Velocity-space Resolved Fast-ion Measurements in the DIII-D Tokamak PDF Download
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Author: Christopher Michael Muscatello
Publisher:
ISBN: 9781267260550
Category :
Languages : en
Pages : 150
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Book Description
Superthermal ions in tokamak plasmas play a critical role in heating and current drive, and their confinement within the core of the plasma is crucial for obtaining ignition and sustaining burn in future reactors. At the DIII-D tokamak, a suite of fast-ion measurements is available to diagnose various properties of the superthermal population. This thesis work involves a contribution to DIII-D's fast-ion diagnostic collection: the 2nd generation fast-ion deuterium alpha (2G FIDA) detector. FIDA works on the principle of measuring the light that is emitted from neutralized fast ions that undergo charge exchange events with injected neutral atoms. 2G FIDA complements the other FIDA installations on DIII-D with its unique velocity-space sampling volume. Output from a synthetic diagnostic code (FIDAsim) that predicts FIDA emission levels is compared with measurements from 2G FIDA. We find that, while the predicted and measured shapes of the FIDA spectra agree well, the absolute magnitude of the spectral amplitudes are inconsistent. Results from various FIDAsim trials are presented adjusting several parameters, and it is hypothesized that mischaracterization of the diagnostic neutral beams is a major source of error. Instabilities in tokamaks can cause fast-ion transport. The sawtooth instability is particularly important because the crash phase has been observed to cause reductions up to 50% in the central fast-ion density. Passing ions of all energies are redistributed, but only low energy trapped ions suffer redistribution. The observations are consistent with transport by flux-attachment. Comparisons with theory suggest that the intensity of sawtooth-induced transport depends on the magnitude of toroidal drift. Instabilities characterized by toroidal and poloidal mode numbers and real frequency can coherently interact with energetic particles through mode-particle resonances. During a sawtooth crash, even fast ions whose energies are above the threshold for flux-attachment can experience transport if their orbits satisfy the bounce-precessional resonance condition. On DIII-D, a spatially localized population of beam ions accelerated above the injection energy by ion-cyclotron radio frequency (ICRF) heating is diminished at a sawtooth crash. Furthermore, fast-ion losses concurrent with sawtooth crashes are observed. Calculations show that mode-particle resonances could be responsible. Transport of energetic particles by resonant interactions pertains to many types of instabilities; other examples besides sawteeth will also be presented. Analysis shows that large amplitude modes cause significant resonant transport of fast particles. Even small amplitude modes can resonantly drive transport if multiple harmonics exist.
Author: Christopher Michael Muscatello
Publisher:
ISBN: 9781267260550
Category :
Languages : en
Pages : 150
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Book Description
Superthermal ions in tokamak plasmas play a critical role in heating and current drive, and their confinement within the core of the plasma is crucial for obtaining ignition and sustaining burn in future reactors. At the DIII-D tokamak, a suite of fast-ion measurements is available to diagnose various properties of the superthermal population. This thesis work involves a contribution to DIII-D's fast-ion diagnostic collection: the 2nd generation fast-ion deuterium alpha (2G FIDA) detector. FIDA works on the principle of measuring the light that is emitted from neutralized fast ions that undergo charge exchange events with injected neutral atoms. 2G FIDA complements the other FIDA installations on DIII-D with its unique velocity-space sampling volume. Output from a synthetic diagnostic code (FIDAsim) that predicts FIDA emission levels is compared with measurements from 2G FIDA. We find that, while the predicted and measured shapes of the FIDA spectra agree well, the absolute magnitude of the spectral amplitudes are inconsistent. Results from various FIDAsim trials are presented adjusting several parameters, and it is hypothesized that mischaracterization of the diagnostic neutral beams is a major source of error. Instabilities in tokamaks can cause fast-ion transport. The sawtooth instability is particularly important because the crash phase has been observed to cause reductions up to 50% in the central fast-ion density. Passing ions of all energies are redistributed, but only low energy trapped ions suffer redistribution. The observations are consistent with transport by flux-attachment. Comparisons with theory suggest that the intensity of sawtooth-induced transport depends on the magnitude of toroidal drift. Instabilities characterized by toroidal and poloidal mode numbers and real frequency can coherently interact with energetic particles through mode-particle resonances. During a sawtooth crash, even fast ions whose energies are above the threshold for flux-attachment can experience transport if their orbits satisfy the bounce-precessional resonance condition. On DIII-D, a spatially localized population of beam ions accelerated above the injection energy by ion-cyclotron radio frequency (ICRF) heating is diminished at a sawtooth crash. Furthermore, fast-ion losses concurrent with sawtooth crashes are observed. Calculations show that mode-particle resonances could be responsible. Transport of energetic particles by resonant interactions pertains to many types of instabilities; other examples besides sawteeth will also be presented. Analysis shows that large amplitude modes cause significant resonant transport of fast particles. Even small amplitude modes can resonantly drive transport if multiple harmonics exist.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 6
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The charge exchange recombination (CER) diagnostic system on the DIII-D tokamak is used to make spatially and temporally resolved measurements of the ion temperature and toroidal and poloidal rotation velocities. This is performed through visible spectroscopic measurements of the Doppler broadened and Doppler shifted HE II 468.6 nm, the CVI 529.1 nm, and the BV 494.5 nm spectral lines which have been excited by charge exchange recombination interactions between the fully stripped ions and the neutral atoms from the heating beams. The plasma viewing optics comprises 32 viewing chords spanning a typical plasma minor radius of 63 cm across the midplane, of which 15 spatial chords span 4.2 cm at the plasma edge just within the separatrix and provide a chord-to-chord spatial resolution of 0.3 cm. Fast camera readout electronics can provide a temporal resolution of 260 [mu]s per time slice, but the effective minimum integration time, at present, is 1 ms which is limited by the detected photon flux from the plasma and the decay times of the phosphors used on the multichannel plate image intensifiers. Significant changes in the edge plasma radial electric field at the L-H transition have been observed, as determined from the CER measurements, and these results are being extensively compared to theories which consider the effects of sheared electric fields on plasma turbulence. 13 refs., 10 figs.
Author: Derek Aiden Sutherland
Publisher:
ISBN:
Category :
Languages : en
Pages : 29
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A study of the prompt losses of injected neutral beam born fast ions was conducted on the DIII-D tokamak at General Atomics using scintillator based fast ion loss detectors (FILD) and a reverse orbit calculation code. Prompt losses, also called first orbit losses, result from injected neutrals that are ionized on orbits that terminate to the outer wall before making a complete neoclassical, poloidal revolution. A strike map code has been developed which generates meshes that overlay optical fast ion signals from the FILD scintillator, providing a measurement of the pitch angles and gyroradii of incident fast ions. The pitch angles and gyroradii of incident ions are inputs to a reverse orbit calculation code used to calculate the trajectories of the incident ions in reverse time back to their birth at the intersection of the reverse orbit and an overlaid neutral beam injection footprint. The megahertz (MHz) sampling frequency of the FILD scintillator, along with finer time resolution neutral beam signals, enabled a comparison of the measured time delay between the onset of the neutral beam injection and the measured FILD loss signals with the calculated transit time based on the path length of the simulated reverse orbit. Consistency between the experimentally measured transit times and the simulation orbit times was observed. This result indicates the generated strike maps which provide a measurement of incident ions' gyroradii and pitch angles are accurate. This study supplements current studies seeking to improve the understanding of fast ion transport due to magnetohydrodynamic (MHD) activity, such as reverse shear Alfven eigenmodes (RSAEs) and toroidal Alfven eigenmodes (TAEs), which will be of great importance for predominately self-heated reactor scenarios.
Author: Daniel Franklin Finkenthal
Publisher:
ISBN:
Category :
Languages : en
Pages : 578
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Category : Aeronautics
Languages : en
Pages : 702
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Category : Power resources
Languages : en
Pages : 782
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Author:
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ISBN:
Category :
Languages : en
Pages : 6
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Measurements of the radial electric field, E{sub r}, with high spatial and high time resolution in H-mode and VH-mode discharges in the DIII-D tokamak have revealed the significant influence of the shear in E{sub r} on confinement and transport in these discharges. These measurements are made using the DIII-D Charge Exchange Recombination (CER) System. At the L-H transition in DIII-D plasmas, a negative well-like E{sub r} profile develops just within the magnetic separatrix. A region of shear in E{sub r} results, which extends 1 to 2 cm into the plasma from the separatrix. At the transition, this region of sheared E{sub r} exhibits the greatest increase in impurity ion poloidal rotation velocity and the greatest reduction in plasma fluctuations. A transport barrier is formed in this same region of E x B velocity shear as is signified by large increases in the observed gradients of the ion temperature, the carbon density, the electron temperature and electron density. The development of the region of sheared E{sub r}, the increase in impurity ion poloidal rotation, the reduction in plasma turbulence, and the transport barrier all occur simultaneously at the L-H transition. Measurements of the radial electric field, plasma turbulence, thermal transport, and energy confinement have been performed for a wide range of plasma conditions and configurations. The results support the supposition that the progression of improving confinement at the L-H transition, into the H-mode and then into the VH-mode can be explained by the hypothesis of the suppression of plasma turbulence by the increasing penetration of the region of sheared E x B velocity into the plasma interior.
Author: Colin Chrystal
Publisher:
ISBN: 9781321197594
Category :
Languages : en
Pages : 151
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The goal of this dissertation was to develop a novel technique for measuring ion poloidal rotation and then using that technique to test poloidal rotation theories. The new poloidal rotation diagnostic has been developed on the DIII-D tokamak. This diagnostic uses charge exchange recombination spectroscopy to measure toroidal rotation on the high- and low-field side of the tokamak midplane to determine the poloidal rotation from a divergence-free description of flow within flux-surfaces. Measurements are made such that no atomic physics calculations are needed to account for the energy dependence of the charge exchange cross section. New techniques for creating magnetic equilibrium reconstructions and performing the spatial calibration have been developed to ensure the accuracy of this new diagnostic. Measurements are made in the core of DIII-D where the spatial resolution is significantly improved when compared to the direct measurement of the poloidal rotation. This diagnostic has been used to investigate impurity poloidal rotation in the core of a variety of plasmas. For the first time on DIII-D, mean poloidal flow spin-up coincident with the formation of an internal transport barrier has been observed. The various measurements of poloidal rotation have been compared with theoretical predictions. Disagreement with neoclassical calculations have been found in H-mode, QH-mode, and the core of internal transport barrier plasmas. The effect of turbulent driven Reynolds stress and fast-ion friction have been investigated as well, and it has been determined that either of these effects, on their own, is insufficient to explain the discrepancy with neoclassical predictions. Modeling results indicate that these effects that are not included in standard neoclassical calculations are important for calculating the poloidal rotation.
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Publisher: ScholarlyEditions
ISBN: 1464964114
Category : Science
Languages : en
Pages : 1751
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Book Description
Issues in Applied, Analytical, and Imaging Sciences Research: 2011 Edition is a ScholarlyEditions™ eBook that delivers timely, authoritative, and comprehensive information about Applied, Analytical, and Imaging Sciences Research. The editors have built Issues in Applied, Analytical, and Imaging Sciences Research: 2011 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Applied, Analytical, and Imaging Sciences Research in this eBook to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Applied, Analytical, and Imaging Sciences Research: 2011 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/.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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New phase space mapping and uncertainty analysis of energetic ion loss data in the DIII-D tokamak provides experimental results that serve as valuable constraints in first-principles simulations of energetic ion transport. Beam ion losses are measured by the fast ion loss detector (FILD) diagnostic system consisting of two magnetic spectrometers placed independently along the outer wall. Monte Carlo simulations of mono-energetic and single-pitch ions reaching the FILDs are used to determine the expected uncertainty in the measurements. Modeling shows that the variation in gyrophase of 80 keV beam ions at the FILD aperture can produce an apparent measured energy signature spanning across 50-140 keV. As a result, these calculations compare favorably with experiments in which neutral beam prompt loss provides a well known energy and pitch distribution.
