Chapter 6 - Scrape-off layer transport on jet

The tokamak plasma boundary, which is typically identified with the area of open field lines known as the scrape-off layer (SOL), determines the degree of plasma-wall interaction. SOL physics, much of which is concerned with the exhaust (removal) of particles and energy from the plasma, has been one of the major topics investigated on JET during the past two decades. In this chapter, SOL transport/exhaust studies on JET are reviewed. The discussion proceeds chronologically, beginning with the limiter SOL and treating in turn the successive divertors (Mk0, MkI, MkIIA, and MkIIGB) with which JET was equipped in subsequent years. When appropriate, old results are reinterpreted in the light of recent improvements in our understanding of edge/SOL turbulence and edge-localized modes (ELMs). Although emphasis is placed on deuterium transport in the SOL, impurity transport is briefly considered. In particular, the effect of divertor closure, of L-mode versus H-mode, and of inter-ELM versus ELM erosion on plasma purity (Z(eff)), radiation (f(rad)), and confinement (tau(E)) is briefly discussed. The chapter concludes with a summary of empirical scaling expressions for SOL profile widths (radial e-folding lengths) in both limiter and divertor configurations.