Study of Macroscopic Oscillations of Detachment front in the linear plasma machine

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Oscillations of the position of the detachment front have been observed in a linear plasma machine with a simulated baffled, divertor. The oscillation, with a back-and-forth motion, of the detachment front along field lines, accompanies a significant oscillation of the neutral helium gas pressure in the divertor region. This is due to the fact that plasma plugging depends on the position of the detachment front. To clarify the oscillation mechanism, neon and hydrogen gas were injected into the divertor region. As the flow rate of the gas injection is increased, the neutral pressure difference, ΔP, between divertor region and the front of the baffle reaches its maximum, ΔP_<max,> then the position of the detachment front Zf and ΔP begin to oscillate. The essential properties of the oscillation, such as Zf - dependency on plasma plugging, are common to all gas species. The amplitude and the period of the oscillations are largest for neon and smallest for hydrogen. The period and amplitude can be mostly dependent on the plasma pressure on the orifice, Pp, for the particular gas species. It was suggested that a modest reduction of Pp for neon can be sustained by ionization, and the significant reduction of Pp for hydrogen may be due to the Molecular Activated Recombination process.