The spatial distribution of the hydrogen atom density was evaluated in a spherical tokamak (ST) plasma sustained only with 28 GHz electron cyclotron heating (ECH). The radially resolved Hδ emissivity was measured using multiple viewing chord spectroscopy and Abel inversion. A collisional-radiative (CR) model analysis of the emissivity resulted in a ground-state hydrogen atom density of 1015-1016 m-3 and an ionization degree of 1-0.85 in the plasma.
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