One method for determining the impedance of an inductively coupled low-pressure argon plasma tube is described. Designed for application to inductively coupled fluorescent light sources, it was a spherical discharge tube and an induction coil wound on its equatorial surface. The pressure of the argon gas is around 100 Pa, and the frequency of the rf coil current is around 10 MHz. By assuming uniformity of the plasma density and electron temperature, an analytic solution for the electromagnetic field is easily obtained. Using this solution, we can obtain a convenient approximate calculation of the spatial distribution of the electric current and plasma impedance. The results of numerical calculation of impedance are given and compared with experimental results.
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