Anomalous transport: Difference between revisions

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The difference between actual transport and the Neoclassical expectation is called "[[:Wiktionary:anomaly|anomalous]]" transport.
The difference between actual transport and the Neoclassical expectation is called "[[:Wiktionary:anomaly|anomalous]]" transport.
It is generally assumed that the anomalous component of transport is generated by turbulence driven by micro-instabilities.
It is generally assumed that the anomalous component of transport is generated by turbulence driven by micro-instabilities.
<ref name="Freidberg">J.P. Freidberg, ''Plasma physics and fusion energy'', Cambridge University Press (2007) ISBN 0521851076</ref>
<ref name="Freidberg">J.P. Freidberg, ''Plasma physics and fusion energy'', Cambridge University Press (2007) {{ISBN|0521851076}}</ref>


== How important is turbulence? ==
== How important is turbulence? ==
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It has been argued that turbulence cannot be responsible for a significant fraction of the anomalous component of transport, since that would lead to high resistivity (due to collisions), which contradicts experimental observation.
It has been argued that turbulence cannot be responsible for a significant fraction of the anomalous component of transport, since that would lead to high resistivity (due to collisions), which contradicts experimental observation.
<ref>L.C. Woods, ''Theory of tokamak transport: new aspects for nuclear fusion reactor design'', John Wiley and Sons (2006) ISBN 3527406255</ref>
<ref>L.C. Woods, ''Theory of tokamak transport: new aspects for nuclear fusion reactor design'', John Wiley and Sons (2006) {{ISBN|3527406255}}</ref>
However, this argument fails to note that anomalous transport may consist of collective events (e.g., ''streamers''), which does not require an enhanced collisionality.
However, this argument fails to note that anomalous transport may consist of collective events (e.g., ''streamers''), which does not require an enhanced collisionality.
As a side remark, this argument does show that the contribution of turbulence to transport is likely ''not'' of the diffusive type (see [[Non-diffusive transport]]).
As a side remark, this argument does show that the contribution of turbulence to transport is likely ''not'' of the diffusive type (see [[Non-diffusive transport]]).
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The plasma potentially produces a plethora of such instabilities, due to the fact that it is in a state far from thermodynamic equilibrium, with steep density, temperature, and pressure gradients.
The plasma potentially produces a plethora of such instabilities, due to the fact that it is in a state far from thermodynamic equilibrium, with steep density, temperature, and pressure gradients.
The most likely candidates involved in generating the observed anomalous transport are:
The most likely candidates involved in generating the observed anomalous transport are:
<ref>J. Weiland, ''Collective modes in inhomogeneous plasma: kinetic and advanced fluid theory'', Plasma physics series, CRC Press (2000) ISBN 0750305894</ref>
<ref>J. Weiland, ''Collective modes in inhomogeneous plasma: kinetic and advanced fluid theory'', Plasma physics series, CRC Press (2000) {{ISBN|0750305894}}</ref>
* Ion Temperature Gradient (ITG) instabilities
* Ion Temperature Gradient (ITG) instabilities
* Electron Temperature Gradient (ETG) instabilities
* Electron Temperature Gradient (ETG) instabilities

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