Hβ Stark broadening in cold plasmas with low electron densities calibrated with Thomson scattering

In the present work Stark broadening measurements have been carried out on low electron density (ne < 5·1019 m− 3) and (relatively) low gas temperature (Tg < 1100 K) argon–hydrogen plasma, under low-intermediate pressure conditions (3 mbar–40 mbar). A line fitting procedure is used to separate the effects of the different broadening mechanisms (e.g. Doppler and instrumental broadening) from the Stark broadening. A Stark broadening theory is extrapolated to lower electron density values, below its theoretical validity regime. Thomson scattering measurements are used to calibrate and validate the procedure. The results show an agreement within 20%, what validates the use of this Stark broadening method under such low density conditions. It is also found that Stark broadened profiles cannot be assumed to be purely Lorentzian. Such an assumption would lead to an underestimation of the electron density. This implies that independent information on the gas temperature is needed to find the correct values of ne.

► Stark broadening measurements at low density and temperature conditions
► Calibration with Thomson scattering
► Indications of the non-Lorentzian shape of the Stark broadening
► Impossibility of simultaneous diagnostic of gas temperature and electron density