【作者】 陈卫东；

【导师】 邹亚明；

【作者基本信息】 复旦大学 ， 原子与分子物理， 2008， 博士

【摘要】 由于体积小,运行成本低,电子束离子阱(EBIT)为高电荷态离子的研究提供了粒子加速器无法比拟的优势。高电荷态离子的双电子复合过程在共振能量下有很大的反应截面,因此是天体物理和热等离子体中非常重要的原子过程。EBIT同时可作为离子源和光子源,并且提供高能且几乎单色的电子束,因此它是研究高电荷态离子双电子复合过程的完美工具,并且为分解研究热等离子体提供了条件。本工作的主要目标是研究一种实验手段能够用于EBIT上对电子-离子碰撞过程的电子能量进行精密的测量,并用这种手段对高电荷态氙离子的KLL双电子复合的共振能量进行精密的研究。为此我们设计并建造了高精密,高稳定的高压分压仪来测量加速电源的电压,并组建了与之匹配的可视化数据获取系统。这里采用高精密,低温度系数和电压系数的厚膜电阻来组装分压仪,利用恒温箱测量温度系数并挑选电阻,同时利用温度控制系统来使温度浮动减小到0.025℃,从而减小了温度浮动带来的分压比不确定度。另外我们利用6 1/2位的高精密的数字万用表测量了电阻值随着电压的变化,即电阻的电压系数,然后从理论上分析了电阻的电压系数的产生机理,通过对测量数据进行拟合得到电压系数的修正曲线。最后我们对分压仪的的分压比,延迟效应等参数进行了测试,得出分压仪的分压比精度好于百万分之一,远超过目前工业上常用的分压器千分之一量级的精度。分压仪输出信号和光子探测器的输出信号通过数据获取系统来记录,储存为光子计数随着电子能量和光子能量分布的矩阵。整个数据获取系统用Visual C++可视化编程,集成了数据采集,实时显示,简单的数据分析等功能。除了加速电压外,EBIT中电子束的能量受到空间电荷效应,离子云对电子束的中和效应,以及漂移管在加上不同电压时产生的几何效应的影响。为了定量了解这些效应的影响,我们在不同电子束流下对高电荷态氙离子的KLL双电子复合的加速电压进行测量,外推出在零束流下的发生共振的加速电压,结合数学与物理的方法,从而分离出了电子束的空间电荷效应和离子云的中和效应。对于漂移管产生的几何效应,这里利用专业的Simion程序进行了计算,并结合离子云在漂移管中的分布得到几何效应的大小。考虑了以上因素以后,并对实验的各个环节产生的测量值偏移和误差来源进行了分析,得到了高电荷态氙离子发生KLL双电子复合的精确共振能量,精度达到世界同等水平。最后将测量结果与FAC程序包的基于对论组态相互作用(RCI)理论、相对论多体微扰(RMBPT)理论计算的结果,以及从参考文献中查到的基于多组态Dirac-Fock(MCDF)理论计算的进行了比较分析。更多还原

【Abstract】 Electron beam ion traps (EBIT) are excellent devices for studying highly charged ions. It takes smaller space and lower cost than particle accelerators. Dielectronic recombination of highly charged ions is very important in astrophysics and hot plasmas, because of its large resonant strength. Since the energy spread of electron beam is as small as several tens of eV, both as ion source and photon source, EBITs are the very tools to study dielectronic recombination of highly charged ions, and to disentangle different atomic processes in hot plasmas.The work attempts to build a new approach to precisely measure the electron energy during electron-ion collision process, and its application to the investigation of the resonant energy KLL dilectronic recombination of highly charged xenon ions. To measure the KLL resonant acceleration voltage of highly charged xenon ions, we designed and constructed a high voltage divider with high precision and high stability. And built a corresponding data acquisition system with graphic-user interface. We adopted high precision, low temperature and voltage coefficient thick film resistors, and built a temperature regulation box to reduce the fluctuation of temperature to as low as 0.025°C, so as to minimize the dividing ratio uncertainty caused by temperature fluctuation. Besides, we measured the resistance change of the resistors when different voltage were applied, i.e. the voltage coefficient of resistors with sophisticated digital multi-meters. After analyzing the mechanism of voltage coefficient, we fit the data with a correction curve. And finally we tested the dividing ratio and time delay of the divider, which shows a precision of less than 1 ppm. The output signal from the divider and the photon detector were recorded by a data acquisition system, which was programmed with visual C++. The system realized the functions of data acquisition, realtime display and simple data analyze ect.Besides the acceleration voltage, the space charge of the electron beam, neu- tralization of ion cloud, and geometry effect from drift tubes also affect the electron beam energy. To measure these effects quantitatively, we measured the acceleration voltage of KLL dielectronic recombination of xenon ions with different beam current, and then fit the data with a formula that combine physical and mathematical deduction, to extrapolate the acceleration voltage when the beam current is zero. So we can separate the space charge effect from the beam energy. For the geometry effect, we simulated the equipotential profile of the drift tues with Simion program. Finally summed all these factor together, we got the precise KLL resonant energy. And we compared our experimental result with the calculation based on relativistic configuration interaction (RCI), relativistic many-body perturbation theory (RMBPT), and multi-configuration Dirac-Fock theory (MCDF) theory.更多还原