Stable regimes, mode transitions and discharge disruptions in a helicon plasma source

Summary form only given. An inductively coupled helicon plasma source demonstrates abrupt changes of discharge regimes which may arise at a smooth variation of external parameters such as input RF power, magnetic field, or driving frequency. These changes are displayed as discontinuous jumps from low to high-density modes, or as discharge disruptions. Abrupt changes of discharge regimes are treated proceeding from the model which assumes the RF power absorption in a helicon source as originating in a linear conversion of helicon waves into electrostatic waves at a plasma edge. The efficiency of conversion and thus of absorption depends strongly on the amplitude of the helicon wave near the plasma boundary. It is low at the anti-resonances of the helicon wave excitation, that is provided that the boundary amplitude of helicon wave is reduced. Since a driving antenna excites in the plasma a variety of spatial modes, the absorbed power varies with plasma density non-monotonically with peaks arising due to different harmonics. The specific shape of the absorption curve depends on the source design, and on the shape of the driving antenna, as well as on the strength and profile of the external magnetic field.