Parametric studies of axial plasma detachment using multiple diagnostics

We investigate the effect of the source parameters on axial plasma detachment in a helicon plasma device. The axial detachment occurs simultaneously along with a spontaneous, self-organized global transition in the plasma dynamics via a transport bifurcation with strong hysteresis [1, 2]. Using spectroscopy we find dramatic changes in the ion and neutral line ratios only near the end of the device at the transition. At the same time, neutral pressure measurements also show a dramatic increase at the transition only near the end of the device. The plasma near the source does the shown these dramatic changes at the transition. We can also visually see the formation of a recombination front near the end of the 3m long plasma device, which confirms the phenomena of axial plasma detachment. The axial detachment also follows the same hysteresis curves associated with the transport bifurcation that led to the transition. The values of the magnetic field threshold for the axial detachment as well as the width of the hysteresis depend on the source parameters (pressure, gas flow rate, rf power etc.).

[1] S. C. Thakur et. al., PSST 23 044006 (2014)

[2] L. Cui et. al., PoP 23 055704 (2016)