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Self-Organised Criticality: Difference between revisions
Self-Organised Criticality (view source)
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Self-Organised Criticality (SOC) is a generic concept, applicable to a host of complex systems | Self-Organised Criticality (SOC) is a generic concept, applicable to a host of complex systems | ||
<ref>[http://en.wikipedia.org/wiki/Self-organised_criticality Self-Organised | <ref>[http://en.wikipedia.org/wiki/Self-organised_criticality Self-Organised Criticality in the Wikipedia]</ref>. | ||
A system is said to be in this state when it is at an ''attractive'' critical point at which it behaves as in a phase transition (i.e., the spatial and temporal scales are scale-invariant, or nearly so). | A system is said to be in this state when it is at an ''attractive'' critical point at which it behaves as in a phase transition (i.e., the spatial and temporal scales are scale-invariant, or nearly so). | ||
Note that ordinary phase transitions are not attractive, and maintaining the system near such a phase transition point requires fine-tuning some system parameters. | Note that ordinary phase transitions are not attractive, and maintaining the system near such a phase transition point requires fine-tuning some system parameters. | ||
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This situation can only occur in systems that are ''not in equilibrium'', in which fluctuations provide a mechanism for regulating the system and keeping it close to criticality. | This situation can only occur in systems that are ''not in equilibrium'', in which fluctuations provide a mechanism for regulating the system and keeping it close to criticality. | ||
In magnetically confined plasmas, this state is thought to be responsible for the global transport phenomena of | In magnetically confined plasmas, this state is thought to be responsible for the global transport phenomena of: | ||
* [[profile consistency]], which is the observation that profiles tend to have roughly the same shape, regardless of the power and location of the applied heating.<ref>[http://dx.doi.org/10.1088/0741-3335/43/12A/325 F. Ryter et al., Plasma Phys. Control. Fusion '''43''', A323 (2001)]</ref> | |||
<ref>[http://dx.doi.org/10.1088/0741-3335/43/12A/325 F. Ryter et al., Plasma Phys. Control. Fusion '''43''', A323 (2001)]</ref> | * the [[Scaling law|Bohm scaling]] of confinement in L-mode (scaling of transport with system size) <ref>[http://dx.doi.org/10.1109/27.650902 B.A. Carreras, IEEE Trans. Plasma Science '''25''', 1281 (1997)]</ref>, and | ||
* power degradation, as reflected in global transport [[Scaling law|scaling laws]]. The scaling of the plasma energy content with injected power is generally found to be sub-linear, i.e., considerably worse than expected from simple diffusion. | |||
The basic explanation for these phenomena is self-regulation of the profiles by turbulence (see [[Anomalous transport]]). | The basic explanation for these phenomena is self-regulation of the profiles by turbulence (see [[Anomalous transport]]). | ||