Experimental determination of S/XB values of W I visible lines

Nishijima, D.; Doerner, R. P.; Baldwin, M. J.; Pospieszczyk, A.; Kreter, A.
December 2009
Physics of Plasmas;Dec2009, Vol. 16 Issue 12, p122503
Academic Journal
The dependence of the number of ionization events per photon, or so called S/XB value, on the electron temperature, Te, for W I lines at λ=400.8, 429.4, 498.2, and 505.3 nm has been experimentally determined by measuring the line emission of W atoms sputtered by Ar plasma bombardment in the PISCES-B linear divertor plasma simulator [R. P. Doerner et al., Phys. Scr. T 111, 75 (2004)]. The measured S/XB values at Te>10 eV are found to agree with theoretical calculations at an effective temperature TW=0.1–0.3 eV, which is treated as a free parameter and affects the population of ground states of W atoms. However, compared with previously reported experimental values of S/XB for the 400.8 nm line, our S/XB values are ∼5–10 times higher. At Te<10 eV, it is seen that the S/XB values increase with decreasing electron density, ne, even with correction of the geometrical loss flux. This indicates that there is a ne dependence of S/XB, which is also confirmed by comparison of W I line intensity ratios with calculations. It should be, however, noted that no single value of TW can explain the measured intensity ratios. This suggests that a more complete collisional-radiative model with more accurate rate coefficients and without using the free parameter TW is required to reproduce the observed ne and Te dependence of S/XB.


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