Observation of compressional Alfven modes during neutral-beam heating on the National Spherical Torus Experiment - art. no. 145001

Neutral-beam-driven compressional Alfven eigenmodes at frequencies below th e ion cyclotron frequency have been observed and identified for the first t ime in the National Spherical Torus Experiment. The modes are observed as a broad spectrum of nearly equally spaced peaks in the frequency range from approximate to0.2 omega (ci) to approximate to1.2 omega (ci). The frequency has a scaling with toroidal field and plasma density consistent with Alfve n-waves. The modes have been observed with high bandwidth magnetic pickup c oils and with a reflectometer.