In this paper we provide evidence that, for fusion energy production, advanced scenarios based on the presence of an internal transport barrier (ITB) have some advantages compared with the standard H-mode operation. This is due to their magnetic properties that affect alpha particle heating and helium exhaust. With identical density and temperature profiles, a qs-profile with reversed central shear, typical of an ITB plasma, is found to provide the same amount of total heating as a monotonous qs-profile, but with a broader heating profile. The overall confinement of alphas is almost the same for both profiles, but the neoclassical, energy-dependent alpha transport barrier due to stagnation orbits is closer to the magnetic axis for the monotonous profile. Therefore, the reversed profile helps to confine 3.5 MeV alphas born over a wider region while letting through the cooled-down He-ash.
Kurki-Suonio, T., Tulkki, V., Sipilä, S., & Salomaa, R. (2006). Fusion alpha performance in advanced scenario plasmas based on reversed central magnetic shear. Plasma Physics and Controlled Fusion, 48(9), 1413-1424. https://doi.org/10.1088/0741-3335/48/9/010