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Long Pulse High Performance Discharges In The Diii D Tokamak
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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 DIII-D Advanced Tokamak Research Overview by :
Download or read book DIII-D Advanced Tokamak Research Overview written by and published by . This book was released on 1999 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: This paper reviews recent progress in the development of long-pulse, high performance discharges on the DIII-D tokamak. It is highlighted by a discharge achieving simultaneously [beta]{sub N}H of 9, bootstrap current fraction of 0.5, noninductive current fraction of 0.75, and sustained for 16 energy confinement times. The physics challenge has changed in the long-pulse regime. Non-ideal MHD modes are limiting the stability, fast ion driven modes may play a role in fast ion transport which limits the stored energy and plasma edge behavior can affect the global performance. New control tools are being developed to address these issues.
Book Synopsis Mémoire adressé à l'assembleé fédérale par le Conseil d'État du canton de Genève dans l'affaire Ochsenbein by :
Download or read book Mémoire adressé à l'assembleé fédérale par le Conseil d'État du canton de Genève dans l'affaire Ochsenbein written by and published by . This book was released on 1872 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis HIGH PERFORMANCE STATIONARY DISCHARGES IN THE DIII-D TOKAMAK. by : 45th ANNUAL MEETING OF DIVISION OF PLASM.
Download or read book HIGH PERFORMANCE STATIONARY DISCHARGES IN THE DIII-D TOKAMAK. written by 45th ANNUAL MEETING OF DIVISION OF PLASM. and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent experiments in the DIII-D tokamak [J.L. Luxon, Nucl. Fusion 42,614 (2002)] have demonstrated high {beta} with good confinement quality under stationary conditions. Two classes of stationary discharges are observed--low q{sub 95} discharges with sawteeth and higher q{sub 95} without sawteeth. The discharges are deemed stationary when the plasma conditions are maintained for times greater than the current profile relaxation time. In both cases the normalized fusion performance ({beta}{sub N}H{sub 89P}/q{sub 95}{sup 2}) reaches or exceeds the value of this parameter projected for Q{sub fus} = 10 in the International Thermonuclear Experimental Reactor (ITER) design [R. Aymar, et al., Plasma Phys. Control. Fusion 44, 519 (2002)]. The presence of sawteeth reduces the maximum achievable normalized {beta}, while confinement quality (confinement time relative to scalings) is largely independent of q{sub 95}. Even with the reduced {beta} limit, the normalized fusion performance maximizes at the lowest q{sub 95}. Projections to burning plasma conditions are discussed, including the methodology of the projection and the key physics issues which still require investigation.
Book Synopsis Long Pulse Advanced Tokamak Discharges in the DIII-D Tokamak by :
Download or read book Long Pulse Advanced Tokamak Discharges in the DIII-D Tokamak written by and published by . This book was released on 2002 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the main goals for the DIII-D research program is to establish an advanced tokamak plasma with high bootstrap current fraction that can be sustained in-principle steady-state. Substantial progress has been made in several areas during the last year. The resistive wall mode stabilization has been done with spinning plasmas in which the plasma pressure has been extended well above the no-wall beta limit. The 3/2 neoclassical tearing mode has been stabilized by the injection of ECH into the magnetic islands, which drives current to substitute the missing bootstrap current. In these experiments either the plasma was moved or the toroidal field was changed to overlap the ECCD resonance with the location of the NTMs. Effective disruption mitigation has been obtained by massive noble gas injection into shots where disruptions were deliberately triggered. The massive gas puff causes a fast and clean current quench with essentially all the plasma energy radiated fairly uniformly to the vessel walls. The run-away electrons that are normally seen accompanying disruptions are suppressed by the large density of electrons still bound on the impurity nuclei. Major elements required to establish integrated, long-pulse, advanced tokamak operations have been achieved in DIII-D: [beta]{sub T} = 4.2%, [beta]{sub p} = 2, f{sub BS} = 65%, and [beta]{sub N}H9 = 10 for 600 ms (H"4[tau]{sub E}). The next challenge is to integrate the different elements, which will be the goal for the next five years when additional control will be available. Twelve resistive wall mode coils are scheduled to be installed in DIII-D during the summer of 2003. The future plans include upgrading the tokamak pulse length capability and increasing the ECH power, to control the current profile evolution.
Book Synopsis Enhanced Performance Discharges in the DIII-D Tokamak with Lighium Wall Conditioning by :
Download or read book Enhanced Performance Discharges in the DIII-D Tokamak with Lighium Wall Conditioning written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Lithium wall conditioning has been used in a recent campaign evaluating high performance negative central shear (NCS) discharges. During this campaign, the highest values of stored energy (4.4 MJ), neutron rate (2.4 x 10[sup 16]/s), and nT[sub i][tau] (7 x 10[sup 20] m[sup -3]-keV-s) achieved to date in DIII-D were obtained. High performance NCS discharges were achieved prior to beginning lithium conditioning, but it is clear that shot reproducibility and performance were improved by lithium conditioning. Central and edge oxygen concentrations were reduced after lithium conditioning, Lithium conditioning, consisting of up to four pellets injected at the end of the preceding discharge, allowed the duration of the usual inter-shot helium glow discharge to be reduced and reproducible high auxiliary power discharges, P[sub NBI][
Book Synopsis STATIONARY HIGH-PERFORMANCE DISCHARGES IN THE DII-D TOKAMAK. by :
Download or read book STATIONARY HIGH-PERFORMANCE DISCHARGES IN THE DII-D TOKAMAK. written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A271 STATIONARY HIGH-PERFORMANCE DISCHARGES IN THE DII-D TOKAMAK. Discharges which can satisfy the high gain goals of burning plasma experiments have been demonstrated in the DIII-D tokamak under stationary conditions at relatively low plasma current (q[sub 95]> 4). A figure of merit for fusion gain ([beta][sub N]H[sub 89]/q[sub 95][sup 2]) has been maintained at values corresponding to!= 10 operation in a burning plasma for> 6 s or 36[tau][sub E] and 2[tau][sub R]. The key element is the relaxation of the current profile to a stationary state with q[sub min]> 1. In the absence of sawteeth and fishbones, stable operation has been achieved up to the estimated no-wall[beta] limit. Feedback control of the energy content and particle inventory allow reproducible, stationary operation. The particle inventory is controlled by gas fueling and active pumping; the wall plays only a small role in the particle balance. The reduced current lessens significantly the potential for structural damage in the event of a major disruption. In addition, the pulse length capability is greatly increased, which is essential for a technology testing phase of a burning plasma experiment where fluence (duty cycle) is important.
Book Synopsis High Performance Plasma Operation on DIII-D During Extended Periods Without Boronization by :
Download or read book High Performance Plasma Operation on DIII-D During Extended Periods Without Boronization written by and published by . This book was released on 2007 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: High performance plasmas, including both hybrid and advanced tokamak (AT) bench-mark discharges, were shown to be highly repeatable in DIII-D over 6000 plasma-seconds of operation during the 2006 campaign with no intervening boron depositions or high temperature bakes. Hybrid and AT discharges with identical control targets were repeated after the initial boronization at the beginning of the 2006 campaign, and again just before and after a second boronization near the end of the 2006 campaign. After a long entry vent between the 2006 and 2007 campaigns, similar discharges were again repeated after the standard high temperature baking and plasma cleanup, but prior to a boronization. Performance metrics, such as [beta], confinement quality, and density control, were extremely well repeated. A low performance daily reference shot (DRS) was also established as a routine monitor of impurity influx. Over the 2006 campaign, the DRS database indicated little to no secular increase in impurity content. Oxygen content and Ni line emission were higher after the intervening vent, but were still minor contributors to plasma contamination. This indicates that erosion of boron films used for wall conditioning will not be a limitation to establishing long pulse high performance discharges in the new generation of superconducting tokamaks if graphite is used as the primary plasma facing material. These results contrast with recent work in devices using high-Z metallic plasma facing materials, where very frequent refreshing of boron films is required for high performance plasma operation.
Book Synopsis Demonstration of High Performance Negative Central Magnetic Shear Discharges on the DIII-D Tokamak by :
Download or read book Demonstration of High Performance Negative Central Magnetic Shear Discharges on the DIII-D Tokamak written by and published by . This book was released on 1996 with total page 37 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 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 1997 with total page 7 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 Development of Burning Plasma and Advanced Scenarios in the DIII-D Tokamak by : T. C. Luce
Download or read book Development of Burning Plasma and Advanced Scenarios in the DIII-D Tokamak written by T. C. Luce and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Significant progress in the development of burning plasma scenarios, steady-state scenarios at high fusion performance, and basic tokamak physics has been made by the DIII-D Team. Discharges similar to the ITER baseline scenario have demonstrated normalized fusion performance nearly 50% higher than required for Q = 10 in ITER, under stationary conditions. Discharges that extrapolate to Q {approx} 10 for longer than one hour in ITER at reduced current have also been demonstrated in DIII-D under stationary conditions. Proof of high fusion performance with full noninductive operation has been obtained. Underlying this work are studies validating approaches to confinement extrapolation, disruption avoidance and mitigation, tritium retention, ELM avoidance, and operation above the no-wall pressure limit. In addition, the unique capabilities of the DIII-D facility have advanced studies of the sawtooth instability with unprecedented time and space resolution, threshold behavior in the electron heat transport, and rotation in plasmas in the absence of external torque.
Book Synopsis Development of Burning Plasma and Advanced Scenarios in the DIII-D Tokamak by :
Download or read book Development of Burning Plasma and Advanced Scenarios in the DIII-D Tokamak written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Significant progress in the development of burning plasma scenarios, steady-state scenarios at high fusion performance, and basic tokamak physics has been made by the DIII-D Team. Discharges similar to the ITER baseline scenario have demonstrated normalized fusion performance nearly 50% higher than required for Q = 10 in ITER, under stationary conditions. Discharges that extrapolate to Q (almost equal to) 10 for longer than one hour in ITER at reduced current have also been demonstrated in DIII-D under stationary conditions. Proof of high fusion performance with full noninductive operation has been obtained. Underlying this work are studies validating approaches to confinement extrapolation, disruption avoidance and mitigation, tritium retention, ELM avoidance, and operation above the no-wall pressure limit. In addition, the unique capabilities of the DIII-D facility have advanced studies of the sawtooth instability with unprecedented time and space resolution, threshold behavior in the electron heat transport, and rotation in plasmas in the absence of external torque.
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 Progress Toward Sustained High-Performance Advanced Tokamak Discharges in DIII-D. by :
Download or read book Progress Toward Sustained High-Performance Advanced Tokamak Discharges in DIII-D. written by and published by . This book was released on 2002 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: Key elements of a sustained advanced tokamak discharge in DIII-D are a large fraction of the total current from bootstrap current (f{sub BS}) and parameters that optimize the capability to use electron cyclotron current drive (ECCD) at [rho] ≈ 0.5 to maintain the desired current profile [1-4]. Increased f{sub BS} results from increasing both the normalized beta ([beta]{sub N}) and the minimum value of the safety factor (q{sub min}). Off-axis ECCD is, for the available gyrotron power, optimized at high [beta]{sub N}, high electron temperature (T{sub e}) and low electron density (n{sub e}). As previously reported [2-4], these required elements have been separately demonstrated: density control at high [beta]{sub N} with n{sub e} ≤ 5 x 1019 m−3 using divertor-region pumping, stability at high [beta], and off-axis ECCD at the theoretically predicted efficiency. This report summarizes recent work on optimizing and integrating these results through evaluation of the dependence of the beta limit on q{sub min} and q95, exploration of discharges with relatively high q{sub min}, testing of feedback control of T{sub e} for control of the q profile evolution, and modification of the current profile time evolution when ECCD is applied.
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 2001 with total page 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.
Book Synopsis Recent Results from the DIII-D Tokamak and Implications for Future Devices by :
Download or read book Recent Results from the DIII-D Tokamak and Implications for Future Devices written by and published by . This book was released on 1995 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: Improvements to the DIII-D tokamak have led to significant new research results and enhanced performance. These results provide important inputs to the design of next generation divertor systems including the upgrade of the DIII-D divertor. The use of graphite for the plasma facing components and careful wall preparation has enabled the routine achievement of regimes of enhanced energy confinement. In elongated discharges, triangularity has been found to be important in attaining good discharge performance as measured by the product of the normalized plasma pressure and the energy confinement time, [beta][tau]{sub E} This constrains the design of the divertor configuration (X-point location). Active pumping of the divertor region using an in-situ toroidal cryogenic pump has demonstrated control of the plasma density in H-mode discharges and allowed the dependence of confinement on plasma density and current to be separately determined. Helium removal from the plasma edge sufficient to achieve effective ash removal in reactor discharges has also been demonstrated using this pumping configuration. The reduction of the heat flux to the divertor plates has been demonstrated using two different techniques to increase the radiation in the boundary regions of the plasma and thus reduce the heat flux to the divertor plates; deuterium gas injection has been used to create a strongly radiating localized zone near the X-point, and impurity (neon) injection to enhance the radiation from the plasma mantle. Precise shaping of the plasma current profile has been found to be important in achieving enhanced tokamak performance. Transiently shaped current profiles have been used to demonstrate regimes of plasmas with high beta and good confinement. Control of the current profile also is important to sustaining the plasma in the Very High (VH)-mode of energy confinement.
