Collective Thomson scattering on alpha density fluctuations in ignited plasma regimes is investigated with reference to a promising candidate source as the mm‐wave gyrotron and a representative ITER‐like plasma regime. It is shown that a number of intrinsic limitations characterize each of the equatorial scattering geometries selected as more promising, namely a backscattering geometry atf0=80 GHz and two similar quasiorthogonal geometries atf0=180 GHz. A lack of spatial resolution typical of the former geometry has to be contrasted with a significant limitation in plasma access typical of the remaining geometries. Other relevant differences concern the requirements in terms of gyrotron power, acceptable stray radiation levels, etc. Special emphasis is given in the work to a discussion of ECE noise, on which the feasibility itself of the alpha collective scattering diagnostics at mm‐waves largely depends in the plasma regimes considered. ©1996 American Institute of Physics.