Fe9+离子3s23p43d 4D7/2与4D5/2能级差的精确测定

The energy level splitting between finestructure level 4D7/2 and 4D5/2 in Fe 9+ ion is extraordinary small that give a strong capability of Magnetic field induced transition (MIT) from 4D7/2, which introduced a possible solution for a directly magnetic measurement in solar corona. However the splitting energy, a key parameter in the solution, is still not well identified neither by calculation nor experiment. In this project, a new method is proposed that: one can acquire a data curve by measuring the changing of the line ratio between the MIT of Fe9+ and one not affected by the magnetic field against the changing of electron density, at the ultra-low energy EBIT. Then generate a data surface according to the calculations for different line ratios, electron densities and splitting energies. Thus a most reliable splitting energy can be acquired by fittings between the experimental curve and the calculation surface. In the proposal, improvements such as notably reducing the error from electron density diagnostic and optimizing the calculation model and method will be applied to reduce the total uncertainty to lower than 6%. This will be the most important step for applying the magnetic field diagnostic to the corona and other high temperature and low density plasma by using the Fe9+ MIT.

Fe9+离子3s23p43d 4D7/2和4D5/2能级具有极小的能级差，这赋予4D7/2能级极强的磁场诱导跃迁（MIT）能力，有望籍此实现太阳日冕磁场的实验观测。为了实现该构想，上述能级差的精确数值是一个最关键的科学数据。但是其不同理论值无法自洽，现有实验值误差过大无法使用。本项目提出一种新的方法来测定该能级差：在超低能电子束离子阱中测量包含Fe9+离子MIT的谱线与不受磁场影响谱线的线强比随电子密度的变化曲线，并通过计算得到该实验条件下电子密度、线强比、能级差的关系曲面，再使用拟合方法从这两组数据中解出最佳能级差。为精确获得该数值，本项目拟采取包括大幅度提高EBIT密度诊断精度以及实验数据优化理论新方法等手段，最终将总误差降低到6%。该能级差数据的准确获得将是推动Fe9+离子MIT对日冕及其他高温稀薄含铁等离子体进行磁场诊断的最关键一步。

Fe9+离子的磁场诱导跃迁有望为日冕磁场测量带来全新的方法，但该方法的关键参数-精细能级差的数值，却无法直接测量。本项目利用电子束离子阱装置的特点，通过设定不同的等离子体参数，实验获得了电子密度，相关线强比，精细能级差这些参量之间的关系曲面，并结合理论计算首次获得了通过实验评估和定标的该数值为3.9cm-1，其精度相比之前的定性实验得到了极大的提高，其自洽性误差达到了15%以内，使其应用于未来空间观测成为可能。为了实现这些目标，本项目也研制了可以大大提升电子密度观测精度的束流成像装置，以及建立适合本实验的多参数拟合方法。在应用方面，本项目也积极与天体物理相关研究机构合作，大力推动本研究成果真正应用于未来中国的太阳观测卫星项目。