Investigation of Current-Density Modification during Magnetic Reconnection by Analysis of Hydrogen-Pellet Deflection

A pellet penetrating the inner region of a tokamak discharge, where the safety factor drops below unity, triggers an instability analogous to a sawtooth crash. Because of the simultaneity of the crash and pellet crossing, the latter is an appropriate probe for investigating the current distribution during reconnection. In this Letter, pellet deflection is used to characterize the associated electron distribution function. The perturbation compatible with the observed trajectory requires a negative current layer on the q = 1 magnetic surface between 3 and 12 times the equilibrium current density and an expulsion of high energy electrons from the plasma core.