Measurement and adjustment of CIAE medical cyclotron magnet

A 30 MeV compact cyclotron used for medical radioactive isotope production is in construction. A program controlled mapping instrument with accuracy 10/sup -4/ was developed. Its probe moves automatically in the 30 mm gap covering a circular area more than 1600 mm in diameter. It makes the mapping efficient and accurate. An iteration method was used for both harmonic and average field shimming. The results were so good that the first harmonic was reduced from more than 10 gauss to about 5 gauss in most of the radius and 70 gauss to about 10 gauss in the central region. Meanwhile the total phase shift which represents the isochronous, was reduced from more than /spl plusmn/90/spl deg/ to about /spl plusmn/20/spl deg/.<>