Outer target heat fluxes and power decay length scaling in L-mode plasmas at JET and AUG

Abstract

Experimental measurements of heat load profiles from infrared thermography in L-mode plasmas from two tokamaks, JET and ASDEX Upgrade, are presented. The power decay length (λq) is extracted via a fitting procedure. The basic dependencies of λq are identified through plasma parameters scans and for the case of fully attached divertor using numerical regressions (after mapping at the mid-plane). The results are compared with previously published H-mode data. Qualitatively, similar trends with the safety factor, toroidal magnetic field and heating power are found though bulk data is about a factor of two larger in L-mode for both devices. Consistently a clear shrinking of the heat channel width is observed at the L–H transition linked with the formation of the pedestal temperature. Extrapolation of the empirical power scaling laws to ITER gives λq≃3.0–4.9mm for L-mode plasma.