Jump and hysteresis of plasma density in the spatial afterglow of inductively coupled plasmas

Abstract

In this work, jump and hysteresis of plasma density between low-density (LD) and high-density (HD) in the spatial afterglow of inductively coupled plasmas are experimentally studied for different gas discharges. A quartz plate with a micropore is used to independently control the pressures in the active plasma and spatial afterglow. The plasma density jump from LD to HD vs the pressure in the spatial afterglow only exists in a larger micropore diameter. By adjusting the pressure back and forth, a hysteresis loop in plasma density is formed. The light intensity and excitation rate vs the pressure corresponds well to the jump and hysteresis of plasma density. Therefore, the abrupt changes in ionization rate are responsible for the jump and hysteresis of plasma density. Compared with argon discharges, the critical pressure for the jump from LD to HD is higher in nitrogen discharges, forming a larger hysteresis loop. For hydrogen discharges, the jump from LD to HD is less significant and the hysteresis loop almost disappears. In argon–hydrogen mixed gas discharges, there is no hysteresis loop in plasma density. Experimental results obtained using Langmuir double probes and spectrometer achieve qualitative agreement in gas discharges mentioned above.