Electrostatic ion cyclotron instabilities driven by parallel ion beam injection

The detailed identification of two instabilities driven by an ion beam injected parallel to the confining magnetic field, a resonant ion cyclotron instability, and a nonresonant ion cyclotron drift wave driven by the density gradient of the beam, is reported. Experimental results are in good agreement with numerical calculations based on the kinetic Vlasov equations. Quasi-linear velocity space diffusion of the beam ions by wave-particle interaction is observed, demonstrating enhanced energy transfer. The relevancy of these results to tokamak neutral beam injection heating is discussed.