Spectroscopic study of recombination continuum in arc-heated cold expanding plasma jet

Cold recombining H2-He mixture plasma and pure He plasma with low electron density are generated by arc discharge followed by expansion into a lower-pressure vessel, and their recombination radiation is analyzed by optical emission spectroscopic measurement. Their electron temperature is determined from the continuum spectra, which is found to agree with those determined from the line intensities of LTE levels within 10% accuracy. Meanwhile, the agreement of electron density is found to be about 20-25%. It is experimentally found that the conventional theory of spectral intensity of the recombination continuum explains the observed continuum spectra very well even for very low electron temperature within the range from 0.07 to 0.2 eV.