Correlation between near scrape-off layer power fall-off length and confinement properties in JET operated with carbon and ITER-like wall

Abstract

Combining high plasma core performance with a suitable power exhaust solution is one of the major challenges in magnetic confinement fusion research. One of the most important power exhaust parameters is the power fall-off length in the scrape-off layer. Two infrared thermography based power fall-off length data sets from JET operated with carbon and ITER-like wall are revisited and compared to recently published scaling laws as well as to confinement and pedestal top parameters. It is shown that the power fall-off length is correlated to confinement, with the highest correlation among the tested parameters being the pedestal top density. The power fall-off length decreases with increasing pedestal top density in variance to the multi-machine scaling law. A similar trend is observed for the pedestal top pressure. This is in agreement with findings at C-Mod showing a scaling of the power fall-off length in various confinement regimes with the volume averaged pressure. Further, it is shown that a variation of the safety factor at constant pedestal top density is not changing the power fall-off length significantly in the two JET data sets.