Heat Transport in the JET Scrape-Off Layer

The DIVIMP/NIMBUS Onion-Skin Model has been used to calculate 2D plasma distributions of ne, Te and Ti in the JET edge, based on boundary conditions measured across the targets with built-in Langmuir probes. Ohmic, L-mode and ELMy H-mode discharges were analysed. From the calculated 2D plasma profiles, values of χ⊥sol (r) were extracted as a function of radial location within the scrape-off layer (SOL), showing that χ⊥sol (r) increases with radius. At the separatrix χ⊥sol (0) was in the range ~0.05 – 1 m2s-1, with the lowest values occuring for H-modes, (between ELMs). It was found that χ⊥sol (r) ~ [Teu(r)]-2, where Teu is the electron temperature at the 'upstream' end of the SOL flux tube. No clear correlation with magnetic field, BT was found. The results are therefore not consistent with either Bohm (χ⊥sol ∝ Teu/B) or Gyro-Bohm (χ⊥sol ∝ Teu3/2/B2 ) scaling. χ⊥sol (0) values were found to be weakly correlated with increasing plasma collisionality in the edge.