α-particle transport-driven current in Tokamaks

It is shown that the radial transport of fusion-born energetic α particles, induced by electrostatic waves traveling in one poloidal direction, is directly connected to a net momentum of α particles in the toroidal direction in tokamaks. Because the momentum change is almost independent of toroidal velocity, the energy required for the momentum generation remains small on an α-particle population sustained by an isotropic time-independent source. By numerical toroidal Monte Carlo calculations it is shown that the current carried by α particles in the presence of intense well penetrated waves can reach several mega-amperes in reactor-sized tokamaks. The current obtained can greatly exceed the neoclassical bootstrap current of the α particles.