Investigation of the electrical discharge parameters in electrodeless inductive lamps with a re-entrant coupler and magnetic core

The inductively coupled fluorescent lamp with a cored induction coil placed in a re-entrant cavity is in fact a coaxial transformer operated in the radiofrequency range between 100 kHz and a few MHz. The magnetic coupling coefficient k between the primary coil and the plasma ring is relatively low because of the open magnetic circuit. The acting mutual inductance M enables us to quantify the interaction between the magnetic field produced by the primary coil current I 1 and the opposing magnetic field produced by the powerful plasma current I 2 . A contra-electromotive force j ω MI 2 is induced in the induction coil L 1 , defining the primary voltage V 1 = I 1 ( R 1 + j ω L 1 ) − j ω MI 2 . The current I 1 induces in the secondary conductive plasma the driving electromotive force j ω MI 1 supplying the secondary load consisting of the average plasma resistance R 2 and the secondary inductance L 2 , according to the equation j ω MI 2 = I 2 ( R 2 + j ω L 2 ). It is the aim of this paper to find a model to determine k on the basis of the measured primary parameters V 1 , I 1 , P 1 , L 1 , R 1 and finally all electrical inaccessible parameters, such as M , V 2 , I 2 , φ 2 , L 2 , R 2 , in order to optimize the discharge and lamp efficacy. The complex characteristic of plasma inductance for this type of lamp is analysed and clarified. Some reflexive basic relations verifying the correctness of the inferred plasma parameters are also developed. The described experiments are related to a lamp working at about 2.6 MHz. Corrections were made to this article on 7 July 2006. The corrections were made to the third line from the end of the right-hand column of page 466 and the second row of table 2 on page 472. The corrected electronic version is identical to the print version.