Download or read book Core Internal Transport Barriers on Alcator C Mod written by Catherine L. Fiore and published by . This book was released on 2000 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: The formation of internal transport barriers (ITB) has been observed in the core region of Alcator C-Mod under a variety of conditions. The improvement in core confinement following pellet injection (pellet enhanced performance or PEP mode) has been well documented on Alcator C-Mod in the past. Recently three new ITB phenomena have been observed which require no externally applied particle or momentum input. Short lived ITBs form spontaneously following the high confinement (H) to low confinement (L) mode transition and are characterized by a large increase in the global neutron production (enhanced neutron or EN modes.) Experiments with ICRF (ion cyclotron range of frequencies) power injection to the plasma off-axis on the high field side results in the central density rising abruptly and becoming peaked. The ITB formed at this time lasts for 10 energy confinement times. The central toroidal rotation velocity decreases and changes sign as the density rises. Similar spontaneous ITBs have been observed in ohmically heated H-mode plasmas. All of these ITB events have strongly peaked density profiles with a minimum in the density scale length occurring near r/a = 0.5 and have improved confinement parameters in the core region of the plasma. Keywords: Alcator C-Mod; confinement; tokamaks; transport phenomena; neutrons.

Download or read book Internal Transport Barriers in Alcator C Mod written by Catherine L. Fiore and published by . This book was released on 2005 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt: Internal transport barriers, marked by steep density and pressure profiles and reduction of core transport are obtained in Alcator C-Mod. Transient single barriers are observed at the back transition from H- to L- mode, and also when pellet injection is accompanied by ICRF power. Double barriers are induced with injection of off-axis ICRF power deposition. These also arise spontaneously in Ohmic H-mode plasmas when the H-mode lasts for several energy confinement times. C-Mod provides a unique platform for studying such discharges: the ions and electrons are tightly coupled by collisions with Ti/Te=1, and the plasma has no internal particle or momentum sources. ITB plasmas with average pressure greater than 1 atmosphere have been obtained. To form an ITB, particle and thermal flux are reduced in the barrier region, allowing the neoclassical pinch to peak the density while maintaining the central temperature. Gyrokinetic simulation suggests that long wavelength drift wave turbulence in the core is marginally stable at the ITB onset, but steepening of the density profile destabilizes trapped electron (TEM) modes inside the barrier. The TEM ultimately drives sufficient outgoing particle flux to balance the inward pinch and halt further density rise, which allows control of particle and impurity peaking.

Download or read book Control of Internal Transport Barriers on Alcator C Mod written by Catherine L. Fiore and published by . This book was released on 2003 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent studies of internal transport and double transport barrier regimes in Alcator C-Mod [I.H. Hutchinson, et al., Phys. Plasmas 1, 1511 (1994)] have explored the limits for forming, maintaining, and controlling these plasmas. C-Mod provides a unique platform for studying such discharges: the ions and electrons are tightly coupled by collisions and the plasma has no internal particle or momentum sources. The double-barrier mode comprised of an edge barrier with an internal transport barrier (ITB) can be induced at will using off-axis ion cyclotron range of frequency (ICRF) injection on either the low or high field side of the plasma with either of the available ICRF frequencies (70 or 80 MHz). When enhanced D [alpha] high confinement mode (EDA H-mode) is accessed in Ohmic plasmas, the double barrier ITB forms spontaneously if the Hmode is sustained for [approx.] high confinement times. The ITBs formed in both Ohmic and ICRF heated plasmas are quite similar regardless of the trigger method. They are characterized by strong central peaking of the electron density, and reduction of the core particle and energy ...

Download or read book Internal Transport Barrier Production and Control in Alcator C Mod written by Catherine L. Fiore and published by . This book was released on 2004 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: (cont.) Examination of the gyrokinetic stability indicates that the density and temperature profiles of the plasma core are inherently stable to long- wavelength drift mode driven turbulence at the onset time of the ITB, but that the increasing density gradients cause the trapped electron mode (TEM) to play a role in providing a control mechanism to ultimately limit the steepness of the density gradient in the ITB region.

Download or read book Investigation of Triggering Mechanism of Internal Transport Barriers on the Alcator C Mod Tokamak Using Thomson Scattering Diagnostic written by Kirill Zhurovich and published by . This book was released on 2007 with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt: Internal transport barriers (ITBs) in tokamak plasmas are characterized by the reduction of transport in one or more of the particle, momentum, or energy channels in the core plasma region. On Alcator C-Mod, significant contributions to ITB studies were made possible with the core Thomson scattering (TS) diagnostic, which measures profiles of electron temperature (0.03

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.

Download or read book Pressure Profile Control of Internal Transport Barrier Plasmas in Alcator C Mod written by John E. Rice and published by . This book was released on 2003 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: Internal transport barrier (ITB) plasmas with peak pressures of 0.25 MPa and pressure gradients as large as 2.5 MPa/m have been produced in Alcator C-Mod using off-axis ICRF heating. The onset of the ITBs is apparent when the pressure gradient exceeds 1.0 MPa/m, which is similar to the JET criterion of [rho]* s/L [equal to or greater than] 0.014. Concomitant with the peaking of the core pressure as the ITB develops is a drop of the toroidal rotation velocity profile inside of the barrier foot; the maximum of the velocity gradient coincides with the peak in the pressure gradient. The quasi-coherent (QC) mode, associated with the enhanced D[alpha] (EDA) H-mode plasmas which evolve the ITBs, breaks up and disappears as the barriers develop, even though the measured edge pedestal parameters remain fixed. The position of the ITB foot has been moved over a range of 1/3 of the plasma minor radius by varying the toroidal magnetic field. The peak in the calculated bootstrap current density profile has correspondingly been regulated over a similar range in plasma minor radius. The location of the density profile foot is found to expand as the toroidal magnetic field is reduced and the ICRF frequency is lowered. The density foot radius is relatively independent of q95, however, in a scan of the plasma current at fixed BT and wave frequency.

Download or read book Confinement and Transport Research in Alcator C Mod written by Martin Greenwald and published by . This book was released on 2005 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: (cont.) This link unified L-mode and H-mode and established a strong connection between local and global transport. Further work on the role of critical gradient lengths and marginal stability lent quantitative support to the ITG theories for ion transport and have helped elucidate nonlinear saturation mechanisms for the turbulence. Local transport studies demonstrated connections between transport channels, with energy, particle and momentum transport varying across regimes in similar ways. Experiments carried out in collaboration with the DIII-D, ASDEX-U and JET groups confirmed the dimensionless scaling approach over the widest available range in machine sizes. These studies suggest that plasma physics is the dominant influence on transport in the core and pedestal for standard L- and H-mode discharges. Dimensionless scaling experiments have shown a strong improvement in confinement with the normalized gyro-size (1/p*). Confinement was found to be Bohm-like in L-mode and gyro-Bohm-like in H-mode. These experiments also showed a strong degradation in confinement with collisionality. Other articles in this issue discuss impurity transport, momentum transport, H-mode pedestal and threshold physics and internal transport barrier regimes.

Download or read book Double Transport Barrier Plasmas in Alcator C Mod written by John E. Rice and published by . This book was released on 2001 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: Double transport barrier plasmas comprised of an edge enhanced Da (EDA) H-mode pedestal and an internal transport barrier (ITB) have been observed in Alcator C-Mod. The ITB can be routinely produced in ICRF heated plasmas by locating the wave resonance off-axis near r/a [approx.] 0.5, provided the target plasma average density is above [approx.] 1.4 1020/m3, and can develop spontaneously in some Ohmic H-mode discharges. The formation of the barrier appears in conjunction with a decrease or reversal in the central (impurity) toroidal rotation velocity. The ITB foot is located near r/a = 0.5, regardless of how the barrier was produced. The ITBs can persist for [approx.] 15 energy confinement times (tE), but exhibit a continuous increase of the central electron density, up to values near 11021/m3 (in the absence of an internal particle source), followed by collapse of the barrier. This barrier is also evident in the ion temperature profiles, and a significant drop of the core thermal conductivity, ceff, when the barrier forms is confirmed by modeling. Application of additional on-axis ICRF heating arrests the density and impurity peaking, which occurs along with an increase (co-current) in the core rotation velocity. Steady state double barrier plasmas have been maintained for 10 tE or longer, with n/nGW [approx.] 0.75 and with a bootstrap fraction of 0.13 near the ITB foot. The trigger mechanism for the ITB formation is presently not understood.

Download or read book Microturbulent Drift Mode Stability Before Internal Transport Barrier Formation in the Alcator C Mod Radio Frequency Heated H mode written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: H-mode experiments on Alcator C-Mod [I.H. Hutchinson, et al., Phys. Plasma 1 (1994) 1511] which exhibit an internal transport barrier (ITB), have been examined with gyrokinetic simulations, near the ITB onset time. Linear simulations support the picture of ion and electron temperature gradient (ITG, ETG) microturbulence driving high [chi][sub i] and [chi][sub e], respectively, and that stable ITG correlates with reduced particle transport and improved ion thermal confinement on C-Mod. In the barrier region ITG is weakly unstable, with a critical temperature gradient higher than expected from standard models. Nonlinear calculations and the role of E x B shear suppression of turbulence outside the plasma core are discussed in light of recent profile measurements for the toroidal velocity. The gyrokinetic model benchmarks successfully against experiment in the plasma core.

Download or read book Issues in Water and Power Engineering 2011 Edition written by and published by ScholarlyEditions. This book was released on 2012-01-09 with total page 651 pages. Available in PDF, EPUB and Kindle. Book excerpt: Issues in Water and Power Engineering / 2011 Edition is a ScholarlyEditions™ eBook that delivers timely, authoritative, and comprehensive information about Water and Power Engineering. The editors have built Issues in Water and Power Engineering: 2011 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Water and Power Engineering in this eBook to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Water and Power Engineering: 2011 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/.

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 Turbulent Transport In Magnetized Plasmas Second Edition written by C Wendell Horton, Jr and published by #N/A. This book was released on 2017-07-21 with total page 522 pages. Available in PDF, EPUB and Kindle. Book excerpt: For a few seconds with large machines, scientists and engineers have now created the fusion power of the stars in the laboratory and at the same time find the rich range of complex turbulent electromagnetic waves that transport the plasma confinement systems. The turbulent transport mechanisms created in the laboratory are explained in detail in the second edition of 'Turbulent Transport in Magnetized Plasmas' by Professor Horton.The principles and properties of the major plasma confinement machines are explored with basic physics to the extent currently understood. For the observational laws that are not understood — the empirical confinement laws — offering challenges to the next generation of plasma students and researchers — are explained in detail. An example, is the confinement regime — called the 'I-mode' — currently a hot topic — is explored.Numerous important problems and puzzles for the next generation of plasma scientists are explained. There is growing demand for new simulation codes utilizing the massively parallel computers with MPI and GPU methods. When the 20 billion dollar ITER machine is tested in the 2020ies, new theories and faster/smarter computer simulations running in near real-time control systems will be used to control the burning hydrogen plasmas.

Download or read book Iter Physics written by C Wendell Horton, Jr and published by World Scientific. This book was released on 2015-06-25 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: The promise of a vast and clean source of thermal power drove physics research for over fifty years and has finally come to collimation with the international consortium led by the European Union and Japan, with an agreement from seven countries to build a definitive test of fusion power in ITER. It happened because scientists since the Manhattan project have envisioned controlled nuclear fusion in obtaining energy with no carbon dioxide emissions and no toxic nuclear waste products.This large toroidal magnetic confinement ITER machine is described from confinement process to advanced physics of plasma-wall interactions, where pulses erupt from core plasma blistering the machine walls. Emissions from the walls reduce the core temperature which must remain ten times hotter than the 15 million degree core solar temperature to maintain ITER fusion power. The huge temperature gradient from core to wall that drives intense plasma turbulence is described in detail.Also explained are the methods designed to limit the growth of small magnetic islands, the growth of edge localized plasma plumes and the solid state physics limits of the stainless steel walls of the confinement vessel from the burning plasma. Designs of the wall coatings and the special 'exhaust pipe' for spent hot plasma are provided in two chapters. And the issues associated with high-energy neutrons — about 10 times higher than in fission reactions — and how they are managed in ITER, are detailed.

Download or read book Energy and Water Development Appropriations For 2006 Part 4B 109 1 Hearings written by and published by . This book was released on 2005 with total page 1444 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fusion Physics written by MITSURU KIKUCHI and published by International Atomic Energy. This book was released on 2002-01-01 with total page 1158 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book 107 2 Hearings Energy and Water Development Appropriations For 2003 Part 4 2002 written by and published by . This book was released on 2002 with total page 1512 pages. Available in PDF, EPUB and Kindle. Book excerpt: