Research And Design For The RF System Of Cyclotrons

This dissertation is concerned with the research and development of the RF system of a compact cyclotron on a virtual prototype platform. The RF cavity of cyclotrons should be one quarter wavelength line or half wavelength line structure, usually work within the VHF, hence with a large body size. Since the cavity generally works in the perfect vacuum environment, the huge cavity body volume will make vacuumization more difficult, and bring more rigorous requirements for space requirement. So to minimize the size of RF cavity means a lot not only from the economical viewpoint, but also from the engineering viewpoint. Based on the target of size-minimization, the RF system of MINItrace is studied and its structure is analyzed with emphasis, especially the effect of SIR and micro-disturbance structure within it is viewed.The RF system of compact cyclotrons with the example of GE MINItrace cyclotron is introduced in this thesis. The analytical work associated with some special structures in the system including the RF Loop, the groove in the central region, the Dee frequency trimmer and the spiral configuration of the high frequency feed-through cable is presented. Among those, the high frequency feed-through cable forming from a section of unclosed copper cable and the equivalent fringing capacitance in the terminal is studied. It acts as the LPF, effectively eliminating the high frequency component in the feed-in signal. The groove in the central region working as a loading capacitance in the open end is also discussed.Besides the dimension of the resonance cavity can be reduced, by employing this structure, the damage caused by the lost particles which have been accelerated can also be avoided since high voltage in phase with those particles is generated in the aperture of the groove when system works, which conduces to the extraction of the particles from the source as well as the absorption of the un-captured low energy particles.With a CYCIAE 100MeV prototype cavity and collected experimental data, the FEM calculation, is carried out using APDL on ANSYS platform. Various grid resolution calculation results are gained and compared with the real metrical ones. The results are quiet accordant with a maximum error of less than 1%, which is allowable in engineering projects. Thus the prediction ability and veracity of cyclotron accelerator RF simulation on this Virtual prototype is testified. Some prominent problems that deserve much attention while carrying on FEM calculation using ANSYS are summarized here, laying the foundation of further calculation.Derived from the basic transmission line theory, conditions on which the minimum electrology length of resonator can be gained with some fixed frequency are deduced and stray frequencies and unloaded Q value of SIR are also analyzed. Then the effect on parasitic modes frequency of SIR's impedance ratio variance is calculated on virtual prototype. At last, the anterior derived conclusion is well testified by simulating the stray frequencies and integrating experimental statistics.The influence trend that micro-disturbance structure acts on resonating frequency in different places is derived. Also by combining its application instance within accelerator and calculation results, the correctness of micro-disturbance theory is proved.