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Local multispecies particle and energy transport in the TFTR tokamak

Description: Studies of local multispecies thermal particle and energy transport in L-mode and supershot deuterium plasmas have been performed on the Tokamak Fusion Test Reactor (TFTR). These studies were undertaken to help gain insight into the anomalous transport properties of the bulk plasma. Such experimental and theoretical studies are valuable for ITER: the relationship of local helium ash and metallic particle transport to local energy transport will be determining factors in plasma current, helium pumping, and divertor material requirements. In addition, differences between electron and ion transport will have important implications for plasma fueling scenarios. Here, attention has been focused on supershots and L-Modes of the same toroidal field, plasma current, neutral beam heating power.
Date: May 1, 1992
Creator: Synakowski, E. J.
Partner: UNT Libraries Government Documents Department

Formation and Structure of Internal and Edge Transport Barriers

Description: The phenomenology of transport barrier formation is reviewed with a focus on physics that may be common to the edge and the core. To this end, the framework of E x B velocity shear reduction of turbulence-induced fluxes, applied to the edge for some time, is studied in light of measurements of core bifurcation dynamics and recent tests of causality. Also, the possible role of the magnetic shear structure in facilitating core barrier formation is examined. Experimental and theoretical challenges for developing predictive capability for reactor-relevant conditions are highlighted by recent observations of spontaneous electric field shear generation far removed from edge effects, and efforts to characterize the plasma edge at and across the L-H transition.
Date: February 1, 1998
Creator: Synakowski, E.J.
Partner: UNT Libraries Government Documents Department

Local transport barrier formation and relaxation in reverse-shear plasmas on the TFTR tokamak

Description: The roles of turbulence stabilization by sheared E x B flow and Shafranov-shift gradients are examined for TFTR. Enhanced Reverse-Shear plasmas. Both effects in combination provide the basis of a positive-feedback model that predicts reinforced turbulence suppression with increasing pressure gradient. Local fluctuation behavior at the onset of ERS confinement is consistent with this framework. The power required for transitions into the ERS regime are lower when high power neutral beams are applied earlier in the current profile evolution, consistent with the suggestion that both effects play a role. Separation of the roles of E x B and Shafranov shift effects was performed by varying the E x B shear through changes in the toroidal velocity with nearly-steady-state pressure profiles. Transport and fluctuation levels increase only when E x B shearing rates are driven below a critical value that is comparable to the fastest linear growth rates of the dominant instabilities. While a turbulence suppression criterion that involves the ratio of shearing to linear growth rates is in accord with many of these results, the existence of hidden dependencies of the criterion is suggested in experiments where the toroidal field was varied. The forward transition into the ERS regime has also been examined in strongly rotating plasmas. The power threshold is higher with unidirectional injection than with balanced injection.
Date: February 1, 1997
Creator: Synakowski, E.J.; Beer, M.A. & Batha, S.H.
Partner: UNT Libraries Government Documents Department

Improvements in the CHERS system for DT experiments on TFTR

Description: Improvements in the charge exchange recombination spectroscopy (CHERS) system have resulted in accurate measurements of T{sub i} and V{sub {phi}} profiles during DT experiments. These include moving the spectrometer detector array and electronics farther away from the tokamak to a low neutron flux location. This relocation has also improved access to all components of the system. Also, a nonplasma-viewing calibration fiber system was added to monitor the change in fiber transmission due to the high flux DT neutrons. Narrowband filtered light transmitted through the calibration fiber is now used as a reference for the VO measurement. At the highest neutron flux of {approximately} 2.5 {times} 10{sup 18} neutrons/see (fusion power {approximately} 6.2 MW) a modest 5% decrease in fiber transmission was observed. Corrections for transmission loss are made and T{sub i} (r,t) and absolute V{sub phi} (r,t) profiles are automatically calculated within four minutes of every shot.
Date: March 1, 1995
Creator: Bush, C.E.; Bell, R. & Synakowski, E.J.
Partner: UNT Libraries Government Documents Department

Measurements of the production and transport of helium ash on the TFTR Tokamak

Description: Helium ash production and transport have been measured in TFTR deuterium-tritium plasmas using charge-exchange recombination spectroscopy. The helium ash confinement time, including recycling effects, is 6--10 times the energy confinement time and is compatible with sustained ignition in a reactor. The ash confinement time is dominated by edge pumping rates rather than core transport. The measured evolution of the local thermal ash density agrees with modeling, indicating that alpha particle slowing-down calculations used in the modeling are reasonable.
Date: March 1, 1995
Creator: Synakowski, E.J.; Bell, R.E. & Budny, R.V.
Partner: UNT Libraries Government Documents Department

The roles of electric field shear and Shafranov shift in sustaining high confinement in enhanced reversed shear plasmas on the TFTR tokamak

Description: The relaxation of core transport barriers in TFTR Enhanced Reversed Shear plasmas has been studied by varying the radial electric field using different applied torques from neutral beam injection. Transport rates and fluctuations remain low over a wide range of radial electric field shear, but increase when the local E x B shearing rates are driven below a threshold comparable to the fastest linear growth rates of the dominant instabilities. Shafranov-shift-induced stabilization alone is not able to sustain enhanced confinement.
Date: February 1, 1997
Creator: Synakowski, E.J.; Beer, M.A. & Batha, S.H.
Partner: UNT Libraries Government Documents Department

New understanding of poloidal rotation measurements in a tokamak plasma

Description: Significant atomic physics corrections to the measured poloidal velocity using charge exchange spectroscopy have been neglected when interpreting impurity poloidal velocity. In the presence of a magnetic field, the gyro motion of the impurity ion along with the finite lifetime of the observed state results in an additional line shift that scales with ion temperature and magnetic field strength. Effects of collisions on the lifetime of excited states, cascades from higher longer-lived n levels, and charge exchange from excited beam neutrals are calculated to determine necessary corrections to the measured poloidal velocity. The accuracy of computed corrections is tested utilizing symmetric upward and downward views from the TFTR poloidal rotation diagnostic.
Date: May 15, 2000
Creator: Bell, R.E. & Synakowski, E.J.
Partner: UNT Libraries Government Documents Department

Non-linear evolution of double tearing modes in tokamaks

Description: The delta prime formalism with neoclassical modifications has proven to be a useful tool in the study of tearing modes in high beta, collisionless plasmas. In this paper the formalism developed for the inclusion of neoclassical effects on tearing modes in monotonic q-profile plasmas is extended to plasmas with hollow current profiles and double rational surfaces. First, the classical formalism of tearing modes in the Rutherford regime in low beta plasmas is extended to q profiles with two rational surfaces. Then it is shown that this formalism is readily extended to include neoclassical effects.
Date: December 17, 1999
Creator: Fredrickson, E.; Bell, M.; Budny, R.V. & Synakowski, E.
Partner: UNT Libraries Government Documents Department

Transport simulations of ITER helium exhaust using recent data from TFTR, TEXTOR and JT-60

Description: Insufficient helium exhaust can seriously degrade the performance of any fusion reactor and has recently been identified as a potentially significant issue for ITER. The effects of variations of the ratios D{sup He}/{chi}i, D{sup He}/D{sup D}, v{sup He}/D{sup He} and of the sawtooth period on helium exhaust in ITER are studied with BALDUR code transport simulations. Recent measurements of D{sup He}/{chi}i, at TFTR, of D{sup He}/D{sup D} at TEXTOR of v{sup He}/D{sup He} at TFTR, TEXTOR, and JT-60 are found compatible with sustained ignition and helium exhaust requirements for ITER. Ignition is found to be critically sensitive to the ratio v{sup He}/D{sup He}, particularly at the plasma edge, and to reduced sawtooth period. These critical dependencies are moderated for reduced helium recycling at the separatrix and for hollow particle diffusivity profiles. 17 refs., 9 figs., 1 tab.
Date: July 1, 1991
Creator: Redi, M.H.; Cohen, S.A. & Synakowski, E.J.
Partner: UNT Libraries Government Documents Department

Visible and Infrared Optical Design for the ITER Upper Ports

Description: This document contains the results of an optical design scoping study of visible-light and infrared optics for the ITER upper ports, performed by LLNL under contract for the US ITER Project Office. ITER is an international collaboration to build a large fusion energy tokamak with a goal of demonstrating net fusion power for pulses much longer than the energy confinement time. At the time of this report, six of the ITER upper ports are planned to each to contain a camera system for recording visible and infrared light, as well as other diagnostics. the performance specifications for the temporal and spatial resolution of this system are shown in the Section II, Functional Specifications. They acknowledge a debt to Y. Corre and co-authors of the CEA Cadarache report ''ITER wide-angle viewing and thermographic and visible system''. Several of the concepts used in this design are derived from that CEA report. The infrared spatial resolution for optics of this design is diffraction-limited by the size of the entrance aperture, at lower resolution than listed in the ITER diagnostic specifications. The size of the entrance aperture is a trade-off between spatial resolution, optics size in the port, and the location of relay optics. The signal-to-noise ratio allows operation at the specified time resolutions.
Date: March 1, 2007
Creator: Lasnier, C; Seppala, L; Morris, K; Groth, M; Fenstermacher, M; Allen, S et al.
Partner: UNT Libraries Government Documents Department

The effect of E{sub r} on MSE measurements of q, a new technique for measuring E{sub r}, and a test of the neoclassical electric field

Description: Previous analysis of motional-Stark Effect (MSE) data to measure the q-profile ignored contributions from the plasma electric field. The MSE measurements are shown to be sensitive to the electric field and require significant corrections for plasmas with large rotation velocities or pressure gradients. MSE measurements from rotating plasmas on the Tokamak Fusion Test Reactor (TFTR) confirm the significance of these corrections and verify their magnitude. Several attractive configurations are considered for future MSE-based diagnostics for measuring the plasma radial electric field. MSE data from TFTR is analyzed to determine the change in the radial electric field between two plasmas. The measured electric field quantitatively agrees with the predictions of neoclassical theory. These results confirm the utility of a MSE electric field measurement.
Date: October 1, 1996
Creator: Zarnstorff, M.C.; Synakowski, E.J.; Levinton, F.M. & Batha, S.H.
Partner: UNT Libraries Government Documents Department

Theory, simulation, and experimental studies of zonal flows

Description: The authors report on current theoretical understanding of the characteristics of self-generated zonal flows as observed in nonlinear gyrokinetic simulations of toroidal ITG turbulence [Science 281, 1835 (1998)], and discuss various possibilities for experimental measurements of signature of zonal flows.
Date: July 13, 2000
Creator: Hahm, T. S.; K.H.Burrell; Z.Lin; Nazikian, R. & Synakowski, E.J.
Partner: UNT Libraries Government Documents Department

Zonal Flow Measurements Concept I

Description: We study the characteristics of self-generated zonal flows as observed in nonlinear global gyrokinetic simulations of toroidal ITG turbulence for typical parameters of DIII-D core plasmas, and discuss various possibilities for experimental measurements and the development of new diagnostics.
Date: October 1, 1999
Creator: Synakowski, E.J.; Burrell, K.H.; Nazikian, R.; Hahm, T.S. & Lin, Z.
Partner: UNT Libraries Government Documents Department

Visible charge exchange recombination spectroscopy on TFTR

Description: Visible charge exchange recombination spectroscopy is routinely used to measure the time evolution of the ion temperature (T{sub i}) and toroidal rotation velocity (v{sub {phi}}) profiles on TFTR. These measurements are made with the CHERS diagnostic, a fiber-optically coupled spectrometer equipped with a two-dimensional photodiode array detector which provides both spectral and spatial resolution. The instrumentation, data analysis techniques, and examples of T{sub i} and v{sub {phi}} measurements are described. Recently, CHERS has been used to perform impurity transport experiments: radial profiles of diffusivities and convective velocities for helium and iron have been deduced from measurements of the time evolutions of He{sup 2+} and Fe{sup 24+} profiles following impurity injection. Examples of these measurements are given. 12 refs., 8 figs.
Date: March 1, 1991
Creator: Stratton, B.C.; Fonck, R.J.; Jaehnig, K.P.; Schechtman, N. & Synakowski, E.J.
Partner: UNT Libraries Government Documents Department

Core Poloidal Rotation and Internal Trnasport Barrier Formation in TFTR

Description: Impurity poloidal rotation velocities have been measured in the core of TFTR plasmas using a new spectroscopic diagnostic. Two types of transitions to enhanced confinement in reversed shear plasmas are examined. A bifurcation in carbon poloidal rotation is observed to occur before the transition to enhanced confinement for one of these types, while other measured plasmas parameters remain constant. A narrow radial region with reversed poloidal rotation and rotational shear is established 60-100 ms before the transition, and is associated with a large negative radial electric field.
Date: January 1, 1998
Creator: Synakowski, E.J.; Levinton, F.M.; Zarnstorff, M.C.; Bell, R.E.; Batha, S.H. & al, et
Partner: UNT Libraries Government Documents Department

Advanced ST Plasma Scenario Simulations for NSTX

Description: Integrated scenario simulations are done for NSTX [National Spherical Torus Experiment] that address four primary milestones for developing advanced ST configurations: high {beta} and high {beta}{sub N} inductive discharges to study all aspects of ST physics in the high-beta regime; non-inductively sustained discharges for flattop times greater than the skin time to study the various current-drive techniques; non-inductively sustained discharges at high {beta} for flattop times much greater than a skin time which provides the integrated advanced ST target for NSTX; and non-solenoidal start-up and plasma current ramp-up. The simulations done here use the Tokamak Simulation Code (TSC) and are based on a discharge 109070. TRANSP analysis of the discharge provided the thermal diffusivities for electrons and ions, the neutral-beam (NB) deposition profile, and other characteristics. CURRAY is used to calculate the High Harmonic Fast Wave (HHFW) heating depositions and current drive. GENRAY/CQL3D is used to establish the heating and CD [current drive] deposition profiles for electron Bernstein waves (EBW). Analysis of the ideal-MHD stability is done with JSOLVER, BALMSC, and PEST2. The simulations indicate that the integrated advanced ST plasma is reachable, obtaining stable plasmas with {beta} {approx} 40% at {beta}{sub N}'s of 7.7-9, I{sub P} = 1.0 MA, and B{sub T} = 0.35 T. The plasma is 100% non-inductive and has a flattop of 4 skin times. The resulting global energy confinement corresponds to a multiplier of H{sub 98(y,2)} = 1.5. The simulations have demonstrated the importance of HHFW heating and CD, EBW off-axis CD, strong plasma shaping, density control, and early heating/H-mode transition for producing and optimizing these plasma configurations.
Date: October 28, 2004
Creator: Kessel, C.E.; Synakowski, E.J.; Gates, D.A.; Harvey, R.W.; Kaye, S.M.; Mau, T.K. et al.
Partner: UNT Libraries Government Documents Department

Nonlinear Turbulence Simulations for NSTX H-modes

Description: Present evidence points to remarkably resilient electron temperature profiles in high-density H-mode plasmas on the National Spherical Torus Experiment (NSTX), suggesting that the underlying electron thermal transport mechanisms respond in a highly nonlinear fashion to changes in the gradients. This paper uses measured plasma profiles as input to linear gyrokinetic analysis to identify candidate micro-instabilities that may be responsible for the electron thermal transport. The criteria for useful nonlinear micro-stability analyses are discussed along with necessary approximations and computational issues.
Date: June 22, 2004
Creator: Redi, M. H.; Kaye, S.; Dorland, W.; Bell, R.; Bourdelle, C.; Ethier, S. et al.
Partner: UNT Libraries Government Documents Department

Transport in Auxiliary Heated NSTX Discharges

Description: The NSTX spherical torus (ST) provides a unique platform to investigate magnetic confinement in auxiliary-heated plasmas at low aspect ratio. Auxiliary power is routinely coupled to ohmically heated plasmas by deuterium neutral-beam injection (NBI) and by high-harmonic fast waves (HHFW) launch. While theory predicts both techniques to preferentially heat electrons, experiment reveals the electron temperature is greater than the ion temperature during HHFW, but the electron temperature is less than the ion temperature during NBI. In the following we present the experimental data and the results of transport analyses.
Date: July 10, 2003
Creator: LeBlanc, B.P.; Bell, M.G.; Bell, R.E.; Bitte, M.L.; Bourdelle, C.; Gates, D.A. et al.
Partner: UNT Libraries Government Documents Department

Confinement Studies of Auxiliary Heated NSTX Plasmas

Description: The confinement of auxiliary heated NSTX discharges is discussed. The energy confinement time in plasmas with either L-mode or H-mode edges is enhanced over the values given by the ITER97L and ITER98Pby(2) scalings, being up to 2-3 times L-mode and 1.5 times H-mode. TRANSP calculations based on the kinetic profile measurements reproduce the magnetics-based determination of stored energy and the measured neutron production rate. Power balance calculations reveal that, in a high power neutral beam heated H-mode discharge, the ion thermal transport is near neoclassical levels, and well below the electron thermal transport, which is the main loss channel. Perturbative impurity injection techniques indicate the particle diffusivity to be slightly above the neoclassical level in discharges with L-mode edge. High-harmonic fast-wave (HHFW) bulk electron heating is described and thermal transport is discussed. Thermal ion transport is found to be above neoclassical level, but thermal electron transport remains the main loss mechanism. Evidences of an electron thermal internal transport barrier obtained with HHFW heating are presented. A description of H-mode discharges obtained during HHFW heating is presented.
Date: May 6, 2003
Creator: LeBlanc, B.P.; Bell, M.G.; Bell, R.E.; Bitter, M.L.; Bourdelle, C.; Gates, D.A. et al.
Partner: UNT Libraries Government Documents Department

Transport Physics in Reversed Shear Plasmas

Description: Reversed magnetic shear is considered a good candidate for improving the tokamak concept because it has the potential to stabilize MHD instabilities and reduce particle and energy transport. With reduced transport the high pressure gradient would generate a strong off-axis bootstrap current and could sustain a hollow current density profile. Such a combination of favorable conditions could lead to an attractive steady-state tokamak configuration. Indeed, a new tokamak confinement regime with reversed magnetic shear has been observed on the Tokamak Fusion Test Reactor (TFTR) where the particle, momentum, and ion thermal diffusivities drop precipitously, by over an order of magnitude. The particle diffusivity drops to the neoclassical level and the ion thermal diffusivity drops to much less than the neoclassical value in the region with reversed shear. This enhanced reversed shear (ERS) confinement mode is characterized by an abrupt transition with a large rate of rise of the density in the reversed shear region during neutral beam injection, resulting in nearly a factor of three increase in the central density to 1.2 X 10(exp 20) cube m. At the same time the density fluctuation level in the reversed shear region dramatically decreases. The ion and electron temperatures, which are about 20 keV and 7 keV respectively, change little during the ERS mode. The transport and transition into and out of the ERS mode have been studied on TFTR with plasma currents in the range 0.9-2.2 MA, with a toroidal magnetic field of 2.7-4.6 T, and the radius of the q(r) minimum, q{sub min}, has been varied from r/a = 0.35 to 0.55. Toroidal field and co/counter neutral beam injection toroidal rotation variations have been used to elucidate the underlying physics of the transition mechanism and power threshold of the ERS mode.
Date: December 31, 1997
Creator: Levinton, F.M.; Batha, S.H.; Beer, M.A.; Bell, M.G.; Budny, R.V.; Efthimion, P.C. et al.
Partner: UNT Libraries Government Documents Department

Kinetic Profiles in NSTX Plasmas

Description: The National Spherical Torus Experiment (NSTX) is a low aspect ratio (R/a approximately 1.3) device with auxiliary heating from neutral-beam injection (NBI) and high-harmonic fast-wave heating (HHFW). Typical NSTX parameters are R(subscript ''0'') = 85 cm, a = 67 cm, I(subscript ''p'') = 0.7-1.4 MA, B(subscript ''phi'') = 0.25-0.45 T. Three co-directed deuterium neutral-beam sources have injected P(subscript ''NB'') less than or equal to 4.7 MW. HHFW plasmas typically have delivered P(subscript ''RF'') less than or equal to 3 MW. Important to the understanding of NSTX confinement are the new kinetic profile diagnostics: a multi-pulse Thomson scattering system (MPTS) and a charge-exchange recombination spectroscopy (CHERS) system. The MPTS diagnostic currently measures electron density and temperature profiles at 30 Hz at ten spatial locations. The CHERS system has recently become available to measure carbon ion temperature and toroidal flow at 17 radial positions spanning the outer half of the minor radius with 20 msec time resolution during NBI. Experiments conducted during the last year have produced a wide range of kinetic profiles in NSTX. Some interesting examples are presented below.
Date: July 10, 2001
Creator: Bell, R.E.; LeBlanc, B.P.; Bourdelle, C.; Ernst, D.R.; Fredrickson, E.D.; Gates, D.A. et al.
Partner: UNT Libraries Government Documents Department

Unified Ideal Stability Limits for Advanced Tokamak and Spherical Torus Plasmas

Description: Ideal magnetohydrodynamic stability limits of shaped tokamak plasmas with high bootstrap fraction are systematically determined as a function of plasma aspect ratio. For plasmas with and without wall stabilization of external kink modes, the computed limits are well described by distinct and nearly invariant values of a normalized beta parameter utilizing the total magnetic field energy density inside the plasma. Stability limit data from the low aspect ratio National Spherical Torus Experiment is compared to these theoretical limits and indicates that ideal nonrotating plasma no-wall beta limits have been exceeded in regimes with sufficiently high cylindrical safety factor. These results could impact the choice of aspect ratio in future fusion power plants.
Date: February 6, 2003
Creator: Menard, J.E.; Bell, M.G.; Bell, R.E.; Gates, D.A.; Kaye, S.M.; LeBlanc, B.P. et al.
Partner: UNT Libraries Government Documents Department

Transport simulations TFTR: Theoretically-based transport models and current scaling

Description: In order to study the microscopic physics underlying observed L-mode current scaling, 1-1/2-d BALDUR has been used to simulate density and temperature profiles for high and low current, neutral beam heated discharges on TFTR with several semi-empirical, theoretically-based models previously compared for TFTR, including several versions of trapped electron drift wave driven transport. Experiments at TFTR, JET and D3-D show that I{sub p} scaling of {tau}{sub E} does not arise from edge modes as previously thought, and is most likely to arise from nonlocal processes or from the I{sub p}-dependence of local plasma core transport. Consistent with this, it is found that strong current scaling does not arise from any of several edge models of resistive ballooning. Simulations with the profile consistent drift wave model and with a new model for toroidal collisionless trapped electron mode core transport in a multimode formalism, lead to strong current scaling of {tau}{sup E} for the L-mode cases on TFTR. None of the theoretically-based models succeeded in simulating the measured temperature and density profiles for both high and low current experiments.
Date: December 1, 1991
Creator: Redi, M.H.; Cummings, J.C.; Bush, C.E.; Fredrickson, E.; Grek, B.; Hahm, T.S. et al.
Partner: UNT Libraries Government Documents Department

Charge exchange recombination spectroscopy measurements in the extreme ultraviolet region of central carbon concentrations during high power neutral beam heating in TFTR (Tokamak Fusion Test Reactor)

Description: The carbon concentration in the central region of TFTR discharges with high power neutral beam heating has been measured by charge-extracted recombination spectroscopy (CXRS) of the C{sup +5} n = 3--4 transition in the extreme ultraviolet region. The carbon concentrations were deduced from absolute measurements of the line brightness using a calculation of the beam attenuation and the appropriate cascade-corrected line excitation rates. As a result of the high ion temperatures in most of the discharges, the contribution of beam halo neutrals to the line brightness was significant and therefore had to be included in the modeling of the data. Carbon concentrations have been measured in discharges with I{sub p} = 1.0-1.6 MA and beam power in the range of 2.6-30 MW, including a number of supershots. The results are in good agreement with carbon concentrations deduced from the visible bremsstrahlung Z{sub eff} and metallic impurity concentrations measured by x-ray pulse-height analysis, demonstrating the reliability of the atomic rates used in the beam attenuation and line excitation calculations. Carbon is the dominant impurity species in these discharges; the oxygen concentration measured via CXRS in a high beam power case was 0.0006 of n{sub e}, compard to 0.04 for carbon. Trends with I{sub p} and beam power in the carbon concentration and the inferred deuteron concentration are presented. The carbon concentration is independent of I{sub p} and decreases from 0.13 at 2.6 MW beam power to 0.04 at 30 MW, while the deuteron concentration increases from 0.25 to 0.75 over the same range of beam power. These changes are primarily the result of beam particle fueling, as the carbon density did not vary significantly with beam power. The time evolutions of the carbon and deuteron concentrations during two high power beam pulses, one which exhibited a carbon bloom and one which ...
Date: September 1, 1989
Creator: Stratton, B.C.; Fonck, R.J.; Ramsey, A.T.; Synakowski, E.J.; Grek, B.; Hill, K.W. et al.
Partner: UNT Libraries Government Documents Department