Spectroscopic determination of the singly ionized helium density in low electron temperature plasmas mixed with helium in a linear divertor plasma simulator

• Published in: Physics of plasmas 2007-10, Vol.14 (10)
• Main Authors: Nishijima, D., Doerner, R. P., Baldwin, M. J., Hollmann, E. M., Seraydarian, R. P., Ueda, Y.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CONFINEMENT TIME; DEUTERIUM; DIVERTORS; ELECTRON DENSITY; ELECTRON TEMPERATURE; HELIUM; HELIUM IONS; ION DENSITY; IONIZATION; MASS SPECTROMETERS; MOLECULES; PLASMA; PLASMA CONFINEMENT; PLASMA DENSITY; PLASMA SIMULATION; SIMULATORS
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.2786063

The spectroscopic method is developed to obtain the He + ion density n He + in low electron temperature, T e = 5 – 20 eV , plasmas mixed with He. Plasmas were produced in the PISCES-B linear divertor plasma simulator [R. P. Doerner et al. , Phys. Scr. T111, 75 (2004)] where the electron densities are n e = ( 1 − 15 ) × 10 18 m − 3 and the ionization degree is ∼ 1 – 10 % . In the method, the He I line intensity I He I at λ = 447.1 nm is used, instead of the He II line intensity in the conventional method. The radial confinement time of He + ions is requisite, and is measured to be at a level of the Bohm confinement time. The He + ion concentration, n He + ∕ n e , is found to be proportional to I HeI , and to weakly depend on n e and T e . Because of the higher ionization energy of He than other species ( D 2 , Ne, and Ar), the measured n He + ∕ n e becomes systematically lower than the He gas pressure fraction, and agrees with data from an omegatron mass spectrometer. The omegatron measurement and estimates of the He + ion loss rates indicate that the influences of vibrationally excited deuterium molecules on the particle balance of He + ions are small at T e ⩾ 10 eV .