This paper describes both structural materials and structural design of the Toroidal Field (TF) coil and Central Solenoid (CS) for the International Thermonuclear Experimental Reactor (ITER). All the structural materials used in the superconducting coil system of the ITER are austenitic stainless steels. Although 316LN is used in the most parts of the superconducting coil system, the cryogenic stainless steels, JJ1 and JK2LB, which were newly developed by the Japan Atomic Energy Agency (JAEA) and Japanese steel companies, are used in the highest stress area of the TF coil case and the whole CS conductor jackets, respectively. These two materials became commercially available based on demonstration of productivity and weldability of materials, and evaluations of 4 K mechanical properties of trial products including welded parts. Structural materials are classified into five grades depending on stress distribution in the TF coil case. JAEA made an industrial specification for mass production based on the ITER requirements. In order to simplify quality control in mass production, JAEA has used materials specified in the material section of “Codes for Fusion Facilities - Rules on Superconducting Magnet Structure (2008)” issued by the Japan Society of Mechanical Engineers (JSME) in October 2008, which was established using an extrapolation method of 4 K material strengths from room temperature strength and chemical compositions developed by JAEA. It enables steel suppliers to easily control the quality of products at room temperature. JAEA has already started actual production with several manufacturing companies. The first JJ1 product to be used in the TF coil case and the first JK2LB jackets for CS were completed in October and September 2013, respectively.
An electric double layer capacitor (EDLC) uses an electric double layer (EDL) in an electrolytic solution. Owing to the extremely small thickness of the EDL, the EDL has huge capacitance. The EDLC is expected to store a large amount of electric energy. This paper reports on the behavior of ions in the EDL. The purpose of the present study is to analyze the behavior of ions in the EDL. For this purpose, capacitance of the EDL in 1 and 5 wt.% NaCl solution at room and low temperature was observed. The NaCl solution was frozen using liquid nitrogen (LN2) while the EDL was formed by voltage application. Afterwards, the discharge current was measured when the frozen NaCl solution melted. The following results were obtained. 1. The capacitance of the frozen EDL by slow cooling is approximately five times larger than that of the EDL at room temperature. 2. The EDL is kept in the frozen NaCl solution after short-circuiting. 3. The capacitance of the frozen EDL by slow cooling is larger than that of the EDL by rapid cooling.