Control of electron heating and confinement through DC coil currents in an inductively coupled plasma under confronting divergent magnetic fields*

Confronting divergent magnetic fields (CDMFs) applied by two DC coils, under which an inductively coupled plasma (ICP) is driven, confine electrons in one side of their separatrix. This would enable plasma sustainment even under low pressures. The confinement region where electron number density n_e is high can be controlled by the DC coil currents via the shape and position of the separatrix. The partial resonance is observed in the resonant region as high electron energy gain G. This region can also be controlled through the coil currents.

When the separatrix arches to the confinement region by changing the ratio between the upper and lower DC coil currents, higher n_e and G in the upper region are expected, because the resonant region approaches the high electric filed region near the RF antenna. We attempted to control the regions where high n_e and G values distribute by letting the resonant region approach high electric fields near the antenna and letting separatrix arches upward. With such an arrangement, we performed Monte Carlo simulations of a low-pressure ICP under the CDMFs at driving frequencies f = 13.56, 27.12, and 40.68 MHz. It was observed that the electron distribution is concentrated in a narrower region and G in the resonant region becomes higher than the case of conventional flat separatrix.