Scaling law: Difference between revisions
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:<math>\tau_E \propto P^{-\alpha}</math> | :<math>\tau_E \propto P^{-\alpha}</math> | ||
where α has a value of | where α has a value of 0.6 ± 0.1. 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]]). | This phenomenon is therefore due to plasma self-organsation (see [[Self-Organised Criticality]]). | ||
== References == | == References == | ||
<references /> | <references /> | ||
Revision as of 12:34, 11 September 2009
Scaling laws are an engineering tool to predict the performance of a system as a function of some significant parameters. [1] Its extended use in magnetic confinement physics reflects the fact that detailed transport calculations or predictions on first principles are difficult in this field. In the latter context, they are mainly used to
- predict the performance of new (larger) devices, such as ITER
- summarize large amounts of experimental data
- make performance comparisons between devices
- 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, τE. (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, τE as the heating power P is increased. Typically:
where α has a value of 0.6 ± 0.1. 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
- ↑ O.J.W.F. Kardaun, Classical methods of statistics: with applications in fusion-oriented plasma physics, Springer Science & Business (2005) ISBN 3540211152