Use of the two‐ion hybrid as an impurity diagnostic

• Published in: The Physics of fluids (1958) 1986-05, Vol.29 (5), p.1651-1658
• Main Authors: Chen, Francis F., Dimonte, G., Christensen, T., Neil, G. R., Romesser, T. E.
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma diagnostic techniques and instrumentation
• ISSN: 0031-9171; 2163-4998
• DOI: 10.1063/1.865629

In a plasma containing more than one ion species, the frequencies of the ion–ion hybrid resonances can be a sensitive measure of the densities of the minor species, but only if the frequency shifts caused by electron motions are small, as experimental observations suggest. By calculating the eigenfrequencies for ion–ion hybrid waves taking into account collisions, Landau damping, electron inertia, electromagnetic effects, and density gradients, it is found that the frequency shifts are not negligible unless k ∥ is extremely small. Treatment of the sheath boundary conditions at the ends of a plasma column shows that the effective value of k ∥ can indeed be sufficiently small, and that the uncorrected resonance frequency is surprisingly accurate over a wide parameter range. Data from an Ar–Xe discharge demonstrate the usefulness of this technique for measuring impurity concentrations.