【作者】 程诚；

【导师】 魏义祥；

【作者基本信息】 清华大学 ， 核科学与技术， 2010， 博士

【摘要】 多脉冲强流电子直线感应加速器（LIA）能够进行多幅闪光X射线照相,是发展先进的闪光X射线照相技术的重要研究课题。为了保证强流电子束的束流品质和多幅闪光X射线照相的图像质量,有必要开展MHz重复频率（多脉冲束流间隔<1μs）强流电子束束流动力学的研究。中国工程物理研究院与清华大学联合研制的小型双脉冲直线感应加速器——“明亮”加速器（Mini-LIA）,为开展强流多脉冲LIA束流动力学研究和解决某些局部关键技术问题创造了条件。论文分析了影响加速器束流输运的主要动力学因素,包括空间电荷效应、束质心螺旋运动和尾场效应的起因及其对强流束输运的影响方式和作用结果,得出了多脉冲强流束束流动力学的研究重点是多脉冲束团之间的尾场作用和束流传输过程中的束流崩溃不稳定性（BBU）效应随传输距离的增长现象。论文还研究了直线感应加速器加速间隙中尾场的产生、衰减及其对多脉冲强流束传输的影响。编写了Minienvelope程序,对单脉冲束流在Mini-LIA输运过程中的束包络进行了计算,并采用PARMELA程序对束团的束质心运动进行了模拟。论文采用CST微波工作室程序对加速腔空心腔和磁芯腔两种结构进行了数值模拟计算,得到了腔中部分TM模式的频率及其纵向特性阻抗R/Q值。建立了加速腔高次模特性参数测量平台,用实验的方法对空心腔和磁芯腔中的TM模式的电磁场进行了辨别与确认,并测量了腔中相应模式的谐振频率和品质因数Q。推导了采用二极模（TM1n0模）的纵向特性阻抗来计算其横向阻抗的公式,计算出了空心腔和金属玻璃磁芯腔TM₁₁₀模的横向阻抗。论文系统研究了测量LIA加速腔横向阻抗的同轴双线η因子法,建立了基于矢量网络分析仪的Mini-LIA加速腔横向阻抗测量平台,实验测量了空心腔和金属玻璃磁芯腔中TM₁₁₀模式的η因子和横向阻抗,取得了与模拟计算相符合的结果,为低Q值感应加速器横向阻抗的测量提供了一种实用的方法。论文最后分析了η因子法测量横向阻抗产生误差的多种原因,并结合模拟计算结果提出了相应的修正误差的方法。论文工作对正在进行的新型LIA的研制具有一定的借鉴意义。更多还原

【Abstract】 It is necessary for advanced X-ray flash radiography to develop linear induction accelerator （LIA） with multi-pulse high-current electron beam because of its multi-flash imaging technology. For needs of good quality of MHz repetition rate （pulse interval less than 1μs） high-current electron beam and multi-flash X-ray imaging, it is important to initiate beam dynamics research. A miniature double-pulse LIA （Mini-LIA） was constructed by CAEP and Tsinghua University in order that multi-pulse high-current beam dynamics is studied and parts of some new key techniques are preliminarily tested on it.Three main dynamics factors——space charge effect, corkscrew and wake field effect influencing high-current beam transportation are compared and contrasted from their physical origins to their deteriorations on the beam. It is pointed out that the emphases of multi-pulse high-current beam dynamics are wake field effect produced among multi-bunch and cumulative beam breakup instability in beam transportation. Decay of wake field generated in LIA accelerating gap and its influence on multi-pulse high-current transportation are analyzed in this paper. A code named Minienvelope is written to simulate beam envelope changes of single-pulse beam moved on Mini-LIA and the variation of beam centroid is simulated by using PARMELA code.By using CST microwave studio code, two structures of LIA cavity——empty cavity and metglas cavity are simulated respectively, and the resonant frequencies of several TM electromagnetic modes in two kinds of cavity as well as their corresponding longitudinal characteristic impedances R/Q are obtained. A bench measurement system is constructed for investigating characteristics of higher order modes （HOM） in Mini-LIA cavity. Discerning and confirmation of TM electromagnetic modes in two cavities are performed, and several TM modes in two cavities as well as their corresponding quality factors are achieved. The transverse impedances of two kinds of cavity are calculated by using a formula deriving from longitudinal characteristic impedances of dipole mode （TM1n0 mode）. This paper describes the principle, method, and techniques of transverse impedance measurement through coaxial twin-lead （ηfactor method）. A bench measurement system based on vector network analyzer is constructed for transverse impedance measuring of Mini-LIA cavity. Theηfactors and transverse impedances of TM₁₁₀ mode in two kinds of cavity are measured by experiment, and the result is consistent with the calculated one. A practical technique of transverse impedance measuring of LIA cavity with low Q is available. At last, analysis to several kinds of measuring error in transverse impedance measurement method withηfactor is performed and methods to correct the errors are discussed in this paper according to simulation result.更多还原