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Self-Organised Criticality: Difference between revisions
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Power degradation shows up in global transport scaling laws, and implies a sub-linear scaling of the plasma energy content with the injected power. | Power degradation shows up in global transport scaling laws, and implies a sub-linear scaling of the plasma energy content with the injected power. | ||
The basic explanation for this phenomenon is self-regulation of the profiles by turbulence. The strong temperature and density gradients in fusion-grade plasmas provide free energy that may drive turbulence. The turbulence then enhances transport locally, leading to a local reduction of gradients and a consequential dampling of the turbulence amplitude. This feedback could be responsible for keeping the gradients below a critical value. Considered locally, | The basic explanation for this phenomenon is self-regulation of the profiles by turbulence. The strong temperature and density gradients in fusion-grade plasmas provide free energy that may drive turbulence. The turbulence then enhances transport locally, leading to a local reduction of gradients and a consequential dampling of the turbulence amplitude. This feedback could be responsible for keeping the gradients below a critical value. Considered locally, the former is a description of a simple marginal state. | ||
But the interaction of such feedback mechanisms on various radial locations would lead to ''avalanche'' behaviour and a true (scale-free) self-organised state. | But the interaction of such feedback mechanisms on various radial locations would lead to ''avalanche'' behaviour and a true (scale-free) self-organised state. | ||
Indeed, there is evidence for avalanching behaviour in numerical simulations, but experimental evidence is scarce. | Indeed, there is direct evidence for avalanching behaviour in numerical simulations, but experimental evidence is scarce. | ||
<ref>[http://link.aps.org/doi/10.1103/PhysRevLett.84.1192 P.A. Politzer, Phys. Rev. Lett. '''84''', 1192 (2000)]</ref> | <ref>[http://link.aps.org/doi/10.1103/PhysRevLett.84.1192 P.A. Politzer, Phys. Rev. Lett. '''84''', 1192 (2000)]</ref> | ||
However, some indirect evidence exists. Typically, such evidence involves the detection of long-range correlations in fluctuations. | |||
<ref>[http://link.aip.org/link/?PHPAEN/6/1885/1 B.A. Carreras et al., Phys. Plasmas '''6''', 1885 (1999)]</ref> | |||
==References== | ==References== | ||
<references /> | <references /> | ||