Design and Performance Test of a Superconducting Compensation Solenoid for SuperKEKB

The construction of a final focusing superconducting magnet system for SuperKEKB is underway. The superconducting magnet system consists of eight quadrupole magnets, four compensation solenoids, and 43 corrector coils. They are installed inside of the particle detector, i.e., Belle-II, which has a superconducting solenoid generating 1.5 T in the magnet center. Four compensation solenoids produce the magnetic field with the opposite direction to the Belle-II solenoid field to reduce the X - Y coupling of the collision beams and achieve the high luminosity of 8 × 10 35 cm -2 · s -1 . The compensation solenoids are wound with a 1.5-mm-thick and 1-mm-wide NbTi wire, which has a critical current of 1.8 kA at 4.2 K and 4 T. The minimum inner and outer radii of the compensation solenoids are approximately 70 and 200 mm, respectively. The length of the longest compensation solenoid is approximately 1.56 m. The maximum operating current and the maximum magnetic field of the solenoids are designed to be less than 450 A and 4 T, respectively. The construction and performance test of a compensation solenoid are completed. In this paper, the magnet design, excitation test, and magnetic field of the compensation solenoid are presented.