Physics of two-ion-species plasmas in a linear plasma device

Understanding of turbulence and transport in multi-ion-species plasmas is important for establishing predictive capability for burning tokamak plasmas with comparable densities of D and T. Fundamental modifications to drift-wave instabilities and resulting turbulence are expected from theoretical studies, including new instabilities driven by dissimilar ion density gradients. In addition, information on the ratio of ion densities is essential in the context of tokamak fueling, although a method for reliably measuring this ratio is currently lacking. Recently, experiments have been performed on a small linear plasma device at UCLA in which mixed Hydrogen-Helium plasmas were created and the relative concentration was varied systematically. Properties of pressure-gradient driven instabilities were documented, and initial results will be presented. Additionally, schemes for directly exciting fluctuations at the ion-ion hybrid resonance were explored, and their viability as a diagnostic for local measurements of the ion density ratio will be discussed as well.