彗星X射线的辐射机理：电荷交换还是keV能量电子的韧致辐射？---实验室精密模拟测量彗星X射线的发射产额

彗星的X射线辐射是由太阳风离子引起的，对其测量能够预测太阳活动及“太空天气”，这对太空开发具有重要意义。以前的主流观点认为其是由太阳风中的高电荷态离子与彗星气体的电荷交换反应所致。2018年，Nature Physics报道了实验室模拟彗星X射线辐射的结果，认为太阳风离子在彗星磁场环境中形成的低杂波有助于加速低能电子至keV能量，其韧致辐射以及碰撞电离是彗星辐射X射线的主要原因。在上述实验报道中，使用高功率激光轰击塑料薄膜产生的二次离子来模拟太阳风离子，故无法测量离子流强从而无法精确确定X射线的辐射产额。本项目基于近代物理研究所成熟的ECR离子源技术，拟设计一套集测量准直聚焦于一体的装置，在0.1 nA精度上实时测量离子源提供的高电荷态离子束流强度(模拟太阳风离子)，同时测量其轰击磁性球靶(模拟彗星)发射的X射线，得到精确的X射线产额，定量研究“keV电子韧致辐射”对彗星X射线辐射的贡献。

The X-ray radiation of comets is caused by solar wind ions. The measurement of such X-rays can predict solar activity and "space weather", which is of great significance for space development. Prior to 2018, the mainstream view was that it was due to the charge exchange reaction between highly charged ions in the solar wind and cometary gases. In 2018, Nature Physics reported the results of laboratory simulation of comet X-ray radiation. It is believed that the lower-hybrid waves formed by solar wind ions in the comet's magnetic field is helpful to accelerate the low-energy electrons to keV energy, and the bremsstrahlung of electrons is the main reason of comet X-ray radiation. In the above experiments, because of the secondary ions generated by bombarding the plastic film with high-power laser to simulate the solar wind ions, it is impossible to measure the ion current and accurately determine the X-ray radiation yield. Based on the mature ECR ion source technology in Institute of Modern Physics, this project plans to design a set of device that will integrate measurements, collimation and focusing of the ion current provided by the ECR source in real time and accurately. At the same time, the accurate X-ray yield will be obtained by measuring the emitted X-rays as the highly charged ions (simulating the solar wind ions) colliding on the magnetized spherical targets (simulating the comet). The contribution of "keV energy electron bremsstrahlung" to the X-ray radiation of comets will be quantitatively studied.