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Highlights • Preliminary design of DEMO first wall 3D surface is presented. • Steady state and controllable perturbations are preented,evaluating the radiated HF density on the wall and the charged particle power. • Different plasma-wall contact phases have been analysed for a list of foresseable and unforeseeable transients. • 3D field line tracing codes were employed to analyse and design discrete high heat flux components surfaces. Abstract The present DEMO breeding blanked design heat load capability is limited to ≈1 MW/m2 for steady state plasma loading, due to the specific requirements on high neutron irradiation capable materials, and high coolant temperature for efficient energy conversion. While this limit is achievable in nominal conditions in the present DEMO blanket concept designs, the greatest challenges arise from the occurrence of plasma transients. The results of simulations of a number of plasma transients are presented in this paper. 3D field-line tracing codes have been used to analyses the maximum heat flux and energy density for a specific first wall shape design, and optimize it. A scoping study has been performed with the thermal analysis code RACLETTE, using a broad range of transient input heat fluxes, on a series of high heat flux (HF) components concepts with tungsten armor, Eurofer steel or copper alloy as heat sink materials, and helium or water as coolant. The results permit the identification of the operational space of the peak HF density that can be tolerated by different plasma facing components, for the different transient models. [ABSTRACT FROM AUTHOR]