B. Ph. van Milligen, R. Sánchez, B. A. Carreras, V. E. Lynch, B. LaBombard, M. A. Pedrosa,C. Hidalgo, B. Gonçalves, R. Balbín and the W7-AS Team

2005

Plasma density fluctuations and electrostatic turbulent fluxes measured at the scrape-off layer of the Alcator C-Mod tokamak [B. LaBombard, R. L. Boivin, M. Greenwald, J. Hughes, B. Lipschultz, D. Mossessian, C. S. Pitcher, J. L. Terry, and S. J. Zweben, Phys. Plasmas 8 , 2107 (2001)], the Wendelstein 7-Advanced Stellarator [H. Renner, E. Anabitarte, E. Ascasibar et al., Plasma Phys. Controlled Fusion 31 , 1579 (1989)], and the TJ-II stellarator [C. Alejaldre, J. Alonso, J. Botija et al., Fusion Technol. 17 , 131 (1990)] are shown to obey a non-Gaussian but apparently universal (i.e., not dependent on device and discharge parameters) probability density distribution (pdf). The fact that a specific shape acts as an attractor for the pdf seems to suggest that emergent behavior and self-regulation are relevant concepts for these fluctuations. This shape is closely similar to the so-called Bramwell, Holdsworth, and Pinton distribution, which does not have any free parameters.