Large Amplitude Stabilization of Flute Growth

Numerical results show that finite amplitude oscillatory but stable flutes can result from exponentially growing flutes which are excited at small amplitudes. The case examined here is an unstable flute in the low-density regime where the flute smearing due to the ion precessional drifts is almost sufficient to produce linear regime stability. The mechanism of nonlinear stabilization can be explained by a plausible extension of the marginal stability condition obtained by linear analysis. That is, at finite amplitude, the basic growth mechanism is reduced by nonlinear effects so that the previously weaker competing process (the change of phase of the charge distribution due to the ion precessional drifts) becomes the stronger mechanism. Total disruption of the basic growth mechanism is not required. One application is that experimental observation of the onset of instability may occur well into the unstable regime predicted by linear analysis, and may thus affect the interpretation of experimental results.