H- to W-mode transitions and properties of a multimode helicon plasma reactor

Abstract

Magnetically enhanced inductively coupled plasmas (MEICPs) typically display mode jumps as power or the magnetic field is increased. Inductive (H-mode) to helicon (W-mode) transitions in research reactors having uniform axial magnetic fields are often accompanied by a change in the spatial model structure and rapid increase in plasma density. In industrial plasma sources, the magnetic field structure is often non-uniform, producing less pure modal structure and transitions. In this paper, the characteristics of research and industrial MEICPs are computationally investigated using results from a three-dimensional plasma equipment model. When excluding the electrostatic term in the solution of Maxwell's equations, experimental observations for mode structure and transitions from H- to W-mode in the research reactor are reproduced and occur coincident with the formation of shorter axial wavelength modes, radial modes and the onset of rotation of the electric fields. Similar scaling laws were observed in the industrial reactor having a flaring magnetic field. Simultaneous H- and W-mode behaviour occurred (as characterized by radial modes and rotation of the electric field) in different regions of the plasma source depending on the local value of the helicon wavelength. When including the electrostatic terms in the solution of Maxwell's equations, more power deposition occurs in the periphery of the reactor and the H- to W-mode transition occurs at lower powers.