Experimental evidence of the non-local response of transport to peripheral perturbations

Abstract

Qualitatively novel results on non-locality phenomena in perturbative transport experiments are reported. Here, non-locality means a rapid response in the core follows an edge perturbation on a time scale far shorter than any standard approximation to the global, diffusive model confinement time. Sequential firing of supersonic molecular beam injection on the HL-2A tokamak sustained the increase in the core temperature in response to the edge perturbation. O-mode reflectometers are introduced to measure density fluctuations and show that the central turbulence is suppressed during nonlocallity, suggesting that the interpretation of the phenomenon due to the formation of an ‘ITB-like’ structure is plausible. ECH switch-off experiments on the HL-2A tokamak demonstrated that the non-local response is sensitive to the deposition location. Taken together, these results suggest that non-locality phenomena have several aspects in common which can be linked to certain simple, generic elements of tokamak turbulence physics.