<i>Tokamaks</i>

Wesson, John; Sen, Amiya K.

doi:10.1063/1.2811022

Cited by 80 publications

(87 citation statements)

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“…In the present modeling it is found that it is impossible to match the experimental radial profile of plasma density in the SOL using a spatially uniform anomalous plasma diffusion coefficient D 1 . As an illustrative case, we solve for 2-D plasma profiles using UEDGE with various values of spatially constant anomalous plasma diffusion coefficient D 1 .…”

Section: Modeling Of Radial Profiles Of Plasma Density and Tempermentioning

confidence: 93%

Modeling of particle and energy transport in the edge plasma of Alcator C-Mod

et al. 1999

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Mat., 196, (1992)]. Matching the experimental plasma density profiles in the scrape-off layer (SOL) requires a spatially dependent effective anomalous diffusion coefficient D 1 growing rapidly towards the wall. The mid-plane pressure of neutral gas, Pmid, is a key parameter that reflects the magnitude of anomalous transport of plasma from the core. Recycling of plasma on the main chamber wall appears to be quite significant, especially in the case of high Pmid ~ 0.3 mTorr when the main wall provides ~ 70% of recycling neutrals in the main chamber. In the upper SOL (well above the x-point) draining of particles by the poloidal flow is weak and thus the particle balance is predominantly radial. For the radial heat transport it is found that energy flux carried by radial plasma convection and by charge-exchange (CX) neutrals is quite significant in SOL. In the high Pmid case, heat conduction by CX neutrals along with radial heat convection by plasma carries most of the power flux (~ 75 %) across the last closed flux surface. In the low Pmid

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Section: Modeling Of Radial Profiles Of Plasma Density and Tempermentioning

confidence: 93%

Modeling of particle and energy transport in the edge plasma of Alcator C-Mod

et al. 1999

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“…An analytical treatment of the orbit motion in the R − z plane can be found in Ref. [16], and a simple expression for the y drift in the small-limit is given by v y (z) = (v ∇B + v curv ) h(z) (see, e.g., Ref. [9]) where h(z) ≡ cos z +ŝz sin z andŝ(r) = r/q(r)dq(r)/dr.…”

Section: Particle Motionmentioning

confidence: 99%

“…Depending on the pitch angle, the particles are passing or trapped (see, e.g., Ref. [16]), and in both cases, their motion can be described -in a field-aligned coordinate system -as a superposition of a "circular" (or slightly elliptical) periodic motion and a constant drift in the binormal direction, in analogy with the usual gyromotion. So we will have to ask whether the effects of gyroaveraging (well understood for the 2D case) will translate into some kind of "orbit averaging" in three dimensions, and to what extent the particle drifts generated by curvature and grad-B drifts (in the 3D case) can lead to effects which resemble those observed in two dimensions.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms and scalings of energetic ion transport via tokamak microturbulence

Hauff

Jenko

2008

Physics of Plasmas

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The turbulent E × B advection of energetic ions in 3D tokamak geometry is investigated both analytically and numerically. It is shown that orbit averaging (leading to a significant reduction of the diffusivity) is only valid for low magnetic shear. At moderate or high magnetic shear, a rather slow decrease of the diffusivity is found, proportional to (E/Te) −1 or (E/Te) −1.5 for particles with a large or small parallel velocity component, respectively. The decorrelation mechanisms responsible for this behavior are studied and explained in detail. Moreover, it is found that resonances between the toroidal drift of the particles and the diamagnetic drift of the turbulence can lead to an enhancement of the fast ion transport.

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“…The plasma pressure normalized by the magnetic energy β = 8πp/B 2 is called plasma beta, and is one of the important parameters of fusion plasmas because it is linked to the fusion reaction rate (Sec. 3.5 in Wesson (2004) and Sec. 5.3 in Freidberg (2007)) and also related to the production of bootstrap current (Sec.…”

Section: Introductionmentioning

confidence: 99%

Electromagnetic gyrokinetic simulation of turbulence in torus plasmas

et al. 2015

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Gyrokinetic simulations of electromagnetic turbulence in magnetically confined torus plasmas including tokamak and heliotron/stellarator are reviewed. Numerical simulation of turbulence in finite beta plasmas is an important task for predicting the performance of fusion reactors and a great challenge in computational science due to multiple spatio-temporal scales related to electromagnetic ion and electron dynamics. The simulation becomes further challenging in non-axisymmetric plasmas. In finite beta plasmas, magnetic perturbation appears and influences some key mechanisms of turbulent transport, which include linear instability and zonal flow production. Linear analysis shows that the ion-temperature gradient (ITG) instability, which is essentially an electrostatic instability, is unstable at low beta and its growth rate is reduced by magnetic field line bending at finite beta. On the other hand, the kinetic ballooning mode (KBM), which is an electromagnetic instability, is destabilized at high beta. In addition, trapped electron modes (TEMs), electron temperature gradient (ETG) modes, and micro-tearing modes (MTMs) can be destabilized. These instabilities are classified into two categories: ballooning parity and tearing parity modes. These parities are mixed by nonlinear interactions, so that, for instance, the ITG mode excites tearing parity modes. In the nonlinear evolution, the zonal flow shear acts to regulate the ITG driven turbulence at low beta. On the other hand, at finite beta, interplay between the turbulence and zonal flows becomes complicated because the production of zonal flow is influenced by the finite beta effects. When the zonal flows are too weak, turbulence continues to grow beyond a physically relevant level of saturation in finite-beta tokamaks. Nonlinear mode coupling to stable modes can play a role in the saturation of finite beta ITG mode and KBM. Since there is a quadratic conserved quantity, evaluating nonlinear transfer of the conserved quantity from unstable modes to stable modes is useful for understanding the saturation mechanism of turbulence.

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Tokamaks

Cited by 80 publications

References 0 publications

Modeling of particle and energy transport in the edge plasma of Alcator C-Mod

Modeling of particle and energy transport in the edge plasma of Alcator C-Mod

Mechanisms and scalings of energetic ion transport via tokamak microturbulence

Electromagnetic gyrokinetic simulation of turbulence in torus plasmas

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