Impurity Transport in Tokamak Plasmas PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Impurity Transport in Tokamak Plasmas PDF full book. Access full book title Impurity Transport in Tokamak Plasmas by Peter Donnel. Download full books in PDF and EPUB format.
Author: Peter Donnel Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Impurity transport is an issue of utmost importance for tokamaks. Indeed high-Z materials are only partially ionized in the plasma core, so that they can lead to prohibitive radiative losses even at low concentrations, and impact dramatically plasma performance and stability. On-axis accumulation of tungsten has been widely observed in tokamaks.While the very core impurity peaking is generally attributed to neoclassical effects, turbulent transport could well dominate in the gradient region at ITER relevant collisionality. Up to recently, first principles simulations of corresponding fluxes were performed with different dedicated codes, implicitly assuming that both transport channels are separable and therefore additive. The validity of this assumption is questionned. Simulations obtained with the gyrokinetic code GYSELA have shown clear evidences of a neoclassical-turbulence synergy for impurity transport and allowed the identification of a mechanism that underly this synergy.An analytical work allows to compute the level and the structure of the axisymmetric part of the electric potential knowing the turbulence intensity. Two mechanisms are found for the generation of poloidal asymmetries of the electric potential: flow compressibility and the ballooning of the turbulence. A new prediction for the neoclassical impurity flux in presence of large poloidal asymmetries and pressure anisotropies has been derived. A fair agreement has been found between the new theoretical prediction for neoclassical impurity flux and the results of a GYSELA simulation displaying large poloidal asymmetries and pressure anisotropies induced by the presence of turbulence.
Author: Peter Donnel Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Impurity transport is an issue of utmost importance for tokamaks. Indeed high-Z materials are only partially ionized in the plasma core, so that they can lead to prohibitive radiative losses even at low concentrations, and impact dramatically plasma performance and stability. On-axis accumulation of tungsten has been widely observed in tokamaks.While the very core impurity peaking is generally attributed to neoclassical effects, turbulent transport could well dominate in the gradient region at ITER relevant collisionality. Up to recently, first principles simulations of corresponding fluxes were performed with different dedicated codes, implicitly assuming that both transport channels are separable and therefore additive. The validity of this assumption is questionned. Simulations obtained with the gyrokinetic code GYSELA have shown clear evidences of a neoclassical-turbulence synergy for impurity transport and allowed the identification of a mechanism that underly this synergy.An analytical work allows to compute the level and the structure of the axisymmetric part of the electric potential knowing the turbulence intensity. Two mechanisms are found for the generation of poloidal asymmetries of the electric potential: flow compressibility and the ballooning of the turbulence. A new prediction for the neoclassical impurity flux in presence of large poloidal asymmetries and pressure anisotropies has been derived. A fair agreement has been found between the new theoretical prediction for neoclassical impurity flux and the results of a GYSELA simulation displaying large poloidal asymmetries and pressure anisotropies induced by the presence of turbulence.
Author: Sanjay Gangadhara Publisher: ISBN: Category : Languages : en Pages : 6
Book Description
Understanding impurity transport in the scrape-off layer (SOL) of tokamak plasmas is a necessary piece of developing the physics basis for designing next-generation reactors. A system for inferring impurity transport parallel and perpendicular to local magnetic field lines has been developed on Alcator C-Mod using gas-injection "plumes". In this system, impurity gas is injected at a fixed position in the SOL via a reciprocating fast-scanning probe, and the resulting emission is imaged. In this paper visible light emission patterns from C+1 and C+2 ions are presented.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Particle orbits in a rotating tokamak plasma are calculated from the equation of motion in the frame that rotates with the plasma. It is found that heavy particles in a rotating plasma can drift away from magnetic surfaces significantly faster with a higher bounce frequency, resulting in a diffusion coefficient much larger than that for a stationary plasma. Particle orbits near the surface of a rotating tokamak are also analyzed. Orbit effects indicate that more impurities can penetrate into a plasma rotating with counter-beam injection. Particle simulation is carried out with realistic experimental parameters and the results are in qualitative agreement with some experimental observations in the Tokamak Fusion Test Reactor (TFTR). 19 refs., 15 figs.
Author: Matthew Logan Reinke Publisher: ISBN: Category : Languages : en Pages : 370
Book Description
In realistic reactor scenarios, high temperature plasmas will be composed of not only the fusion reactants and products, but also impurities introduced purposefully or unintentionally from plasma facing materials. In tokamaks it is often assumed, sometimes erroneously, that surfaces of constant main ion pressure are also surfaces of constant impurity pressure. Although the same underlying physics determine impurity momentum balance along closed magnetic field lines, the increased mass and charge of high-Z impurities weights terms differently. Their large mass enhances inertial effects like the centrifugal force from toroidal rotation, and( can lead to accumulation of heavy impurities on the outboard side of a flux surface. Their high charge enhances ion-impurity friction and makes impurities sensitive to small poloidal variations in the electrostatic potential. In Alcator C-Mod, 2D (R,Z) measurements of photon emission from high-Z impurities reveal significant variations of impurity density on a flux surface. Poloidal variations, normalized to the flux surface average, I 2/(n ) , have been measured up to ~ 1/3, and separate cases of impurities accumulating on the inboard and outboard side of a flux surface are observed, depending on local plasmas conditions. Experiments demonstrate that these asymmetries are due to a combination of inertia., poloidal electric fields and ion-impurity friction, and measurements are compared to existing neoclassical parallel impurity transport theory. This is the first time centrifugal force has been observed to cause a substantial asymmetry in a plasma with no external momentum input and where the flow is entirely self-generated. Magnetically trapped fast ions, sustained by ion cyclotron waves, create a poloidally varying electrostatic potential which causes high-Z impurities to accumulate on the inboard side. Existing theory is extended to include this effect by incorporating a species that has an anisotropic pressure tensor. Experimental measurements in plasmas where the minority resonance layer is scanned show good qualitative and quantitative agreement with this extended theory. The sensitivity of 51/(nz) to fast-ions demonstrates the opportunity for the impurity asymmetry to be used as a novel diagnostic tool and calls into question prior work on in/out asymmetries in neutral beam heated plasmas. /down asymmetries in the banana regime are unable to be explained by ion/impurity friction in the trace limit, nZZ 2 /n
Author: Francesco Sciortino Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
As a whole, this work provides one of the highest-fidelity assessments of cross-field impurity transport in tokamaks, offering the means to extend comparisons between theory and experiments in the particle transport channel.
Author: Peter Donnel
Author: Peter Donnel
Author: A. Ödblom
Author: F. Spineanu
Author: Sanjay Gangadhara
Author: Samuel Alan Cohen
Author: K. L. Wong
Author: 
Author: Matthew Logan Reinke
Author: W. M. Stacey (Jr)
Author: Francesco Sciortino