Temperature stabilization of a K110 variable energy cyclotron magnet.

For a large-scale cyclotron using normal conducting magnet coils, 10 h or more are required to obtain a highly stable magnetic field because heat transfer from the coils changes the temperature of the magnets gradually. To suppress the heat transfer and stabilize the magnet temperature in the TIARA K110 cyclotron, water-cooled copper plates were inserted between the main coil and the magnetic yoke. The heat generated by the main coil depends on its circulating current, which depends on the accelerated ion beam. To stabilize the magnet temperature, a technique was developed to control the temperature of the cooling water of the copper plates depending on the main coil current. Consequently, the temperature of the magnet was stabilized successfully to 24 ± 0.3 °C for various ion beams, and the magnetic field was maintained at ΔB/B = 1 × 10 after a few hours from initiating cyclotron operation.