Experiments at high elongations in DIII-D

The limitations to elongation in D-shaped plasmas in the DIII-D tokamak are discussed. It was found that as the triangularity is increased and l(sub i) is decreased that the n = 0 mode takes on an increasingly non-rigid character. The analysis shows two aspects of the behavior; first, an increasing variation of the m/n = 1/0 component across flux surfaces and second, an increase in the relative amplitude of a m/n = 3/0 component which couples to the m/n = 1/0 component and further destabilizes the mode.