Temporal Characteristics of the Torus Plasma in an Inductively Coupled Fluorescent Lamp

Low-pressure mercury ‒ argon torus plasma generated in an inductively coupled fluorescent lamp was investigated. The tem poral characteristics of the torus plasma from the ignition stage to the stable stage were analyzed by applying the transformer model. The power transfer efficiency was found to be over 90%, and the coupling coefficient was around 0.75. The current density and the electric field strength of the torus plasma were comparable to those of the positive column of a conventional fluorescent lamp. The finite element method was used to analyze the relative electron density distribution in the plasma. The absolute density profile of the electron was estimated by combining the average electron density experimentally determined with the calculated filling factor of the electron. The maximum electron density estimated was around 1.5 × 10 12 cm − 3 in the steady state, nearly equal to that experimentally determined by the double probe. The discharge took about one hour to reach the steady state. This can be explained by the mercury transport from the amalgam, which was fixed at the tip of a long, narrow glass tube that penetrated the excitation coil to the discharge vessel. The analysis technique presented in this paper is useful to explain the temporal characteristics of inductive torus plasma as well as the interaction between the plasma and the excitation coil.