Progress of tungsten spectral modeling for ITER edge plasma diagnostics based on tungsten spectroscopy in LHD
Progress of tungsten spectral modeling for ITER edge plasma diagnostics based on tungsten spectroscopy in LHD
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DOI：
10.1016/j.nme.2021.100923
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发表时间：
2021-01
影响因子：
2.6
通讯作者：
I. Murakami;D. Kato;T. Oishi;M. Goto;Y. Kawamoto;C. Suzuki;H. Sakaue;S. Morita
中科院分区：
文献类型：
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作者：
I. Murakami;D. Kato;T. Oishi;M. Goto;Y. Kawamoto;C. Suzuki;H. Sakaue;S. Morita
钨离子在堆芯等离子体中的强辐射冷却是聚变堆的重要问题之一。偏滤器等离子体、刮除层和主等离子体中钨密度的定量分析依赖于钨离子光谱模型的准确性。我们建立了钨离子的碰撞辐射（CR）模型来估算钨离子的谱线强度，并在大螺旋装置（LHD）上同时测量了钨离子从极紫外（EUV）到可见光的光谱，验证了钨离子的CR模型。在4.5-7 nm的EUV光谱中测量的所谓未分辨跃迁阵列（UTA）通常见于电子温度约为1 keV的聚变等离子体中，这对应于ITER的边缘温度。UTA很强，在此温度下对辐射功率的贡献很大，因此需要CR模型计算来重现UTA以估计钨辐射功率。我们已经开发了CR模型，包括复合过程，这是没有考虑之前的钨离子，作为一个混合模型与精细结构的水平和配置平均水平的W25+-W39+离子。UTA的6 nm峰仍然不能很好地再现，但是来自更高能级的复合过程和级联可以增强光谱强度。研究了W28+离子激发态双电子复合的贡献，但W27+离子的贡献很小。在2-4 nm处n = 4-5跃迁峰的光谱轮廓随复合过程变化不大。对LHD等离子体EUV光谱测量结果的分析表明，由于钨离子辐射功率大，钨离子首先聚集到核心等离子体中，产生空心温度分布，随后NBI加热使中心电子温度恢复，EUV光谱中再次出现UTA，但强度较前期有所减弱。UTA的强度和从EUV光谱估计的电子温度的降低表明，钨被向外传输，并且发射EUV光谱的钨的量减少到约1/4。
Strong radiative cooling by tungsten ions in the core plasma is one of issues in fusion reactors. Quantitative analysis of tungsten density in divertor plasma, scrape-off layer, and main plasma relies on accuracy of spectroscopic model of tungsten ions. We have developed a collisional-radiative (CR) model for tungsten ions to estimate line intensities of tungsten ions and also have measured tungsten spectra in wide wavelength region from extreme ultraviolet (EUV) to visible wavelengths simultaneously in the Large Helical Device (LHD) with tungsten pellet injection to validate the CR model for tungsten ions. So-called unresolved transition array (UTA) measured in EUV spectra at 4.5–7 nm are commonly seen in fusion plasmas with electron temperature of around 1 keV, which corresponds to edge temperature in ITER. The UTA is strong and largely contributes to the radiation power at this temperature, so the CR model calculation is required to reproduce the UTA to estimate the tungsten radiation power. We have developed the CR model to include recombination processes, which were not considered before for tungsten ions, as a hybrid model with fine-structure levels and configuration-averaged levels for W25+–W39+ions. The 6 nm-peak of UTA is not still reproduced well, but the recombination processes and cascade from higher levels can enhance spectral intensities. Contribution of dielectronic recombination from the excited states of W28+ions is examined but it is small for W27+ions. The spectral profiles of n = 4–5 transition peaks at 2–4 nm do not change much with recombination processes. Analysis of measured EUV spectra in LHD plasma shows that tungsten is accumulated first into core plasma to produce hollow temperature distribution due to large radiation power of tungsten ions, and continuous NBI heating recovers central electron temperature and the UTA appears again in EUV spectra with weaker intensity than one at the earlier phase. Reduced intensity of UTA and electron temperature estimated from EUV spectra indicate that tungsten is transported outward and the amount of tungsten emitting EUV spectra is reduced to about 1/4.