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Confinement And Stability Of Vh Mode Discharges In The Diii D Tokamak
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Book Synopsis Confinement and Stability of VH-mode Discharges in the DIII-D Tokamak by :
Download or read book Confinement and Stability of VH-mode Discharges in the DIII-D Tokamak written by and published by . This book was released on 1992 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: A regime of very high confinement (VH-mode) has been observed in neutral beam-heated deuterium discharges in the DIII-D tokamak with thermal energy confinement times up to [approx]3.6 times that predicted by the ITER-89P L-mode scaling and 2 times that predicted by ELM-free H-mode thermal confinement scalings. This high confinement has led to increased plasma performance, n[sub D] (0)T[sub i](0)[tau][sub E] = 2 [times] 10[sup 20] m[sup [minus]3] keV sec with I[sub p] = 1.6 MA, B[sub T] = 2.1 T, Z[sub eff] [le] 2. Detailed transport analysis shows a correspondence between the large decrease in thermal diffusivity in the region 0.75 [le] [rho] [le] 0.9 and the development of a strong shear in the radial electric field in the same region. This suggests that stabilization of turbulence by sheared E [times] B flow is responsible for the improved confinement in VH-mode. A substantial fraction of the edge plasma entering the second regime of stability may also contribute to the increase in confinement. The duration of the VH-mode phase has been lengthened by feedback controlling the input power to limit plasma beta.
Book Synopsis Optimized Profiles for Improved Confinement and Stability in the DIII-D Tokamak by :
Download or read book Optimized Profiles for Improved Confinement and Stability in the DIII-D Tokamak written by and published by . This book was released on 1995 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Simultaneous achievement of high energy confinement, [tau]{sub E}, and high plasma beta, [beta], leads to an economically attractive compact tokamak fusion reactor. High confinement enhancement, H = [tau]{sub E}/[tau]{sub E-ITER89P} = 4, and high normalized beta [beta]{sub N} = [beta]/(I/aB) = 6%-m-T/MA, have been obtained in DIII-D experimental discharges. These improved confinement and/or improved stability limits are observed in several DIII-D high performance operational regimes: VH-mode, high l{sub i} H-mode, second stable core, and high beta poloidal. The authors have identified several important features of the improved performance in these discharges: details of the plasma shape, toroidal rotation or ExB flow profile, q profile and current density profile, and pressure profile. From the improved physics understanding of these enhanced performance regimes, they have developed operational scenarios which maintain the essential features of the improved confinement and which increase the stability limits using localized current profile control. The stability limit is increased by modifying the interior safety factor profile to be nonmonotonic with high central q, while maintaining the edge current density consistent with the improved transport regimes and the high edge bootstrap current. They have calculated high beta equilibria with [beta]{sub N} = 6.5, stable to ideal n = 1 kinks and stable to ideal ballooning modes. The safety factor at the 95% flux surface is 6, the central q value is 3.9 and the minimum in q is 2.6. The current density profile is maintained by the natural profile of the bootstrap current, and a modest amount of electron cyclotron current drive.
Book Synopsis VH-Mode Discharges in the DIII-D Tokamak by :
Download or read book VH-Mode Discharges in the DIII-D Tokamak written by and published by . This book was released on 1992 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: Introduction. A regime of very high confinement (VH-mode) has been observed in divertor discharges in DIII-D. The VH-mode, first seen following the initial boronization of the DIII-D vessel in 1991, exhibits total energy confinement a factor of 2.5 to 3.5 greater than that predicted by the ITER89-P L-mode scaling relation. Also, confinement of thermal energy alone is greater than 1.6 times that of the JET/DIII-D H-mode scaling and in many cases has exceeded twice that amount. VH-mode is observed during a long (≤0.8 sec) ELM-free phase of the discharges. At the beginning of the ELM-free period, the plasma appears to be in H-mode, with confinement near that predicted by the JET/DIII-D scaling. In the usual H-mode, confinement is observed to decrease or remain constant over time. In the present discharges, confinement has been observed to remain nearly constant for up to hundreds of milliseconds, after which the behavior sharply deviates from H-mode as the confinement begins to increase over time. This increase in confinement continues until the occurrence of a beta- related ([beta]>2.8I/aB) global MHD event, which rapidly decreases the plasma stored energy with a temperature reduction across the entire profile. Magnetic measurements indicate that at least in some cases, this event includes both an internal n = 1 mode and a more localized high-n mode near the edge. After this event, the plasma relaxes into an ELMing H-mode phase. As a consequence of the boronization, the plasmas in these discharges are unusually clean, with very low radiated power. In previous H-mode discharges, the radiated power increased during the ELM-free, sometimes reaching levels comparable with the input power if the ELM-free period was long enough. Also, Z{sub eff}is constant or decreasing over the length of the discharge, with a central value of ≈1. It is noted that most of the energy in these discharges is thermal energy, with ≤10% contained in fast ions.
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 The Role of the Radial Electric Field in Confinement and Transport in H-mode and VH-mode Discharges in the DIII-D Tokamak by :
Download or read book The Role of the Radial Electric Field in Confinement and Transport in H-mode and VH-mode Discharges in the DIII-D Tokamak written by and published by . This book was released on 1993 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: Measurements of the radial electric field, E{sub r}, with high spatial and high time resolution in H-mode and VH-mode discharges in the DIII-D tokamak have revealed the significant influence of the shear in E{sub r} on confinement and transport in these discharges. These measurements are made using the DIII-D Charge Exchange Recombination (CER) System. At the L-H transition in DIII-D plasmas, a negative well-like E{sub r} profile develops just within the magnetic separatrix. A region of shear in E{sub r} results, which extends 1 to 2 cm into the plasma from the separatrix. At the transition, this region of sheared E{sub r} exhibits the greatest increase in impurity ion poloidal rotation velocity and the greatest reduction in plasma fluctuations. A transport barrier is formed in this same region of E x B velocity shear as is signified by large increases in the observed gradients of the ion temperature, the carbon density, the electron temperature and electron density. The development of the region of sheared E{sub r}, the increase in impurity ion poloidal rotation, the reduction in plasma turbulence, and the transport barrier all occur simultaneously at the L-H transition. Measurements of the radial electric field, plasma turbulence, thermal transport, and energy confinement have been performed for a wide range of plasma conditions and configurations. The results support the supposition that the progression of improving confinement at the L-H transition, into the H-mode and then into the VH-mode can be explained by the hypothesis of the suppression of plasma turbulence by the increasing penetration of the region of sheared E x B velocity into the plasma interior.
Book Synopsis Development of a Tokamak Plasma Optimized for Stability and Confinement by :
Download or read book Development of a Tokamak Plasma Optimized for Stability and Confinement written by and published by . This book was released on 1995 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Advanced Tokamak Research on the DIII-D Tokamak by :
Download or read book Advanced Tokamak Research on the DIII-D Tokamak written by and published by . This book was released on 1994 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Energy Research Abstracts written by and published by . This book was released on 1994-02 with total page 484 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Regimes of Improved Confinement and Stability in DIII-D Obtained Through Current Profile Modifications by :
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.
Book Synopsis Impact of Edge Current Density and Pressure Gradient on the Stability of DIII-D High Performance Discharges by :
Download or read book Impact of Edge Current Density and Pressure Gradient on the Stability of DIII-D High Performance Discharges written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the major goals of advanced tokamak research is to develop plasma configurations with good confinement and improved stability at high[beta]. In DIII-D, various high performance configurations with H- and VH-mode edges have been produced. These include discharges with poloidal cross sections in the forms of dee and crecent shapes, single- and double-null divertors, and with various central magnetic shear profiles and current profile peakedness. All these discharges exhibit confinement in the outer plasma region which leads to a large edge pressure gradient and a large edge bootstrap current driven by this steep pressure gradient. These edge conditions often drive an instability near the edge region which can severely degrade the discharge performance. An understanding of this edge instability is essential to sustain an enhance discharge performance.
Book Synopsis Controlled Fusion and Plasma Physics by : Kenro Miyamoto
Download or read book Controlled Fusion and Plasma Physics written by Kenro Miyamoto and published by CRC Press. This book was released on 2006-10-23 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt: Resulting from ongoing, international research into fusion processes, the International Tokamak Experimental Reactor (ITER) is a major step in the quest for a new energy source.The first graduate-level text to cover the details of ITER, Controlled Fusion and Plasma Physics introduces various aspects and issues of recent fusion research activities through the shortest access path. The distinguished author breaks down the topic by first dealing with fusion and then concentrating on the more complex subject of plasma physics. The book begins with the basics of controlled fusion research, followed by discussions on tokamaks, reversed field pinch (RFP), stellarators, and mirrors. The text then explores ideal magnetohydrodynamic (MHD) instabilities, resistive instabilities, neoclassical tearing mode, resistive wall mode, the Boltzmann equation, the Vlasov equation, and Landau damping. After covering dielectric tensors of cold and hot plasmas, the author discusses the physical mechanisms of wave heating and noninductive current drive. The book concludes with an examination of the challenging issues of plasma transport by turbulence, such as magnetic fluctuation and zonal flow. Controlled Fusion and Plasma Physics clearly and thoroughly promotes intuitive understanding of the developments of the principal fusion programs and the relevant fundamental and advanced plasma physics associated with each program.
Book Synopsis Scientific and Technical Aerospace Reports by :
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 548 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Recent Results from the DIII-D Tokamak by :
Download or read book Recent Results from the DIII-D Tokamak written by and published by . This book was released on 1995 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: The goal of the DIII-D program is to provide the integrated basis for commercially attractive steady state fusion power plants. Significant progress toward this goal has been achieved, enabled by system improvements including an error field correction coil, an expanded diagnostic set, a digital plasma control system, and high power rf systems. Simultaneous improvements in both the confinement and stability have been achieved during both VH-mode and negative central shear discharges. Fully non-inductive discharges with high bootstrap current fraction have been obtained. The divertor program has demonstrated simultaneous reduction of divertor heat flux and effective particle control using gas puffing and an in-vessel cryopump. Control of the wall particle inventory, He exhaust, and characterization of the scrapeoff layer and divertor plasma have been achieved. Progress has also been made in addressing additional specific needs for ITER: investigation of basic transport scaling, disruption characterization and avoidance, material erosion, and steady state beta limits.
Book Synopsis Stability of Negative Central Magnetic Shear Discharges in the DIII-D Tokamak by :
Download or read book Stability of Negative Central Magnetic Shear Discharges in the DIII-D Tokamak written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Discharges with negative central magnetic shear (NCS) hold the promise of enhanced fusion performance in advanced tokamaks. However, stability to long wavelength magnetohydrodynamic modes is needed to take advantage of the improved confinement found in NCS discharges. The stability limits seen in DIII-D experiments depend on the pressure and current density profiles and are in good agreement with stability calculations. Discharges with a strongly peaked pressure profile reach a disruptive limit at low beta, [beta][sub N]=[beta] (I/aB)[sup -1][le] 2.5 (% m T/MA), caused by an n= 1 ideal internal kink mode or a global resistive instability close to the ideal stability limit. Discharges with a broad pressure profile reach a soft beta limit at significantly higher beta, [beta][sub N]= 4 to 5, usually caused by instabilities with n> 1 and usually driven near the edge of the plasma. With broad pressure profiles, the experimental stability limit is independent of the magnitude of negative shear but improves with the internal inductance, corresponding to lower current density near the edge of the plasma. Understanding of the stability limits in NCS discharges has led to record DIII-D fusion performance in discharges with a broad pressure profile and low edge current density.
Book Synopsis Scientific and Technical Aerospace Reports by :
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 610 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Book Synopsis Long-Pulse, High-Performance Discharges in the DIII-D Tokamak by :
Download or read book Long-Pulse, High-Performance Discharges in the DIII-D Tokamak written by and published by . This book was released on 2000 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: Significant progress in obtaining high performance discharges for many energy confinement times in the DIII-D tokamak has been realized since the previous IAEA meeting. In relation to previous discharges, normalized performance H"0 has been sustained for>5 [tau]{sub E} with q{sub min}>1.5. (The normalized performance is measured by the product [beta]{sub N} H9 indicating the proximity to the conventional [beta] limits and energy confinement quality, respectively.) These H-mode discharges have an ELMing edge and [beta] H" 5%. The limit to increasing [beta] is a resistive wall mode, rather than the tearing modes previously observed. Confinement remains good despite the increase in q. The global parameters were chosen to optimize the potential for fully non-inductive current sustainment at high performance, which is a key program goal for the DIII-D facility in the next two years. Measurement of the current density and loop voltage profiles indicate H"5% of the current in the present discharges is sustained non-inductively. The remaining ohmic current is localized near the half radius. The electron cyclotron heating system is being upgraded to replace this remaining current with ECCD. Density and [beta] control, which are essential for operating advanced tokamak discharges, were demonstrated in ELMing H-mode discharges with [beta]{sub N}H9 H"7 for up to 6.3 s or H"34 [tau]{sub E}. These discharges appear to be in resistive equilibrium with q{sub min} H"1.05, in agreement with the current profile relaxation time of 1.8 s.
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.
