Application of ICRF waves in tokamaks beyond heating
Interaction of waves in the ion cyclotron range of frequencies (ICRF) with a plasma has a number of key properties that make them attractive beyond pure heating. First, the waves can interact resonantly with either the plasma ions or electrons. In the case of ion cyclotron damping, a small number of resonant ions are often accelerated to high energies. These ions, apart from heating the bulk plasma via Coulomb collisions, can increase fusion reactivity, affect plasma stability and drive current. They have also been invaluable in diagnostic applications and simulations of fusion-born 3.5 MeV alpha-particles. The second key property of ICRF waves is the transfer of wave momentum to the plasma. This allows one to drive current, affect plasma rotation and induce radial transport of the fast-ions with toroidally directed waves. Finally, ICRF power deposition is rather narrow and its location can be externally controlled, which has important applications in improving the plasma performance, affecting the local plasma transport and providing a tool for plasma transport studies. Representative examples from present-day tokamak experiments are reviewed to highlight the available capabilities.