Basic Parameters in Heat Transport in Argon-Helium Mixed Gas Arcs.

Abstract

The research presented here is aimed at clarifying some basic heat transport mechanisms in argon-helium gas tungsten arcs. Two factors that are of great importance in the heat balance of the arc and still lack understanding are the radiative power loss and the anode fall voltage. In this research, Langmuir probe experiments were performed to estimate the anode voltage drop. The radiative power production of the arc was measured using a commercial radiation power meter.From the results of the Langmuir probe experiments it was found that the anode voltage drop and the electron temperature at 1.5 mm above the anode are fairly constant up until helium contents of75%. Only when pure helium is used as a shielding gas, the anode voltage drop rises considerably.As the radiative power production of a plasma is directly linked to its electron density, the electron density profiles were measured using a new method based on IR radiation first proposed by Ohji and Eager.The radiative power of the arc decreases considerably when introducing helium into an argon arc. The radiative power in pure helium arcs is one order of magnitude smaller than in pure argon arcs.When inserting a high pass filter with a 600 nm cut-off wavelength, the measured power in helium arcs is even more drastically reduced compared to that in pure argon arcs.Furthermore, the maximum electron densities found in arcs containing helium are too low compared to theoretical values calculated from the Saha equation.