4,378
edits
Anomalous transport: Difference between revisions
no edit summary
No edit summary |
|||
| (10 intermediate revisions by 4 users not shown) | |||
| Line 4: | Line 4: | ||
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? == | ||
| Line 13: | Line 13: | ||
<ref>[http://dx.doi.org/10.1088/0741-3335/36/5/002 J.W. Conner and H.R. Wilson, ''Survey of theories of anomalous transport'', Plasma Phys. Control. Fusion '''36''' (1994) 719-795]</ref> | <ref>[http://dx.doi.org/10.1088/0741-3335/36/5/002 J.W. Conner and H.R. Wilson, ''Survey of theories of anomalous transport'', Plasma Phys. Control. Fusion '''36''' (1994) 719-795]</ref> | ||
=== Arguments | === Arguments for === | ||
An important argument suggesting that anomalous transport is important to the degree that it often dominates the total transport is the [[Scaling law|scaling]] of transport with heating power and machine size. | An important argument suggesting that anomalous transport is important to the degree that it often dominates the total transport is the [[Scaling law|scaling]] of transport with heating power and machine size. | ||
| Line 21: | Line 21: | ||
<ref name="Freidberg" /> | <ref name="Freidberg" /> | ||
the cited [[Scaling law|scaling laws]] can be rewritten in terms of the temperature dependence (eliminating the heating power dependence). | the cited [[Scaling law|scaling laws]] can be rewritten in terms of the temperature dependence (eliminating the heating power dependence). | ||
Then, classical and neoclassical estimates would predict that the confinement increases with ''T'' (namely: ''τ<sub>E</sub>'' ∝ ''T<sup>0.5</sup>'', associated with collisionality). | Then, classical and neoclassical estimates would predict that the confinement increases with ''T'' (namely: ''τ<sub>E</sub>'' ∝ ''T<sup>0.5</sup>'', associated with [[Collisionality|collisionality]]). | ||
However, the experimental scalings give a ''decrease'' with ''T'' | However, the experimental scalings give a ''decrease'' with ''T'' | ||
(namely: ''τ<sub>E</sub>'' ∝ ''T<sup>α</sup>'' with '' α'' < -1). | (namely: ''τ<sub>E</sub>'' ∝ ''T<sup>α</sup>'' with '' α'' < -1). | ||
| Line 33: | Line 33: | ||
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]]). | ||
| Line 41: | Line 41: | ||
The physical mechanism behind anomalous transport has not been fully clarified. | The physical mechanism behind anomalous transport has not been fully clarified. | ||
However, it is generally assumed that anomalous transport is the consequence of microscopic instabilities. | However, it is generally assumed that anomalous transport is the consequence of microscopic instabilities. | ||
The plasma potentially produces a plethora of such instabilities. | 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> | |||
* Ion Temperature Gradient (ITG) instabilities | * Ion Temperature Gradient (ITG) instabilities | ||
* Electron Temperature Gradient (ETG) instabilities | * Electron Temperature Gradient (ETG) instabilities | ||
* | * Collisionless Trapped Electron Modes (TEM) <ref>[http://link.aps.org/doi/10.1103/PhysRevLett.33.1329 B. Coppi and G. Rewoldt, ''New Trapped-Electron Instability'', Phys. Rev. Lett. '''33''' (1974) 1329 - 1332]</ref> <ref>[http://link.aps.org/doi/10.1103/PhysRevLett.95.085001 F. Ryter et al, ''Experimental Study of Trapped-Electron-Mode Properties in Tokamaks: Threshold and Stabilization by Collisions'', Phys. Rev. Lett. '''95''' (2005) 085001]</ref> | ||
* Dissipative Trapped Electron Modes (DTEM) | |||
''(to be completed; references needed)'' | ''(to be completed; references needed)'' | ||