Turbulence and Transport Measurements in Alcator C-Mod and Comparisons with Gyrokinetic Simulations PDF Download
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Author: Paul Chappell Ennever
Publisher:
ISBN:
Category :
Languages : en
Pages : 139
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Book Description
Turbulence in tokamak plasmas is the primary means by which energy is transported from the core of the plasma to the edge, where it is lost, and is therefore the main limitation of tokamak plasma performance. Dilution of the main-ion species was found to have a stabilizing effect on ion gyroradius scale turbulence in tokamak plasmas. Dilution of deuterium tokamak plasmas is the reduction of the ratio of the deuterium ion density to the electron density, nD=ne, to less than 1.0 through the introduction of low-Z impurity species into the plasma. Controlled dilution experiments were performed on Alcator C-Mod wherein plasmas at a range of electron density and plasma current were seeded with nitrogen while a cryopump held the electron density fixed. The electron density fluctuations due to turbulence were monitored using a phase contrast imaging (PCI) diagnostic, an absolutely calibrated diagnostic that measures the line-integral of the electron density fluctuations along 32 vertical chords. In these experiments the seeding reduced the PCI density fluctuations, and had a stabilizing effect on the ion energy transport. The seeding also reversed the direction of intrinsic rotation in certain cases. Nonlinear simulations using the gyrokinetic turbulence code GYRO were performed using measured kinetic profiles from the dilution experiments both before and after the nitrogen seeding. The GYRO simulations reproduced the observed reduction in the turbulent ion energy transport with the nitrogen seeding. The GYRO simulated turbulent density fluctuations were compared to the PCI measurements using a synthetic diagnostic, and they were found to be consistent. GYRO simulations were also performed varying only the main ion dilution to explore the theoretical effects of the dilution on energy transport. Through this it was found that the dilution reduced the turbulent ion energy transport in a wide variety of cases, but primarily increased the critical gradient at low densities, and primarily reduced the stiffness of the transport at high densities. This dilution effect is related to observations of reductions in energy transport from seeding on other tokamaks, and will likely have an impact on ITER and future fusion reactors.
Author: Paul Chappell Ennever
Publisher:
ISBN:
Category :
Languages : en
Pages : 139
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Book Description
Turbulence in tokamak plasmas is the primary means by which energy is transported from the core of the plasma to the edge, where it is lost, and is therefore the main limitation of tokamak plasma performance. Dilution of the main-ion species was found to have a stabilizing effect on ion gyroradius scale turbulence in tokamak plasmas. Dilution of deuterium tokamak plasmas is the reduction of the ratio of the deuterium ion density to the electron density, nD=ne, to less than 1.0 through the introduction of low-Z impurity species into the plasma. Controlled dilution experiments were performed on Alcator C-Mod wherein plasmas at a range of electron density and plasma current were seeded with nitrogen while a cryopump held the electron density fixed. The electron density fluctuations due to turbulence were monitored using a phase contrast imaging (PCI) diagnostic, an absolutely calibrated diagnostic that measures the line-integral of the electron density fluctuations along 32 vertical chords. In these experiments the seeding reduced the PCI density fluctuations, and had a stabilizing effect on the ion energy transport. The seeding also reversed the direction of intrinsic rotation in certain cases. Nonlinear simulations using the gyrokinetic turbulence code GYRO were performed using measured kinetic profiles from the dilution experiments both before and after the nitrogen seeding. The GYRO simulations reproduced the observed reduction in the turbulent ion energy transport with the nitrogen seeding. The GYRO simulated turbulent density fluctuations were compared to the PCI measurements using a synthetic diagnostic, and they were found to be consistent. GYRO simulations were also performed varying only the main ion dilution to explore the theoretical effects of the dilution on energy transport. Through this it was found that the dilution reduced the turbulent ion energy transport in a wide variety of cases, but primarily increased the critical gradient at low densities, and primarily reduced the stiffness of the transport at high densities. This dilution effect is related to observations of reductions in energy transport from seeding on other tokamaks, and will likely have an impact on ITER and future fusion reactors.
Author: Liang Lin (Ph. D.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 189
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Book Description
(cont.) Our study shows that although the short wavelength turbulence in the ETG range is unstable in the linear ohmic regime, the nonlinear simulation with k[theta][rho]s up to 4 does not raise the electron thermal diffusivity to the experimental level, where k[theta] is the poloidal wavenumber and [rho]s is the ion-sound Larmor radius. The H-Mode studies focus on plasmas before and during internal transport barrier formation in an enhanced D[alpha], H-Mode plasma. The simulated fluctuations from GYRO agree with experimental measurements in the ITG regime. GYRO also shows good agreement in transport predictions with experimental measurements after reducing the ion temperature gradient (~15%) and adding ExB shear suppression, all within the experimental uncertainty.
Author: James L. Terry
Publisher:
ISBN:
Category :
Languages : en
Pages : 12
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Book Description
The intermittent turbulent transport in the scrape-off-layers of Alcator C-Mod, DIII-D, and NSTX is studied experimentally. On DIII-D the fluctuations of both density and temperature have strongly non-Gaussian statistics, and events with amplitudes above 10 times the mean level are responsible for large fractions of the net particle and heat transport, indicating the importance of turbulence on the transport. In C-Mod and NSTX the turbulence is imaged with a very high density of spatial measurements. The 2-D structure and dynamics of emission from a localized gas puff are observed, and intermittent features (also sometimes called 3blobs4) are typically seen. On DIII-D the turbulence is imaged using BES and similar intermittent features are seen. The dynamics of these intermittent features are discussed. The experimental observations are compared with numerical simulations of edge turbulence. The electromagnetic turbulence in a 3-D geometry is computed using non-linear plasma fluid equations. The wavenumber spectra in the poloidal dimension of the simulations are in reasonable agreement with those of the C-Mod experimental images once the response of the optical system is accounted for. The resistive ballooning mode is the dominant linear instability in the simulations.
![Observations of the Turbulence in the Scrape-off-layers of Alcator C-Mod and NSTX and Comparisons with Simualtion [sic] PDF](https://books.google.com/books/content/images/frontcover/lcIttwAACAAJ?fife=w80-h100)
Author: James L. Terry
Publisher:
ISBN:
Category :
Languages : en
Pages : 44
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Book Description
The intermittent turbulent transport in the scrape-off-layer of Alcator C-Mod and NSTX is studied experimentally by imaging with a very high density of spatial measurements. The 2-D structure and dynamics of emission from a localized gas puff are observed, and intermittent features (also sometimes called "filaments" or "blobs") are typically seen. The characteristics of the spatial structure of the turbulence and their relationship to the time-averaged SOL profiles are discussed. The experimental observations are compared with 3-D non-linear numerical simulations of edge turbulence. Radial profiles of the poloidal wavenumber spectra and the poloidal scale length from the simulations are in reasonable agreement with those obtained from the experimental images, once the response of the optical system is accounted for. The resistive ballooning mode is the dominant linear instability in the simulations. The ballooning character of the turbulence is also consistent with fluctuation measurements made at the inboard and outboard midplane, where normalized fluctuation levels are found to be about ten times smaller on the inboard side. For discharges near the density limit, turbulent structures are seen on closed flux surfaces. Keywords: turbulence; edge plasma; fluctuations; transport phenomena; resistive instabilities.
Author: M. H. Redi
Publisher:
ISBN:
Category : Computer simulation
Languages : en
Pages : 4
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Book Description
Author: Choongki Sung
Publisher:
ISBN:
Category :
Languages : en
Pages : 478
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Book Description
The comprehensive analysis was performed to study turbulent transport in Alcator CMod plasmas in this thesis. A new Correlation Electron Cyclotron Emission (CECE) diagnostic was designed and installed as a part of this thesis work. Using this diagnostic, we measured local T fluctuations in r/a >/~ 0.75 in C-Mod for the first time. This thesis work provided new information about the Ohmic confinement transition, from the linear to the saturated confinement regime with the increase in average density. It was found that Te fluctuations near the edge (r/a0~.85) tend to decrease across the Ohmic confinement transition. Although the Ohmic confinement transition has been considered predominantly as a result of the linear turbulence mode transition, we found no changes in the dominant turbulence mode across this transition via gyrokinetic analysis using the code, GYRO. The GYRO simulations performed near the edge reproduce experimental ion heat flux and Te fluctuations, but electron heat flux was under-predicted. Considering that both ion heat flux and the T fluctuations mainly come from ion scale turbulence, the under-prediction of electron heat flux suggests the importance of electron scale turbulence. Intrinsic rotation reversals in C-Mod plasmas were studied in this thesis. Similar changes in electron temperature fluctuations, the reduction of Te fluctuations near the edge, were observed across RF rotation reversals and Ohmic rotation reversals. The gyrokinetic and self-similarity analyses also showed similarities between rotation reversals in Ohmic and RF heated discharges. These observations suggest that the physics of Ohmic confinement transition and the rotation reversal can be applied to the physics of rotation reversal in RF heated discharges. This thesis also found the reduction of Te fluctuations inside pedestal region with the transition from low to high energy confinement regime, which indicates the changes in core turbulence are correlated with the global energy confinement.
Author: C Wendell Horton, Jr
Publisher: #N/A
ISBN: 9813225904
Category : Science
Languages : en
Pages : 522
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Book Description
For a few seconds with large machines, scientists and engineers have now created the fusion power of the stars in the laboratory and at the same time find the rich range of complex turbulent electromagnetic waves that transport the plasma confinement systems. The turbulent transport mechanisms created in the laboratory are explained in detail in the second edition of 'Turbulent Transport in Magnetized Plasmas' by Professor Horton.The principles and properties of the major plasma confinement machines are explored with basic physics to the extent currently understood. For the observational laws that are not understood — the empirical confinement laws — offering challenges to the next generation of plasma students and researchers — are explained in detail. An example, is the confinement regime — called the 'I-mode' — currently a hot topic — is explored.Numerous important problems and puzzles for the next generation of plasma scientists are explained. There is growing demand for new simulation codes utilizing the massively parallel computers with MPI and GPU methods. When the 20 billion dollar ITER machine is tested in the 2020ies, new theories and faster/smarter computer simulations running in near real-time control systems will be used to control the burning hydrogen plasmas.
Author: Alexander James Creely
Publisher:
ISBN:
Category :
Languages : en
Pages : 369
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Book Description
This thesis developed hardware and analysis techniques to measure two validation constraints experimentally, and then applied these constraints in the validation of plasma turbulent transport models on two tokamaks, Alcator C-Mod and ASDEX Upgrade, resulting in both greater physics understanding of multi-scale turbulent interactions and greater confidence in predictions for future fusion devices. On the path toward the clean, sustainable, and safe energy of a fusion power plant, experiment and modeling each contribute something unique. Before one can in good faith use plasma turbulent transport models to explain turbulent dynamics or predict machine performance, however, one must ensure that these models can correctly reproduce experimentally measured conditions on existing devices. Validation, the process of determining how accurately a model represents reality, has thus become a key endeavor in fusion energy research. First, this thesis developed an analysis technique to measure the electron perturbative thermal diffusivity based on tracking the propagation of heat pulses generated by partial sawtooth crashes. In addition, correlation electron cyclotron emission (CECE) hardware was constructed on both Alcator C-Mod and ASDEX Upgrade, and analysis techniques were derived, in order to measure turbulent electron temperature fluctuations. These validation constraints were applied to two turbulent transport models, the nonlinear gyrokinetic model and the quasi-linear gyrofluid model. In particular, these constraints were used to study the importance of multi-scale turbulent effects (due to coupling between ion- and electron-scales) in correctly modeling plasma behavior. The gyrokinetic codes GYRO and GENE were validated on Alcator C-Mod and ASDEX Upgrade respectively, using both constraints developed in this thesis as well as ion and electron heat fluxes from power balance, revealing that in some cases ionscale simulations are sufficient to match experimental constraints, while in other cases multi-scale effects are important. To investigate this discrepancy, a novel type of validation study was performed with the gyrofluid code TGLF, including many discharges from both machines. This study resulted in two physical criteria that determine when multi-scale effects are important, and when ion-scale simulations are sufficient to model the plasma behavior, shedding light on the physical phenomena that govern the importance of multi-scale turbulent effects.
Author: M. H. Redi
Publisher:
ISBN:
Category : Computer simulation
Languages : en
Pages : 4
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Book Description
Author:
Publisher: ScholarlyEditions
ISBN: 1490107819
Category : Science
Languages : en
Pages : 1198
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Book Description
Issues in Nuclear, High Energy, Plasma, Particle, and Condensed Matter Physics: 2013 Edition is a ScholarlyEditions™ book that delivers timely, authoritative, and comprehensive information about High Energy Physics. The editors have built Issues in Nuclear, High Energy, Plasma, Particle, and Condensed Matter Physics: 2013 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about High Energy Physics in this book to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Nuclear, High Energy, Plasma, Particle, and Condensed Matter Physics: 2013 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.
