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.

Download or read book Edge Plasma Phenomena in the Alcator C Mod Tokamak Measured by High Resolution X ray Imaging Diagnostics written by Thomas Sunn Pedersen and published by . This book was released on 2000 with total page 206 pages. Available in PDF, EPUB and Kindle. Book excerpt: (cont.) A second array views the top of the plasma. The x-ray emissivity measured with this array also shows a distinct and narrow pedestal in H-mode. However, it is located significantly closer to the separatrix and is often narrower. Both of these differences increase with the safety factor at the edge, q95. Thus, there is a significant poloidal asymmetry in the impurity density in the H-mode edge region, which increases with q95. Therefore, the impurity transport in the H-mode edge is highly two-dimensional. The strong poloidal asymmetries measured show some quantitative agreement with theories developed to explain poloidal impurity asymmetries. However, none of the theories are strictly applicable to the Alcator C-Mod edge, and they all significantly underestimate the actual asymmetries that we observe.

Download or read book High Resolution Edge Thomson Scattering Measurements of the Alcator C Mod Tokamak written by Jerry Wayne Hughes and published by . This book was released on 2000 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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:

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.

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:

Download or read book Fast Photodiode Diagnostic on Alcator C Mod Tokamak to Study the Plasma Edge SOL Structure written by Baʹlint Vetoʺ and published by . This book was released on 2005 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) For the first time, the poloidal measurements of the plasma edge brightness with and without the D2 neutral gas puff yielded an estimate for the vertical extent of the neutral gas puff. The steady state inboard and outboard D, brightness profiles are also compared during two consecutive periods of L and H mode operation. The time lagged cross correlation calculated for neighboring views revealed quickly propagating local brightness maxima (blobs). The phase velocity of these systematically moving brightness perturbations ranges from -1 to 1 km/s inside the separatrix and becomes uniform outside the separatrix at 0.5 km/s where the positive velocity indicates radially outward motion. Downward propagating perturbations are also observed in the outboard SOL.

Download or read book High Resolution Bolometry on the Alcator C Mod Tokamak written by Réjean Louis Boivin and published by . This book was released on 1998 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The High Resolution Video Capture System on the Alcator C Mod Tokamak written by Aaron J. Allen and published by . This book was released on 1996 with total page 14 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 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:

Download or read book Impurity Plume Experiments in the Edge Plasma of the Alcator C Mod Tokamak written by Sanjay Gangadhara and published by . This book was released on 2003 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: The physics of impurity transport in response to a local gas injection in the scrape-off-layer (SOL) of Alcator C-Mod is investigated. Carbon "plumes'' are formed at variable locations in the SOL -- up to the separatrix -- by puffing deuterated ethylene gas (C2D4) through the end of a reciprocating fast-scanning probe. CCD cameras are used to simultaneously record C+1 and C+2 emission patterns from two near-perpendicular views. The plume dispersal patterns are found to yield direct qualitative information about plasma flow, including the direction of VExB near the separatrix. Impurity transport and plasma-surface interaction physics implicit in the 3-D plume structure is explored in detail using a Monte Carlo impurity transport code, with the aim of extracting background plasma-flow quantities. A number of important local effects involving plasma-probe interaction have been identified: a vertical ExB drift near the probe surface, a parallel electric field above the probe tip arising from plasma recycling off the probe surface, and sputtering of a carbon layer that dynamically forms on the probe surface. The emission patterns are also found to yield important information on flows in the SOL: radial electric field (Er) in the near SOL and volume-averaged values of the parallel Mach number in the far SOL. Er values obtained from plume data compare favorably with estimates of Er based on the poloidal propagation velocity of edge plasma fluctuations measured by the scanning probe. Comparisons between parallel Mach numbers obtained from the plume data and probe measurements indicate that the probe over-estimates the parallel flow towards the divertor in the far SOL. This result supports the picture of particle balance in the SOL of Alcator C-Mod being dominated by main-chamber recycling, with weak plasma flow into the divertor.

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.

Download or read book Dissertation Abstracts International written by and published by . This book was released on 2004 with total page 858 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Physics and Application of Impurity Plume Dispersal as an Edge Plasma Flow Diagnostic on the Alcator C Mod Tokamak written by Sanjay Gangadhara and published by . This book was released on 2003 with total page 273 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) A Monte Carlo impurity transport code (LIM) was used to simulate the plumes. Results indicate that contributions to the emission from sputtering explain the cross-field plume width, and that the parallel extent of emission generated in the far SOL is well-described using a sputter launch-energy distribution for the impurities. In the near SOL, the presence of a localized parallel electric field arising from background ion recycling off the probe surface is necessary to explain the parallel extent of emission generated in this region. This electric field accelerates impurity ions formed near the probe tip away from the probe, causing jet-like behavior. LIM was also used to investigate causes for the vertical elongation of the impurity emission. Results suggest the existence of a probe-induced E x B drift, of order ca. 1000 m/s in the near SOL. This drift may be responsible for the transport of both impurity and bulk plasma ions down the probe axis. Values for vII in the far SOL and Er in the near SOL have been extracted from the plume structure. A comparison between plume and probe results for Er suggests that calculations which employ a probe-sheath model may be in error, and that measurement of the poloidal propagation velocity of edge plasma fluctuations may be a more reliable means of inferring Er from probe data. Comparisons between plume- and probe-inferred values for the parallel Mach number suggest that the probe over-estimates parallel flow to the divertor in the far SOL, where effects of short field line connection to the divertor are important ...

Download or read book High Energy X ray Measurements During Lower Hybrid Current Drive on the Alcator C Tokamak written by Scott Charles Texter and published by . This book was released on 1986 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advances in Measurement and Modeling of the High confinement mode Pedestal on the Alcator C Mod Tokamak written by Jerry Wayne Hughes and published by . This book was released on 2005 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt: Edge transport barrier (ETB) studies on the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511, (1994)] investigate pedestal scalings and radial transport of plasma and neutrals. Pedestal profiles show trends with plasma operational parameters such as total current IP . A ballooning-like I2P dependence is seen in the pressure gradient, despite calculated stability to ideal ballooning modes. A similar scaling is seen in the near scrape-off-layer for both low-confinement (L-mode) and H-mode discharges, possibly due to electromagnetic fluid drift turbulence setting transport near the separatrix. Neutral density diagnosis allows examination of D0 fueling in H-modes, yielding profiles of effective particle diffusivity in the ETB, which vary as IP is changed. Edge neutral transport is studied using a 1D kinetic treatment. In both experiment and modeling, the C-Mod density pedestal exhibits a weakly increasing pedestal density and a nearly invariant density pedestal width as the D0 source rate increases. Identical modeling performed on pedestal profiles typical of DIII-D [Nucl. Fusion 42, 614, (2002)] reveal differences in pedestal scalings qualitatively similar to experimental results.