Download or read book Velocity space Resolved Fast ion Measurements in the DIII D Tokamak written by Christopher Michael Muscatello and published by . This book was released on 2012 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book The Charge Exchange Recombination Diagnostic System on the DIII D Tokamak written by and published by . This book was released on 1991 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book A Study of Prompt Fast Ion Losses from Neutral Beam Injection in the DIII D Tokamak written by Derek Aiden Sutherland and published by . This book was released on 2012 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book The Measurement of Absolute Helium Ion Density Profiles on the DIII D Tokamak Using Charge Exchange Recombination Spectroscopy written by Daniel Franklin Finkenthal and published by . This book was released on 1994 with total page 578 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 702 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Energy Research Abstracts written by and published by . This book was released on 1995 with total page 782 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Role of the Radial Electric Field in Confinement and Transport in H mode and VH mode Discharges in the DIII D Tokamak written by and published by . This book was released on 1993 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Experimental Tests of the Theory of Poloidal Rotation in the DIII D Tokamak written by Colin Chrystal and published by . This book was released on 2014 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Issues in Applied Analytical and Imaging Sciences Research 2011 Edition written by and published by ScholarlyEditions. This book was released on 2012-01-09 with total page 1751 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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/.

Download or read book Mapping and Uncertainty Analysis of Energy and Pitch Angle Phase Space in the DIII D Fast Ion Loss Detector written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Phase Space Effects on Fast Ion Distribution Function Modeling in Tokamaks written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Integrated simulations of tokamak discharges typically rely on classical physics to model energetic particle (EP) dynamics. However, there are numerous cases in which energetic particles can suffer additional transport that is not classical in nature. Examples include transport by applied 3D magnetic perturbations and, more notably, by plasma instabilities. Focusing on the effects of instabilities, ad-hocmodels can empirically reproduce increased transport, but the choice of transport coefficients is usually somehow arbitrary. New approaches based on physics-based reduced models are being developed to address those issues in a simplified way, while retaining a more correct treatment of resonant wave-particle interactions. The kick model implemented in the tokamaktransport code TRANSP is an example of such reduced models. It includes modifications of the EP distribution by instabilities in real and velocity space, retaining correlations between transport in energy and space typical of resonant EP transport. The relevance of EP phase space modifications by instabilities is first discussed in terms of predicted fast ion distribution. Results are compared with those from a simple, ad-hoc diffusive model. It is then shown that the phase-space resolved model can also provide additional insight into important issues such as internal consistency of the simulations and mode stability through the analysis of the power exchanged between energetic particles and the instabilities.

Download or read book Discrete Inverse Problems written by Per Christian Hansen and published by SIAM. This book was released on 2010-01-01 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book gives an introduction to the practical treatment of inverse problems by means of numerical methods, with a focus on basic mathematical and computational aspects. To solve inverse problems, we demonstrate that insight about them goes hand in hand with algorithms.

Download or read book Doppler Measurements in the Edge of the Alcator C Mod Tokamak Using a High resolution Visible Spectrometer written by Alexander Turner Graf and published by . This book was released on 2008 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Measurement and Simulation of Deuterium Balmer alpha Emission from First orbit Fast Ions and the Application to Neutral Density and General Fast ion Loss Detection in the DIII D Tokamak written by Nathan Glynn Bolte and published by . This book was released on 2015 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spectra of the Balmer-alpha radiation of first-orbit fast ions after charge exchange with edge neutrals have been measured in the DIII-D tokamak. Several collimated optics systems view the edge region--while avoiding any active beams--and carry light to a spectrometer tuned to the region of the 656.1 nm deuterium-alpha line. Viewing geometry and the high energy of the lost ions produce Doppler shifts, which effectively separate the fast-ion contributions from the bright, cold edge light. Modulation of the fast-ion source allows for time-evolving background subtraction. A model has been developed for the spectra of these first-orbit fast ions. The passive fast-ion D-alpha simulation (P-FIDAsim) is a forward model consisting of an experimentally- validated beam model, an ion orbit-following code, a collisional-radiative model, and a synthetic spectrometer. Eighty-six experimental spectra were obtained using 6 different neutral beam fast-ion sources and 13 different viewing chords. Parameters such as plasma current, toroidal field, electron density, plasma cross-sectional shape, and number of x-points were varied. Uncalibrated experimental spectra have an overall Spearman rank correlation coefficient with the shape of simulated spectra of 0.58 with subsets of cases rising to a correlation of 0.80. A single set of calibrated spectra (shot 152817) was measured and is used to estimate the neutral density throughout the cross-section of the tokamak. This is done by inverting the simulated spectra in order to nd the best neutral density (in a least squares sense) required to best match the experimental spectra. The resulting 2D neutral density shows the expected increase toward each x-point. The average neutral density is found to be 3.3 x 105 cm ̄3 at the magnetic axis, 2.3 x 108 cm ̄3 in the core, 8.1 x 109 cm ̄3 at the plasma boundary, and 1.1 x 1011 cm ̄3 near the wall. A technique is developed which--after using first-orbit light to calibrate the system--can quantify losses from a wider variety of mechanisms. Fast-ion losses resulting from sawtooth crashes (shot 149941) is estimated to eject 1.2% of the fast-ion inventory, in good agreement with a 1.7% loss estimate made by the TRANSP code.

Download or read book Seventh Carolus Magnus Summer School on Plasma and Fusion Energy Physics written by and published by . This book was released on 2006 with total page 514 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Physics Briefs written by and published by . This book was released on 1992 with total page 820 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Velocity Space Stability of Counterstreaming Ion Tokamak Plasmas written by D. L. Jassby and published by . This book was released on 1976 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: