载气中N_(2)浓度影响介质阻挡放电离子化效率的数值模拟研究

Numerical Simulation Study on the Influence of N_(2) Concentration in Carrier Gas on Ionization Efficiency of Dielectric Barrier Discharge

随着公共安全、食品安全检测领域对现场质谱检测需求的日益增加,介质阻挡放电离子源技术得到了较快的发展。其中的工作气体浓度通过影响介质阻挡放电的离子化效率从而对质谱检测信噪比产生较大作用。本文建立了在He-N_(2)混合载气作用下的包含7种反应离子的等离子体流体动力学模型,并采用该二维模型,探究了N_(2)浓度对介质阻挡放电离子源离子化能力的影响。结果表明,通过在He载气中引入不同N_(2)量可以改变等离子体射流质子化水簇团反应的关键中间体粒子数密度含量,提高离子源的离子化效果;特别地,当N_(2)摩尔分数为1.5%时,有效粒子数密度最高。此外,本文还研究了介质的管径及介电常数对粒子平均密度的影响。结果表明,粒子数密度含量随着介质管径和相对介电常数增加而逐渐减小。通过对不同N_(2)摩尔分数、介质管径和相对介电常数的参数化分析,将优化设计介质阻挡放电离子源结构,从而最终提高现场质谱检测的灵敏度和稳定性。

As the rising demand for risk factor detection via mass spectrometry technology in the field of public safety and food safety,dielectric barrier discharge ion(DBDI)source has been rapidly developed.The concentration of the working gas in DBDI plays an important role in the signal/noise ratio of mass spectrometry detection by affecting ionization efficiency.In this study,a plasma fluid model of dielectric barrier discharge ionization containing 7 reactive ions under the action of He-N_(2)mixed carrier gas was established,and the two-dimensional plasma fluid model was used to explore the influence of N_(2)concentration on the ionization ability of the ion source.The results showed that the introduction of different amounts of N_(2) into the He carrier gas could change the species number density of the plasma jet protonated water cluster reaction,and thus improve the ionization efficiency.In particular,it was found that the maximal number density of effective species could be achieved when the mole fraction of N_(2)in carrier gas was 1.5%.In addition,the influence of design parameters,such as the diameter and the relative permittivity,on the number density of species was also considered in case studies and discussions.The results showed that the number density of species would gradually decrease with the increase of the tube diameter and the relative permittivity.The detailed parametric analyses of the N_(2)mole fraction of carrier gas,the tube diameter and relative permittivity of the dielectric barrier will facilitate the ionization source structure,and finally improve the sensitivity and the stability of mass spectrometry detection.