An interferometric and spectroscopic study on a high-current argon arc

The plasmas under investigation have been generated in a 4 mm bore wall-stabilised arc operating at atmospheric pressure with currents in the range 20 to 100 A in argon as well as in a mixture of argon and hydrogen. The electron density was determined with a statistical error of less than 1% by means of 2 lambda interferometry at lambda 632.8 nm and lambda 1152.3 nm. Possible systematic uncertainty caused by excited atoms was estimated to be less than 3% for the electron density range 1.89*10 16 cm -3 <or=N e <or=1.64*10 17 cm -3 . Under the assumption of local thermodynamical equilibrium, experimental transition probabilities were obtained for the Ar I 430.0 nm line (A nm =3.2*10 5 s -1 +or-7%) and the Ar II 480.6 nm line (A nm =7*10 7 s -1 +or-14%). The values are not line-wing corrected. For the considered electron density range, the experimental half and quarter widths (in the reduced wavelength scale) of the H beta line were found to be constant within the limits of the experimental accuracy. In addition, it is shown that the experimental data of the Ar I 1430.0 nm line transition probabilities given in the literature can be brought to a common value by considering the present reduced widths of the H beta line profile.