The transition from the slab to the toroidal branch of the ion temperature gradient (ITG) mode was studied by first exciting the slab (ITG) mode and gradually raising the magnetic curvature in the Columbia Linear Machine. Modest levels of magnetic curvature destablized and reduced the real frequency of the mode in accordance with the prediction from a simple theory. However, with further increase in mirror ratio and trapped particles, the observed mode amplitude decreased and the parallel wavelength greatly increased. This may be a hybrid ITG dissipative trapped electron mode.

• Received 27 May 1993

DOI:https://doi.org/10.1103/PhysRevLett.72.3997