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Research and development of a heat-pump water heater. Volume 2. R and D task reports

Description: The heat pump water heater is a device that works much like a window air conditioner except that heat from the home is pumped into a water tank rather than to the outdoors. The objective established for the device is to operate with a Coefficient of Performance (COP) of 3 or, an input of one unit of electric energy would create three units of heat energy in the form of hot water. With such a COP, the device would use only one-third the energy and at one-third the cost of a standard resistance water heater. This Volume 2 contains the final reports of the three major tasks performed in Phase I. In Task 2, a market study identifies the future market and selects an initial target market and channel of distribution, all based on an analysis of the parameters affecting feasibility of the device and the factors that will affect its market acceptance. In the Task 3 report, the results of a design and test program to arrive at final designs of heat pumps for both new water heaters and for retrofitting existing water heaters are presented. In the Task 4 report, a plan for an extensive field demonstration involving use in actual homes is presented. Volume 1 contains a final summary report of the information in Volume 2.
Date: August 1, 1978
Creator: Dunning, R.L.; Amthor, F.R. & Doyle, E.J.
Partner: UNT Libraries Government Documents Department

Research and development of a heat pump water heater. Volume 1. Final summary report

Description: An electric heat pump water heater with an operating efficiency, E/sub R/, of 2.5 in average conditions of 70 to 75/sup 0/F ambient air and 55 to 60/sup 0/F supply water has been designed. With losses taken into account, the coefficient of performance (COP) is 2.8 or within 10% of the design objective. Separate heat pump designs are available for new water heaters and for retrofitting of existing ones. For both models, the compressor, evaporator, fan and controls are mounted in a round cabinet set on top of the water heater. The condenser is a dual tube direct immersion type which enters the tank through a special 4-in. hole in the top of new tanks. For retrofit units, the condenser is in the form of a helix and is screwed into the tank through the hole normally used by the lower resistance element. Early estimates for the cost of the device are between $200 to $250 more than for an electric resistance water heater. Using this estimate, the payback for many applications will be between one and two years with some being less than one year. The payback period is dependent on the amount of hot water consumption and the price of electricity. In warm climates, the benefit/cost ratio will be improved by higher efficiency from warmer ambient air and by the value of free air conditioning and dehumidification provided while the unit is operating. In colder climates, the improved efficiency from colder supply water and the higher operating savings from higher kilowatt-hour use because of the colder water tend to offset the effect of the less favorable climate. A field demonstration of one hundred water heater heat pumps is planned in which each of 20 utilities will purchase, install and service five units, and install, service and monitor instrumentation ...
Date: August 1, 1978
Creator: Dunning, R.L.; Amthor, F.R. & Doyle, E.J.
Partner: UNT Libraries Government Documents Department

Physics of turbulence control and transport barrier formation in DIII-D

Description: This paper describes the physical mechanisms responsible for turbulence control and transport barrier formation on DIII-D as determined from a synthesis of results from different enhanced confinement regimes, including quantitative and qualitative comparisons to theory. A wide range of DIII-D data support the hypothesis that a single underlying physical mechanism, turbulence suppression via E x B shear flow is playing an essential, though not necessarily unique, role in reducing turbulence and transport in all of the following improved confinement regimes: H-mode, VH-mode, high-{ell}{sub i} modes, improved performance counter-injection L-mode discharges and high performance negative central shear (NCS) discharges. DIII-D data also indicate that synergistic effects are important in some cases, as in NCS discharges where negative magnetic shear also plays a role in transport barrier formation. This work indicates that in order to control turbulence and transport it is important to focus on understanding physical mechanisms, such as E x B shear, which can regulate and control entire classes of turbulent modes, and thus control transport. In the highest performance DIII-D discharges, NCS plasmas with a VH-mode like edge, turbulence is suppressed at all radii, resulting in neoclassical levels of ion transport over most of the plasma volume.
Date: October 1996
Creator: Doyle, E.J.; Burrell, K.H. & Carlstrom, T.N.
Partner: UNT Libraries Government Documents Department

The role of the radial electric field in confinement and transport in H-mode and VH-mode discharges in the DIII-D tokamak

Description: 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 {times} 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 {times} B velocity into the plasma interior.
Date: August 1, 1993
Creator: Gohil, P.; Burrell, K. H.; Groebner, R. J.; Osborne, T. H.; Doyle, E. J. & Rettig, C. L.
Partner: UNT Libraries Government Documents Department

Turbulent Radial Correlation Lengths in the DIII-D Tokamak

Description: Measurements of the radial correlation length Ar of density fluctuations have been made on the DIII-D tokamak in a variety of L-mode discharges. These measurements span the radial region 0.5 < {rho} < 1 and are found to scale approximately as {rho}{sub {theta},s} or 5-10 {rho}{sub s}. Here {rho}{sub {theta},s} is the poloidal ion Larmor radius calculated using local T{sub e} and poloidal magnetic field and {rho}{sub s} is the same except calculated using the total magnetic field. The {Delta}r data were obtained from a heterodyne reflectometer system. Comparisons to published analytic formulas of Ar have been carried out for a particular discharge condition. The measurements are found to be comparable in magnitude and radial dependence with a slab type formulation of ion temperature gradient (ITG) driven turbulence as well as an electron drift wave turbulence type prediction. Predictions from toroidal ITG and a different slab ITG model were found to be outside the error bars of the measurements. In addition, a detailed comparison to a non-linear gyro-kinetic turbulence code has begun. These and other similar comparisons are believed to be important as they serve to test and benchmark theory and codes as well as to help identify the type(s) of turbulence involved.
Date: August 1, 2000
Creator: Rhodes, T.L.; Leboeuf, J.-N.; Sydora, R.; Doyle, E.J.; Moyer, R.A.; Rettig, C.L. et al.
Partner: UNT Libraries Government Documents Department

MECHANISMS FOR ELECTRON TRANSPORT BARRIER FORMATION IN THE DIII-D TOKAMAK

Description: The E x B shear stabilization paradigm explains much of the phenomenology of ion thermal transport in tokamaks. Behavior in the electron channel, however, has continued to challenge our understanding. Recent experiments in DIII-D and elsewhere produce regions where electron thermal transport is almost completely eliminated with intense, localized, direct electron heating. Simulations of DIII-D discharges identify {alpha}-stabilization, local magnetic shear stabilization due to the Shafranov shift, as the dominant turbulence reduction mechanism in these experiments and may point the way toward regimes with simultaneous electron and ion internal transport barriers.
Date: February 1, 2001
Creator: GREENFIELD, C.M.; PRATER, R.; STAEBLER, G.M.; KINSEY, J.E.; BURRELL, K.H.; BOO, J.C. De et al.
Partner: UNT Libraries Government Documents Department

Operational Enhancements in DIII-D Quiescent H-Mode Plasmas

Description: In recent DIII-D experiments, we concentrated on extending the operating range and improving the overall performance of quiescent H-mode (QH) plasmas. The QH-mode offers an attractive, high-performance operating mode for burning plasmas due to the absence of pulsed edge-localized-mode-driven losses to the divertor (ELMs). Using counter neutral-beam injection (NBI), we achieve steady plasma conditions with the presence of an edge harmonic oscillation (EHO) replacing the ELMs and providing control of the edge pedestal density. These conditions have been maintained for greater than 4s ({approx}30 energy confinement times, {tau}{sub E}, and 2 current relaxation times, {tau}{sub R} [1]), and often limited only by the duration of auxiliary heating. We discuss results of these recent experiments where we use triangularity ramping to increase the density, neutral beam power ramps to increase the stored energy, injection of rf power at the electron cyclotron (EC) frequency to control density profile peaking in the core, and control of startup conditions to completely eliminate the transient ELMing phase.
Date: June 27, 2005
Creator: Casper, T A; Burrell, K H; Doyle, E J; Gohil, P; Lasnier, C J; Leonard, A W et al.
Partner: UNT Libraries Government Documents Department

Density and Temperature Profile Modifications with Electron Cyclotron Power Injection in Quiescent Double Barrier Discharges on DIII-D

Description: Quiescent double barrier (QDB) conditions often form when an internal transport barrier is created with high-power neutral-beam injection into a quiescent H-mode (QH) plasma. These QH-modes offer an attractive, high-performance operating scenario for burning plasma experiments due to their quasi-stationarity and lack of edge localized modes (ELMs). Our initial experiments and modeling using ECH/ECCD in QDB shots were designed to control the current profile and, indeed, we have observed a strong dependence on the q-profile when EC-power is used inside the core transport barrier region. While strong electron heating is observed with EC power injection, we also observe a drop in the other core parameters; ion temperature and rotation, electron density and impurity concentration. These dynamically changing conditions provide a rapid evolution of T{sub e} T{sub i} profiles accessible with 0.3 < (T{sub e} T{sub i}){sub axis} < 0.8 observed in QDB discharges. We are exploring the correlation and effects of observed density profile changes with respect to these time-dependent variations in the temperature ratio. Thermal and particle diffusivity calculations over this temperature ratio range indicate a consistency between the rise in temperature ratio and an increase in transport corresponding to the observed change in density.
Date: October 11, 2005
Creator: Casper, T A; Burrell, K H; Doyle, E J; Gohil, P; Lasnier, C J; Leonard, A W et al.
Partner: UNT Libraries Government Documents Department

OVERVIEW OF H-MODE PEDESTAL RESEARCH ON DIII-D

Description: Developing an understanding of the processes that control the H-mode transport barrier is motivated by the significant impact this small region (typically <2% of the minor radius) can have on overall plasma performance. Conditions at the inner edge of the H-mode transport barrier can strongly influence the overall energy confinement, and the maximum density, and therefore fusion power, that can be achieved with the typically flat H-mode density profiles [1,2]. The ELM instability, which usually regulates the pressure gradient in the H-mode edge, can result in large power loads to, and erosion of, the divertor targets in a reactor scale device [3]. The goal of H-mode pedestal research at DIII-D is to: (1) develop a physics based model that would allow prediction of the conditions at the top of the H-mode pedestal, (2) develop an understanding of processes which control Type I ELM effects in the core and divertor, and (3) explore alternatives to the Type I ELM regime.
Date: July 1, 2001
Creator: OSBORNE, T.H.; BURRELL, K.H.; CARLSTROM, T.N.; CHU, M.S.; DOYLE, E.J.; FERRON, J.R. et al.
Partner: UNT Libraries Government Documents Department

PROGRESS IN QUANTIFYING THE EDGE PHYSICS OF H-MODE REGIME IN DIII-D

Description: Edge conditions in DIII-D are being quantified in order to provide insight into the physics of the H-mode regime. Electron temperature is not the key parameter that controls the L-H transition. Gradients of edge temperature and pressure are much more promising candidates for such parameters. The quality of H-mode confinement is strongly correlated with the height of the H-mode pedestal for the pressure. The gradient of the pressure appears to be controlled by MHD modes, in particular by kink-ballooning modes with finite mode number n. For a wide variety of discharges, the width of the barrier is well described with a relationship that is proportional to ({beta}{sub p}{sup ped}){sup 1/2}. An attractive regime of confinement has been discovered which provides steady-state operation with no ELMs, low impurity content and normal H-mode confinement. A coherent edge MHD-mode evidently provides adequate particle transport to control the plasma density and impurity content while permitting the pressure pedestal to remain almost identical to that observed in ELMing discharges.
Date: October 1, 2000
Creator: GROEBNER, R.J.; BAKER, D.R.; BOEDO, J.A.; BURRELL, K.H.; CARLSTROM, T.N.; DERANIAN, R.D. et al.
Partner: UNT Libraries Government Documents Department

Stability in High Gain Plasmas in DIII-D

Description: Fusion power gain has been increased by a factor of 3 in DIII-D plasmas through the use of strong discharge shaping and tailoring of the pressure and current density profiles. H-mode plasmas with weak or negative central magnetic shear are found to have neoclassical ion confinement throughout most of the plasma volume. Improved MHD stability is achieved by controlling the plasma pressure profile width. The highest fusion power gain Q (ratio of fusion power to input power) in deuterium plasmas was 0.0015. which extrapolates to an equivalent Q of 0.32 in a deuterium-tritium plasma and is similar to values achieved in tokamaks of larger size and magnetic fields.
Date: January 1, 1997
Creator: Lazarus, E. A.; Hong, R. M.; Navratil, G. A.; Sabbagh, S.; Strait, E. J.; Rice, B. W. et al.
Partner: UNT Libraries Government Documents Department

Characterization and Modification of Edge-Driven Instabilities in the DIII-D Tokamak

Description: The character of edge localized modes (ELMs) and the height of the edge pressure pedestal in DIII-D tokamak H-mode discharges have been modified by varying the discharge shape (triangularity and squareness) and the safety factor, increasing the edge radiation, and injecting deuterium pellets. Changes in the ELM frequency and amplitude, and the magnitude of the edge pressure gradient, and changes in the calculated extent of the region of access to the ballooning mode second stability regime are observed.
Date: July 1, 1999
Creator: Ferron, J.R.; Lao, L.L.; Osborne, T.H.; Strait, E.J.; Turnbull, A.D.; Miller, R.L. et al.
Partner: UNT Libraries Government Documents Department

RECENT EXPERIMENTAL STUDIES OF EDGE AND INTERNAL TRANSPORT BARRIERS IN THE DIII-D TOKAMAK

Description: Results from recent experiments on the DIII-D tokamak have revealed many important details on transport barriers at the plasma edge and in the plasma core. These experiments include: (a) the formation of the H-mode edge barrier directly by pellet injection; (b) the formation of a quiescent H-mode edge barrier (QH-mode) which is free from edge localized modes (ELMs), but which still exhibits good density and radiative power control; (c) the formation of multiple transport barriers, such as the quiescent double barrier (QDB) which combines a internal transport barrier with the quiescent H-mode edge barrier. Results from the pellet-induced H-mode experiments indicate that: (a) the edge temperature (electron or ion) is not a critical parameter for the formation of the H-mode barrier, (b) pellet injection leads to an increased gradient in the radial electric field, E{sub r}, at the plasma edge; (c) the experimentally determined edge parameters at barrier transition are well below the predictions of several theories on the formation of the H-mode barrier, (d) pellet injection can lower the threshold power required to form the H-mode barrier. The quiescent H-mode barrier exhibits good density control as the result of continuous magnetohydrodynamic (MHD) activity at the plasma edge called the edge harmonic oscillation (EHO). The EHO enhances the edge particle transport while maintaining a good energy transport barrier. The ability to produce multiple barriers in the QDB regime has led to long duration, high performance plasmas with {beta}{sub NH{sub 89}} values of 7 for up to 10 times the confinement time. Density profile control in the plasma core of QDB plasmas has been demonstrated using on-axis ECH.
Date: August 1, 2002
Creator: GOHIL, P.; BAYLOR, L.R.; BURRELL, K.H.; CASPER, T.A.; DOYLE, E.J.; GREENFIELD, C.M. et al.
Partner: UNT Libraries Government Documents Department

Physics of the L-mode to H-mode transition in tokamaks

Description: Combined theoretical and experimental work has resulted in the creation of a paradigm which has allowed semi-quantitative understanding of the edge confinement improvement that occurs in the H-mode. Shear in the E {times} B flow of the fluctuations in the plasma edge can lead to decorrelation of the fluctuations, decreased radial correlation lengths and reduced turbulent transport. Changes in the radial electric field, the density fluctuations and the edge transport consistent with shear stabilization of turbulence have been seen in several tokamaks. The purpose of this paper is to discuss the most recent data in the light of the basic paradigm of electric field shear stabilization and to critically compare the experimental results with various theories.
Date: July 1, 1992
Creator: Burrell, K. H.; Carlstrom, T. N.; Gohil, P.; Groebner, R. J.; Kim, J.; Osborne, T. H. et al.
Partner: UNT Libraries Government Documents Department

Regimes of improved confinement and stability in DIII-D obtained through current profile modifications

Description: 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, {ell}{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 {ell}{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 {ell}{sub i} other current profile parameters, such as its distribution near the edge region, may also affect the confinement enhancement.
Date: September 1, 1992
Creator: Lao, L. L.; Ferron, J. R.; Taylor, T. S.; Chan, V. S.; Osborne, T. H.; Burrell, K. H. et al.
Partner: UNT Libraries Government Documents Department

DIII-D Experiments and Modeling of Core Confinement in Quiescent Double Barrier Plasmas

Description: 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.
Date: October 24, 2003
Creator: Jayakumar, J; Casper, T A; Lasnier, C J; Burrell, K H; Doyle, E J; Gohil, P et al.
Partner: UNT Libraries Government Documents Department

Edge Stability and Performance of the ELM-Free Quiescent H-Mode and the Quiescent Double Barrier Mode on DIII-D

Description: The quiescent H (QH) mode, an edge localized mode (ELM)-free, high-confinement mode, combines well with an internal transport barrier to form quiescent double barrier (QDB) stationary state, high performance plasmas. The QH-mode edge pedestal pressure is similar to that seen in ELMing phases of the same discharge, with similar global energy confinement. The pedestal density in early ELMing phases of strongly pumped counter injection discharges drops and a transition to QH-mode occurs, leading to lower calculated edge bootstrap current. Plasmas current ramp experiment and ELITE code modeling of edge stability suggest that QH-modes lie near an edge current stability boundary. At high triangularity, QH-mode discharges operate at higher pedestal density and pressure, and have achieved ITER level values of {beta}{sub PED} and {nu}*. The QDB achieves performance of {alpha}{sub N}H{sub 89} {approx} 7 in quasi-stationary conditions for a duration of 10 tE, limited by hardware. Recently we demonstrated stationary state QDB discharges with little change in kinetic and q profiles (q{sub 0} > 1) for 2 s, comparable to ELMing ''hybrid scenarios'', yet without the debilitating effects of ELMs. Plasma profile control tools, including electron cyclotron heating and current drive and neutral beam heating, have been demonstrated to control simultaneously the q profile development, the density peaking, impurity accumulation and plasma beta.
Date: December 3, 2004
Creator: West, W P; Burrell, K H; Casper, T A; . Doyle, E J; Snyder, P B; Gohil, P et al.
Partner: UNT Libraries Government Documents Department

QUIESCENT DOUBLE BARRIER H-MODE PLASMAS IN THE DIII-D TOKAMAK

Description: High confinement (H-mode) operation is the choice for next-step tokamak devices based either on conventional or advanced tokamak physics. This choice, however, comes at a significant cost for both the conventional and advanced tokamaks because of the effects of edge localized modes (ELMs). ELMs can produce significant erosion in the divertor and can affect the beta limit and reduced core transport regions needed for advanced tokamak operation. Experimental results from DIII-D [J.L. Luxon, et al., Plasma Phys. and Contr. Nucl. Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987) Vol. I, p. 159] this year have demonstrated a new operating regime, the quiescent H-mode regime, which solves these problems. We have achieved quiescent H-mode operation which is ELM-free and yet has good density and impurity control. In addition, we have demonstrated that an internal transport barrier can be produced and maintained inside the H-mode edge barrier for long periods of time (>3.5 seconds or >25 energy confinement times {tau}{sub E}), yielding a quiescent double barrier regime. By slowly ramping the input power, we have achieved {beta}{sub N} H{sub 89} = 7 for up to 5 times the {tau}{sub E} of 150 ms. The {beta}{sub N} H{sub 89} values of 7 substantially exceed the value of 4 routinely achieved in standard ELMing H-mode. The key factors in creating the quiescent H-mode operation are neutral beam injection in the direction opposite to the plasma current (counter injection) plus cryopumping to reduce the density. Density and impurity control in the quiescent H-mode is possible because of the presence of an edge magnetic hydrodynamic (MHD) oscillation, the edge harmonic oscillation, which enhances the edge particle transport while leaving the energy transport unaffected.
Date: November 1, 2000
Creator: BURRELL, K.H.; AUSTIN, M.E.; BRENNAN, D.P.; DeBOO, J.C.; DOYLE, E.J.; FENZI, C. et al.
Partner: UNT Libraries Government Documents Department

DIII-D Quiescent Double Barrier Regime Experiments and Modeling

Description: Discharges characteristic of the quiescent double barrier (QDB) regime [1] are attractive for development of advanced tokamak (AT) scenarios relevant to fusion reactors [2] and they offer near term advantages for exploring and developing control techniques. We continue to explore the QDB regime in DIII-D to improve understanding of formation and control of these discharges and to explore scaling to steady-state reactors. The formation of an internal transport barrier (ITB) provides a naturally peaked core pressure profile. This peaking in density in combination with the H-mode-like edge barrier and pedestal provide a path to high performance. We have achieved {beta}{sub N}H{sub 89P} {approx} 7 for several energy confinement times ({le} 25 {tau}{sub E}). We discuss here a combination of modeling and experiments using electron cyclotron heating (ECH) and current drive (ECCD) to demonstrate steady state, current-driven equilibria and control of the current distribution, safety factor q, and density profile. Experimental conditions leading to formation of the QDB discharge require establishing two distinct and separated barrier regions, a core region near {rho} {approx} 0.5 and an edge barrier outside {rho} > 0.95, {rho} is the square root of toroidal flux (radial coordinate). A region of higher transport due to a change in polarity of the E x B shearing rate [1] separates the core barrier from the H-mode edge. It is this separation in barriers that so far has required use of counter-NBI to establish QDB conditions. Balanced NBI should also allow this separation of barriers. The edge corresponds to the quiescent H-mode (QH) conditions [3]. In this quiescent edge region, the normally observed transient loss associated with edge-localized-mode (ELM) activity is replaced with a steady particle loss driven by a coherent oscillation residing outside the pedestal region. This edge harmonic oscillation (EHO) [2] typically exhibits 2 or 3 harmonics of ...
Date: July 1, 2002
Creator: Casper, T.A.; Burrell, K.H.; DeBoo, J.C.; Doyle, E.J.; Gohil, P.; Greenfield, C.M. et al.
Partner: UNT Libraries Government Documents Department

Confinement and stability of VH-mode discharges in the DIII-D tokamak

Description: 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.
Date: October 1, 1992
Creator: Taylor, T.S.; Osborne, T.H.; Burrell, K.H.; Carlstrom, T.N.; Chan, V.S.; Chu, M.S. et al.
Partner: UNT Libraries Government Documents Department

Regimes of improved confinement and stability in DIII-D obtained through current profile modifications

Description: 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, [ell][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 [ell][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 [ell][sub i] other current profile parameters, such as its distribution near the edge region, may also affect the confinement enhancement.
Date: September 1, 1992
Creator: Lao, L.L.; Ferron, J.R.; Taylor, T.S.; Chan, V.S.; Osborne, T.H.; Burrell, K.H. et al.
Partner: UNT Libraries Government Documents Department

Suppression of Large Edge Localized Modes with a Stochastic Magnetic Boundary in High Confinement DIII-D Plasmas

Description: Large sub-millisecond heat pulses due to Type-I ELMs have been reproducibly eliminated in DIII-D for periods approaching 7 energy confinement times with small dc currents driven in a simple magnetic perturbation coil. The current required to eliminate all but a few isolated Type-I ELM impulses during a perturbation coil pulse lasting several seconds is less than 0.4% of plasma current. Based on vacuum magnetic field line modeling, perturbation fields from the coil resonate strongly with plasma flux surfaces across most of the pedestal region (0.9 {le} {psi}{sub N} {le} 1.0) when q95 = 3.7{plus_minus}0.2 creating small remnant magnetic islands surrounded by weakly stochastic field lines. Under the best ELM suppression conditions, the stored energy, {beta}N and H-mode quality factor are unaffected by the perturbation field along with the electron pressure profile, radial electric field and poloidal rotation across the pedestal. Consequently, the H-mode transport barrier and global energy confinement time is also unaltered in these cases. Although some isolated ELM-like events typically occur during the perturbation coil pulse, long periods free of large Type-I ELMs ({Delta}t > 4-6 {tau}{sub E}) have been reproduced numerous times, on multiple experimental run days. Several Type-I ELM suppression and modification behaviors have been identified and studied over a range of discharge conditions including those matching the ITER scenario 2 flux surface shape and aspect ratio scaled down by a factor of 3.5 to fit in the DIII-D vacuum vessel. Since large Type-I ELM impulses represent a severe constraint on the survivability of the divertor target plates in future fusion devices such as ITER, a proven method of eliminating these impulses is critical for the development of tokamak reactors. Results presented in this paper suggest that non-axisymmetric edge magnetic perturbations could be a promising option for controlling ELMs in future tokamaks such as ITER.
Date: October 18, 2004
Creator: Evans, T E; Moyer, R A; Watkins, J G; Osborne, T H; Thomas, P R; Becoulet, M et al.
Partner: UNT Libraries Government Documents Department