ELM-averaged power exhaust on JET

Abstract

This paper describes experiments performed on JET over the past two years dedicated to characterizing ELM-averaged power exhaust (based on time-averaged divertor power deposition profiles), with an emphasis on unfuelled, Type-I ELMy H-mode. Radial energy transport in the scrape-off layer (SOL) is found to behave differently in the ion and electron channels: the former is dominated by (neo-)classical ion conduction, i.e. by diffusion of heat due to ion–ion collisions, while the latter appears to be governed by turbulent convection, most likely driven by MHD interchange and/or drift-Alfven instabilities. Comparison of forward and reversed field experiments indicates that classical drifts can explain the observed in–out poloidal asymmetry in the heat loads deposited on the divertor. Whereas the role of ELMs needs further characterization, a coherent picture of ELM-averaged power exhaust can be formed by considering the role of collisional heat diffusion in the highly dissipative SOL turbulence.