Enhanced D Alpha H Mode Studies In The Alcator C Mod Tokamak

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Enhanced D-Alpha H-mode Studies in the Alcator C-Mod Tokamak

Author : Earl S. Marmar
Publisher :
ISBN 13 :
Total Pages : 6 pages
Book Rating : 4.:/5 (65 download)

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Book Synopsis Enhanced D-Alpha H-mode Studies in the Alcator C-Mod Tokamak by : Earl S. Marmar

Download or read book Enhanced D-Alpha H-mode Studies in the Alcator C-Mod Tokamak written by Earl S. Marmar and published by . This book was released on 2000 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: A favorable regime of H-mode confinement, seen on the Alcator C-Mod tokamak is described. Following a brief period of ELM-free H-mode, the plasma evolves into the Enhanced D-Alpha (EDA) H-mode which is characterized by very good energy confinement, the complete absence of large, intermittent type I ELMs, finite impurity and majority species confinement, and low radiated power fraction. Accompanying the EDA H-mode, a quasi-coherent (QC) edge mode is observed, and found to be responsible for particle transport through the edge confinement barrier. The QC-mode is localized within the strong density gradient region, and has poloidal wavenumber and lab-frame frequency of 100 kHz. Parametric studies show that the conditions which promote EDA include moderate safety factor, high triangularity (d>0.35) and high target density (ne>1.2x20 m-3). EDA H-mode is readily obtained in purely ohmic and well as in ICRF auxiliary-heated discharges.

Comparisons of Small Edge Localized Mode H-Mode Regimes on the Alcator C-Mod and JFT-2M Tokamaks

Author : Amanda E. Hubbard
Publisher :
ISBN 13 :
Total Pages : 16 pages
Book Rating : 4.:/5 (641 download)

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Book Synopsis Comparisons of Small Edge Localized Mode H-Mode Regimes on the Alcator C-Mod and JFT-2M Tokamaks by : Amanda E. Hubbard

Download or read book Comparisons of Small Edge Localized Mode H-Mode Regimes on the Alcator C-Mod and JFT-2M Tokamaks written by Amanda E. Hubbard and published by . This book was released on 2005 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: Comparisons of H-mode regimes were carried out on the Alcator C-Mod and JFT-2M tokamaks. Shapes were matched apart from aspect ratio, which is lower on C-Mod. The High Recycling Steady (HRS) H-mode on JFT-2M and Enhanced D-alpha (EDA) regime on C-Mod, which both feature very small or no ELMs, are found to have similar access conditions in q95-nu* space, occurring for pedestal collisionality nu* greater than 1. Differences in edge fluctuations were found, with lower frequencies but higher mode numbers on C-Mod. In both tokamaks an attractive regime with small ELMs on top of an enhanced D-alpha baseline was obtained at moderate nu* and higher pressure. The JFT-2M shape favoured the appearance of ELMs on C-Mod, and also resulted in the appearance of a lower frequency component of the quasicoherent mode during EDA.

Turbulence and Transport Studies with Phase Contrast Imaging in the Alcator C-Mod Tokamak and Comparisons with Gyrokinetic Simulations

Download Turbulence and Transport Studies with Phase Contrast Imaging in the Alcator C-Mod Tokamak and Comparisons with Gyrokinetic Simulations PDF Online Free

Author : Liang Lin (Ph. D.)
Publisher :
ISBN 13 :
Total Pages : 189 pages
Book Rating : 4.:/5 (535 download)

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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.

Study of High Performance Mode Access Conditions on the Alcator C-Mod Tokamak

Author : Yunxing Ma
Publisher :
ISBN 13 :
Total Pages : 210 pages
Book Rating : 4.:/5 (851 download)

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Book Synopsis Study of High Performance Mode Access Conditions on the Alcator C-Mod Tokamak by : Yunxing Ma

Download or read book Study of High Performance Mode Access Conditions on the Alcator C-Mod Tokamak written by Yunxing Ma and published by . This book was released on 2013 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt: Usually when sufficient heating power is injected, tokamak plasma will make an abrupt transition into a state with improved confinement, known as the high-confinement mode, or H-mode. Given the greatly enhanced fusion yield, H-mode is foreseen as the baseline scenario for the future plasma operation of the International Thermonuclear Experimental Reactor (ITER). Many research efforts have been given to understand the criteria for H-mode access. To further contribute to this research, a primary focus of this thesis is characterizing the H-mode access conditions in the Alcator C-Mod tokamak, across a broad range of plasma density, magnetic field, and plasma current. In addition, dedicated experiments were designed and executed on C-Mod, to explore the effects of divertor geometry, ICRF resonance location, and main ion species on H-mode access conditions. Results from these experiments will be included in this thesis. The underlying physics of H-mode access is very complex, and the critical mechanisms remain largely unresolved. To promote our understanding, some models proposed for the H-mode transition are tested, using well documented local plasma conditions, obtained in C-Mod experiments. In particular, this thesis pioneers the test of a recently developed model for H-mode threshold power predictions.

Pedestal Profiles and Measurements in C-Mod Enhanced D-alpha H-modes

Author : Amanda E. Hubbard
Publisher :
ISBN 13 :
Total Pages : 18 pages
Book Rating : 4.:/5 (65 download)

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Book Synopsis Pedestal Profiles and Measurements in C-Mod Enhanced D-alpha H-modes by : Amanda E. Hubbard

Download or read book Pedestal Profiles and Measurements in C-Mod Enhanced D-alpha H-modes written by Amanda E. Hubbard and published by . This book was released on 2000 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: High resolution measurements on the Alcator C-Mod tokamak [I.H. Hutchinson et al, Phys. Plasmas 1, 1551 (1994)] of the transport barrier in the "Enhanced Da" (EDA) regime, which has increased particle transport without large edge localized modes, show steep density and temperature gradients over a region of 2-5 mm, with peak pressure gradients up to 12 MPa/m. Evolution of the pedestal at the LH transition is consistent with a large, rapid drop in thermal conductivity across the barrier. A quasi-coherent fluctuation in density, potential and Bpol, with fo%7E50-150 kHz and kq%7E 4 cm-1, always appears in the barrier during EDA, and drives a large particle flux. Conditions to access the steady-state EDA regime in deuterium include d> 0.35, q95> 3.5 and L-mode target line average density> 1.2 x 1020 m-3. A reduced q95 limit is found for hydrogen discharges.

Phase Contrast Imaging on the Alcator C-Mod Tokamak

Author : Alexander Mazurenko
Publisher :
ISBN 13 :
Total Pages : 320 pages
Book Rating : 4.:/5 (54 download)

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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.

Edge Transport Barrier Studies on the Alcator C-Mod Tokamak

Author : Jerry Wayne Hughes
Publisher :
ISBN 13 :
Total Pages : 452 pages
Book Rating : 4.:/5 (641 download)

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Book Synopsis Edge Transport Barrier Studies on the Alcator C-Mod Tokamak by : Jerry Wayne Hughes

Download or read book Edge Transport Barrier Studies on the Alcator C-Mod Tokamak written by Jerry Wayne Hughes and published by . This book was released on 2005 with total page 452 pages. Available in PDF, EPUB and Kindle. Book excerpt: Edge transport barriers (ETBs) in tokamak plasmas accompany transitions from low confinement (L-mode) to high confinement (H-mode) and exhibit large density and temperature gradients in a narrow pedestal region near the last closed flux surface (LCFS). Because tokamak energy confinement depends strongly on the boundary condition imposed by the edge plasma pressure, one desires a predictive capability for the pedestal on a future tokamak. On Alcator C-Mod, significant contributions to ETB studies were made possible with edge Thomson scattering (ETS), which measures profiles of electron temperature (20 [leq] Te[eV] [leq] 800) and density (0.3 [leq] ne[10^20m^-3] [leq] 5) with 1.3-mm spatial resolution near the LCFS. Profiles of Te, ne, and pe = neTe are fitted with a parameterized function, revealing typical pedestal widths [delta] of 2-6mm, with [delta]Te [geq] [delta]ne , on average. Pedestals are examined to determine existence criteria for the enhanced D[alpha] (EDA) H-mode. A feature that distinguishes this regime is a quasi-coherent mode (QCM) near the LCFS. The presence or absence of the QCM is related to edge conditions, in particular density, temperature and safety factor q. Results are consistent with higher values of both q and collisionality [nu]* giving the EDA regime. Further evidence suggests that increased abs([nabla]pe) may favor the QCM; thus EDA may have relevance to low-[nu]* reactor regimes, should sufficient edge pressure gradient exist.

ICRF-heated Enhanced Confinement Modes in the Alcator C-mod Tokamak

Author : Yuichi Takase
Publisher :
ISBN 13 :
Total Pages : 24 pages
Book Rating : 4.:/5 (363 download)

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Book Synopsis ICRF-heated Enhanced Confinement Modes in the Alcator C-mod Tokamak by : Yuichi Takase

Download or read book ICRF-heated Enhanced Confinement Modes in the Alcator C-mod Tokamak written by Yuichi Takase and published by . This book was released on 1996 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt:

An Experimental and Theoretical Study of the "Quasi-Coherent Fluctuations" in a High Density Tokamak Plasma

Download An Experimental and Theoretical Study of the

Author : Alexander Mazurenko
Publisher :
ISBN 13 :
Total Pages : 38 pages
Book Rating : 4.:/5 (65 download)

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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.

Tokamaks

Author : John Wesson
Publisher : Oxford University Press
ISBN 13 : 0199592233
Total Pages : 828 pages
Book Rating : 4.1/5 (995 download)

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Book Synopsis Tokamaks by : John Wesson

Download or read book Tokamaks written by John Wesson and published by Oxford University Press. This book was released on 2011-10-13 with total page 828 pages. Available in PDF, EPUB and Kindle. Book excerpt: The tokamak is the principal tool in controlled fusion research. This book acts as an introduction to the subject and a basic reference for theory, definitions, equations, and experimental results. The fourth edition has been completely revised, describing their development of tokamaks to the point of producing significant fusion power.

The Shoelace Antenna

Author : Theodore Golfinopoulos
Publisher :
ISBN 13 :
Total Pages : 318 pages
Book Rating : 4.:/5 (892 download)

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Book Synopsis The Shoelace Antenna by : Theodore Golfinopoulos

Download or read book The Shoelace Antenna written by Theodore Golfinopoulos and published by . This book was released on 2014 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: The "Shoelace" antenna is a unique device built to induce short-wavelength fluctuations in the edge plasma of the Alcator C-Mod tokamak, at a wave number and in the frequency range associated with the Quasi-Coherent Mode (QCM). The QCM is a continuous, drift-mode-like fluctuation, restricted to the low-field side of the tokamak in a 3 mm region around the last closed flux surface, and spanning both open and closed field lines. The study presented here is motivated by the fact that the QCM plays a crucial role in regulating particle transport across the plasma boundary in the Enhanced D[alpha](EDA) H-mode. It is this transport channel which sustains the EDA H-mode, flushing impurities from the plasma without the appearance of bursting Edge Localized Modes (ELMs). Because of the damage they cause to first-wall components, large-amplitude ELMs do not extrapolate to a full-size, steady state fusion reactor, and so it is of critical importance for the worldwide fusion research endeavor to identify, understand, and exploit ELM-free mechanisms of impurity flushing. It is in this context that the antenna's mission is defined. The Shoelace antenna is wound with field-aligned rungs spaced to produce a perpendicular wave number, k = 1.5 ± 0.1 cm-1, that precisely matches the QCM spatial structure, while the power system, with custom matching network, provides up to 2 kW of radio-frequency source power at any frequency in the band, 45

Impurity Screening Studies in the Alcator C-mod Tokamak

Author : G. M. McCracken
Publisher :
ISBN 13 :
Total Pages : 9 pages
Book Rating : 4.:/5 (363 download)

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Book Synopsis Impurity Screening Studies in the Alcator C-mod Tokamak by : G. M. McCracken

Download or read book Impurity Screening Studies in the Alcator C-mod Tokamak written by G. M. McCracken and published by . This book was released on 1996 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Issues in Nuclear, High Energy, Plasma, Particle, and Condensed Matter Physics: 2013 Edition

Author :
Publisher : ScholarlyEditions
ISBN 13 : 1490107819
Total Pages : 1198 pages
Book Rating : 4.4/5 (91 download)

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Book Synopsis Issues in Nuclear, High Energy, Plasma, Particle, and Condensed Matter Physics: 2013 Edition by :

Download or read book Issues in Nuclear, High Energy, Plasma, Particle, and Condensed Matter Physics: 2013 Edition written by and published by ScholarlyEditions. This book was released on 2013-05-01 with total page 1198 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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/.

Experimental Application and Numerical Study of Reflectometry in the Alcator C-Mod Tokamak

Author : Yijun Lin
Publisher :
ISBN 13 :
Total Pages : 182 pages
Book Rating : 4.:/5 (496 download)

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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.

Double Transport Barrier Experiments on Alcator C-Mod

Author : Stephen J. Wukitch
Publisher :
ISBN 13 :
Total Pages : 42 pages
Book Rating : 4.:/5 (65 download)

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Book Synopsis Double Transport Barrier Experiments on Alcator C-Mod by : Stephen J. Wukitch

Download or read book Double Transport Barrier Experiments on Alcator C-Mod written by Stephen J. Wukitch and published by . This book was released on 2002 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt: Double transport barrier modes (simultaneous core and edge transport barrier) have been observed with off-axis ion cyclotron range of frequencies (ICRF) heating in the Alcator C-Mod tokamak [I.H. Hutchinson et al., Phys. Plasmas 1, 1511(1994)]. An internal transport barrier (ITB) is routinely produced in enhanced D[alpha] H-mode (EDA) discharges where the minority ion cyclotron resonance layer is at r/a (0.5) during the current flat top phase of the discharge. The density profile becomes peaked without the presence of a particle source in the plasma core and continues to peak until the increased core impurity radiation arrests the improved energy confinement, ultimately leading to a barrier collapse. With the addition of moderate (0.6 MW) central ICRF heating, the double barrier mode was maintained for as long as the ICRF power was applied and modeling shows that the internal thermal barrier was maintained throughout the discharge. The presence of sawteeth throughout most of the ITB discharge allows sawtooth induced heat pulse analysis to be performed. This analysis indicates that there is an abrupt radial discontinuity in the heat pulse time to peak profile when an ITB is present. Furthermore, this discontinuity appears to move into the core plasma from the edge region in about 0.2 sec, several confinement times. The deduced thermal diffusivity, Xhp indicates a barrier exists in the electron thermal transport, the barrier is limited to a narrow radial region, and the transport is unaffected outside this narrow radial extent.

Fusion Science and Technology

Author :
Publisher :
ISBN 13 :
Total Pages : 512 pages
Book Rating : 4.:/5 (318 download)

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Book Synopsis Fusion Science and Technology by :

Download or read book Fusion Science and Technology written by and published by . This book was released on 2008 with total page 512 pages. Available in PDF, EPUB and Kindle. Book excerpt:

H-mode Pedestal and L-H Transition Studies on Alcator C-Mod

Author : Jerry Wayne Hughes
Publisher :
ISBN 13 :
Total Pages : 104 pages
Book Rating : 4.:/5 (641 download)

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Book Synopsis H-mode Pedestal and L-H Transition Studies on Alcator C-Mod by : Jerry Wayne Hughes

Download or read book H-mode Pedestal and L-H Transition Studies on Alcator C-Mod written by Jerry Wayne Hughes and published by . This book was released on 2005 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt: H-mode research on Alcator C-Mod is described, with a focus on the edge transport barrier (ETB). ETB pedestals are characterized using several diagnostics, leading to a thorough description of profile structure in H-mode. L-H transition criteria are discussed, along with the fast evolution of the pedestal following the L-H transition. H-mode regimes are described in terms of their edge transport characteristics and the local edge parameters favoring each. Empirical scalings of the pedestal with operational parameters are found, helping to illuminate physics governing the pedestal structure, and the relationship between edge transport and global confinement is discussed. Dimensionless comparisons between discharges on different tokamaks are discussed. Finally, ongoing work and directions for the future are described.