Development of a magnetic field measurement instrument for compact cyclotrons

A magnetic field measurement instrument for compact cyclotrons has been developed. Forty-eight Hall sensors are used for magnetic measurements, and a set of four Hall sensors is allocated to each channel. The magnetic field and the offset are tabulated with a permanent 4,500-G magnet. The measurement device is made to be thin, long, and rectangular, to overcome the narrow gap between upper and lower hills in a compact cyclotron (2 ∼ 3 cm). This instrument measures a magnetic field signal in the unit of Tesla and transforms it to a voltage signal as an output. The instrument has a 0.1-percent field-measurement stability margin and can be used to measure the magnetic field produced by a 9-MeV cyclotron magnet.