Preceding propagation of turbulence pulses at heat avalanche events

Plasma transport cannot be explained only by local models, and non-local transport effects must be considered. In this study, the Large Helical Device (LHD) is used to clarify the spatio-temporal characteristics of avalanche and turbulence spreading phenomena, which have been identified as a cause of non-local transport. An electron internal transport barrier (e-ITB) collapse phenomenon is targeted to induce large observable turbulence spreading phenomena. In the LHD, when thermal avalanche phenomena accompanying the collapse of the e-ITB occur, both turbulence and thermal pulses are generated near the foot of the e-ITB and propagate to the peripheral region faster than the diffusion time, but the propagation speed of turbulence pulses is about 10 km/s, which is faster than that of thermal pulses, which is about 1.5 km/s. Existing models estimate that both heat and turbulence propagate at a speed of about 1 km/s, but the turbulence pulse propagates more than an order of magnitude faster than this prediction.The results of this study indicate the existence of a phenomenon that cannot be explained by existing models, namely, the simultaneous propagation of avalanches and turbulence, and provide important insight into the physical mechanism of non-local transport.