winding pack. Considering the case structure, high-assembling accuracy and other strict requirements, 316LN in special extruded form has been developed. In the present study, the microstructure and mechanical properties of the material were investigated. The microstructure of the 316LN material was analyzed by means of the optical microscopy, transmission electron microscope, and X-ray diffraction. It was observed that the material presents fine grain size and a single austenitic phase. Moreover, the intergranular corrosion resistance of the 316LN was evaluated and the results indicated that it exhibited a remarkable intergranular corrosion resistance. The tensile properties of materials were measured at both room and cryogenic temperatures. The 0.2% offset yield strength (<inline-formula><tex-math notation=LaTeX>

Status of design and manufacturing of the ITER Central Solenoid and Correction Coils

R_{p0.2}

The design, analysis and alignment of EAST divertor

</tex-math></inline-formula>), ultimate tensile strength (<inline-formula><tex-math notation=LaTeX>

Microstructural characteristics of the laser welded joint of ITER correction coil sub case

R_{m}

Qualification of structural stainless steel products for the ITER correction coil cases

</tex-math></inline-formula>), and elongation at break ( <italic>A</italic>) at 4.2xa0K were determined to be higher than 800 MPa, 1500 MPa, and 40%, respectively. Furthermore, the <italic>J-integral</italic> fracture toughness of the 316LN was tested through means of an unloading compliance method at 4.2xa0K and the plane strain fracture toughness <inline-formula><tex-math notation=LaTeX>

Requirements for qualification of manufacture of the ITER Central Solenoid and Correction Coils

K_{Ic}

Fatigue tests on ITER PF6 coil helium inlet at 77K

</tex-math></inline-formula> converted from the <italic>J-integral</italic> are well above the specified value of 180 MPa√m. In addition, the fatigue test and fatigue crack growth rate of the 316LN stainless steel were also investigated at 4.2 K. According to these results, all requirement of the case material including uniform microstructure, excellent corrosion resistance, and good mechanical properties established by the ITER IO are confirmed.

Extrusion process of 316LN L-shape stainless steel and manufacture process of ITER side correction coil box

The Final Design of the Central Solenoid (CS) of the ITER Magnet system is currently being completed by the US ITER Domestic Agency (USDA) and the manufacturing line of the coil under installation at the suppliers premises in the USA. The Central Solenoid includes 6 identical Nb3Sn coil modules independently powered and enclosed inside a precompression structure preventing their separation. The CS structure includes 9 subsets, made of Nitronic 50 high strength austenitic stainless steel, evenly distributed around the stack of the 6 modules.