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 1P 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, 21S–31P (501.567nm), 21S–71P (335.455nm), and 23P–73D (370.500nm).