Small valley gap magnet design for a 10MeV PET cyclotron

Low energy compact cyclotrons applied in Positron Emission Tomography (PET) have foreseeable prospects with the growing demands in medical applications. Compared with conventional ‘deep valley’ magnet type, the cyclotron magnet with small valley gap (SVG) has higher average magnetic field which reduces magnet pole size, but smaller field flutter also decreases the axial focusing of beam. Considering that the main purpose of PET cyclotrons is to produce short-lived isotopes which need moderate beam intensity and quality, the SVG type magnet can fulfill the requirements. And beam loss due to Lorentz strip caused by high magnetic field is insignificant with low energy beam. This paper describes the design and considerations of SVG type magnet including the central region for a 10MeV PET cyclotron. Mechanical considerations and field mapping system are introduced.