Close collisions of fusion alpha-particles with thermal plasma ions (both of impurities and of main component) give rise to formation of high energy `halo` in the ion velocity space, extending to the energies of MeV-range even for rather heavy ions, like iron. The implications of this process for the diagnostics of the burning plasma have been discussed. There seem to be possible two versions of the diagnostics: * measurement of Doppler contours of the lines radiated by noncompletely stripped impurity ions, * detection of prompt losses of light impurities. In both versions the spatial resolution can be attained by injecting into the plasma the pellets containing the desired impurities. Another option is to detect the prompt losses of 7 MeV alpha-particles formed by collisions between 3.5 MeV alpha-particles. (au).