Spectroscopic Mapping of the Nonequilibrium between Electron and Excitation Temperatures in a 1 ATM Helium ARC

The thermostatic states of a 100 amp, 1.016 bar, free-burning helium short arc with a 10 mm electrode gap are mapped from spectroscopic measurements at eight cross sections. The theoretical model used is a multifluids model extended to consider nonequilibrium between electron and excitation temperatures, as well as simple nonequilibrium among excited electronic levels. Seven helium lines are used to determine population densities and upper level excitation temperatures. The electron density is calculated from continuum intensity measurements at C4690. Electron temperatures are found from an astrophysical method suggested by Athay and Menzel. The effective total excitation temperature is obtained by iteration using the multifluids model. The results indicate total excitation temperature values close to the usually calculated "LTE" temperatures, but electron temperatures up to three times larger than the total excitation temperature on the arc centerline near the electrodes. The ratio is approximately 1.5 in the middle of the arc. The heavy particle kinetic temperatures appear to follow the electron temperature, except near the anode, where they drop to values smaller than the total excitation temperatures.