Rotationally symmetrical electric fields and electron density distributions in a microwave plasma used in optical fibre production

Using the finite difference method, rotationally symmetrical field strengths are calculated in a coaxial microwave resonator, such as used for the production of optical fibres. A linear relation between electron density and microwave power consumption at each position inside the plasma is assumed. In this way the electron density distribution can be calculated in a self-consistent manner. The energy parameter involved (MW power per electron-ion pair sustained in the plasma) is adjusted so that experimentally obtained emission spectra with local resolution in axial and radial directions are reproduced within reasonable limits. The increase in gas temperature in the discharge has been taken into account. This simple model reproduces the most important relationships found experimentally, the MW-power dependence, the pressure dependence and the axial and radial variation of the emitted light intensity. It can easily be extended to other geometries and plasma gases. Fully three-dimensional calculations are also possible provided enough computer capacity is available.