.100 Mev Cyclotron Centre Area Test Stand For Magnetic Field Measurement And Shimming

With the development of science and technology, along with the higher demand placed on high intensity beam, people have gradually transferred their focus from classical cyclotron to high intensity compact cyclotron, which have a number of advantages. However, because of the intrinsic asymmetry of the magnet, imperfection of the machining, magnet assembly error and other factors, the real field in median plane will easily depart from the isochronous filed in compact cyclotron with a very small gap. In the meantime, the imperfection field resulted from those factors is the main reason to affect the quality of accelerated beam. Only through measurement and shimming can the imperfection field be effectively reduced or avoided.The task was correlated with the construction of a 100MeV compact cyclotron undergone at China Institute of Atomic Energy (CIAE). In the cyclotron, the particles will be accelerated about 450 turns. In order to obtain a good beam quality, the integral phase shift of centre particle will be controlled within±30°, that is to say, the field error in median plane is smaller than 1.18×E-04. Obviously the old design method of mapping system in CYCIAE-30 could not meet the above requirement. By the measurement and shimming to centre region model (CRM) cyclotron, we expect to grasp the design method of mapping system which will be used in 100MeV compact cyclotron. Meanwhile, we can study and apply the shimming method to the first harmonic field in compact cyclotron.The final goal for the measurement and shimming to CRM is to achieve the following results: the field will be basically close to the isochronous field, and the integral phase shift will be controlled within±20°; after shimming to the first harmonic field, the amplitude of the first harmonic field will be less than 15 gauss around the extraction region and centre region, while in other region the amplitude will be less than 5 gauss.The task of this research involves the hall probe measurement system, the measurement to magnetic field, the analysis to the field data, the machining size of shimming bars according to the analytical data and the method to shim the first harmonic field.