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Phase Contrast Imaging On The Alcator C Mod Tokamak
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Book Synopsis Phase Contrast Imaging on the Alcator C-Mod Tokamak by : Alexander Mazurenko
Download or read book Phase Contrast Imaging on the Alcator C-Mod Tokamak written by Alexander Mazurenko and published by . This book was released on 2001 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt: Phase Contrast Imaging (PCI) is a new diagnostic that was built for the Alcator C-Mod tokamak. It measures line-integrated (along 12 vertical chords) plasma density perturbations with good temporal (2-500 kHz) and wavenumber (0.5-12 /cm) resolution. The Quasi-Coherent (QC) fluctuation mode was studied using the PCI and other diagnostics. The mode was found to cause fluctuation of density, electric and magnetic field in the plasma edge with typical frequency of 100 kHz and typical poloidal wavenumber of about 5/cm. The mode was found to be responsible for confinement properties of the "Enhanced D-alpha H-mode" (a particularly favorable regime of tokamak operation). Through numerical modeling, the physical origin of the fluctuations was tentatively identified as "resistive X-point" mode (a kind of resistive ballooning mode strongly affected by the X-point configuration of magnetic field lines). The PCI system has been upgraded to detect waves in the ion cyclotron range of frequencies (ICRF, 40-80 MHz) by means of optical heterodyning - a technique based on modulation of the diagnostic laser beam near the wave frequency. The upgraded system was then used to study propagation of the Fast Magnetosonic Waves. These waves, which have never been measured in detail in past experiments, are being used to heat the tokamak plasma at the megawatt power level. The measured results were compared to the simple cold-plasma dispersion relation and to predictions of the full-wave 3D numerical modeling.
Book Synopsis Turbulence and Transport Studies with Phase Contrast Imaging in the Alcator C-Mod Tokamak and Comparisons with Gyrokinetic Simulations by :
Download or read book Turbulence and Transport Studies with Phase Contrast Imaging in the Alcator C-Mod Tokamak and Comparisons with Gyrokinetic Simulations written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Cataloged from PDF version of thesis.
Book Synopsis Turbulence and Transport Studies with Phase Contrast Imaging in the Alcator C-Mod Tokamak and Comparisons with Gyrokinetic Simulations by : Liang Lin (Ph. D.)
Download or read book Turbulence and Transport Studies with Phase Contrast Imaging in the Alcator C-Mod Tokamak and Comparisons with Gyrokinetic Simulations written by Liang Lin (Ph. D.) and published by . This book was released on 2009 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: (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.
Book Synopsis Diagnostic Systems on Alcator C-Mod by : Nils Plesner Basse
Download or read book Diagnostic Systems on Alcator C-Mod written by Nils Plesner Basse and published by . This book was released on 2005 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: An overview of the diagnostics installed on the Alcator C-Mod tokamak [I. H. HUTCHINSON et al., Phys. Plasmas, Vol. 1, p. 1511 (1994)] is presented. Approximately twenty-five diagnostic systems are being operated on C-Mod. The compact design of the machine and the cryostat enclosing the vacuum vessel and magnetic field coils make access challenging. Diagnostics are used to study four focus areas: Transport, plasma boundary, waves and macrostability. There is significant overlap between these topics and they all contribute towards the burning plasma and advanced tokamak thrusts. Several advanced and novel diagnostics contribute to the investigation of C-Mod plasmas, e.g. electron cyclotron emission, phase-contrast imaging, gas-puff imaging, probe measurements and active magnetohydrodynamic antennas.
Book Synopsis An Experimental and Theoretical Study of the "Quasi-Coherent Fluctuations" in a High Density Tokamak Plasma by : Alexander Mazurenko
Download or read book An Experimental and Theoretical Study of the "Quasi-Coherent Fluctuations" in a High Density Tokamak Plasma written by Alexander Mazurenko and published by . This book was released on 2001 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Quasi-Coherent (QC) mode, observed at high densities during enhanced D-alpha (EDA) H-Mode in the Alcator C-Mod tokamak, has been studied with a phase contrast imaging (PCI) diagnostic. The QC mode is believed to be responsible for the reduced particle (and impurity) confinement during H-mode operation, so as to allow quasi-steady state operation of the tokamak. It is proposed that the QC mode is a form of resistive ballooning mode known as the resistive X-point mode. The measured dispersion and mode stability are found to be in good agreement with the resistive X-point mode predicted by the BOUT (Boundary Plasma Turbulence) code.
Book Synopsis Overview of Recent Alcator C-Mod Research by : Earl S. Marmar
Download or read book Overview of Recent Alcator C-Mod Research written by Earl S. Marmar and published by . This book was released on 2002 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: (cont.) Phase Contrast Imaging (PCI) has been used to directly detect density fluctuations driven by ICRF waves in the core of the plasma, and mode conversion to an intermediate wavelength Ion Cyclotron Wave has been observed for the first time. The bursty turbulent density fluctuations, observed to drive rapid cross-field particle transport in the edge plasma, appear to play a key role the dynamics of the density limit. Preparations for quasi-steady-state Advanced Tokamak studies with lower hybrid current drive are well underway, and time dependent modeling indicates that regimes with high bootstrap fraction can be produced.
Book Synopsis Experimental Application and Numerical Study of Reflectometry in the Alcator C-Mod Tokamak by : Yijun Lin
Download or read book Experimental Application and Numerical Study of Reflectometry in the Alcator C-Mod Tokamak written by Yijun Lin and published by . This book was released on 2001 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt: The amplitude modulated ordinary-mode reflectometer in the Alcator C-Mod tokamak is used to study the quasi-coherent (QC) continuous edge fluctuations in enhanced Da (EDA) H-modes. Reflectometer data show that the QC fluctuations are localized near the center of the density pedestal. The radial width (FWHM) is usually in the range of 0.1 - 0.3 cm. The width increases with the increase of resistivity rl. The line-integrated fluctuation level approximately scales with (v*q95).56. This result indicates that higher q95, higher density, and lower temperature are favored for the QC fluctuations. Neither the location nor the width changes significantly in an EDA H-mode period, while the frequency and level vary. A 2-D full-wave code has been developed to simulate and quantitatively interpret reflectometry signals. The code uses the finite-difference time-domain method to solve Maxwell's equations in two dimensions. Perfectly-matched layers are used as the boundary. The Huygens source technique is used to generate Gaussian beams and separate the reflected waves from the total field. Simulations based on realistic 2-D geometry of the Alcator C-Mod reflectometer provide a calibration curve by which we can relate the QC fluctuations in reflectometry signals to plasma density fluctuations. Results indicate that the line-integrated fluctuation level derived from reflectometry is similar to that measured by the phase contrast imaging system. Simulations also indicate that plasma curvature extends the reflectometry response to fluctuations of high poloidal wavenumber. A preliminary study indicates that reflectometry can be used to estimate the correlation length of the turbulence in Alcator C-Mod provided that the fluctuation level is small.
Book Synopsis High Resolution Visible Continuum Imaging Diagnostic on the Alcator C-Mod Tokamak by : Earl S. Marmar
Download or read book High Resolution Visible Continuum Imaging Diagnostic on the Alcator C-Mod Tokamak written by Earl S. Marmar and published by . This book was released on 2000 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Edge Turbulence Imaging in the Alcator C-Mod Tokamak by : S. J. Zweben
Download or read book Edge Turbulence Imaging in the Alcator C-Mod Tokamak written by S. J. Zweben and published by . This book was released on 2001 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis An Experimental Study of Turbulence by Phase-contrast Imaging in the DIII-D Tokamak by : Stefano Coda
Download or read book An Experimental Study of Turbulence by Phase-contrast Imaging in the DIII-D Tokamak written by Stefano Coda and published by . This book was released on 1997 with total page 924 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis A Study of Reversed Shear Alfvén Eigenmodes in Alcator C-Mod with Phase Contrast Imaging by : Eric Matthias Edlund
Download or read book A Study of Reversed Shear Alfvén Eigenmodes in Alcator C-Mod with Phase Contrast Imaging written by Eric Matthias Edlund and published by . This book was released on 2009 with total page 209 pages. Available in PDF, EPUB and Kindle. Book excerpt: Shear Alfvén waves are a fundamental mode of magnetized plasma oscillation and may exist in tokamak plasmas as eigenmodes with a global structure and discrete frequencies. The inhomogeneity of the plasma profiles in conjunction with tokamak geometry tends to focus the Alfvén waves in regions of near uniformity defined by local extrema in the Alfvén continuum, a quantity which describes the local Alfvén resonance frequency for particular mode numbers. Modes excited in the vicinity of these near uniform regions may be weakly damped and excited by energetic ions. The reversed shear Alfvén eigenmode (RSAE), localized deep in the plasma core, is typically associated with a minimum in q in reversed magnetic shear configurations. RSAEs have proven especially useful for MHD spectroscopy, that is the inference of plasma equilibrium properties through their frequency spectra, due to their high sensitivity to the value of qmin. Reversed shear equilibria during the current ramp-up phase and sawtoothing phase are studied through the spatial and temporal characteristics of the RSAEs. Analysis of the spatial structures of RSAEs measured by phase contrast imaging, and interpreted with a synthetic diagnostic using numerical results from the ideal MHD code NOVA, provides constraints on the evolution of qmi,. Additional observations including mode coupling, mode tunneling, and minimum frequency scaling are discussed in light of theoretical and numerical models, with commentary on possible future experiments.
Book Synopsis Edge Plasma Phenomena in the Alcator C-Mod Tokamak Measured by High Resolution X-ray Imaging Diagnostics by :
Download or read book Edge Plasma Phenomena in the Alcator C-Mod Tokamak Measured by High Resolution X-ray Imaging Diagnostics written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: By Thomas Sunn Pedersen.
Book Synopsis Visible Spectroscopic Imaging on the Alcator C-Mod Tokamak by : Christopher James Boswell
Download or read book Visible Spectroscopic Imaging on the Alcator C-Mod Tokamak written by Christopher James Boswell and published by . This book was released on 2003 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) 3) Two-dimensional emissivity profiles of visible continuum (420-430nm) have been measured and found to be an order of magnitude too large when compared to expected levels from electron-ion bremsstrahlung and radiative recombination. Several atomic and molecular processes have been considered to explain the enhanced continuum. However, none of the considered processes could explain the continuum level without particle densities inconsistent with current modeling efforts. The visible imaging system was also used in identifying the causes of impurity injections during discharges, in identifying the failure of invessel components, and as a monitor of vessel and plasma conditions. Both the physics results and the operational benefits of the visible imaging system show that the system is a valuable quantitative and qualitative diagnostic.
Book Synopsis Phase Contrast Imaging Measurements and Modeling of Short Wavelength Turbulence in the DIII-D Tokamak by : James Robert Dorris (III.)
Download or read book Phase Contrast Imaging Measurements and Modeling of Short Wavelength Turbulence in the DIII-D Tokamak written by James Robert Dorris (III.) and published by . This book was released on 2010 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt: The DIII-D phase contrast imaging (PCI) diagnostic has been upgraded and used to measure turbulence in the outer plasma region (0.7
Book Synopsis Studies of Ion Cyclotron Range of Frequencies Mode Conversion with Phase Contrast Imaging and Full-wave Simulations in Alcator C-Mod by : Naoto Tsujii
Download or read book Studies of Ion Cyclotron Range of Frequencies Mode Conversion with Phase Contrast Imaging and Full-wave Simulations in Alcator C-Mod written by Naoto Tsujii and published by . This book was released on 2012 with total page 211 pages. Available in PDF, EPUB and Kindle. Book excerpt: Radio frequency (rf) waves in the ion cyclotron range of frequencies (ICRF) are widely used for heating fusion plasmas. In a multi-ion-species plasma, the launched fast waves convert to ion cyclotron waves and ion Bernstein waves in the vicinity of the two-ion hybrid resonance between the cyclotron resonances. The mode converted waves are of interest as actuators to optimize plasma performance through current drive and flow drive. Numerical simulations are essential to describe these processes accurately in a realistic tokamak geometry, and it is important that these simulation codes be validated against experiment. The phase contrast imaging (PCI) technique has been used on Alcator C-Mod to measure directly the rf waves. The measurements were compared to predictions of full-wave simulations using a synthetic diagnostic method. The measured mode converted wave intensity was found to be a factor of ~50 weaker than what was expected from the linear wave theory in a strong mode conversion regime. The agreement improved when the wave intensity was weaker, which is a possible indication of nonlinear wave physics being involved.
Book Synopsis Turbulence and Transport Measurements in Alcator C-Mod and Comparisons with Gyrokinetic Simulations by : Paul Chappell Ennever
Download or read book Turbulence and Transport Measurements in Alcator C-Mod and Comparisons with Gyrokinetic Simulations written by Paul Chappell Ennever and published by . This book was released on 2016 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Design of a phase contrast imaging diagnostic to study plasma density fluctuations in the Texas Experimental Tokamak-Upgrade by : Romik Chatterjee
Download or read book Design of a phase contrast imaging diagnostic to study plasma density fluctuations in the Texas Experimental Tokamak-Upgrade written by Romik Chatterjee and published by . This book was released on 1992 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt:
