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Transport And Performance In Diii D Discharges With Weak Or Negative Central Magnetic Shear
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Book Synopsis Transport and Performance in DIII-D Discharges with Weak Or Negative Central Magnetic Shear by :
Download or read book Transport and Performance in DIII-D Discharges with Weak Or Negative Central Magnetic Shear written by and published by . This book was released on 1996 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: Discharges exhibiting the highest plasma energy and fusion reactivity yet realized in the DIII-D tokamak have been produced by combining the benefits of a hollow or weakly sheared central current profile with a high confinement (H-mode) edge. In these discharges, low power neutral beam injection heats the electrons during the initial current ramp, and {open_quotes}freezes in{close_quotes} a hollow or flat central current profile. When the neutral beam power is increased, formation of a region of reduced transport and highly peaked profiles in the core often results. Shortly before these plasmas would otherwise disrupt, a transition is triggered from the low (L-mode) to high (H-mode) confinement regimes, thereby broadening the pressure profile and avoiding the disruption. These plasmas continue to evolve until the high performance phase is terminated nondisruptively at much higher [beta]{sub T} (ratio of plasma pressure to toroidal magnetic field pressure) than would be attainable with peaked profiles and an L-mode edge. Transport analysis indicates that in this phase, the ion diffusivity is equivalent to that predicted by Chang-Hinton neoclassical theory over the entire plasma volume. This result is consistent with suppression of turbulence by locally enhanced E x B flow shear, and is supported by observations of reduced fluctuations in the plasma. Calculations of performance in these discharges extrapolated to a deuterium-tritium fuel mixture indicates that such plasmas could produce a DT fusion gain Q{sub DT} = 0.32.
Download or read book כובשים במצוקה written by and published by . This book was released on 1983 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Local Analysis of Confinement and Transport in Neutral Beam Heated DIII-D Discharges with Negative Magnetic Shear by :
Download or read book Local Analysis of Confinement and Transport in Neutral Beam Heated DIII-D Discharges with Negative Magnetic Shear written by and published by . This book was released on 1996 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: High triangularity double-null discharges with weak or negative central magnetic shear and with both an L-mode and an H-mode edge have been produced on DIII-D. The L-mode edge cases are characterized by peaked toroidal rotation, ion temperature, and plasma density profiles with reduced ion transport in the negative shear region. The H-mode edge cases have broader profiles consistent with reduced ion transport, to the neoclassical level, over the entire plasma cross section. The L-mode edge cases have a greater reduction in central ion diffusivity with stronger negative shear while the H-mode edge cases do not exhibit this dependence. Plasma fluctuation measurements show that a dramatic reduction in turbulence accompanies the improved ion confinement. Calculations of sheared E x B flow indicate that this mechanism can overcome the [eta]{sub i} mode growth rate in the region of reduced transport.
Book Synopsis Summary Record of the 1st Part of the 20th Meeting, Held at the Palais Des Nations, Geneva, on Monday, 12 February 1990 by :
Download or read book Summary Record of the 1st Part of the 20th Meeting, Held at the Palais Des Nations, Geneva, on Monday, 12 February 1990 written by and published by . This book was released on 1990 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Confinement and Stability of DIII-D Negative Central Shear Discharges by :
Download or read book Confinement and Stability of DIII-D Negative Central Shear Discharges written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Negative central magnetic shear (NCS) discharges with[Beta][sub N][le] 4, H[le] 3, and up to 80% of the current non-inductively driven are reproducibly produced in the DIII-D tokamak. Strong peaking of T[sub i], plasma rotation, and in some cases n[sub e] are observed inside the NCS region. Transport analysis shows that the core ion thermal diffusivity is substantially reduced and near the neoclassical value after the formation of the internal transport barrier. The negative central shear is necessary but not sufficient for the formation of this transport barrier. The power required for the formation appears to increase with the toroidal magnetic field. The high performance phase of H-mode NCS discharges often ends with an ELM-like collapse initiated from the edge whereas the L-mode discharges which have a more peaked pressure profile tend to end with a more global n= 1 MHD event.
Book Synopsis Core Turbulence and Transport Reduction in DIII-D Discharges with Weak Or Negative Magnetic Shear by :
Download or read book Core Turbulence and Transport Reduction in DIII-D Discharges with Weak Or Negative Magnetic Shear written by and published by . This book was released on 1997 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: Core turbulence fluctuation levels have been suppressed in DIII-D discharges with weak or negative magnetic shear (NCS) near the magnetic axis. In some weak magnetic shear discharges the ion thermal transport has been reduced to neoclassical levels throughout the whole plasma. The cause of the transport reduction is investigated by calculating the stability of toroidal drift waves, i.e., ion temperature gradient modes (ITG) and trapped electron modes (TE), with a comprehensive gyrokinetic linear stability code. It is found that the ITG modes and TE modes are stabilized by ExB velocity shear. The ExB velocity shear is primarily responsible for the spontaneous growth of a region of suppressed ion thermal transport. Surprisingly, the negative magnetic shear and Shafranov shift are only weak stabilizing influences for the ITG and TE modes in the DIII-D cases studied. Negative magnetic shear does eliminate the ideal magnetohydrodynamic ballooning mode instability which is a necessary access criteria for these improved core confinement regimes. Dilution of the thermal ions by fast ions from the heating beams and hot ions compared to electrons are found to be important stabilizing influences in the core.
Book Synopsis Rotational and Magnetic Shear Stabilization of Magnetohydrodynamic Modes and Turbulence in DIII-D High Performance Discharges by :
Download or read book Rotational and Magnetic Shear Stabilization of Magnetohydrodynamic Modes and Turbulence in DIII-D High Performance Discharges written by and published by . This book was released on 1996 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: The confinement and the stability properties of the DIII-D tokamak high performance discharges are evaluated in terms of rotational and magnetic shear with emphasis on the recent experimental results obtained from the negative central magnetic shear (NCS) experiments. In NCS discharges, a core transport barrier is often observed to form inside the NCS region accompanied by a reduction in core fluctuation amplitudes. Increasing negative magnetic shear contributes to the formation of this core transport barrier, but by itself is not sufficient to fully stabilize the toroidal drift mode (trapped- electron-[eta]{sub i}mode) to explain this formation. Comparison of the Doppler shift shear rate to the growth rate of the [eta]{sub i} mode suggests that the large core {bold E x B} flow shear can stabilize this mode and broaden the region of reduced core transport . Ideal and resistive stability analysis indicates the performance of NCS discharges with strongly peaked pressure profiles is limited by the resistive interchange mode to low [Beta]{sub N}> 2.3. This mode is insensitive to the details of the rotational and the magnetic shear profiles. A new class of discharges which has a broad region of weak or slightly negative magnetic shear (WNS) is described. The WNS discharges have broader pressure profiles and higher values than the NCS discharges together with high confinement and high fusion reactivity.
Book Synopsis Characteristics of the Scrape-off Layer in DIII-D High-performance Negative Central Magnetic Shear Discharges by :
Download or read book Characteristics of the Scrape-off Layer in DIII-D High-performance Negative Central Magnetic Shear Discharges written by and published by . This book was released on 1996 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this paper the authors present measurements of the global power and particle balance in the high-performance phase of negative central magnetic shear (NCS) discharges and compare with reference VH-mode discharges. The principal differences observed are that NCS has a much lower fraction of the total input power flowing into the boundary, less core radiation, and larger rate of stored energy increase as a fraction of total power. Scrape-off layer (SOL) temperature and divertor heat flux profiles, and radiation profiles at the midplane, are similar to VH-mode. Due to the good core particle confinement and efficient fueling by neutral beam injection (NBI), with little gas puffing, the gas load on the walls and the recycling are very low during the NCS discharges. This results in a rate of density rise relative to beam fueling at the L to H transition time which is 1/3 of the value for VH transitions, which is in turn 1/2 that for L-to-ELMing-H-mode transitions.
Book Synopsis Turbulent Transport in Magnetized Plasmas by : Wendell Horton
Download or read book Turbulent Transport in Magnetized Plasmas written by Wendell Horton and published by World Scientific. This book was released on 2012 with total page 518 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book explains how magnetized plasmas self-organize in states of electromagnetic turbulence that transports particles and energy out of the core plasma faster than anticipated by the fusion scientists designing magnetic confinement systems in the 20th century. It describes theory, experiments and simulations in a unified and up-to-date presentation of the issues of achieving nuclear fusion power.
Download or read book חכמי התלמוד written by and published by . This book was released on 1931 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis 23rd European Physical Society Conference on Controlled Fusion and Plasma Physics by :
Download or read book 23rd European Physical Society Conference on Controlled Fusion and Plasma Physics written by and published by . This book was released on 1996 with total page 524 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Progress Towards Sustainment of Internal Transport Barriers in DIII-D. by :
Download or read book Progress Towards Sustainment of Internal Transport Barriers in DIII-D. written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Neutral beam heated discharges with internal transport barriers (ITB) have been observed in most of the world's major tokamaks including DIII-D, TFTR, JT-60U and JET. Improved core confinement has been observed over a range of q profiles, including negative central magnetic shear (NCS) and weak positive shear. In discharges with an L-mode edge, the duration of ITBs is generally limited to a few energy confinement times ([tau][sub e]) by low-n MHD activity driven by the steep core pressure gradient or by q[sub min] passing through low-order rational values. In order for ITBs to be useful in achieving a more compact advanced tokamak, the radius of the ITB must be expanded and the pressure gradient must be controlled in order to optimize[beta][sub N] and the bootstrap alignment. In this paper, the authors discuss the results of recent experiments on DIII-D to produce and sustain ITBs for longer pulse lengths. Three techniques are evaluated: (1) reduction of neutral beam power (P[sub NBI]) and plasma current to form a weaker ITB which can be sustained; (2) use of an ELMing H-mode edge to help broaden the pressure profile and improve MHD instability; (3) modification of the plasma shape (squareness) to achieve smaller ELMs with a lower density pedestal at the edge.
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.
Book Synopsis 16th IEEE/NPSS Symposium Fusion Engineering by :
Download or read book 16th IEEE/NPSS Symposium Fusion Engineering written by and published by . This book was released on 1995 with total page 900 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Transport Simulation of Negative Magnetic Shear Discharges by :
Download or read book Transport Simulation of Negative Magnetic Shear Discharges written by and published by . This book was released on 1994 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the present work the authors present simulations which show that the hollow current profile can be maintained in quasi-steady state through a self-consistently determined combination of bootstrap current and neutral beam and rf current drive. Controllability of the q profile is demonstrated by eliminating low m/n mode number instabilities from these discharges by maintaining q> 1.5 at all times, starting from appropriate initial conditions. At moderately high?{sub p}, the bootstrap current can be a substantial fraction of the total current and the ability to maintain the proper total current density profile depends on the bootstrap current profile and the availability of suitable localized heating and current drive. In these simulations, they use electron cyclotron heating, ion cyclotron heating, and electron cyclotron and fast wave current drive. The ability to maintain the profiles is demonstrated using several energy transport models. Self-consistent transport simulations are used to model the SSC discharges using the ONETWO transport code coupled to rf heating and current drive packages FASTWAVE and TORAY. To accurately model inductive and driven current profile evolution, the additional source terms that arise in Faradays̀ law due to internal flux surface motion are included by coupling the transport calculations to a fixed boundary equilibrium code. To test the sensitivity of the results to the transport model used, they model DIII-D discharges using thermal conductivities consistent with improved confinement DIII-D discharges, and with the Rebut-Lallia-Watkins model of energy transport.
Book Synopsis Fusion Technology 1996 by : C. Varandas
Download or read book Fusion Technology 1996 written by C. Varandas and published by Elsevier. This book was released on 2012-12-02 with total page 1057 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of these proceedings was to provide a platform for the exchange of information on the design, construction and operation of fusion experiments. The technology which is being developed for the next step devices and fusion reactors was also covered.
Book Synopsis Modeling of Current Profile Evolution and Equilibria in Negative Central Shear Discharges in the DIII-D Experiment by :
Download or read book Modeling of Current Profile Evolution and Equilibria in Negative Central Shear Discharges in the DIII-D Experiment written by and published by . This book was released on 1996 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent DIII-D advanced tokamak experiments with negative central shear (NCS) have resulted in operation at high normalized [beta], [beta]{sub N}=[beta]/(I/aB), to 4.2, confinement enhancement factors to H=4 (H=[tau]{sub E}/[tau]ITER-89P), and record neutron rates for DIII-D to 2.4X1016 neutrons/sec. These data were obtained during high triangularity, single and double null diverted operation with peaked (L-mode) and broad (H-mode) pressure profiles. We are modeling the spatial and temporal current profile evolution for these discharges using Corsica, a predictive 1-1/2 D equilibrium and transport code. Current profile evolution is self-consistently determined by including current diffusion resulting from current drive due to early neutral beam injection during the ohmic current ramp-up phase of the discharge and the bootstrap current drive associated with pressure profile evolution.
