ITER's volumetric thermal power density (volume of reactor + plasma) will be 50 kW/m^3, some 400x worse than the volumetric power density of a commercial PWR (reactor vessel + core).
ITER also use a CuZr alloy backing up its first wall materials. This material is unsuitable for long neutron exposure. DEMO would have to use RAFM steel instead there, with an order of magnitude lower thermal conductivity. As a result, the power/area at the surface of the first wall in DEMO may be even lower than in ITER.
ITER also use a CuZr alloy backing up its first wall materials. This material is unsuitable for long neutron exposure. DEMO would have to use RAFM steel instead there, with an order of magnitude lower thermal conductivity. As a result, the power/area at the surface of the first wall in DEMO may be even lower than in ITER.