Experimental Measurements and Modeling of Impurity Transport in the Divertor and Boundary Plasma of DIII-D. PDF Download
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Languages : en
Pages : 4
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Analysis of trace impurity injection experiments on DIII-D during a beam power scan is presented. Spectroscopic measu- rements indicate that as beam power is increased, and concomitantly ELM frequency and scrape-off-layer thickness increase while energy confinement decreases, the core impurity content decreases only slightly. Modeling of the edge plasma using the UEDGE 2D and NEWT1D plasma fluid codes indicate that as beam power is increased, the parallel forces on an impurity ion increase in the direction from the divertor and toward the core plasma. Experiments using the divertor cryopump to induce higher parallel particle flow toward the divertor demonstrate significant reduction in core impurity content. These results indicate that parallel forces on impurity ions in the scrape off layer are playing a significant role in core impurity content.
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Category :
Languages : en
Pages : 4
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Book Description
Analysis of trace impurity injection experiments on DIII-D during a beam power scan is presented. Spectroscopic measu- rements indicate that as beam power is increased, and concomitantly ELM frequency and scrape-off-layer thickness increase while energy confinement decreases, the core impurity content decreases only slightly. Modeling of the edge plasma using the UEDGE 2D and NEWT1D plasma fluid codes indicate that as beam power is increased, the parallel forces on an impurity ion increase in the direction from the divertor and toward the core plasma. Experiments using the divertor cryopump to induce higher parallel particle flow toward the divertor demonstrate significant reduction in core impurity content. These results indicate that parallel forces on impurity ions in the scrape off layer are playing a significant role in core impurity content.
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Category : Aeronautics
Languages : en
Pages : 548
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Category : Power resources
Languages : en
Pages : 782
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Author:
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Category : Aeronautics
Languages : en
Pages : 1148
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Category :
Languages : en
Pages : 33
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In a magnetically diverted tokamak, the scrape-off layer (SOL) and divertor plasma provides separation between the first wall and the core plasma, intercepting impurities generated at the wall before they reach the core plasma. The divertor plasma can also serve to spread the heat and particle flux over a large area of divertor structure wall using impurity radiation and neutral charge exchange, thus reducing peak heat and particle fluxes at the divertor strike plate. Such a reduction will be required in the next generation of tokamaks, for without it, the divertor engineering requirements are very demanding. To successfully demonstrate a radiative divertor, a highly radiative condition with significant volume recombination must be achieved in the divertor, while maintaining a low impurity content in the core plasma. Divertor plasma properties are determined by a complex interaction of classical parallel transport, anomalous perpendicular transport, impurity transport and radiation, and plasma wall interaction. In this paper the authors describe a set of experiments on DIII-D designed to provide detailed two dimensional documentation of the divertor and SOL plasma. Measurements have been made in operating modes where the plasma is attached to the divertor strike plate and in highly radiating cases where the plasma is detached from the divertor strike plate. They also discuss the results of experiments designed to influence the distribution of impurities in the plasma using enhanced SOL plasma flow. Extensive modeling efforts will be described which are successfully reproducing attached plasma conditions and are helping to elucidate the important plasma and atomic physics involved in the detachment process.
Author:
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ISBN:
Category : Science
Languages : en
Pages : 584
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Category : Controlled fusion
Languages : en
Pages : 838
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Author: K. Herschbach
Publisher: Newnes
ISBN: 0444599738
Category : Technology & Engineering
Languages : en
Pages : 892
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The objective of the Symposium on Fusion Technology (SOFT) conference is to set the stage for the exchange of information on the design, construction, and operation of fusion experiments and the technology which is being developed for the next-step devices and for fusion reactors. These proceedings therefore present an up-to-date and throrough review of the state-of-the art in this dynamic field.
Author: Matthew Parsons
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Tungsten is a commonly used material in the divertor of fusion reactors, a region in which the plasma-facing components are exposed to extreme fluxes of particles and heat being exhausted from the reactor core. The interaction between the plasma ions and the solid tungsten plasma-facing components leads to an erosion of the tungsten surfaces. When those tungsten particles enter the plasma, they are able to migrate to the core where they radiative away power and cool down the plasma. In order to maintain a hot enough core to produce net energy from a fusion reactor, only a small concentration of tungsten can be tolerated in the core. As such, it is necessary to develop strategies to minimize the amount of tungsten which leaks out of the divertor and migrates to the core. In order for tungsten impurities to reach the core, they must travel along the Scrape-off-Layer boundary region. Tungsten transport along the Scrape-off-Layer is understood to be primarily a balance between frictional forces acting to bring tungsten impurities downstream to the divertor targets and an ion temperature gradient force which acts to bring tungsten impurities upstream toward the core. In principle, it should be possible to change the balance of these forces, and in turn the amount of tungsten arriving in the core. This dissertation explores the potential of injecting impurities with a small atomic number Z to manipulate the forces acting on tungsten in the Scrape-off-Layer, with the goal of minimizing the amount of tungsten reaching the plasma core. In this dissertation, an experiment in the DIII-D tokamak is developed and carried out to assess tungsten divertor leakage under a variety of low-Z impurity injection conditions. Measurements of the tungsten content of the plasma upstream from the divertor region have been made using collector probes, along with simultaneous measurement of the rate of tungsten erosion from the divertor. Analysis of this data, including the pattern of tungsten deposition along the probes, clearly indicates that tungsten divertor leakage and Scrape-off-Layer transport are impacted by a combination of the injection rate and injection location of low-Z impurity gas. To understand the physical mechanisms leading to this change in tungsten transport, improvements have been made to a widely used code for modeling tungsten transport. Namely, the models used for the friction and ion temperature gradient forces in the DIVIMP impurity tracing code have been updated to include the effects of low-Z impurity interaction with tungsten. This enables a workflow using the SOLPS-ITER code plus DIVIMP to model tungsten transport in the Scrape-off-Layer in scenarios with low-Z impurity injection, which previously was not possible with the DIVIMP code and is prohibitively computer-intensive for the SOLPS-ITER code alone. Interpretive modeling of the DIII-D experiment, using the updated approach with SOLPS-ITER + DIVIMP, shows that the low-Z impurities play a critical role in determining the transport of tungsten impurities in the Scrape-off-Layer. Increased particle collisionality in the divertor during low-Z impurity injection enhances the ability of the friction force to retain tungsten impurities in the divertor. Further, suppression of the ion temperature gradient force, both due to radiative cooling during low-Z impurity injection and due to a change in the collisional dynamics in the presence of low-Z impurities, acts further to reduce tungsten divertor leakage. The combination of experimental and modeling results in this dissertation demonstrate clearly that low-Z impurity injection is a viable actuator to reduce tungsten divertor leakage in tokamaks.
Author: Ruth Laengner
Publisher: Forschungszentrum Jülich
ISBN: 3893369244
Category :
Languages : en
Pages : 175
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