基于ECR的大体积等离子体源中氢离子能量分布的质谱研究
Mass Spectrometry Studies of Hydrogen Ions Energy Distributions in an ECR- based Large Volume Plasma Source
AI总结：
本研究通过MBMS等设备测量基于ECR的LVPS中H⁻离子能量分布，结合LP与MBMS数据得出H⁻密度等关键参数，为H⁻体产生提供了有利依据。
AI中文摘要：
在连接到大体积等离子体源（LVPS，直径1米，高度1米）的紧凑型ECR等离子体源（CEPS）中，使用连续波（CW）微波（功率400-600 W，频率2.45 GHz），在氢气压力为1-3 mTorr的条件下产生等离子体，等离子体沿CEPS的磁场膨胀进入LVPS。使用Hiden Analytical HPR 60分子束质谱仪（MBMS）测量下游等离子体中的H⁻离子能量分布函数（IEDFs）。此前对LVPS的等离子体表征研究表明，下游等离子体条件有利于H⁻离子的体产生。当MBMS探头朝向等离子体流放置在下游80 cm处，在400 W、1 mTorr条件下，测得典型的H⁻计数率为3×10^5 counts/s，同时存在明显的高能尾（≤20 eV），这些及其他结果已进行详细分析。正离子光谱显示，所有情况下H₃⁺的计数始终很高（60-70%），H₂⁺和H⁺的计数分别为30-35%和少量。结合朗缪尔探针（LP）和MBMS的数据，可确定MBMS探头孔前的近似密度：在500 W、2 mTorr条件下，n_(H⁺)=9.6×10^9 cm⁻³，n_(H₂⁺)=1.7×10^10 cm⁻³，n_(H₃⁺)=4.3×10^10 cm⁻³，下游80 cm处对应的H⁻密度n_(H⁻)=3.9×10^8 cm⁻³。考虑到H⁻因散射和损耗造成的所有损失，H⁻损耗的有效平均自由程为12.4 cm。由于H⁻形成发生在源出口下游约10-30 cm处，确定形成区的近似平均H⁻密度为5.5×10^10 cm⁻³。考虑到实验使用的腔室体积和面积较大，且所用功率非常适中，该值对于H⁻的体产生而言非常可观。
英文摘要：
Plasma is produced in a Large Volume Plasma Source (LVPS; dia. = 1 m, height = 1m) using CW microwaves (= 400 - 600 W, 2.45 GHz), in a compact ECR plasma source (CEPS) attached to LVPS, at hydrogen gas pressures = 1 - 3 mTorr. Plasma expands along the CEPS magnetic field into LVPS. A Hiden Analytical HPR 60 molecular beam mass spectrometer (MBMS) is used to measure the H^- ion energy distribution functions (IEDFs) in the downstream plasma. Previous plasma characterization studies in LVPS indicated favourable downstream plasma conditions for volume production of H^- ions. Measurements conducted with the MBMS probe aligned facing the plasma flow = 80 cm downstream, gave typical H^- count rates = 3 x 10^5 counts /s, at = 400 W, = 1 mTorr, along with a distinct high energy tail (<= 20 eV). These and other results are analyzed in detail. The positive ion spectrum showed the H_3^+ count to be consistently high in all cases (= 60-70 %); the counts for H_2^+ and H^+ were =30-35 % and a =few %. Combining the Langmuir probe (LP) and MBMS data it is possible to determine the approximate densities in front of the MBMS probe aperture. At = 500 W and = 2 mTorr, one finds: n_(H^+) = 9.6 x 10^9 cm^(-3), n_(H_2^+) = 1.7 x 10^10 cm^(-3) and n_(H_3^+) = 4.3 x 10^10 cm^(-3). The corresponding H^- density, = 80 cm downstream is n_(H^-) = 3.9 x 10^8 cm^(-3). Accounting for all H^- losses due to scattering and destruction, one finds the effective mean free path for H^- loss to be = 12.4 cm. Noting that H^- formation takes place about = 10 - 30 cm downstream of the source exit, the approximate average H^- density in the formation zone is determined as = 5.5 x 10^10 cm^(-3). This value is remarkably encouraging for H^- production in volume mode, considering the large chamber volume and area, as well as the very moderate power used for the experiments.
