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本文利用多道高分辨发射光谱对电子回旋共振(ECR)激发氘负离子数密度进行研究. 基于Yacora氘原子碰撞辐射模型, 结合氘原子分子谱线相对强度测量, 估算电子回旋共振激发的氘负离子密度. 对ECR源区和扩散区不同位置的氘原子及氘分子特征谱线进行测量, 发现源区的$ {{\mathrm{D}}}_{{\mathrm{\alpha }}} $特征谱线强度远高于$ {{\mathrm{D}}}_{{\mathrm{\beta }}} $的强度, $ {I}_{{{\mathrm{D}}}_{{\mathrm{\alpha }}}}/{I}_{{{\mathrm{D}}}_{{\mathrm{\beta }}}} $比高达23, 表明存在着$ {{\mathrm{D}}}^{-} $中性化机制, 选择性地增强了特征谱线强度; 进一步拟合估算了源区的$ {{\mathrm{D}}}^{-} $密度, 约为$ 3.6\times {10}^{15}\;{{\mathrm{m}}}^{-3} $; 相对于源区, 扩散区的$ {{\mathrm{D}}}^{-} $密度大幅下降. 由于ECR源区腔体小, 等离子体和壁的相互作用较强, 重组脱附过程会产生更多振动激发态氘分子, 增强了解离附着反应, 有利于氘负离子的产生; 另一方面, ECR等离子体中源区与扩散区间存在的空间电场阻碍了氘负离子的轴向输运, 氘负离子的产生和损失是局域性的; 这些使源区与扩散区间存在较大的$ {{\mathrm{D}}}^{-} $密度梯度.
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关键词:
- 氘负离子源 /
- 发射光谱 /
- 电子回旋共振等离子体
The electron cyclotron resonance (ECR) plasma is characterized by low working pressure and high dissociation rate, and it has important applications in the deuterium negative ion $ {{\mathrm{D}}}^{-} $ source technology. In this paper, the Yacora collisional-radiative model is applied to the emission spectrum diagnosis of $ {{\mathrm{D}}}^{-} $ in ECR deuterium plasma. The $ {{\mathrm{D}}}^{-} $ density is estimated by using the $ {I}_{{{\mathrm{D}}}_{{\mathrm{\alpha }}}}/{I}_{{{\mathrm{D}}}_{{\mathrm{\beta }}}} $ ratio and the relative intensity of other deuterium molecular lines, thereby avoiding complex calibration procedure of absolute intensity. The spatial structure of $ {{\mathrm{D}}}^{-} $ is studied by the multichannel emission spectrum measured in the source region and diffusion region. The experiments are conducted on a 2.45-GHz ECR plasma source at a deuterium gas pressure of 1 Pa and microwave power of 660 W. The Balmer series of atomic deuterium ($ {{\mathrm{D}}}_{{\mathrm{\alpha }}} $, $ {{\mathrm{D}}}_{{\mathrm{\beta }}} $, $ {{\mathrm{D}}}_{{\mathrm{\gamma }}} $, $ {{\mathrm{D}}}_{{\mathrm{\delta }}} $) and the Fulcher band Q-branches of molecular deuterium are measured in the source region and expanding region of the ECR plasma. It is found that the intensity of $ {{\mathrm{D}}}_{{\mathrm{\alpha }}} $ in the source region is much higher than that of $ {{\mathrm{D}}}_{{\mathrm{\beta }}} $, specifically, the $ {I}_{{{\mathrm{D}}}_{{\mathrm{\alpha }}}}/{I}_{{{\mathrm{D}}}_{{\mathrm{\beta }}}} $ ratio reaches as high as 23, indicating a selective enhancement of Balmer lines due to the mutual neutralization process of $ {{\mathrm{D}}}^{-} $. Furthermore, $ {{\mathrm{D}}}^{-} $ density in the source region is estimated to be about $ 3.6\times {10}^{15}\;{{\mathrm{m}}}^{-3} $, and the $ {{\mathrm{D}}}^{-} $ density in the expanding region decreases significantly. In the ECR plasma source region, the plasma-wall interaction is strong due to the small volume of the cavity. The recombination desorption process produces more vibrationally excited molecules, thereby further enhancing the dissociation attachment reaction, which is beneficial to the generation of deuterium negative ions. On the other hand, the axial electric field within the ECR plasma inhibits the axial transport of $ {{\mathrm{D}}}^{-} $, suggesting that the production and loss of $ {{\mathrm{D}}}^{-} $ are both localized. These characteristics of the ECR plasma source contribute to the formation of a large gradient of $ {{\mathrm{D}}}^{-} $ density between the source region and the expanding region. -
图 4 A, B, C位置谱线相对强度的实验值与模型拟合值
Fig. 4. The experimental and fitted line ratios at A, B, C positions.
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