Simple relations between scrape-off layer parameters of high recycling divertors Part II: Further relations

Abstract

In Part I it was shown that values of Teu and neu in the SOL of single null, high recycling divertor discharges in JET and Alcator C-Mod are related approximately as Teu ∝ n1/2eu, where (Teu, neu) are the values of plasma temperature and density on any given flux tube at the `upstream' end, for example, halfway between the two targets. This implies that theupstream radial decay length can be expected to approximately satisfy λn/λT ≈ 1/2,in the conduction limited regime. Other simple correlations, such as between target ion saturationcurrent density, Jsat,t, and neu are also implied, and are found to hold for thedatabase considered. The variation of neu with ⟨ne⟩ is established for the JET database and this is used to express the region in (⟨ne ⟩, PSOL) space for conduction limited operation, i.e. the respective transitions to sheath limited and detached divertor regimes.