Some electrical effects in the keyhole plasma in deep penetration cw CO2 laser welding

The process of laser welding of a material has been extensively studied from an experimental point of view and considerable mathematical modelling has been carried out on the cw aspects of the process as well. For a cw CO2 laser a partially ionised plasma is likely to exist in the keyhole, emerging from it to produce a turbulent plume in which variations of electrical charge density have been observed. The presence of large temperature gradients near the keyhole walls in conjunction with the Onsager/de Groot relations has the consequence that there must be an electrical potential gradient in the plasma and associated space-charge distribution. These effects are analysed and quantitative relations obtained for the case of a steel work piece.