Proceedings of the US-Japan Fusion Cooperation Program Exchange P148 Workshop on Advanced Current Drive Concepts

Low frequency, long wavelength instabilities may be excited in a tokamak plasma with current driven by a neutral beam injection. Specifically, when the beam parallel velocity is greater than the Alfven velocity of the background plasma, the Alfven waves are expected to become unstable for high enough beam density and may cause degradation of the beam current. Particle simulations were carried out to study these instabilities and their nonlinear effects on the current. In addition, waves in the ion cyclotron frequency range are also investigated.