  A model for incomplete reconnection in sawtooth crashes is presented. The
reconnection inflow during the crash phase of sawteeth self-consistently
convects the high pressure core toward the reconnection site, raising the
pressure gradient there. Reconnection shuts off if the diamagnetic drift speed
at the reconnection site exceeds a threshold, which may explain incomplete
reconnection. The relaxation of magnetic shear after reconnection stops may
explain the destabilization of ideal interchange instabilities reported
previously. Proof-of-principle two-fluid simulations confirm this basic
picture. Predictions of the model compare favorably to data from the Mega
Ampere Spherical Tokamak. Applications to transport modeling of sawteeth are
discussed. The results should apply across tokamaks, including ITER.
