Electrodynamics of a Low-pressure Electrode Microwave Discharge

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Results are given of self-consistent two-dimensional simulation of self-sustained steady electrode microwave discharge in a chamber at the end of central conductor of a coaxial line. The discharge parameters are calculated in the diffusion mode in hydrogen at pressures of 0.5, 2, and 8 torr and incident power of 30–200 W. The dependence of matching between the discharge chamber and delivery path on the geometric dimensions of the chamber is investigated in the presence of plasma. It is demonstrated that the length of central electrode is the key factor affecting the structure of plasma formation and its matching with the pumping wave. The maxima and minima of matching alternate when the central electrode is elongated by quarter wave. The maxima and minima of matching for the case of low pressure (< 2 torr) are shifted by λ/4 relative to those for high pressure (> 2 torr). The problem of maximal energy input to the discharge region at the end of antenna-type electrode is analyzed. It is demonstrated that a restriction exists on the maximal energy input to such a discharge (and, accordingly, on the size of plasma formation). These restrictions are associated either with the runaway of discharge toward the generator or with the ignition of discharge in the region of entry of antenna into the chamber.

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