Optical emission and self mode transition of low frequency inductively coupled plasmas driven by crossed internal oscillating currents

Optical emission and self induced electrostatic (E)-to-electromagnetic (H) mode transition in a newly-developed plasma reactor are investigated. Volume uniform, high density Ar/N2 plasmas are generated by means of transverse unidirectional currents driven by a low frequency RF power of 460 kHz in a 23 cm height and 32 cm diameter reactor. Plasma properties are investigated using a high-resolution optical emission spectroscope. The measurements reveal that the spatial profiles of the excited atomic naturals and singly ionized ions feature a high degree of uniformity in radial and axial directions. A spatially homogeneous E-mode discharge is observed at a power level as small as 40 W. At RF power exceeding a transition threshold of 230 W, the integral emission intensity suddenly jumps to approximately one order of magnitude (H-mode). Further increase of RF power results in a gradual rise of the optical emission intensity. This phenomenon is reproducible for all discharges under the investigation. Furthermore, a spontaneous E-$>$H mode transition (``self-transition'') is observed at input power slightly below the conventional transition threshold value.