摘要
双电子复合(DR)过程作为重要的电子-离子非弹性碰撞现象之一,是实验室高温等离子体和天体等离子体中影响等离子体电离平衡的一种很重要原子动力学过程,它对建立和维持等离子体的电离平衡以及对离子激发态布居起着主导作用。高精度的DR强度、截面以及速率系数是模拟和诊断各种天体等离子体及实验室等离子体和研制X射线激光的重要参数。
在国际热核聚变实验反应堆(ITER)的设计中,偏滤器将完全采用钨材料。而在偏滤器等离子体的辐射冷却过程中,复合过程是高离化态钨离子辐射损失的重要原因。同时,钨还将用作等离子体诊断探针元素。因此,对钨离子双电子复合(DR)过程的研究有很重要的实际应用价值。
本文利用相对论组态相互作用方法对等核系列钨离子的双电子复合过程进行了研究。对类铷W~(37+)离子的研究结果表明:在电子温度为1eV-5×10~4eV范围内,4p电子激发对DR速率系数的贡献最大,且4l壳层电子激发对DR速率系数的贡献在低温时,远大于3l壳层电子激发的贡献,随着温度的增加,3l壳层电子激发对DR速率系数的贡献逐渐增大,当电子温度到达650 eV时,3l壳层电子激发对DR速率系数的贡献达到总DR速率系数的12.5%。所以在温度较高的等离子体环境中,3l激发的贡献必须予以考虑。随着温度的增加,Δn= 2芯激发的DR速率系数逐渐增大,最大可以达到总DR速率系数的22%。
对于W~(38+),W~(44+)和W~(46+)离子的研究结果表明:对于W~(46+)离子,在电子温度kT_e>5eV时,3d电子激发的贡献最大。对于W~(44+)离子,在中低温时4s电子激发的贡献最大,在较高温时3d电子激发的贡献最大。对于W~(38+)离子,4p电子激发的DR速率系数始终最大,在高温时3d电子激发的贡献接近4p电子激发的贡献。随着温度的增加,W~(38+),W~(44+)和W~(46+)离子芯激发的DR速率系数逐渐增大,最大分别可达到总DR速率系数的26%,22.5%和21%。
The knowledge of accurate dielectronic recombination (DR) rates of heavy ions is crucial for the study of ionization balance of highly ionized elements in hot plasmas. The process therefore plays an important role in the theoretical modeling of plasmas, whether in the laboratory or in astrophysical sources such as the solar corona. This knowledge is also essential for the research of X-ray lasers especially for calculating the populating and depopulating of lasing levels.
Tungsten will be used for a certain plasma-facing components in the divertor region of the International Thermonuclear Experimental Reactor (ITER), and will also be used for the diagnostics of the erosion of heavy species into the plasma. For divertor plasma modeling and radiative cooling studies, accurate atomic data for highly ionized tungsten ions are essential, especially data on recombination processes that are a major source of radiation losses.
We calculate the dielectronic recombination rate coefficients of W~(37+) ions by using the Flexible Atomic Code (FAC). The results are presented for total DR rate coefficients of the temperature from 1 to 5×10~4 eV. It shows that the contribution from 4p subshell excitation dominates in the whole energy region, it larger than 4d subshell excitation near one order of magnitude. DR rate coefficients from 4s, 4p and 4d subshell excitations increase with the decreasing electron temperature in the low temperature. The contribution from 3d shell excitation play an additional important role in the total DR rate coefficients at high temperature, and the relative contributions from 3s, 3p and 3d subshell excitations increase smoothly with the increasing temperature. The relative contribution from△n = 2 core excitation increases smoothly with increasing temperature and is about 20% at 5500 eV. The radiative recombination (RR) and three-body recombination (TBR) rate coefficients, which are also two important recombination processes in plasmas. The results show that the DR rate coefficients are great than the RR rate coefficients and TBR rate coefficients for the whole energy region. Clearly, DR is predominate the ionization balance.
Detailed calculations of DR rate coefficients of W~(46+), W~(44+) and W~(38+) ions by using the Flexible Atomic Code (FAC). For W~(46+) ions, when electron temperature kT_e>5 eV, the contribution from 3d subshell excitation dominates. And for W~(44+) ions, the contribution from 4s subshell excitation dominates at low electron temperature and 3d subshell excitation dominates at higher electron temperature. For W~(38+) ions, the contribution from 4p subshell excitation dominates in the whole energy region, and 3d shell excitation play an additional important role in the total DR rate coefficients at high temperature. The relative contribution from△n = 2 core excitation is about 26%,22.5% and 21% at 50000 eV, respectively.
引文
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