Doppler and Stark broadenings of spectral lines of highly excited helium atoms for measurement of detached recombining plasmas in MAP-II divertor simulator

Abstract The shapes of atomic helium spectral lines from various excited states were measured in the MAP (material and plasma)-II linear divertor simulator at the University of Tokyo, using a high-resolution visible–near-ultraviolet spectrometer with image magnification optics. A steady state pure helium plasma was produced by a direct current arc discharge in the volumetric recombination-dominated regime, where both the ionizing and the recombining components could be observed up to higher excited states. Highly excited states (principal quantum number n ⩾ 6) of helium atoms are dominated by the recombining component, except the 1 P states that are optically coupled with the ground state. Therefore, we propose a method to determine the neutral temperature, electron density, and ion temperature in the recombining plasmas from the spectral line shapes with Doppler and Stark broadenings of three different transitions, 2 1 S–3 1 P (501.567 nm), 2 1 S–7 1 P (335.455 nm), and 2 3 P–7 3 D (370.500 nm).