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Impurity behaviour in PBX L- and H-mode plasmas
- Source :
- Nuclear Fusion. 29:231-250
- Publication Year :
- 1989
- Publisher :
- IOP Publishing, 1989.
-
Abstract
- Intrinsic impurity behaviour and transport properties in neutral beam heated L- and H-mode PBX tokamak plasmas were studied with a variety of impurity diagnostics. Central impurity accumulation was most often observed in H-mode discharges; sometimes it resulted in a thermal collapse due to high central metallic radiation (~1.5 W • cm−3). The impurity accumulation was evident from peaked Zeff and radiated power profiles and was further substantiated by specific vacuum ultraviolet and X-ray spectroscopy measurements. It is shown that impurity accumulation was neither unique nor inevitable in H-mode discharges and it could be suppressed by sufficient gas puffing. Central impurity accumulation was also seen in L-mode plasmas even with co-injected neutral beams. This usually occurred at high beam power and relatively low density. While there was no significant difference in the degree of accumulation between L-mode and H-mode discharges, the Zeff profile itself was more peaked in the H-mode because the electron density profiles are flatter in H-mode plasmas than in L-mode plasmas. The degree of accumulation increased as Zeff(0) itself increased, which suggests that neoclassical convection and diffusion driven by both impurity-impurity and impurity-plasma ion collisions contribute to the central plasma particle transport.
Details
- ISSN :
- 17414326 and 00295515
- Volume :
- 29
- Database :
- OpenAIRE
- Journal :
- Nuclear Fusion
- Accession number :
- edsair.doi...........3b9f508f7a3235b04a3e51a2029c920a