Continuum Self-Organized-Criticality Model of Turbulent Heat Transport in Tokamaks

Abstract

A simple generic one-dimensional continuum model of driven dissipative systems is proposed to explain self-organized bursty heat transport in tokamaks. Extensive numerical simulations of this model reproduce many features of present day tokamaks such as submarginal temperature profiles, intermittent transport events, 1/f scaling of the frequency spectra, propagating fronts, etc. This model utilizes a minimal set of phenomenological parameters, which may be determined from experiments and/or simulations. Analytical and physical understanding of the observed features has also been attempted.

Effects of impurity seeding and charge non-neutrality on electromagnetic electron temperature gradient modes in a tokamak

“…Thus, these thresholds may also prove invaluable in testing the idea that the "stiffness" of the T e profiles is caused by ETG modes. Studies of ͑R / L T c ͒ crit are also of importance in explaining observations similar to selforganized criticality and other large scale intermittent transport events, avalanche speeds of the order of few hundred meters per second, 16 etc. Critical thresholds are also interesting because they are analytically tractable.…”

The magnetosphere as a complex system

“…Recent observations seem to suggest that plasmas, under certain conditions, demonstrate very complex behavior, that includes self-similar behavior, emergence and self-organization, phase transitions, turbulence, spatio-temporal chaos, and so on (Lu and Hamilton, 1991;Carreras et al, 1996;Boffeta et al, 1999;Klimas et al, 2000;Tangri et al, 2003;Valdivia et al, 2003;Borovsky et al, 2003).…”

“…6d for β = 0.5). The existence of this regime depends strongly of the ratio η min /η max (Tangri et al, 2003). These oscillations may be related to some periods in which the magnetosphere seems to be oscillating, i.e., saw-tooth like oscillations (see Fig.…”

Hysteresis Provides Self-Organization in a Plasma Model

“…For J c η min < S 0 < S p , we can have a quasi-periodic situation (see Valdivia et al, 2005 for an example using β = 0.5). This regime depends on the ratio η min /η max and β (Tangri et al, 2003). 2.…”