Download or read book The Dependence of Core Rotation on Magnetic Configuration and the Relation to the H mode Power Threwhold in Alcator C Mod Plasmas with No Momentum Input written by John E. Rice and published by . This book was released on 2004 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: The observed toroidal rotation in Alcator C-Mod Ohmic L-mode plasmas has been found to depend strongly on magnetic configuration. For standard discharges with a lower single null and the ion BxNB drift downward, and with BT = 5.4 T, IP = 0.8 MA and ne = 1.4 x 1020/m3, the core toroidal rotation is measured to be in the range of 10-20 km/s (counter-current). Similar plasmas with upper single null have significantly stronger counter-current rotation, in the range of 30-50 km/s. The rotation depends very sensitively on the distance between the primary and secondary separatrices in near double null plasmas, with changes of ~ 25 km/s occurring over a variation of a few millimeters in this distance. Application of ICRF power has been found to increase the rotation in the co-current direction. The transition to H-mode is seen to occur in these standard plasmas when the core rotation reaches a characteristic value, near 0 km/s, hence higher input power is needed to induce the transition in the upper single null configuration.

Download or read book Driven Rotation Self Generated Flow and Momentum Transport in Tokamak Plasmas written by John Rice and published by Springer Nature. This book was released on 2022-01-13 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive look at the state of the art of externally driven and self-generated rotation as well as momentum transport in tokamak plasmas. In addition to recent developments, the book includes a review of rotation measurement techniques, measurements of directly and indirectly driven rotation, momentum sinks, self-generated flow, and momentum transport. These results are presented alongside summaries of prevailing theory and are compared to predictions, bringing together both experimental and theoretical perspectives for a broad look at the field. Both researchers and graduate students in the field of plasma physics will find this book to be a useful reference. Although there is an emphasis on tokamaks, a number of the concepts are also relevant to other configurations.

Download or read book Fusion Science and Technology written by and published by . This book was released on 2008 with total page 808 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fusion Nucl aire written by and published by . This book was released on 2006-05 with total page 944 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Spontaneous Toroidal Rotation in Alcator C Mod Plasmas with No Momentum Input written by John E. Rice and published by . This book was released on 2005 with total page 102 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spontaneoustoroidal rotation of impurity ions has been observed in the core of Alcator C-Mod plasmas with no external momentum input. The magnitude of the rotation rangesfrom -60 km/s(coun ter-current) in limiter L-mode discharges to +140 km/s (co-current) in ICRF heated H-mode plasmas. The core rotation in L-mode plasmasisgenerally counter-current and isfound to depend strongly on the magnetic topology; in near double null discharges, the core rotation changes by 25 km/swith a variation of a few millimetersin the distance between the primary and secondary separatrices. In H-mode plasmas, the rotation increments in the co-current direction with the toroidal rotation velocity increase proportional to the corresponding stored energy increase, normalized to the plasma current. These discharges exhibit a positive Er in the core. Immediately following the transition from L-mode into enhanced Da (EDA) H-mode, the co-current rotation appears near the plasma edge and propagates to the center on a time scale similar to the energy confinement time, but much less than the neo-classical momentum diffusion time, indicating both the role of the plasma boundary in the dynamics of the H-mode transition and the anomalous nature of momentum transport. Rotation velocity profilesare flat in EDA H-mode plasmasand centrally peaked for ELM-free Hmodes, demonstrating the effects of an inward momentum pinch. In EDA H-mode discharges that develop internal transport barriers (ITBs), the core toroidal rotation inside of the barrier foot is observed to drop on a time scale similar to the core pressure profile peaking (100s of ms), indicating a negative Er well in the core region.

Download or read book Observations of Anomalous Momentum Transport in Alcator C Mod Plasmas with No Momentum Input written by John E. Rice and published by . This book was released on 2003 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) In EDA H-mode discharges which develop internal transport barriers, the velocity profiles become hollow in the center, indicating the presence of a negative radial electric field well in the vicinity of the barrier foot. Upper single null diverted and inner wall limited L-mode discharges exhibit strong counter-current rotation (with V[phi](0) [approx.] -60 km/s in some cases), which may be related to the observed higher H-mode power threshold in these configurations. For plasmas with locked modes, the toroidal rotation is observed to stop (V[phi]

Download or read book Transport driven Scrape off Layer Flows and the X point Dependence of the L H Power Threshold in Alcator C Mod written by Brian LaBombard and published by . This book was released on 2004 with total page 62 pages. Available in PDF, EPUB and Kindle. Book excerpt: Factor of ~2 higher power thresholds for low- to high-confinement mode transitions (LH) with unfavorable x-point topologies in Alcator C-Mod [Phys. Plasmas 1, 1511 (1994)] are linked to flow boundary conditions imposed by the scrape-off layer (SOL). Ballooning-like transport drives flow along magnetic field lines from low- to high-field regions with toroidal direction dependent on upper/lower x-point balance; the toroidal rotation of the confined plasma responds, exhibiting a strong counter-current rotation when Bx B points away from the x-point. Increased auxiliary heating power (rf, no momentum input) leads to an L-H transition at approximately twice the edge electron pressure gradient when Bx B points away. As gradients rise prior to the transition, toroidal rotation ramps toward the co-current direction; the H-mode is seen when the counter-current rotation imposed by the SOL flow becomes compensated. Remarkably, L-H thresholds in lower-limited discharges are identical to lower x-point discharges; SOL flows are also found similar, suggesting a connection.

Download or read book Toroidal Rotation and Momentum Transport in Alcator C Mod Plasmas with No Momentum Input written by John E. Rice and published by . This book was released on 2003 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: The time evolution of toroidal rotation velocity profiles has been measured in Alcator C-Mod [I.H. Hutchinson et al., Phys. Plasmas (1), 1511 (1994)] plasmas using a tangentially viewing x-ray spectrometer array. The strong co-current toroidal rotation in enhanced D[alpha] (EDA) high confinement mode (H-mode) plasmas is observed to propagate in from the edge on a time scale similar to the energy confinement time. The ensuing steady state rotation velocity profiles in both Ohmic and ion cyclotron range of frequencies (ICRF) heated EDA H-modes, which are generated in the absence of any external momentum input, are found to be relatively flat. These profiles may be simulated by a simple diffusion model with the boundary condition of an edge rotation, which appears during the H-mode period. The observed profiles are well matched by the simulations using a momentum diffusivity of [approx.]0.1 m2/s, which is much larger than the calculated neo-classical value, and the momentum transport may be regarded as anomalous. The Alcator C-Mod rotation observations have been compared in detail with the calculations of neo-classical and sub-neo-classical theory, to the predictions from modeling of ICRF wave induced energetic ion orbit shifts, and to estimates from turbulence driven mechanisms. The magnitude and scalings of the observed rotation results are in accord with neo-classical and sub-neo-classical calculations, but the measured momentum diffusivity is higher than the predictions by a large fraction. The prediction of rotation reversal with a high magnetic field side resonance location for ICRF wave induced ion orbit shifts has not been observed in the experiments. While the turbulence driven rotation calculations are mostly qualitative, they represent some of the observed features.

Download or read book The L to H mode Transition and Momentum Confinement in Alcator C Mod Plasmas written by John Reel Walk (Jr.) and published by . This book was released on 2010 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt: Using a spatially-resolving x-ray spectrometer system, toroidal impurity rotation in Alcator C-Mod plasmas was measured. The propagation of the rotational velocity from the edge to the core of the plasma column was measured during the L- to H-mode transition. Momentum transport was measured in both Ohmic and ICRF-heated discharges, which produced EDA and ELM-free H-modes. The momentum transport was modeled by a simplified diffusion model, in which momentum diffusivity was substantially higher than neoclassically predicted values.

Download or read book Investigation of Intrinsic Rotation Dependencies in Alcator C Mod Using a New Data Analysis Workflow written by Daniel Joowon Kwak and published by . This book was released on 2015 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: Toroidal rotation, important for suppressing various turbulent modes, mitigating MHD instabilities, and preventing locked modes that cause disruptions, may not be sufficiently generated by external devices in larger devices i.e. ITER. One possible solution is intrinsic rotation, self-generated flow without external momentum input, which has been observed in multiple tokamaks. More specifically, rotation reversals, a sudden change in direction of intrinsic rotation without significant change in global plasma parameters, have also been observed and are not yet fully understood. Studying this phenomenon in ohmic L-mode plasmas presents a rich opportunity to gain better understanding of intrinsic rotation and of momentum transport as a whole. The literature presents many different hypotheses, and this thesis explores three in particular. The first two hypotheses each posits a unique parameter as the primary dependency of reversals - the dominant turbulent mode, or the fastest growing turbulent mode(TEM/ITG), and the local density and temperature profile gradients, especially the electron density gradient, respectively. Other studies state that neoclassical effects cause the reversals and one study in particular presents a 1-D analytical model. Utilizing a new data analysis workflow built around GYRO, a gyrokinetic-Maxwell solver, hundreds of intrinsic rotation shots at Alcator C-Mod can be processed and analyzed without constant user management, which is used to test the three hypotheses. By comparing the rotation gradient u', a proxy variable indicative of the core toroidal intrinsic rotation velocity, to the parameters identified by the hypotheses, little correlation has been found between u' and the dominant turbulence regime and the ion temperature, electron temperature, and electron density profile gradients. The plasma remains ITG-dominated based on linear stability analysis regardless of rotation direction and the local profile gradients are not statistically significant in predicting the u'. Additionally, the experimental results in C-Mod and ASDEX Upgrade have shown strong disagreement with the 1 -D neoclassical model. Strong correlation has been found between u' and the effective collisionality Veff. These findings are inconsistent with previous experimental studies and suggest that further work is required to identify other key dependencies and/or uncover the complex physics and mechanisms at play.

Download or read book Dependence of the L to H mode Power Threshold on Toroidal Rotation and the Link to Edge Turbulence Dynamics written by and published by . This book was released on 2008 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: The injected power required to induce a transition from L-mode to H-mode plasmas is found to depend strongly on the injected neutral beam torque and consequent plasma toroidal rotation. Edge turbulence and flows, measured near the outboard midplane of the plasma (0.85

Download or read book Plasma Science written by National Academies of Sciences Engineering and Medicine and published by . This book was released on 2021-02-28 with total page 291 pages. Available in PDF, EPUB and Kindle. Book excerpt: Plasma Science and Engineering transforms fundamental scientific research into powerful societal applications, from materials processing and healthcare to forecasting space weather. Plasma Science: Enabling Technology, Sustainability, Security and Exploration discusses the importance of plasma research, identifies important grand challenges for the next decade, and makes recommendations on funding and workforce. This publication will help federal agencies, policymakers, and academic leadership understand the importance of plasma research and make informed decisions about plasma science funding, workforce, and research directions.

Download or read book H mode Regimes and Observations of Central Toroidal Rotation in Alcator C mod written by Martin Greenwald and published by . This book was released on 1998 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Observations of Toroidal Rotation Suppression with ITB Formation in ICRF and Ohmic H mode Alcator C Mod Plasmas written by John E. Rice and published by . This book was released on 2000 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: Co-current central toroidal rotation has been observed in Alcator C-Mod plasmas with on-axis ICRF heating. The rotation velocity increases with plasma stored energy and decreases with plasma current. Very similar behavior has been seen during Ohmic H-modes, which suggests that the rotation, generated in the absence of an external momentum source, is not principally an ICRF effect. A scan of the ICRF resonance location across the plasma has been performed in order to investigate possible influences on the toroidal rotation. With a slight reduction of the toroidal magnetic field from 4.7 to 4.5 T and a corresponding shift of the ICRF resonance from r/a = -0.36 to -0.48, the central toroidal rotation significantly decreased in concert with the formation of an internal transport barrier (ITB). During the ITB period, the electrons and impurities peaked continuously for . Comparison of the observed rotation and neo-classical predictions indicates that the core radial electric field changes from positive to negative during the ITB phase. Similar rotation suppression and ITB formation have been observed during some Ohmic H-mode discharges.

Download or read book Global Momentum Confinement Times in Alcator C Mod H and I Regime Plasmas written by Michelle M. Victora and published by . This book was released on 2014 with total page 45 pages. Available in PDF, EPUB and Kindle. Book excerpt: Using a spatially-resolving x-ray spectrometer system, the toroidal rotation velocity in Alcator C-Mod plasmas is measured and analyzed. At the L-H and L-I transition, there is a co-current movement in the toroidal rotation velocity.The propagation of this rotational velocity from the edge to the core of the torus was measured following the L- to H- and L- to I-mode transitions. A hyperbolic tangent fit was used to determine a single variable for rise time in rotational velocity. The hyperbolic tangent fit parameter acts as a proxy for the global momentum confinement time, which is then compared to other plasma parameters. Through this compaxison, we found an decrease in rise time in correlation with increasing density(n)/current(I), particularly distinctive in the range of 1-2.5 x 1020 (MA x m3)-1. Due to a lack of overlap in density between I- and H-mode, we find this may be indicative of an overall decrease in rise time between L- to I- and L- to H-mode transitions. In order to explore this possibility, we must achieve I-mode runs with the same current and density as Hmode to determine if there is still a decrease between the two transitions.

Download or read book A Comparison of Plasma Ion Rotation and Magnetic Mode Rotation in Alcator C Mod written by Justin Anthony Sarlese and published by . This book was released on 2002 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: There is still much to be learned about the ion toroidal rotation, the magnetic mode rotation, and the conditions under which they couple in a tokamak plasma. One way to better our understanding of these is through a comparison of the ion impurity rotation frequency and the sawtooth precursor frequency under various plasma conditions. In order to perform this analysis for a large number of experimental shots in Alcator C-Mod, an automated routine was written for determining the sawtooth precursor frequencies and loading these frequencies into a database, along with the ion impurity rotation frequencies and other plasma parameters taken at the times of the sawtooth precursors. It was determined that these frequencies agree most of the time, and their disagreement is in many cases the result of ion impurity rotation frequencies above 23kHz, sometimes the result of RF heating in excess of 4.2MW. According to the data in the database, there is a linear dependence between the two frequencies and WMHD/IP, as has been observed with previous research; however, comparable correlation exists between the frequencies and [beta]p, [beta]N, and WMHD/IP2. At the same time, there appear to be candidate power laws for the two frequencies which include [beta]P, [beta]N, WMHD and IP, WMHD/IP, and WMHD/IP2.

Download or read book High Power Density H modes in Alcator C Mod written by Yuichi Takase and published by . This book was released on 1996 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: