Feasibility Study of Lost-Alpha-Particle Measurements by Probe Technique in ITER

A feasibility study for a fast-ion-loss detector in ITER has been carried out. Taking into account the basic requirements for measuring magnetohydrodynamic (MHD)-induced fast-ion (fusion-born alpha particles and ions from external heating systems) losses and the harsh environments expected in ITER plasmas, a solution based on a reciprocating probe installed in an equatorial port is suggested. In agreement with previous studies, Monte Carlo simulations of alpha-particle load on the first wall in MHD quiescent plasmas indicate that the main losses will be concentrated below the midplane, in the region of blanket module (BM) 15 to BM 18. Orbit tracing and thermal analysis, including plasma photonic and particle fluxes together with nuclear heating, have been performed to estimate the most suitable measurement timing and position of the reciprocating probe, enabling the detection of escaping alpha particles with pitch angles from [approximately]0 to 85 deg. This large velocity space ensures the detection of escaping alpha particles on both passing and trapped orbits, allowing the study of the interaction between alpha particles and a rich variety of MHD instabilities.