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Neoclassical transport: Difference between revisions
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The theory takes account of all particle motion associated with toroidal geometry; specifically, ''∇ B'' and curvature drifts, and passing and trapped particles (banana orbits). | The theory takes account of all particle motion associated with toroidal geometry; specifically, ''∇ B'' and curvature drifts, and passing and trapped particles (banana orbits). | ||
The theory is valid for all collisionality regimes, and includes effects due to resistivity and viscosity. An important prediction of the theory is the [[Bootstrap current|bootstrap current]]. | The theory is valid for all [[Collisionality|collisionality]] regimes, and includes effects due to resistivity and viscosity. An important prediction of the theory is the [[Bootstrap current|bootstrap current]]. | ||
''(Further detail needed)'' | ''(Further detail needed)'' | ||
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Neoclassical theory is based on a set of assumptions that limit its range of applicability and explain why it is not capable of predicting transport in all magnetic confinement devices and under all circumstances. | Neoclassical theory is based on a set of assumptions that limit its range of applicability and explain why it is not capable of predicting transport in all magnetic confinement devices and under all circumstances. | ||
These are: | These are: | ||
* Maxwellianity. This assumption implies that a certain minimum level of collisionality is needed in order to ensure that Maxwellianisation is effective. The strong drives and resulting gradients that characterise fusion-grade plasmas often lead to a violation of this assumption. | * Maxwellianity. This assumption implies that a certain minimum level of [[Collisionality|collisionality]] is needed in order to ensure that Maxwellianisation is effective. The strong drives and resulting gradients that characterise fusion-grade plasmas often lead to a violation of this assumption. | ||
* A fixed geometry. Neoclassical transport is calculated in a static magnetic geometry. In actual experiments (especially Tokamaks), the magnetic field evolves along with the plasma itself, leading to a modification of net transport. While a slow evolution (with respect to typical transport time scales) should not be problematic, rapid changes (such as magnetic reconnections) are outside of the scope of the theory. | * A fixed geometry. Neoclassical transport is calculated in a static magnetic geometry. In actual experiments (especially Tokamaks), the magnetic field evolves along with the plasma itself, leading to a modification of net transport. While a slow evolution (with respect to typical transport time scales) should not be problematic, rapid changes (such as magnetic reconnections) are outside of the scope of the theory. | ||
* The linearity of the model. Neoclassical theory is a linear theory in which profiles are computed from sources, boundary conditions, and transport coefficients (that depend linearly on the profiles). No non-linear feedback of the profiles on the transport coefficients is contemplated. However, there are many experimental studies that show that the profiles feed back non-linearly on transport (via [[TJ-II:Turbulence|turbulence]]), leading to some degree of [[Self-Organised Criticality|self-organisation]]. | * The linearity of the model. Neoclassical theory is a linear theory in which profiles are computed from sources, boundary conditions, and transport coefficients (that depend linearly on the profiles). No non-linear feedback of the profiles on the transport coefficients is contemplated. However, there are many experimental studies that show that the profiles feed back non-linearly on transport (via [[TJ-II:Turbulence|turbulence]]), leading to some degree of [[Self-Organised Criticality|self-organisation]]. | ||