2D display of tungsten impurity in a free-burning arc using laser-induced fluorescence

Abstract

We present laser-induced fluorescence (LIF) measurements, spatially and temporally resolved, of tungsten impurities eroded from the cathode of a free-burning argon arc. Saturation, but more drastically quenching processes limit a quantitative evaluation of the measurements. Applying a special measuring technique, we were able to determine relative densities and, via a Boltzmann plot, excitation temperatures. A 2D display of the metal impurity can be obtained with a planar LIF arrangement. It shows the distribution of that part of metal component being in a distinct mode of ionization and excitation. As known, the population distribution of the tungsten impurity is dominated by strong demixing effects.

The effects of metal vapour in arc welding

“…While the precise values of electron temperature may be incorrect as a consequence of the problems with applying Thomson scattering to thermal plasmas mentioned above, the trends found are expected to be reliable. Kühn et al [26] used laser-induced fluorescence to measure the distribution of tungsten atoms and ions evaporated from the cathode in a free-burning arc in argon. The arc currents were less than 10 A, and therefore not relevant to arc welding.…”

A spatially resolved relaxation method for pLTE plasma diagnostics in free-burning arcs

“…The experimental setup shown in figure 3 was similar to the setups we used in [1][2][3], so we point out just the main features and enhancements here.…”

“…In previous papers [1][2][3] we presented results from diagnostics in the near-cathode region of a low-current free-burning arc in argon. We found four phenomenologically distinguishable discharge modes and concentrated our work on two of them, namely the 'diffuse mode' and the 'blue-core mode'.…”

Near-cathode region of a free-burning arc: a spectroscopic investigation

“…However, noble gas lines in arc plasmas show mostly monotonically decreasing profiles, which are far less prone to error for Abel inversion [23]. The spectroscopic investigations were accompanied by Thomson and Rayleigh scattering measurements as well as LIF measurements (see also [14,15,24]).…”

“…It would be desirable to have independent diagnostic techniques to extend and confirm our knowledge of the plasma parameters in the region close to the cathode. Due to the shortcomings of the already applied laser-based techniques in this region [14,24], we see further possibilities in laser-based absorption spectroscopy (to measure population densities of energetically low lying levels) and interferometry (to measure electron densities independent of emission spectroscopy).…”