Anomalous transport: Difference between revisions

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 === Arguments in favour ===
-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. The phenomenon of [[Scaling law|power degradation]], universally observed in all devices, is an indication that standard (linear, diffusive) transport theories are inadequate to explain all transport, since these would not predict power degradation.
+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. The phenomenon of [[Scaling law|power degradation]], universally observed in all devices, is an indication that standard transport theories are inadequate to explain all transport, since these would not predict power degradation.
-However, the matter is complicated by the fact that the transport coefficients themselves are functions of the (local) plasma parameters, so that the (non-anomalous) transport theory becomes non-linear.
+Following Freidberg,
+<ref>J.P. Freidberg, ''Plasma physics and fusion energy'', Cambridge University Press (2007) ISBN	0521851076</ref>
+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: ''&tau;<sub>E</sub>'' &prop; ''T<sup>0.5</sup>'', associated with collisionality).
+However, the experimental scalings give a ''decrease'' with ''T''
+(namely: ''&tau;<sub>E</sub>'' &prop; ''T<sup>&alpha;</sup>'' with '' &alpha;'' &lt; -1).
+This unexpected behaviour is explained from increased turbulence levels (and enhanced transport) at higher values of (the gradients of) ''T''.
 [[Profile consistency]] indicates that [[Self-Organised Criticality|self-organisation]] plays an important role in transport, and this can only be the case when instabilities or turbulence are able to regulate the profiles, i.e., when they carry an important fraction of transport.