Compressional Alfven and ion-ion hybrid waves excited by energetic beam ions are studied in plasmas with two ion species. In our experiment, a hydrogendeuterium (H-D) plasma is used to produce instabilities similar to those likely to be present in the burning deuterium-tritium plasmas of future tokamaks. Modes are suppressed in the deuterium cyclotron frequency range with increasing hydrogen gas puffing.
