Exploration of the Super H-mode Regime on DIII-D and Potential Advantages for Burning Plasma Devices PDF Download
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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.
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Languages : en
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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: National Academies of Sciences, Engineering, and Medicine
Publisher: National Academies Press
ISBN: 0309487463
Category : Science
Languages : en
Pages : 341
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Fusion offers the prospect of virtually unlimited energy. The United States and many nations around the world have made enormous progress toward achieving fusion energy. With ITER scheduled to go online within a decade and demonstrate controlled fusion ten years later, now is the right time for the United States to develop plans to benefit from its investment in burning plasma research and take steps to develop fusion electricity for the nation's future energy needs. At the request of the Department of Energy, the National Academies of Sciences, Engineering, and Medicine organized a committee to develop a strategic plan for U.S. fusion research. The final report's two main recommendations are: (1) The United States should remain an ITER partner as the most cost-effective way to gain experience with a burning plasma at the scale of a power plant. (2) The United States should start a national program of accompanying research and technology leading to the construction of a compact pilot plant that produces electricity from fusion at the lowest possible capital cost.
Author: National Academies of Sciences, Engineering, and Medicine
Publisher: National Academies Press
ISBN: 0309469333
Category : Science
Languages : en
Pages : 61
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In January 2003, President George W. Bush announced that the United States would begin negotiations to join the ITER project and noted that "if successful, ITER would create the first fusion device capable of producing thermal energy comparable to the output of a power plant, making commercially viable fusion power available as soon as 2050." The United States and the other ITER members are now constructing ITER with the aim to demonstrate that magnetically confined plasmas can produce more fusion power than the power needed to sustain the plasma. This is a critical step towards producing and delivering electricity from fusion energy. Since the international establishment of the ITER project, ITER's construction schedule has slipped and ITER's costs have increased significantly, leading to questions about whether the United States should continue its commitment to participate in ITER. This study will advise how to best advance the fusion energy sciences in the United States given developments in the field, the specific international investments in fusion science and technology, and the priorities for the next ten years developed by the community and the Office of Fusion Energy Sciences (FES) that were recently reported to Congress. It will address the scientific justification and needs for strengthening the foundations for realizing fusion energy given a potential choice of U.S. participation or not in the ITER project, and develops future scenarios in either case. This interim report assesses the current status of U.S. fusion research and of the importance of burning plasma research to the development of fusion energy as well as to plasma science and other science and engineering disciplines. The final report will present strategies that incorporate continued progress toward a burning plasma experiment and a focus on innovation.
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We continue to explore Quiescent Double Barrier (QDB) operation on DIII-D to address issues of critical importance to internal transport barrier (ITB) plasmas. QDB plasmas exhibit both a core transport barrier and a quiescent, H-mode edge barrier. Both experiments and modeling of these plasmas are leading to an increased understanding of this regime and it's potential advantages for advanced-tokamak (AT) burning-plasma operation. These near steady plasma conditions have been maintained on DIII-D for up to 4s, times greater than 35[tau][sub E], and exhibit high performance with [beta][sub N]> 2.5 and neutron production rates S[sub n] [approx] 1 x 10[sup 16]s[sup -1]. Recent experiments have been directed at exploring both the current profile modification effects of electron cyclotron current drive (ECCD) and electron cyclotron (ECH) heating-induced changes in temperature, density and impurity profiles. We use model-based analysis to determine the effects of both heating and current drive on the q-profile in these QDB plasmas. Experiments based on predictive modeling achieved a significant modification to the q-profile evolution [1] resulting from the non-inductive current drive effects due to direct ECCD and changes in the bootstrap and neutral beam current drive components. We observe that the injection of EC power inside the barrier region changes the density peaking from n[sub e]/n[sub e] = 2.1 to 1.5 accompanied by a significant reduction in the core carbon and high-Z impurities, nickel and copper.
Author: T. H. Osborne
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Languages : en
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We continue to explore Quiescent Double Barrier (QDB) operation on DIII-D to address issues of critical importance to internal transport barrier (ITB) plasmas. QDB plasmas exhibit both a core transport barrier and a quiescent, H-mode edge barrier. Both experiments and modeling of these plasmas are leading to an increased understanding of this regime and it's potential advantages for advanced-tokamak (AT) burning-plasma operation. These near steady plasma conditions have been maintained on DIII-D for up to 4s, times greater than 35{tau}{sub E}, and exhibit high performance with {beta}{sub N}> 2.5 and neutron production rates S{sub n} {approx} 1 x 10{sup 16}s{sup -1}. Recent experiments have been directed at exploring both the current profile modification effects of electron cyclotron current drive (ECCD) and electron cyclotron (ECH) heating-induced changes in temperature, density and impurity profiles. We use model-based analysis to determine the effects of both heating and current drive on the q-profile in these QDB plasmas. Experiments based on predictive modeling achieved a significant modification to the q-profile evolution [1] resulting from the non-inductive current drive effects due to direct ECCD and changes in the bootstrap and neutral beam current drive components. We observe that the injection of EC power inside the barrier region changes the density peaking from n{sub e}/n{sub e} = 2.1 to 1.5 accompanied by a significant reduction in the core carbon and high-Z impurities, nickel and copper.
![The Quiescent H-mode Regime for High Performance Edge Localized Mode-stable Operation in Future Burning Plasmas [The Quiescent H-mode Regime for High Performance ELM-stable Operation in Future Burning Plasmas]. PDF](https://books.google.com/books/content/images/frontcover/s8AHuAEACAAJ?fife=w80-h100)
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For the first time, DIII-D experiments have achieved stationary quiescent H-mode (QH-mode) operation for many energy confinement times at simultaneous ITER-relevant values of beta, confinement, and safety factor, in an ITER similar shape. QH-mode provides excellent energy confinement, even at very low plasma rotation, while operating without edge localized modes (ELMs) and with strong impurity transport via the benign edge harmonic oscillation (EHO). By tailoring the plasma shape to improve the edge stability, the QH-mode operating space has also been extended to densities exceeding 80% of the Greenwald limit, overcoming the long-standing low-density limit of QH-mode operation. In the theory, the density range over which the plasma encounters the kink-peeling boundary widens as the plasma cross-section shaping is increased, thus increasing the QH-mode density threshold. Here, the DIII-D results are in excellent agreement with these predictions, and nonlinear MHD analysis of reconstructed QH-mode equilibria shows unstable low n kink-peeling modes growing to a saturated level, consistent with the theoretical picture of the EHO. Furthermore, high density operation in the QH-mode regime has opened a path to a new, previously predicted region of parameter space, named "Super H-mode" because it is characterized by very high pedestals that can be more than a factor of two above the peeling-ballooning stability limit for similar ELMing H-mode discharges at the same density.
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OAK-B135 High confinement mode (H-mode) operation is a leading scenario for burning plasma devices due to its inherently high energy-confinement characteristics. The quiescent H-mode (QH-mode) offers these same advantages with the additional attraction of more steady edge conditions where the highly transient power loads due to edge localized mode (ELM) activity is replaced by the steadier power and particle losses associated with an edge harmonic oscillation (EHO). With the addition of an internal transport barrier (ITB), the capability is introduced for independent control of both the edge conditions and the core confinement region giving potential control of fusion power production for an advanced tokamak configuration. The quiescent double barrier (QDB) conditions explored in DIII-D experiments exhibit these characteristics and have resulted in steady plasma conditions for several confinement times ([approx] 26[tau][sub E]) with moderately high stored energy, [beta][sub N]H[sub 89][approx] 7 for 10[tau][sub E].
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Pages : 11
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A collaborative program has been initiated to measure helium (He) transport and exhaust on DIII-D in L-mode, ELM-free H-mode, and ELMing H-mode. These diverted plasmas operating in enhanced confinement regimes should provide valuable information for the International Thermonuclear Experimental Reactor (ITER). To simulate the presence of He ash in DIII-D, a 50 ms He puff is injected into a DIII-D plasma, resulting in a He concentration of [approximately] 15%. The time dependence of the He density profiles in the plasma core is measured with charge-exchange recombination spectroscopy and the He spatial distribution on the diverter floor is studied with an impurity monitor array. The dependence of core transport diffusivities as a function of ELM frequency have been studied and the first demonstration made of He exhaust from an H-mode plasma in a diverted tokamak. The exhaust rate of He from these ELMing H-mode plasmas appears to be within the acceptable range for a fusion reactor, like ITER, based on a measured value of [tau]*[sub He]/[tau]E [approx]14.
