Avalanche statistics of fluctuation-induced fluxes from the SLPM and the W7-AS stellarator

Measurements of fluctuating floating potentials and ion saturation currents at different radial locations in the Santander Linear Plasma Machine (Castellanos et al 2005 Plasma Phys. Control. Fusion47 2067) and at the edge of the W7-AS stellarator by means of radially movable Langmuir probes allow to infer the corresponding fluctuation-induced radial flux temporal series. Avalanche-like transport events are identified in the time series and statistically characterized in terms of avalanche size/duration/quiet-time distributions and size-duration scaling relations. Transport is diffusive in the inner and intermediate radial region of the SLPM r < r_tr ≈ 2.6 cm, undergoing a transition at r_tr, becoming non-diffusive in the outermost region of the device, r > r_tr. Here, the results obtained at the edge of the W7-AS stellarator are similar to those found in SLPM for r > r_tr, i.e. consistent with what would be expected for scale-free, self-similar plasma transport dynamics near a critical state.. Authors: Mier, Jose Angel [Universidad de Cantabria, Santander (Spain)] (ORCID:0000000244111744); Blanco, J. [Universidad de Cantabria, Santander (Spain)] (ORCID:0009000966313804); Sánchez, R. [Universidad Carlos III de Madrid (Spain)] (ORCID:0000000315933930); Castellanos, O. F. [Universidad Estatal Península de Santa Elena, Libertad (Ecuador)]; Newman, D. E. [University of Alaska, Fairbanks, AK (United States)] (ORCID:0000000258350287). DOE Contract: SC0018076. Subjects: Avalanches; Fluctuations; Fusion energy; Plasma turbulence; Transport properties; Turbulent Transport