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

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.