On excitation of Alfven waves by energetic particles in fusion and space plasmas

Alfvén waves are prevalent in laboratory fusion and space plasmas. While, e.g., in magnetospheric space plasmas, Shear Alfvén Waves (SAW) could be externally excited by solar wind perturbations; in laboratory fusion plasmas, they are often spontaneously excited via resonance with energetic particles (EPs). These EPs can be either produced by external heating in current experiments or fusion alpha particles in future burning plasmas. SAW, in turn, can break the symmetry of EP phase space dynamics and leads to their enhanced losses; detrimental to achieving the ignition. In this talk, we will discuss the linear and nonlinear physics of the SAW-EP instabilities using the “fishbone” paradigm in fusion plasmas. Specifically, we will discuss the important roles played by plasmas non-uniformities and magnetic field geometries, derive the “fishbone dispersion relation” as well as its generalization, and extend it to the nonlinear regime. Theoretical features of magnetospheric SAW instabilities excited by EPs injected during magnetic storms will also be discussed.