Effective Low Magnetic Field Jc(B) Scaling of ITER Nb3Sn Strands by Magnetization and Critical Current Measurements

For the International Thermonuclear Experimental Reactor magnets, a significant fraction of the Nb3Sn conductors will be operating at a low field (B < 4 T), such as the outer turns of the central solenoid modules and toroidal field winding packs, while so far, the Ic(B,T, ) parameterization has been derived from measurements carried out at higher fields (B ≥ 7 T). It may not be accurate enough to adopt this parameterization for the extrapolation of the conductors' operating performance in terms of critical current (Ic) and current sharing (Tcs). The critical current characteristic can be effectively extended to the lower field region by means of a relation between the magnetization and critical current. The parameterization of the derived critical current scaling law Jc(B) is processed for the field range of the magnetization measurement (0 < B ≤ 9 T) and the critical current measurements (7 ≤ B < 12 T) in order to cover the full range up to 12 T

New design of cable-in-conduit conductor for application in future fusion reactors

The China Fusion Engineering Test Reactor (CFETR) is a new tokamak device whose magnet system includes toroidal field, central solenoid (CS) and poloidal field coils. The main goal is to build a fusion engineering tokamak reactor with about 1 GW fusion power and self-sufficiency by blanket. In order to reach this high performance, the magnet field target is 15 T. However, the huge electromagnetic load caused by high field and current is a threat for conductor degradation under cycling. The conductor with a short-twist-pitch (STP) design has large stiffness, which enables a significant performance improvement in view of load and thermal cycling. But the conductor with STP design has a remarkable disadvantage: it can easily cause severe strand indentation during cabling. The indentation can reduce the strand performance, especially under high load cycling. In order to overcome this disadvantage, a new design is proposed. The main characteristic of this new design is an updated layout in the triplet. The triplet is made of two Nb3Sn strands and one soft copper strand. The twist pitch of the two Nb3Sn strands is large and cabled first. The copper strand is then wound around the two superconducting strands (CWS) with a shorter twist pitch. The following cable stages layout and twist pitches are similar to the ITER CS conductor with STP design. One short conductor sample with a similar scale to the ITER CS was manufactured and tested with the Twente Cable Press to investigate the mechanical properties, AC loss and internal inspection by destructive examination. The results are compared to the STP conductor (ITER CS and CFETR CSMC) tests. The results show that the new conductor design has similar stiffness, but much lower strand indentation than the STP design. The new design shows potential for application in future fusion reactors