本文介绍了二维PIC(Particle in cell)方法,这种方法常用于粒子动力学模拟中空间电荷作用的计算。并比较了以时间为自变量(t-code)和以纵向位置为自变量(z-code)的两种动力学模拟程序;针对“国家重点基础研究发展规划”洁净核能项目中...本文介绍了二维PIC(Particle in cell)方法,这种方法常用于粒子动力学模拟中空间电荷作用的计算。并比较了以时间为自变量(t-code)和以纵向位置为自变量(z-code)的两种动力学模拟程序;针对“国家重点基础研究发展规划”洁净核能项目中的射频四极(RFQ)加速器结构参数,给出了单束加速和正、负离子束同时加速两种情况下,t-code和z-code模拟得出的传输效率。结果表明,当束团的相位宽度大或能散大时,z-code 在计算空间电荷作用时会引入相对较大的误差,从而应该使用t-code来进行动力学模拟,以获得更准确的结果。展开更多
A four-vane radio-frequency quadrupole(RFQ)accelerator is under construction for the Compact Pulsed Hadron Source(CPHS)project at Tsinghua University.The 3 m-long RFQ will accelerate a 50 keV proton beam from the ECR ...A four-vane radio-frequency quadrupole(RFQ)accelerator is under construction for the Compact Pulsed Hadron Source(CPHS)project at Tsinghua University.The 3 m-long RFQ will accelerate a 50 keV proton beam from the ECR source to 3 MeV,and deliver it to the downstream drift tube linac(DTL)with a peak current of 50 mA,pulse length of 0.5 ms and beam duty factor of 2.5%.The inter-vane voltage is designed to increase with the longitudinal position to produce a short RFQ.Coupling plates are therefore not necessary.The cavity cross section and vane-tip geometry are tailored as a function of the longitudinal position,while limiting the peak surface electric field to 1.8 Kilpatrick.The RFQ is designed,manufactured,and installed at Tsinghua University.We also present the tuning and cold test results of the RFQ accelerator.After final tuning,the relative error of the quadrupole field is within 2%,and the admixture of the two dipole modes are less than 2%of the quadrupole mode.展开更多
为提高虚阴极振荡器微波能量转换效率,使用2.5维全电磁P IC(particle in ce ll)软件对向内发射同轴虚阴极振荡器进行数值模拟,优化设计了阳极反射板与阴极发射区之间距离D,并研究了阳极网透射区宽度B对能量转换效率的影响。模拟发现:选...为提高虚阴极振荡器微波能量转换效率,使用2.5维全电磁P IC(particle in ce ll)软件对向内发射同轴虚阴极振荡器进行数值模拟,优化设计了阳极反射板与阴极发射区之间距离D,并研究了阳极网透射区宽度B对能量转换效率的影响。模拟发现:选取适当的D值可提高效率,同时随着B的增大,能量转换效率逐渐增大并趋近一稳定值。模拟所得微波振荡主频与理论值符合较好。优化结果为:在阴、阳极半径分别为7 cm和5.5 cm,二极管电压250 kV,电流20 kA条件下,得到主频3.45 GH z,3 dB带宽约3%,微波功率310MW,能量转换效率6.8%的窄带微波输出。展开更多
文摘本文介绍了二维PIC(Particle in cell)方法,这种方法常用于粒子动力学模拟中空间电荷作用的计算。并比较了以时间为自变量(t-code)和以纵向位置为自变量(z-code)的两种动力学模拟程序;针对“国家重点基础研究发展规划”洁净核能项目中的射频四极(RFQ)加速器结构参数,给出了单束加速和正、负离子束同时加速两种情况下,t-code和z-code模拟得出的传输效率。结果表明,当束团的相位宽度大或能散大时,z-code 在计算空间电荷作用时会引入相对较大的误差,从而应该使用t-code来进行动力学模拟,以获得更准确的结果。
基金the National Natural Science Foundation of China under Grant Nos 91126003 and 11175096.
文摘A four-vane radio-frequency quadrupole(RFQ)accelerator is under construction for the Compact Pulsed Hadron Source(CPHS)project at Tsinghua University.The 3 m-long RFQ will accelerate a 50 keV proton beam from the ECR source to 3 MeV,and deliver it to the downstream drift tube linac(DTL)with a peak current of 50 mA,pulse length of 0.5 ms and beam duty factor of 2.5%.The inter-vane voltage is designed to increase with the longitudinal position to produce a short RFQ.Coupling plates are therefore not necessary.The cavity cross section and vane-tip geometry are tailored as a function of the longitudinal position,while limiting the peak surface electric field to 1.8 Kilpatrick.The RFQ is designed,manufactured,and installed at Tsinghua University.We also present the tuning and cold test results of the RFQ accelerator.After final tuning,the relative error of the quadrupole field is within 2%,and the admixture of the two dipole modes are less than 2%of the quadrupole mode.
