Hydrogen Balmer beta: The separation between line peaks for plasma electron density diagnostics and self-absorption test

We propose a diagnostic technique for the measurement of plasma electron number density, N_e, based on the wavelength separation between peaks, Δλ_PS, of hydrogen Balmer beta line, H_β. In favor of the proposed diagnostic technique we demonstrate high sensitivity of Δλ_PS on N_e and low sensitivity on plasma elementary processes and plasma parameters that may distort the line profile. These properties of Δλ_PS enable reliable N_e plasma diagnostics in the presence of considerable self-absorption. On the basis of available theoretical data tables for the H_β line profiles, simple N_e=f(Δλ_PS) formulas are proposed. Their validity is experimentally confirmed in a low initial pressure pulsed discharge for the N_e range of (0.2–7)⁎10²³ m⁻³. The agreement of the proposed formulas with another diagnostic technique is well within 10%. In addition, the difference in N_e values obtained from peak separation and from the H_β line width is successfully used as a self-absorption test for line profile. - Highlights: • Separation between peaks of H_β line proposed for electron density diagnostics. • Derived formulas for peak separations versus electron density. • Formulas tested in high electron density low pressure pulsed arc. • Applications of formulas in optically thick plasmas proven. • Method for hydrogen Balmer beta line self-absorption testing proposed