[Table of Contents]

Plasma and Fusion Research

Volume 5, S2089 (2010)

Regular Articles

Self-Reversal in Hydrogen Lyman-α Line Profile
Motoshi GOTO and Shigeru MORITA
National Institute for Fusion Science, Toki 509-5292, Japan
(Received 8 December 2009 / Accepted 20 March 2010 / Published 10 December 2010)


A detailed spectral profile of the Lyman-α line of neutral hydrogen, i.e., the transition from n = 2 to the ground state, where n is the principal quantum number, was measured with a vacuum ultraviolet spectrometer for the plasma in the Large Helical Device. Self-reversal was observed in the spectral profile when the plasma density was increased with repetitive injection of hydrogen pellets. A one-dimensional radiation transport model was used for creating the Lyman-α spectral profile, for which an emission and absorption medium with a slab geometry and constant plasma parameters were assumed. The population density of the n = 2 level generally has a peaked spatial profile even with constant ground state density because of the reabsorption effect which is essential for the emergence of self-reversal in the spectral profile. We used the n = 2 level population distribution in the medium by Molisch et al. [Radiation Trapping in Atomic Vapours, Oxford University, Oxford, 1998] and evaluated the Lyman-α spectral profile as a function of the optical thickness. The observed line profile was found to be well fitted, for example, with a ground state density of 5.2 × 1018 m−3 and a medium thickness of 10 cm when a Lorentzian profile having a full width at half maximum of 0.0018 nm is adopted for the emission and absorption coefficients.


Lyman-α, self-reversal, reabsorption effect, LHD, internal diffusion barrier

DOI: 10.1585/pfr.5.S2089


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This paper may be cited as follows:

Motoshi GOTO and Shigeru MORITA, Plasma Fusion Res. 5, S2089 (2010).