Extraction Beam Loss Study And Design Key Components For The Extraction System Of Hust Superconducting Cyclotron

The special dose distribution property and good clinical manifestation have made proton therapy earn more and more attention in the field of tumor treatment.China have also invested a lot to develop the technologies related to proton therapy and supports “development of proton radiotherapy equipment based on superconducting cyclotron” during the 13 th five years plan.The extraction system,directly influencing the beam extraction efficiency and quality,is the most challenging subsystem in superconducting cyclotron design.Owing to the high magnetic field in the superconducting cyclotron,the turn separation is so small that the beam might piles up at the extraction radius.Therefore,the beam loss rate is extremely high in the extraction zone,leading to severe thermal effect and radiation effect.Thermal effect results in structure deformation or destruction,while radiation effect causes activation or damage of materials,even leading to coil quench shutting down the cyclotron.Obviously,the control of beam loss is of great significance from the perspective of stable operation and low cost of maintenance of the superconducting cyclotron.This paper proposes a design scheme of the extraction system of the superconducting cyclotron and presents the design parameters of harmonic coil,electrostatic deflector and magnetic channel respectively.For the harmonic coil,its spatial arrangement mode is presented.For the electrostatic deflector,its whole design process is introduced and its electromagnetic performance to deflect proton beam is evaluated,moreover a test platform is designed to study the breakdown phenomenon of the deflector.For the magnetic channel,this paper also proposes its combination method and a set of structure parameters.In order to minimize the risk of destruction caused by the proton beam loss,fluid-solidheat coupling analysis for the deflector has been conducted by applying computational fluid dynamics(CFD)on ANSYS 16.0 software.The maximum temperatures of the septum in various cases of cooling water flow,septum thickness and material have been investigated respectively.Noted that the suitable cooling water flow ranges from 0.2L/min to 0.4L/min,and tungsten keeps lowest temperature and minimum deformation in three tested materials.Numerical simulation to radiation effect have been investigated by employing Monte Carlo Geant4 code after setting the initial beam parameters precisely.The energy depositions of proton in diverse septum materials are compared.Meanwhile,the energy and angular distributions of secondary particles are obtained.The results based on those analyses will give us valuable references to improve the extraction system design,providing implications for the radiation shielding and beam loss control of this superconducting cyclotron.