Edge Localized Mode Control in DIII-D Using Magnetic Perturbation-Induced Pedestal Transport Changes 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 Edge Localized Mode Control in DIII-D Using Magnetic Perturbation-Induced Pedestal Transport Changes PDF full book. Access full book title Edge Localized Mode Control in DIII-D Using Magnetic Perturbation-Induced Pedestal Transport Changes by R. Schneider. Download full books in PDF and EPUB format.
Author: R. Schneider
Publisher:
ISBN:
Category :
Languages : en
Pages : 11
Get Book Here
Book Description
Edge localized mode (ELM) control is a critical issue for ITER because the impulsive power loading from ELMs is predicted to limit the divertor lifetime to only a few hundred full-length pulses. Consequently, a technique that replaces the ELM-induced transport with more continuous transport while preserving the H-mode pedestal height and core performance would significantly improve the viability of ITER. One approach is to use edge resonant magnetic perturbations (RMPs) to enhance pedestal transport enough to reduce the pedestal pressure gradient {del}p{sub ped} below the stability limit for Type I ELMs. In DIII-D, n = 3 RMPs have been used to eliminate Type I ELMs when the edge safety factor is in the resonant window q95 {approx} 3.5 without degrading confinement in H-modes with ITER-relevant pedestal collisionalities v*{sub e} {approx} 0.2. The RMP reduces {del}p{sub ped} as expected, with {del}p{sub ped} controlled by the RMP amplitude. Linear peeling-ballooning (P-B) stability analysis indicates that the ELMs are suppressed by reducing {del}p{sub ped} below the P-B stability limit. The {del}p{sub ped} reduction results primarily from an increase in particle transport, not electron thermal transport. This result is inconsistent with estimates based on quasi-linear stochastic diffusion theory based on the vacuum field (no screening of the RMP). The particle transport increase is accompanied by changes in toroidal rotation, radial electric field, and density fluctuation level {tilde n} in the pedestal, suggesting increased fluctuation-driven particle transport.
Author: R. Schneider
Publisher:
ISBN:
Category :
Languages : en
Pages : 11
Get Book Here
Book Description
Edge localized mode (ELM) control is a critical issue for ITER because the impulsive power loading from ELMs is predicted to limit the divertor lifetime to only a few hundred full-length pulses. Consequently, a technique that replaces the ELM-induced transport with more continuous transport while preserving the H-mode pedestal height and core performance would significantly improve the viability of ITER. One approach is to use edge resonant magnetic perturbations (RMPs) to enhance pedestal transport enough to reduce the pedestal pressure gradient {del}p{sub ped} below the stability limit for Type I ELMs. In DIII-D, n = 3 RMPs have been used to eliminate Type I ELMs when the edge safety factor is in the resonant window q95 {approx} 3.5 without degrading confinement in H-modes with ITER-relevant pedestal collisionalities v*{sub e} {approx} 0.2. The RMP reduces {del}p{sub ped} as expected, with {del}p{sub ped} controlled by the RMP amplitude. Linear peeling-ballooning (P-B) stability analysis indicates that the ELMs are suppressed by reducing {del}p{sub ped} below the P-B stability limit. The {del}p{sub ped} reduction results primarily from an increase in particle transport, not electron thermal transport. This result is inconsistent with estimates based on quasi-linear stochastic diffusion theory based on the vacuum field (no screening of the RMP). The particle transport increase is accompanied by changes in toroidal rotation, radial electric field, and density fluctuation level {tilde n} in the pedestal, suggesting increased fluctuation-driven particle transport.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 10
Get Book Here
Book Description
We have made two significant discoveries in our recent studies of quiescent H-mode (QH-mode) plasmas in DIII-D. First, we have found that we can control the edge pedestal density and pressure by altering the edge particle transport through changes in the edge toroidal rotation. This allows us to adjust the edge operating point to be close to, but below the ELM stability boundary, maintaining the ELM-free state while allowing up to a factor of two increase in edge pressure. The ELM boundary is significantly higher in more strongly shaped plasmas, which broadens the operating space available for QH-mode and leads to improved core performance. Second, for the first time on any tokamak, we have created QH-mode plasmas with strong edge co-rotation; previous QH-modes in all tokamaks had edge counter rotation. This result demonstrates that counter NBI and edge counter rotation are not essential conditions for QH-mode. Both these investigations benefited from the edge stability predictions based on peeling-ballooning mode theory. The broadening of the ELM-stable region with plasma shaping is predicted by that theory. The theory has also been extended to provide a model for the edge harmonic oscillation (EHO) that regulates edge transport in the QH-mode. Many of the features of that theory agree with the experimental results reported either previously or in the present paper. One notable example is the prediction that co-rotating QH-mode is possible provided sufficient shear in the edge rotation can be created.
Author: Tyler Brett Cote
Publisher:
ISBN:
Category :
Languages : en
Pages : 193
Get Book Here
Book Description
Recent experimental observations have found toroidally localized MHD instabilities in the plasma edge during operation with applied magnetic perturbations on ASDEX Upgrade in H-mode with low collisionality. Large edge plasma displacements are induced by a stable kink response to the 3D magnetic perturbations. This kink response results in localized changes of geometric quantities, which in turn leads to the localization of MHD instabilities in the plasma edge. Infinite-n ideal MHD ballooning theory is shown to predict the existence of these instabilities, as well as the observed toroidal localization. Utilizing 3D VMEC equilibria, the local geometric parameters determining ideal stability, include the local magnetic shear, normal curvature, and geodesic curvature, are calculated for experimentally relevant conditions. It is found that these shaping parameters have significant levels of 3D variation, with the local magnetic shear being the dominant factor behind changes in the local geometry. This behavior leads to a significant decrease in the stabilizing line-bending energy for certain field lines, resulting in the localization of the ballooning instability. Furthermore, it is observed that a finite amount of magnetic perturbation (and subsequent edge perturbation) is necessary to modify the local geometry and excite the localized instability, leading to a threshold behavior. Additional experimental evidence suggests that this mechanism for destabilizing localized ballooning modes may have consequences for ELM stability during applied magnetic perturbations. The new PB3D code provides a framework for studying peeling-ballooning instabilities utilizing 3D VMEC equilibria but still requires significant testing and development. Axisymmetric benchmark exercises show PB3D fails to replicate the results of other MHD codes for experimentally relevant 2D equilibria. Errors in the current-peeling response implementation are identified as a possible source of these discrepancies, which future work will look to correct.
Author: Jonathan Robert Pearson
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Fast-ion transport caused by the combination of MHD and a mock-up test-blanket module (TBM) coil is measured in the DIII-D tokamak. The primary diagnostic is an infrared camera that measures the heat flux on the tiles surrounding the coil. The combined effects of the TBM and four other potential sources of transport are studied: neoclassical tearing modes, Alfén eigenmodes, sawteeth, and applied resonant magnetic perturbation fields for the control of edge localized modes. Lastly, a definitive synergistic effect is observed at sawtooth crashes where, in the presence of the TBM, the localized heat flux at a burst increases from 0.36 ± 0.27 to 2.6 ± 0.5 MW m$-$2.
Author: Jonathan Pearson
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 14
Get Book Here
Book Description
The tangentially viewing visible and vertically viewing infrared cameras systems on DIII-D were upgraded to permit emission measurements during edge localized modes (ELMs) with integration times as short as 1 and 100 [mu]s respectively. The visible system was used to obtain 2-D poloidal profiles of CIII (465 nm) and D{sub {alpha}} (656.3 nm) emission with 20 [mu]s integration during various stages of ELM events in the lower DIII-D divertor. The infrared (IR) system was used to measure the heat flux to the divertor targets at 10 kHz with 100 [mu]s exposure. Upgrades to the data processing and storage systems permitted efficient comparison of the temporal evolution of these measurements.
![H-mode and VH-mode Confinement Improvement in DIII-D: Investigations of Turbulence, Local Transport, and Active Control of the Shear in the E[times] B Flow PDF](https://books.google.com/books/content/images/frontcover/k735jwEACAAJ?fife=w80-h100)
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
The hypothesis of stabilization of turbulence by shear in the E[times] B drift speed successfully predicts the observed turbulence reduction and confinement improvement seen at the L to H transition. This same hypothesis is the best explanation to date for the further confinement improvement seen in the plasma core when the plasma goes from H-mode to VH-mode. Consequently, the most fundamental question for H-mode studies now is: how is the electric field E[sub r] formed? The radial force balance equation relates E[sub r] to the main ion pressure gradient[triangledown]P[sub i], poloidal rotation[nu][sub[theta]i], and toroidal rotation[nu][sub[phi]i]. In the plasma edge, direct measurements show[triangledown]P[sub i] and[nu][sub[theta]i] are the important terms at the L to H transition, with[triangledown]P[sub i] being the dominant, negative term throughout most of the H-mode. Since E[sub r] is observed to change prior to the change in[triangledown]P[sub i], the authors infer that main ion rotation, probably[nu][sub[theta]i], changes first, triggering the transition. E[sub r] is seen to change prior to the change in fluctuations, consistent with E[times] B shear causing the change in fluctuations and transport. In the plasma core, E[sub r] is primarily related to[nu][sub[phi]i]. There is a clear temporal and spatial correlation between the change in E[times] B shear and the region of local confinement improvement when the plasma goes from H-mode to VH-mode. Direct manipulation of[nu][sub[phi]i] and E[times] B shear using the drag produced by a non-axisymmetric magnetic perturbation has produced clear changes in local transport consistent with the E[times] B shear stabilization hypothesis. The implications of these results for theories of the L to H and H to VH transitions will be discussed. 83 refs., 5 figs.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
In a new high pedestal regime ("Super H-mode") we predicted and accessed DIII-D. Super H-mode was first achieved on DIII-D using a quiescent H-mode edge, enabling a smooth trajectory through pedestal parameter space. By exploiting Super H-mode, it has been possible to access high pedestal pressures at high normalized densities. And while elimination of Edge localized modes (ELMs) is beneficial for Super H-mode, it may not be a requirement, as recent experiments have maintained high pedestals with ELMs triggered by lithium granule injection. Simulations using TGLF for core transport and the EPED model for the pedestal find that ITER can benefit from the improved performance associated with Super H-mode, with increased values of fusion power and gain possible. In similar studies demonstrate that the Super H-mode pedestal can be advantageous for a steady-state power plant, by providing a path to increasing the bootstrap current while simultaneously reducing the demands on the core physics performance.
Author: Andrew Oakleigh Nelson
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
The H-mode pedestal, characterized by steep gradients and reduced transport, is an essential feature of tokamak plasmas that couples the cold Scrape-Off-Layer (SOL) to the hot, fusion-relevant core. Though existing magnetohydrodynamic models yield some insight into the pedestal, they are (due to the complexity of interaction between the pedestal and the rest of the plasma) unable to fully predict pedestal behavior from generalized plasma conditions. To progress towards a more comprehensive understanding of pedestal dynamics, a larger context must be considered. Using state-of-the-art modeling and perturbative experimental techniques on DIII-D, this thesis develops a broader empirical understanding of dynamic pedestal behavior that will inform future modeling efforts.The pedestal obeys the physics of the continuity equation, which is set by the sourcing of particles, inter-ELM transport, and boundary conditions. In this light, three phenomena are selected for in-depth study: fueling, transport, and SOL interactions. First, the effect of particle sources on the pedestal structure is examined through a series of dedicated experiments on DIII-D. Gas and pellet fueling techniques are applied to change the neutral ionization profile at similar plasma conditions, showing that the structure of the pedestal can vary significantly with changes to the neutral source profile. Second, a novel experimental technique is used to probe the nature of inter-ELM turbulence, which is linked to the evolution and recovery of the pedestal structure. Additional current is induced in the pedestal region of several DIII-D plasmas, providing a first-of-its-kind experimental demonstration of microtearing modes (MTMs) in the tokamak edge. MTMs may contribute strongly to intense heat fluxes through the pedestal region, potentially providing the groundwork for an entirely physics-based predictive model of pedestal behavior. Finally, to develop a physics understanding of how the SOL boundary condition couples with the pedestal over the course of an entire plasma discharge, detailed modeling work is performed with the UEDGE code as a function of pedestal and ELM conditions. In this section, we establish a dynamic connection between the pedestal structure and divertor behavior, highlighting the need for a comprehensive approach to pedestal physics.
