Rotation and neoclassical ripple transport in ITER

Paul, Elizabeth; Landreman, Matt; Poli, F. M.; Spong, D. A.; Smith, H. M.; Dorland, W.

doi:10.1088/1741-4326/aa7fa4

Cited by 15 publications

(16 citation statements)

References 88 publications

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“…(2017) (for the time being, uses a pitch-angle scattering collision operator), and therefore retains the tangential magnetic drift (among the two codes mentioned some paragraphs above, does not retain the tangential magnetic drift, whereas a way to try to retain it in has been recently reported in Paul et al. 2017). Finally, a remark on the scope of this paper is in order.…”

Section: Introductionmentioning

confidence: 99%

Electrostatic potential variations on stellarator magnetic surfaces in low collisionality regimes

Calvo¹,

Velasco²,

Parra³

et al. 2018

J. Plasma Phys.

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The component of the neoclassical electrostatic potential that is non-constant on the magnetic surface, that we denote byφ, can affect radial transport of highly charged impurities, and this has motivated its inclusion in some modern neoclassical codes. The number of neoclassical simulations in whichφ is calculated is still scarce, partly because they are usually demanding in terms of computational resources, especially at low collisionality. In this paper the size, the scaling with collisionality and with aspect ratio, and the structure ofφ on the magnetic surface are analytically derived in the 1/ν, √ ν and superbanana-plateau regimes of stellarators close to omnigeneity; i. e. stellarators that have been optimized for neoclassical transport. It is found that the largestφ that the neoclassical equations admit scales linearly with the inverse aspect ratio and with the size of the deviation from omnigeneity. Using a model for a perturbed omnigeneous configuration, the analytical results are verified and illustrated with calculations by the code KNOSOS. The techniques, results and numerical tools employed in this paper can be applied to neoclassical transport problems in tokamaks with broken axisymmetry. † Recently, both the prevalence of the radial electric field in the transport of impurities and the absence of impurity screening in three-dimensional magnetic fields have been brought into question for several collisionality regimes Helander et al. 2017).

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Section: Introductionmentioning

confidence: 99%

Electrostatic potential variations on stellarator magnetic surfaces in low collisionality regimes

Calvo¹,

Velasco²,

Parra³

et al. 2018

J. Plasma Phys.

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“…The amplitude of the ripples is clearly lower when the number of toroidal coils is higher. For example, in JET tokamak, by reducing the number of coils from 32 to 16, the ripples level increased from 1 to 10% [18][19][20][21][22][23][24]. As we see in Figs.…”

Section: Experimental Setup and Resultsmentioning

confidence: 70%

“…is the thermal speed of species j and cj is the gyrofrequency. Physically, it means that the effective collision frequency eff = ∕ is less than the bounce time of a ripple-trapped particle b = 1∕2 v Th N∕R , but higher than the drift frequency circa of a complete superbanana orbit in the mirror azimuth of the torus [8][9][10][11].…”

Section: Ripple Transportmentioning

confidence: 99%

Ripple transport and neoclassical diffusion in IR-T1 tokamak

2019

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In tokamaks, small variations in the magnetic field create ripple. The discontinuous nature of the magnetic field coils in an axisymmetric torus conduces to additional particle trapping, and it is responsible for an additional neoclassical diffusion. Ripples also reduce the particle removal efficiency and disturb plasma confinement and cause constraints in the design of magnet of fusion reactor. Therefore, it is quite important to include the ripple for the design of plasma edge components. Herein, several considerations are taken into account to calculate and evaluate the diffusion coefficient and ion heat conductivity in ripple transport and also to compare it with neoclassical mode.

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“…We also do not consider the effects of magnetic drifts tangential to the flux surface in (2.1), as these only become important when is small (Paul et al. 2017).…”

Section: Drift Kinetic Equationmentioning

confidence: 99%

An adjoint method for neoclassical stellarator optimization

et al. 2019

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Received xx; revised xx; accepted xx)Stellarators are a promising route to steady-state fusion power. However, to achieve the required confinement, the magnetic geometry must be highly optimized. This optimization requires navigating high-dimensional spaces, often necessitating the use of gradient-based methods. The gradient of the neoclassical fluxes is expensive to compute with classical methods, requiring O(N ) flux computations, where N is the number of parameters. To reduce the cost of the gradient computation, we present an adjoint method for computing the derivatives of moments of the neoclassical distribution function for stellarator optimization. The linear adjoint method allows derivatives of quantities which depend on solutions of a linear system, such as moments of the distribution function, to be computed with respect to many parameters from the solution of only two linear systems. This reduces the cost of computing the gradient to the point that the finite-collisionality neoclassical fluxes can be used within an optimization loop.With the neoclassical adjoint method, we compute solutions of the drift kinetic equation and an adjoint drift kinetic equation to obtain derivatives of neoclassical quantities with respect to geometric parameters. When the number of parameters in the derivative is large (O(10 2 )), this adjoint method provides up to a factor of 200 reduction in cost. We demonstrate adjoint-based optimization of the field strength to obtain minimal bootstrap current on a surface. With adjoint-based derivatives, we also compute the local sensitivity to magnetic perturbations on a flux surface and identify regions where tight tolerances on error fields are required for control of the bootstrap current or radial transport. Furthermore, the solve for the ambipolar electric field is accelerated using a Newton method with derivatives obtained from the adjoint method.

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Rotation and neoclassical ripple transport in ITER

Cited by 15 publications

References 88 publications

Electrostatic potential variations on stellarator magnetic surfaces in low collisionality regimes

Electrostatic potential variations on stellarator magnetic surfaces in low collisionality regimes

Ripple transport and neoclassical diffusion in IR-T1 tokamak

An adjoint method for neoclassical stellarator optimization

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