Pushing Particles with Waves: Current Drive and α-Channeling

Authors: N. Fisch

Abstract: It can be advantageous to push particles with waves in tokamaks or other magnetic confinement devices, relying on wave-particle resonances to accomplish specific goals.  Waves that damp on electrons or ions in toroidal fusion devises can drive currents if the waves are launched with toroidal  asymmetry. Theses currents are important for tokamaks, since  they operate in the absence  of an electric field with curl, enabling steady state operation. The lower  hybrid  wave and the electron cyclotron wave have been demonstrated to drive significant currents.  Non-inductive current also stabilizes deleterious tearing  modes. Waves can also be used to broker the energy transfer between  energetic alpha  particles and the background plasma. Alpha particles born through  fusion  reactions in a tokamak reactor  tend to slow down on electrons, but that could  take up to hundreds of milliseconds. Before that happens, the energy  in these alpha particles can destabilize on collisionless timescales toroidal  Alfven modes  and other  waves, in a way deleterious to energy confinement. However, it has been speculated that this energy might be instead  be channeled instead  into useful energy, that heats fuel ions or drives cunent. An important question is the extent  to which  these effects can be accomplished together

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