Influence of Manufacturing Accuracy on Magnetic Field Distribution in Magnet for HTS Rotating Gantry

Because of its high curative effects and low burden on patients, carbon ion cancer therapy is becoming more widely used. The accelerated carbon ions are delivered to patients via electromagnets on a rotating gantry. One advantage of a rotating gantry is that a tumor can be irradiated with carbon ions from any direction without changing the posture of the patient. On the other hand, because of the high magnetic rigidity of carbon ions, rotating gantries for carbon cancer therapy are about three times heavier than those for proton cancer therapy, according to our estimation. Use of high-temperature superconducting (HTS) magnets has been considered for reducing the size of the rotating gantry for carbon cancer therapy. For accurate irradiation, these HTS magnets must generate high-uniformity magnetic fields, and the shape of the HTS coils was designed by 3-D analysis to generate uniform magnetic fields. In our design, saddle-shaped HTS coils were used since they can efficiently generate a magnetic field. The conductor positions and the coil end shape were optimized to generate a uniform magnetic field. On the other hand, it was difficult to maintain the HTS conductor in the designed saddle shape because it has a tapelike shape and anisotropic flexibility in bending. In this paper, the winding accuracy of the fabricated HTS saddle-shaped coil was measured, and the influence of the measurement result on the magnetic field distribution was evaluated.