title: An analysis of the influence of impurities on fast particle attenuation and on fast ion spectral shape in LHD.
abstract: Neutral particle fluxes measured by neutral particle analyzers can provide information about the ion temperature as well as the non-Maxwellian anisotropic ion distribution tails from neutral beam injection and ion cyclotron radio frequency heating. In the case of multidirectional diagnostics employing high resolution atomic energy spectrometers, the neutral atomic flux source is not localized in contrast to pellet charge exchange or diagnostic neutral beam methods. The correct interpretation of such measurements from plasma in a complex toroidally asymmetric geometry, like that of LHD, requires careful numerical modeling of the neutral flux formation. Previously a measured neutral flux calculation scheme was developed and was used for the LHD geometry and a suitable analytic expression for ionization cross sections sigma(s)(z)(E,n(e),T(e),Z(eff)) of impurities was formulated by Janev et al. [Nucl. Fusion 29, 2125 (1989)]. In this paper, the attenuation of fast particles by impurities is incorporated into the neutral flux calculation scheme and the influence of impurities on the calculated neutral flux spectra is shown. Finally, the behavior of the calculated and experimental suprathermal particle distributions is compared for pure hydrogen and for argon impurity seeded plasmas.
authors.affiliation: National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
authors.forename: Evgeny A
authors.initials: EA
authors.lastname: Veshchev
authors.forename: Pavel R
authors.initials: PR
authors.lastname: Goncharov
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Ozaki
authors.forename: Shigeru
authors.initials: S
authors.lastname: Sudo