The Research And Design Of A Linear Hybrid Single Cavity Injector For Cancer Therapy Facility Based On Direct Plasma Injection Scheme

In recent years,with the increasing demand for heavy ion cancer therapy devices in hospitals,the design and manufacturing technology of medical heavy ion accelerator devices have been further developed.In general,the main optimization of the heavy ion cancer therapy devices could be divided into the optimization of synchrotron accelerator and the optimization of linear injector.The optimization of the linear injector is the subject of this research.Generally,the main goal of the optimization of linear injector is to shorten the length of the linear injector,improve the injection efficiency,reduce the auxiliary facilities and improve the stability and reliability of the injection system.Different from the conventional heavy ion linear injectors which consist of an RFQ,a medium energy beam transport(MEBT)line and a DTL(drift tube lianc),the injector adopted in this research is a kind of Hybrid Single Cavity(HSC)which is comprised of an RFQ and DTL that directly connected.The HSC takes the Interdigital-H(IH)structure which owns high shunt impedance,high gradient and high acceleration effi-ciency in the medium and low energy range,and the RFQ vanes and the DTL tubes are installed in order on the supporting stems.Because the RFQ and the DTL are connected directly without the transition section MEBT,the HSC linear injector not only shortens the accelerator length,but also makes the auxiliary devices of the RFQ and DTL inte-grated.The difficulties of the HSC structure are the match of the electromagnetic fields and beam transport between the RFQ and DTL,which are the research focuses of the paper,too.According to the design requirements of the existing heavy ion cancer therapy equipment for the linear injector,the HSC injector working at 100will accelerate C⁶⁺with peak current of 208)from 0.020)(1/to 40)(1/,in which the RFQ will accelerate C⁶⁺to the energy of 0.6 Me V/u and the DTL will accelerate the ions from the RFQ to 40)(1/.The multi-particle simulation results show that the transmission efficiency of the whole HSC is 71.1%.The total length of the HSC electrode is 3273.38)8),which includes the length of the RFQ,the DTL and the matching section.The RF structure design of the HSC linear injector is mainly divided into the fol-lowing parts:(1)The research on the structural parameters of the unit structure of the four-rod RFQ and the IH-DTL.(2)The research on the whole HSC RF design.The key points of the HSC RF design are the frequency design,the electromagnetic field distri-bution design,the tuner design and the design to solve the field distortion problem in the matching section.The multi-physics analysis of the cavity of the HSC linear injector shows that,the temperature rise,the deformation and the stress of the HSC cavity could be controlled within a safe range when running at the duty factor of 1%.The cavity temperature,deformation,surface stress and frequency shift have also been studied under different duty factors and without cooling system.The innovations of this research:The coupled window structure is used to solve the problem of field distortion in matching section for the first time.The research re-sults demonstrate that the effects of the field distortion in the matching section could be reduced by the coupled window structure.At the same time,the coupled window struc-ture has little effects on the frequency and the electromagnetic field coupling.From the perspective of machining,the coupled window structure does not require additional RF components,and the structure is simple which greatly reducing the machining of the coupling device.