Observation of zero current density in the core of JET discharges with lower hybrid heating and current drive - art. no. 115001

Simultaneous current ramping and application of lower hybrid heating and cu rrent drive (LHCD) have produced a region with zero current density within measurement errors in the core (r/a less than or equal to 0.2) of JET tokam ak optimized shear discharges. The reduction of core current density is con sistent with a simple physical explanation and numerical simulations of rad ial current diffusion including the effects of LHCD. However, the core curr ent density is clamped at zero, indicating the existence of a physical mech anism which prevents it from becoming negative.