Magnetic flux conversion in the DIII-D high-beta hybrid scenario

In DIII-D hybrid scenario discharges, the rate of poloidal magnetic energy consumption is more than the rate of energy flow from the poloidal field coils. This is evidence that there is a conversion of toroidal flux to poloidal flux, which may account for a process known as flux pumping that leads to anomalous broadening of the current profile. The hybrid is a promising high confinement scenario for ITER. The broader current profile aids discharge sustainment by raising the minimum safety factor above unity thereby avoiding sawtooth-triggered 2/1 tearing modes that spoil energy confinement. During long ( 1.5s) stationary intervals with constant stored magnetic energy, a significant flux state deficit rate >10 mV was observed. This anomalous consumption of poloidal flux only occurred in discharges with ?N > 2.5 and when a relatively benign 3/2 tearing mode was present. This suggests the tearing mode plays a critical role in flux conversion. Studies have shown that 3D core displacements can lead to flux conversion, suggesting that the 3/2 tearing mode and its 2/2 side band produce helical perturbations in the core velocity and magnetic field capable of producing a dynamo EMF that drives the observed current redistribution.