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.
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.
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.
Download or read book LONG PULSE HIGH PERFORMANCE DISCHARGES IN THE DIII 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: 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[approx]10 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] H[sub 89] indicating the proximity to the conventional[beta] limits and energy confinement quality, respectively.) These H-mode discharges have an ELMing edge and[beta][approx][le] 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[approx]75% 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]H[sub 89][approx] 7 for up to 6.3 s or[approx] 34[tau][sub E]. These discharges appear to be in resistive equilibrium with q[sub min][approx] 1.05, in agreement with the current profile relaxation time of 1.8 s.
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.
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.
Download or read book Analysis and Modeling of DIII D Hybrid Discharges and Their Extrapolation to ITER written by M. R. Wade and published by . This book was released on 2006 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent experiments on tokamaks around the world [1-5] have demonstrated discharges with moderately high performance in which the q-profile remains stationary, as measured by the motional Stark effect diagnostic, for periods up to several {tau}{sub R}. Hybrid discharges are characterize by q{sub min} {approx} 1, high {beta}{sub N}, and good confinement. These discharges have been termed hybrid because of their intermediate nature between that of an ordinary H-mode and advanced tokamak discharges. They form an attractive scenario for ITER as the normalized fusion performance ({beta}{sub N}H{sub 89P}/q{sub 95}{sup 2}) is at or above that for the ITER baseline Q{sub fus} = 10 scenario, even for q{sub 95} as high as 4.6. The startup phase is thought to be crucial to the ultimate evolution of the hybrid discharge. An open question is how hybrid discharges achieve and maintain their stationary state during the initial startup phase. To investigate this aspect of hybrid discharges, we have used the CORSICA code to model the early stages of a discharge. Results clearly indicate that neoclassical current evolution alone is insufficient to account for the time evolution of the q-profile and that an addition of non-inductive current source must be incorporated into the model to reproduce the experimental time history. We include non-inductive neutral beam and bootstrap current sources in the model, and investigate the difference between simulations with these sources and the experimentally inferred q-profile. Further, we have made preliminary estimates of the spatial structure of the current needed to bring the simulation and experiment into agreement. This additional non-inductive source has not been tied to any physical mechanism as yet. We present these results and discuss the implications for hybrid startup on ITER.
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.
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.
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 Development in DIII D of High Beta Discharges Appropriate for Steady state Tokamak Operation With Burning Plasmas written by and published by . This book was released on 2008 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book M moire adress l assemble f d rale par le Conseil d tat du canton de Gen ve 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:
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][
Download or read book DEVELOPMENT IN THE DIII D TOKAMAK OF HYBRID OPERATION SCENARIOS FOR BURNING PLASMA EXPERIMENTS written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: OAK-B135 The basic parameters of proposed burning plasma experiments such as ITER and FIRE have been chosen based on analysis of multi-machine databases of confinement, stability, and divertor operation. given these specifications, it is of interest to run discharges in present-day machines such as DIII-D to verify the design basis and evaluate the margin available to achieve the mission goals. it is especially important to operate discharges which are stationary with respect to the current relaxation time scale ([tau][sub R]) since it is well-known that higher performance can be achieved transiently. Attention has been focused on validating the baseline scenario for diverted machines--ELMing H-mode discharges with q[sub 95]= 3 with sawteeth. However, there is also interest in the ITER program to assess the feasibility of operating the tokamak in a mode to maximize the neutron fluence for the purpose of testing the design of various components critical to the nuclear fuel cycle and energy conversion systems in a fusion power plant. It was originally envisioned that these discharges would be intermediate between an inductive burn (baseline) scenario and a fully noninductive (steady state) scenario; therefore, this type of discharge has become known as a hybrid scenario. In the course of investigating these hybrid scenarios in DIII-D, two key results have been obtained. First, stationary discharges with q[sub 95]> 4 have been obtained which project to Q[sub fus][approx] 10 in ITER. The projected duration of these discharges in ITER when using the full inductive flux capability is> 4000 s. (The significant engineering issues of site heat capacity, activation, and tritium consumption are beyond the scope of this work). Second, utilizing the same plasma initiation techniques as developed for the hybrid scenario, discharges at q[sub 95]= 3.2 project to near ignition in ITER, even with reduced parameters. This indicates the ITER design has significant performance margin and possesses the physics capability to carry out an extensive nuclear testing program. These same q[sub 95]= 3.2 discharges project to Q[sub fus]> 5 in FIRE, even with pessimistic confinement scalings.
Download or read book The Franco American Convention Relative to Double Taxation written by Emmet McCaffery and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book written by and published by . This book was released on 1983 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
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.
