Interchange instability
= Interchange instability
{wiki}
An instability in which neighboring <flux tubes> exchange positions across a <pressure gradient> or other stratification, reducing the appropriate potential <energy>. Unfavorable <magnetic field-line curvature> can drive the exchange; parallel variation bends the <magnetic field> and introduces stabilizing <magnetic tension>. In a steep-gradient low-<plasma beta> local <Z-pinch>, $\omega^2=k_\parallel^2v_A^2-2p_0/(\rho_0RL_p)$.