Download or read book Toroidal Rotation and Core Ion Confinement with RF Heating in DIII D written by and published by . This book was released on 1999 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: Shear in the E x B flow velocity can stabilize turbulent transport [1], and so it is of interest to understand the physics behind electric field generation and modification in the tokamak. In DIII-D the core radial electric field in many regimes is generated by flow velocities driven by momentum input from neutral beam injection (NBI). In a variety of conditions it is observed that direct electron heating is accompanied by a reduction in the NBI driven toroidal rotation velocity, U{sub {phi}}, and the ion temperature, T{sub i}, primarily in the core, [rho]
Download or read book Reduction of Toroidal Rotation by Fast Wave Power in DIII D written by and published by . This book was released on 1997 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: The application of fast wave power in DIII-D has proven effective for both electron heating and current drive. Since the last RIF Conference FW power has been applied to advanced confinement regimes in DIII-D; negative central shear (NCS), VH- and H-modes, high [beta]{sub p}, and high-li. Typically these regimes show enhanced confinement of toroidal momentum exhibited by increased toroidal rotation velocity. Indeed, layers of large shear in toroidal velocity are associated with transport barriers. A rather common occurrence in these experiments is that the toroidal rotation velocity is decreased when the FW power is turned on, to lowest order independent of whether the antennas are phased for co or counter current drive. At present all the data is for co-injected beams. The central toroidal rotation can be reduced to 1/2 of the non-FW level. Here the authors describe the effect in NCS discharges with co-beam injection.
Download or read book Nuclear Fusion written by and published by . This book was released on 2008-10 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 2001 with total page 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.
Download or read book Radio Frequency Power in Plasmas written by Tak K. Mau and published by American Inst. of Physics. This book was released on 2001-11-09 with total page 570 pages. Available in PDF, EPUB and Kindle. Book excerpt: This proceedings volume includes the most recent research advances in the application of RF power in plasmas, mainly in fusion science. Most papers deal with plasma heating and current drive, profile control, and stabilization using RF techniques, with some on RF sources and launchers. New and exciting results from all major tokamak experiments, and from theory and modeling are included. There is also a paper on RFplasma application in space propulsion by an active NASA astronaut. This book is a valuable reference for the RF researchers in fusion and other disciplines.
Download or read book Ion Thermal Confinement in the TFTR Enhanced Confinement Regime written by and published by . This book was released on 1988 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Measurements of the plasma ion temperature and toroidal rotation speed profiles have allowed the study of ion thermal transport in the TFTR hot ion enhanced confinement regime. Central ion temperatures up to 30 keV and rotation speeds up to 8 x 105 m/sec have been confirmed with new diagnostic measurements, and the ion thermal diffusivity is found to be non-neoclassical and comparable to the anomalous electron thermal diffusivity. The dominant effects of strong rotation are the down-shifting of the neutral beam energies in the plasma frame, which results in reduced ion and electron heating on axis, and the presence of off-axis ion heating from viscous damping of the plasma rotation. 14 refs., 3 figs.
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.
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 TOROID ROTATION IN NEUTRAL BEAM HEATED DISCHARGES IN DIII D written by and published by . This book was released on 2002 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is known that the toroidal angular momentum and the ion thermal energy are correlated in tokamak discharges heated by neutral beam injection. Here, data from ten years of measurements on DIII-D are considered, for representative discharges from all types and all conditions. The ratio of simple replacement times for momentum and energy is found to order this correlation indicating that these times are approximately equal, across the minor radius. Representative discharges of several types are discussed in more detail, as well as transport analysis results for the momentum and thermal ion diffusivities.
Download or read book Energy Research Abstracts written by and published by . This book was released on 1993-10 with total page 578 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book His Sound City Jests written by and published by . This book was released on 1611 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Regimes of Improved Confinement and Stability in DIII D Obtained Through Current Profile Modifications written by and published by . This book was released on 1992 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: Several regimes of improved confinement and stability have been obtained in recent experiments in the DIII-D tokamak by dynamically varying the toroidal current density profile to transiently produce a poloidal magnetic field profile with more favorable confinement and stability properties. A very peaked current density profile with high plasma internal inductance, l{sub i}, is produced either by a rapid change in the plasma poloidal cross section or by a rapid change in the total plasma current. Values of thermal energy confinement times nearly 1.8 times the JET/DIII-D ELM-free H-mode thermal confinement scaling are obtained. The confinement enhancement factor over the ITER89-P L-mode confinement scaling, H, is as high as 3. Normalized toroidal beta, [beta]{sub N}, greater than 6%-m-T/MA and values of the product [beta]{sub N}H greater than 15 have also been obtained. Both the confinement and the maximum achievable [beta] vary with l{sub i} and decrease as the current profile relaxes. For strongly shaped H-mode discharges, in addition to the current density profile peakedness, as measured by l{sub i} other current profile parameters, such as its distribution near the edge region, may also affect the confinement enhancement.
Download or read book H mode and VH mode Confinement Improvement in DIII D Investigations of Turbulence Local Transport and Active Control of the Shear in the E times B Flow written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The hypothesis of stabilization of turbulence by shear in the E[times] B drift speed successfully predicts the observed turbulence reduction and confinement improvement seen at the L to H transition. This same hypothesis is the best explanation to date for the further confinement improvement seen in the plasma core when the plasma goes from H-mode to VH-mode. Consequently, the most fundamental question for H-mode studies now is: how is the electric field E[sub r] formed? The radial force balance equation relates E[sub r] to the main ion pressure gradient[triangledown]P[sub i], poloidal rotation[nu][sub[theta]i], and toroidal rotation[nu][sub[phi]i]. In the plasma edge, direct measurements show[triangledown]P[sub i] and[nu][sub[theta]i] are the important terms at the L to H transition, with[triangledown]P[sub i] being the dominant, negative term throughout most of the H-mode. Since E[sub r] is observed to change prior to the change in[triangledown]P[sub i], the authors infer that main ion rotation, probably[nu][sub[theta]i], changes first, triggering the transition. E[sub r] is seen to change prior to the change in fluctuations, consistent with E[times] B shear causing the change in fluctuations and transport. In the plasma core, E[sub r] is primarily related to[nu][sub[phi]i]. There is a clear temporal and spatial correlation between the change in E[times] B shear and the region of local confinement improvement when the plasma goes from H-mode to VH-mode. Direct manipulation of[nu][sub[phi]i] and E[times] B shear using the drag produced by a non-axisymmetric magnetic perturbation has produced clear changes in local transport consistent with the E[times] B shear stabilization hypothesis. The implications of these results for theories of the L to H and H to VH transitions will be discussed. 83 refs., 5 figs.
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.
Download or read book DIII D Experiments and Modeling of Core Confinement in Quiescent Double Barrier Plasmas written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We continue to explore Quiescent Double Barrier (QDB) operation on DIII-D to address issues of critical importance to internal transport barrier (ITB) plasmas. QDB plasmas exhibit both a core transport barrier and a quiescent, H-mode edge barrier. Both experiments and modeling of these plasmas are leading to an increased understanding of this regime and it's potential advantages for advanced-tokamak (AT) burning-plasma operation. These near steady plasma conditions have been maintained on DIII-D for up to 4s, times greater than 35[tau][sub E], and exhibit high performance with [beta][sub N]> 2.5 and neutron production rates S[sub n] [approx] 1 x 10[sup 16]s[sup -1]. Recent experiments have been directed at exploring both the current profile modification effects of electron cyclotron current drive (ECCD) and electron cyclotron (ECH) heating-induced changes in temperature, density and impurity profiles. We use model-based analysis to determine the effects of both heating and current drive on the q-profile in these QDB plasmas. Experiments based on predictive modeling achieved a significant modification to the q-profile evolution [1] resulting from the non-inductive current drive effects due to direct ECCD and changes in the bootstrap and neutral beam current drive components. We observe that the injection of EC power inside the barrier region changes the density peaking from n[sub e]/n[sub e] = 2.1 to 1.5 accompanied by a significant reduction in the core carbon and high-Z impurities, nickel and copper.
Download or read book Ion Cyclotron Heating of a Plasma and Energy Confinement in a Toroidal Quadrupole written by T. Takizuka and published by . This book was released on 1974 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt:
