Observations of Anomalous Transport in Tokamak Plasmas with No Momentum Input PDF Download
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Author: William Davis Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 16
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Book Description
Anomalous momentum transport has been observed in Alcator C-Mod tokamak plasmas. The time evolution of core impurity toroidal rotation velocity profiles has been measured with a crystal x-ray spectrometer array. Following the L-mode to EDA (enhanced D[/sub/ alpha]) H-mode transition in both Ohmic and ICRF heated discharges, the ensuing co-current toroidal rotation velocity, which is generated in the absence of any external momentum source, is observed to propagate in from the edge plasma to the core with a time scale of order of the observed energy confinement time, but much less than the neo-classical momentum confinement time. The steady state toroidal rotation velocity profiles in EDA H-mode plasmas are relatively flat and the momentum transport can be simulated with a simple diffusion model. Assuming the L-H transition produces an instantaneous edge velocity source (which disappears at the H- to L-mode transition), the momentum transport may be characterized by a diffusivity, with values of 0.07 m2/s during EDA H-mode and 0.2 m2/s in L-mode. These values are large compared to the calculated neo-classical momentum diffusivities. Velocity profiles during ELM-free H-modes are centrally peaked, which suggests inward momentum convection; the observed profiles are matched with simulations including an inward convection velocity of 10 m/s. 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.
Author: William Davis Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 16
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Book Description
Anomalous momentum transport has been observed in Alcator C-Mod tokamak plasmas. The time evolution of core impurity toroidal rotation velocity profiles has been measured with a crystal x-ray spectrometer array. Following the L-mode to EDA (enhanced D[/sub/ alpha]) H-mode transition in both Ohmic and ICRF heated discharges, the ensuing co-current toroidal rotation velocity, which is generated in the absence of any external momentum source, is observed to propagate in from the edge plasma to the core with a time scale of order of the observed energy confinement time, but much less than the neo-classical momentum confinement time. The steady state toroidal rotation velocity profiles in EDA H-mode plasmas are relatively flat and the momentum transport can be simulated with a simple diffusion model. Assuming the L-H transition produces an instantaneous edge velocity source (which disappears at the H- to L-mode transition), the momentum transport may be characterized by a diffusivity, with values of 0.07 m2/s during EDA H-mode and 0.2 m2/s in L-mode. These values are large compared to the calculated neo-classical momentum diffusivities. Velocity profiles during ELM-free H-modes are centrally peaked, which suggests inward momentum convection; the observed profiles are matched with simulations including an inward convection velocity of 10 m/s. 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.
Author: John Rice
Publisher: Springer Nature
ISBN: 3030922669
Category : Science
Languages : en
Pages : 158
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Book Description
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.
Author: MITSURU KIKUCHI
Publisher: International Atomic Energy
ISBN:
Category : Antiques & Collectibles
Languages : en
Pages : 1158
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Book Description
Humans do not live by bread alone. Physically we are puny creatures with limited prowess, but with unlimited dreams. We see a mountain and want to move it to carve out a path for ourselves. We see a river and want to tame it so that it irrigates our fields. We see a star and want to fly to its planets to secure a future for our progeny. For all this, we need a genie who will do our bidding at a flip of our fingers. Energy is such a genie. Modern humans need energy and lots of it to live a life of comfort. In fact, the quality of life in different regions of the world can be directly correlated with the per capita use of energy [1.1–1.5]. In this regard, the human development index (HDI) of various countries based on various reports by the United Nations Development Programme (UNDP) [1.6] (Fig. 1.1), which is a parameter measuring the quality of life in a given part of the world, is directly determined by the amount of per capita electricity consumption. Most of the developing world (~5 billion people) is crawling up the UN curve of HDI versus per capita electricity consumption, from abysmally low values of today towards the average of the whole world and eventually towards the average of the developed world. This translates into a massive energy hunger for the globe as a whole. It has been estimated that by the year 2050, the global electricity demand will go up by a factor of up to 3 in a high growth scenario [1.7–1.9]. The requirements beyond 2050 go up even higher.
Author: Matthew Logan Reinke
Publisher:
ISBN:
Category :
Languages : en
Pages : 370
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Book Description
In realistic reactor scenarios, high temperature plasmas will be composed of not only the fusion reactants and products, but also impurities introduced purposefully or unintentionally from plasma facing materials. In tokamaks it is often assumed, sometimes erroneously, that surfaces of constant main ion pressure are also surfaces of constant impurity pressure. Although the same underlying physics determine impurity momentum balance along closed magnetic field lines, the increased mass and charge of high-Z impurities weights terms differently. Their large mass enhances inertial effects like the centrifugal force from toroidal rotation, and( can lead to accumulation of heavy impurities on the outboard side of a flux surface. Their high charge enhances ion-impurity friction and makes impurities sensitive to small poloidal variations in the electrostatic potential. In Alcator C-Mod, 2D (R,Z) measurements of photon emission from high-Z impurities reveal significant variations of impurity density on a flux surface. Poloidal variations, normalized to the flux surface average, I 2/(n ) , have been measured up to ~ 1/3, and separate cases of impurities accumulating on the inboard and outboard side of a flux surface are observed, depending on local plasmas conditions. Experiments demonstrate that these asymmetries are due to a combination of inertia., poloidal electric fields and ion-impurity friction, and measurements are compared to existing neoclassical parallel impurity transport theory. This is the first time centrifugal force has been observed to cause a substantial asymmetry in a plasma with no external momentum input and where the flow is entirely self-generated. Magnetically trapped fast ions, sustained by ion cyclotron waves, create a poloidally varying electrostatic potential which causes high-Z impurities to accumulate on the inboard side. Existing theory is extended to include this effect by incorporating a species that has an anisotropic pressure tensor. Experimental measurements in plasmas where the minority resonance layer is scanned show good qualitative and quantitative agreement with this extended theory. The sensitivity of 51/(nz) to fast-ions demonstrates the opportunity for the impurity asymmetry to be used as a novel diagnostic tool and calls into question prior work on in/out asymmetries in neutral beam heated plasmas. /down asymmetries in the banana regime are unable to be explained by ion/impurity friction in the trace limit, nZZ 2 /n
Author: John Wesson
Publisher: Oxford University Press
ISBN: 0199592233
Category : Science
Languages : en
Pages : 828
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Book Description
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.
Author:
Publisher:
ISBN:
Category : Fusion reactors
Languages : en
Pages : 808
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Author: Aaron John Redd
Publisher:
ISBN:
Category : Plasma instabilities
Languages : en
Pages : 506
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Book Description
There is experimental and theoretical evidence of anomalous transport near the magnetic axis in tokamak plasmas, a region in which drift modes are linearly stable. Experimental evidence suggests that this additional transport is strongly affected by the plasma geometry (i.e., elongation and triangularity), more so than drift modes[1]. The finite-beta kinetic ballooning instability is predicted to exist close to the magnetic axis and is strongly affected by the plasma geometry. In this study, we explore the properties of the kinetic ballooning mode with the comprehensive electromagnetic kinetic stability calculations of the FULL code. Using FULL, we quantify the parametric dependence of kinetic ballooning transport on various plasma parameters, including the flux-surface elongation and triangularity, the normalized pressure beta and the flux-surface inverse aspect ratio. Based on these stability calculations, an algebraic kinetic ballooning transport model is developed. Also included in this dissertation are two independent studies of transport in tokamak plasmas, carried out with the BALDUR predictive transport code. In the first study, the sensitivity of these transport simulations to boundary and initial conditions is examined. In the second, a transport model developed by Ottaviani, Horton and Erba (OHE) is incorporated into the BALDUR code, and the density and temperature profiles predicted by this model are compared to experiment for a series of experimental discharges.
Author:
Publisher:
ISBN:
Category : Nuclear fusion
Languages : en
Pages : 324
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Author:
Publisher:
ISBN:
Category : Power resources
Languages : en
Pages : 438
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Author:
Publisher:
ISBN:
Category : Controlled fusion
Languages : en
Pages : 576
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