Production and Identification of a Collisionless, Curvature-Driven, Trapped-Particle Instability

The Columbia Linear Machine has been redesigned to enter the parameter regime of the collisionless, curvature-driven, trapped-particle instability. With the new machine configuration, a strong ($\frac{\tilde{n}}{N}\gtrsim 60\%$), coherent mode is observed which bears all the characteristics of this instability. These include strong localization to the mirror cell, broad radial-mode structure, and MHD-like body motion of the plasma column. Furthermore, the mode exhibits all the correct parametric dependences of increasing mode amplitude with increasing mirror ratio and rf power, and decreasing mirror-cell length.