太阳风中的高电荷态重离子在彗星、行星及卫星表面诱发的硬X射线的实验室模拟

X-ray emission of comets, planets and moons has aroused great interest of astronomers, for example, America, Europe and Japan have launched, respectively, the "Chandra", "Newton" and "Suzaku" high resolution X-ray satellites dedicating to measure the X-ray emission from these celestial bodies. Extensive observations have been made at present, and the forming mechanism for soft x-rays below 1.0 keV has formed a consensus. For hard X-rays above 1 keV, however, not only the observed results are not much, but also the physical interpretation is of great difference. This project will use slow N, O and Si ions produced by the Electron Beam Ions Source (EBIS) that has been built newly at Institute of Modern Physics, Chinese Academy of Sciences, to simulate the highly charged heavy ions (HCHI) in solar wind, and the augite, olivine and quartz insulating materials to simulate the surfaces of comets and other celestial bodies. The projectiles’s hard X-rays produced by charge exchange between the HCHI and the surface electrons, and the targets’ hard X-rays due to surface charging will be measured as the slow N, O and Si ions colliding the surfaces. Time constant of the surface charging and neutralization processes will be measured exactly using the phase-modulated beams provided by the EBIS. Basing on the simulaiton of hard X-ray emission from surfaces of comets and other celestial bodies induced by HCHI irradiation in solar wind, this project plans to further interpretate the hard X-ray data observed by astronomical telescopes.

彗星、行星及卫星的X射线发射现象引起了天文学家的极大兴趣，美、欧、日先后发射了“钱德拉”、“牛顿”和“朱雀”号高分辨X射线卫星对这些天体进行观察。对于小于1.0 keV的软X射线，目前已获得了广泛的观察数据，且对形成机制取得了一致共识。对于大于1.0 keV的硬X射线，不仅观察数据不多，而且物理解释存在较大差异。本项目选用近代物理研究所新建成的EBIS装置提供的低能高品质N、O和Si离子束模拟太阳风中高电荷态重离子，选用辉石、橄榄石和石英等绝缘靶材料模拟彗星等天体的表面成份，测量辐照过程中发射的硬X射线谱，定量研究“电荷交换”和“表面充电”两种机制分别对入射离子和靶原子发射的硬X射线的贡献，并利用EBIS提供的脉冲束精确测量充、放电过程的时间常数。本项目通过对太阳风中的高电荷态重离子辐照彗星、行星及卫星表面诱发硬X射线的实验室模拟，期望进一步理解近些年来天文望远镜所观察的硬X射线辐射数据。

依据本项目的计划及需求，我们研制了实验室模拟彗星X射线辐射的实验终端。研制了实验所需的硬件设备：包括专用天体物理靶室、洪式电子枪、表面清洁离子枪、靶室支架、五维真空调角器、样品支架、束流密度计、束流线、静电透镜、精密法拉第筒；设计制作了两台亚nA级别的电流表，并编写了相应的Labview控制读取软件；购买了SDD探测器、涡轮分子泵、真空计等设备。利用本项目研制的实验终端，在近物所一台ECR离子源上完成了本项目的实验部分。我们分别选用了Nq+(q=3,4,5,6)、Oq+(q=3,5,6,7)离子，引出高压（对应离子能量）从1.5至20.0 kV，分别与绝缘石英石，透明方解石，角闪石等绝缘矿物靶，以及Al、Fe、Ni和Cu四种金属靶相互作用，测量了发射的X射线。我们研究了靶的特征X射线谱随入射离子速度以及电荷态的依赖关系，以及靶表面是否充电对靶的特征K-X射线谱的影响。