Experimental study of an ion-temperature-gradient driven instability in a linear machine

An ion-temperature-gradient driven instability is investigated in the Columbia Linear Machine (CLM). A transit-time RF technique is used to heat the core of the plasma column. This produces the peaked ion temperature profile with the parameter eta i = delta ln T i / delta ln n exceeding the critical value ( approximately 1.4) required for onset of the instability. Along with the peaked temperature profile, a new feature in the density fluctuation spectrum is observed. This mode has an azimuthal mode number m=2 and propagates in the ion diamagnetic drift direction. It is identified as an eta i mode. The mode is similar to the one studied previously in the CLM using DC biased meshes for heating the ions.