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 ($\frac{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{n}}{N}\ensuremath{\gtrsim}60%$), 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.