Evidence of E x B staircase in HL-2A L-mode tokamak discharges

Theory and simulation suggest the existence of an E x B staircase in the plasma core consisting of a series of nested m/n=0/0 E x B shear layers that regulate turbulent transport across the layers together with mesoscale transport events occurring between them. Here, we show evidence for these phenomena in HL-2A L-mode discharges. Both high resolution electron cyclotron emission T e profiles and frequency modulated continuous wave reflectometer n e profiles show multiple gradient corrugations. The analysis of simultaneous poloidally and radially separated beam emission spectroscopy turbulent density fluctuation measurements over most of the minor radius of the plasma provides the evidence of eddy tilting and propagation direction reversals largely coincident with the profile corrugations, with long-range transport events occurring between these locations. The results provide significant additional evidence for the existence of an ExB staircase that influences particle and heat transport in L-mode discharges.