The term Scrape-Off Layer (SOL) refers to the plasma region characterized by open field lines (commencing or ending on a material surface).
- With limiter plasmas, this region is the region outside the Last Closed Flux Surface (LCFS).
- With divertor plasmas, this region is the region outside the separatrix.
In divertor plasmas, the SOL absorbs most of the plasma exhaust (particles and heat) and transports it along the field lines to the divertor plates. Hence, this region is of prime importance for future reactors.
Transport in the SOL is very different from transport in the confined plasma due to the open field lines: it is predominantly convective (rather than diffusive). Typically, the density decays exponentially away from the LCFS. This does not mean that the detailed transport is easy to understand or model: intermittency is very strong in the SOL region.    
- S.I. Krasheninnikov, On scrape off layer plasma transport, Phys. Lett. A, 283, 5-6 (2001) 368
- D.A. D'Ippolito et al, Blob Transport in the Tokamak Scrape-off-Layer, Contrib. Plasma Phys, 44, 1-3 (2004) 205
- A. Loarte et al, Chapter 4: Power and particle control, Nucl. Fusion 47 (2007) S203
- S.I. Krasheninnikov et al., Recent theoretical progress in understanding coherent structures in edge and SOL turbulence, J. Plasma Phys. 74 (2008) 679