National Institute for Fusion Science

At the National Institute for Fusion Science, in seeking the future fusion power generation we are moving forward with conceptual designs for the helical fusion reactor. Considering the system for the fusion power plant that will generate power from heat released by the fusion reactor, it is necessary to compose designs that are appropriate for the equipment, beginning with the power generation equipment. Here what is important is the system design. In this report we will introduce system design research that will determine the overall image of the helical fusion reactor and the fusion power plant.

The fusion reactor will be composed of numerous instruments. In the area facing plasma, there will be instruments for removing the heat generated by the fusion and evacuation devices for removing impurities from inside a plasma. And outside the vacuum vessel will be the superconducting coils which produce the magnetic field container for confining plasma, the devices for supplying fuel to a plasma and for heating plasma, and devices for measuring plasma conditions. Looking at the complete fusion power plant, there will be numerous types of equipment not part of the fusion reactor structure, such as equipment for cooling the superconducting coils, equipment for generating power from the heat removed from the fusion reactor, equipment for refining the fuel, and equipment that performs maintenance. The instruments that will compose the fusion power plant each have complicated systems, and because the performance of one instrument will influence the performance of another instrument and they will share space, each cannot be designed independently. Further, as a power plant, together with enhancing safety and reliability, a harmonious design that can be constructed inexpensively and in a short period of time is desired. For this reason, it is necessary to compose a full image of the design while balancing between equipment.

The most important job in system design is deciding upon the size of the fusion reactor, the strength of the magnetic field, and the fundamental specifications of the electric power generation. These specifications, ultimately, will determine each equipment’s detailed design, and for that reason, it will be necessary to undertake trial manufactures of the equipment and to conduct a large-scale computer simulation. Time and money will be necessary. In the first place, in order to design the equipment, it will be necessary to establish conditions for installation space, load-bearing strength, and the amount of heat. Therefore, first, we will assign fundamental specifications to a certain degree of accuracy. There will be used for the calculation program called the system code that will express as a simple model all of the elements, including the equipment, which will compose the fusion power plant and the plasma. Because the system code uses a simple model, the calculations will be completed quickly and then will be investigated while frequently changing the conditions. But existing simple models could not skillfully reproduce the helical fusion reactor’s qualities because the reactor will take a three-dimensional, complicated shape. Thus, we used experiments conducted in the Large Helical Device and computer simulation results, compiled a database for various plasma shapes and superconducting coil shapes, and developed a specific system code that balances high-speed calculations and accurate performance predictions. The system code that we developed is at present being used for determining the basic specifications of the helical fusion reactor, for which conceptual designs are advancing.

When the basic specifications are decided upon, the next system design task will be discussing the floor-plan and installation space, methods for maintenance, and other factors by considering the specific shape of each piece of equipment. In addition, the question of how each piece of equipment will be utilized in the operation of the fusion reactor, too, must be considered in terms of the system in its entirety. These discussions will move ahead parallel with the detailed designs of each piece of equipment. And we are advancing with work that reflects plans for equipment design.