A superconducting toroidal magnet with quasi-force-free configuration

A quasi-force-free toroidal magnet has been designed and constructed with 1.8kg, 0.5mm in diameter multifilamentary twisted NbTi composite wire. The magnet major radius is 13.7cm and minor radius is 1.17cm. During test the magnet reached 279A critical current, 6.4T peak field and 14.4kJ stored energy, the superconductor current density is 4 × 10⁵A/cm². This is corresponding to the magnet "short-sample" performance, when the angle between current and field is near 17°. The test result demonstrated clearly the advantage of superconducting force-free magnet and the correctness of the design method.