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Scaling law: Difference between revisions
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* make performance comparisons between devices | * make performance comparisons between devices | ||
* make educated guesses at local transport mechanisms | * make educated guesses at local transport mechanisms | ||
== Confinement time scaling == | |||
The main performance parameter that is subjected to scaling law analysis is the [[Energy confinement time|energy confinement time]], τ<sub>E</sub>. ''(Sources for standard scaling laws needed)'' | |||
== Power degradation == | |||
One of the remarkable and initially unexpected properties of magnetically confined plasmas is the reduction of the [[Energy confinement time|energy confinement time]], τ<sub>E</sub> as the heating power ''P'' is increased. Typically: | |||
:<math>\tau_E \propto P^{-\alpha}</math> | |||
where α has a value of about 0.7. The reason for this behaviour has not been fully clarified. However, it seems obvious that an increase of ''P'' will lead to an increase of (temperature and density) gradients, and thus an increase of "free energy" available to instabilities and turbulence. This then leads to an increase of transport, producing the observed confinement degradation. | |||
This phenomenon is therefore due to plasma self-organsation (see [[Self-Organised Criticality]]). | |||
== References == | == References == | ||
<references /> | <references /> | ||