Study on high rigid coil structure aiming to minimize the weight of superconducting magnets in fusion reactors

为了减轻磁体的重量和成本，采用间接冷却和刚性超导体对核聚变反应堆用超导磁体进行了概念设计研究。在此基础上，研究了该方法的可行性和减重效果。我们提出了一种新型的铝合金夹套Nb3Sn超导体作为刚性超导体，并设计了一种用于高能中子聚变反应堆FFHR的间接冷却线圈结构。从消除稳态核加热、支持电磁力和淬火保护等方面的研究，证实了间接冷却线圈是一种很有前途的核聚变磁体。采用三维有限元模型计算了FFHR线圈的应力和应变分布。应力和应变均低于允许值。线圈支撑结构的厚度可以比有限元模型中假设的厚度更小。与传统导体的比较表明，所提出的超导体具有较高的刚性和可减轻线圈重量的优点。为了验证铝合金包覆Nb3Sn超导体的制备工艺，研制了一种亚尺度10ka级超导体。我们开发了一种导体制造工艺，使用最近开发的摩擦搅拌焊接（FSW）技术，使用摩擦加热。我们成功地在8t下携带了19ka，实验证明了该候选超导体的可行性。对Nb3Sn进行热处理后，将导体绕线。需要进一步的研究来开发一种不降低超导性能的导体缠绕工艺。

Conceptual design studies on a superconducting magnet for a fusion reactor have been performed using indirect cooling and a rigid superconductor in order to reduce the weight and the cost of the magnet. Then the feasibility and the effect on the weight reduction were investigated. We proposed a novel aluminum-alloy-jacketed Nb3Sn superconductor for the rigid superconductor and designed an indirect-cooled coil structure for the heliotron fusion reactor FFHR. From the studies of elimination of steady-state nuclear heating, support of electromagnetic force, and quench protection, it is confirmed that the indirect-cooled coil is a promising candidate for fusion magnets. Stress and strain distributions in the coil of FFHR were calculated by using three dimensional FEM model. The stress and strain were all below the allowable values. The thickness of the support structural of the coil can be more reduced than that of assumed in the FE model. Comparison with conventional conductors indicates that the proposed superconductor has high rigidity and the coil weight can be reduced.To demonstrate the fabrication process of the aluminum-alloy-jacketed Nb3Sn superconductor, a sub-scale 10 kA-class superconductor was developed. We developed a conductor fabrication process using a recently developed friction stir welding (FSW) technique that uses friction heating. We succeeded in carrying 19 kA at 8 T. The experiments demonstrated the feasibility of this candidate superconductor. The conductor will be wound after the heat treatment of Nb3Sn. Further investigation will be required to develop a winding processes of the conductor without degradation of superconducting properties.