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  • 1
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Evidence is presented for the role of radial electric field shear in enhanced confinement regimes attained without sharp bifurcations or transitions. Temperature scans at constant density, created in the reheat phase following deuterium pellet injection into supershot plasmas in the Tokamak Fusion Test Reactor [J. D. Strachan, et al., Phys. Rev. Lett. 58, 1004 (1987)] are simulated using a physics-based transport model. The slow reheat of the ion temperature profile, during which the temperature nearly doubles, is not explained by relatively comprehensive models of transport due to Ion Temperature Gradient Driven Turbulence (ITGDT), which depends primarily on the (unchanging) electron density gradient. An extended model, including the suppression of toroidal ITGDT by self-consistent radial electric field shear, does reproduce the reheat phase. The extended reheat at constant density is observed in supershot but not L-Mode plasmas. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neoclassical simulations of alpha particle density profiles in high fusion power plasmas on the Tokamak Fusion Test Reactor [Phys. Plasmas 5, 1577 (1998)] are found to be in good agreement with measurements of the alpha distribution function made with a sensitive active neutral particle diagnostic. The calculations are carried out in Hamiltonian magnetic coordinates with a fast, particle-following Monte Carlo code which includes the neoclassical transport processes, a recent first-principles model for stochastic ripple loss and collisional effects. New calculations show that monotonic shear alpha particles are virtually unaffected by toroidal field ripple. The calculations show that in reversed shear the confinement domain is not empty for trapped alphas at birth and allow an estimate of the actual alpha particle densities measured with the pellet charge exchange diagnostic. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1768-1770 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The MINGL database system is an integrated set of tools which provides a means of collecting and managing diagnostic data and transport code results from TFTR. An interactive menu-driven format allows users to collect scalar and profile data from various data sources into shareable INGRES databases. LOCUS and INGRES/QUEL/SQL interfaces make it easy to browse, select, compare, and display the data in one of several formats. Utilities exist for managing the individual data sets and restricting their accessibility, for indexing the tables by author, and for maintaining a table of contents for an entire database. The modularity of the system allows automated database-server applications for between-shot analysis and display.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-beta, low-aspect-ratio ("compact") stellarators are promising solutions to the problem of developing a magnetic plasma configuration for magnetic fusion power plants that can be sustained in steady state without disrupting. These concepts combine features of stellarators and advanced tokamaks and have aspect ratios similar to those of tokamaks (2–4). They are based on computed plasma configurations that are shaped in three dimensions to provide desired stability and transport properties. Experiments are planned as part of a program to develop this concept. A β=4% quasi-axisymmetric plasma configuration has been evaluated for the National Compact Stellarator Experiment (NCSX). It has a substantial bootstrap current and is shaped to stabilize ballooning, external kink, vertical, and neoclassical tearing modes without feedback or close-fitting conductors. Quasi-omnigeneous plasma configurations stable to ballooning modes at β=4% have been evaluated for the Quasi-Omnigeneous Stellarator (QOS) experiment. These equilibria have relatively low bootstrap currents and are insensitive to changes in beta. Coil configurations have been calculated that reconstruct these plasma configurations, preserving their important physics properties. Theory- and experiment-based confinement analyses are used to evaluate the technical capabilities needed to reach target plasma conditions. The physics basis for these complementary experiments is described. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Perturbative experiments on the Tokamak Fusion Test Reactor [Phys. Plasmas 4, 1736 (1997)] (TFTR) have investigated transport in reverse shear plasmas. On TFTR, reverse magnetic shear plasmas bifurcate into two states with different transport properties: reverse shear (RS) and enhanced reverse shear (ERS) with improved core confinement. Measurements of the 14 MeV t(d,n)α neutrons and charge-exchange recombination radiation spectra are used to infer the trace tritium and helium profiles, respectively. The profile evolution indicate the formation of core particle transport barriers in ERS plasmas. The transport barrier is manifested by an order-of-magnitude reduction in the particle diffusivity (DT,DHe) and a smaller reduction in the pinch within the reverse shear region. The low diffusivities are consistent with neoclassical predictions. Furthermore, DT and DHe(approximate)χeff, the effective thermal diffusivity. Although the measured coefficients imply no helium ash accumulation, the situation is uncertain in a reactor due to unknown χeff scaling.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tearing-type modes are observed in most high confinement operation regimes in the Tokamak Fusion Test Reactor (TFTR) [Nucl. Fusion 35, 1429 (1995)]. Three different methods are used to measure the magnetic island widths: external magnetic coils, internal temperature fluctuation from electron cyclotron emission (ECE) diagnostics and an experiment where the plasma major radius is rapidly shifted ("Jog" experiments). A good agreement between the three methods is observed. Numerical and analytic calculations of Δ′ (the tearing instability index) are compared with an experimental measurement of Δ′ using the tearing mode eigenfunction mapped from the jog data. The obtained negative Δ′ indicates that the observed tearing modes cannot be explained by the classical current-gradient-driven tearing theory. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1316-1325 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The potential performance, in deuterium-tritium plasmas, of a new enhanced confinement regime with reversed magnetic shear [enhanced reversed shear (ERS) mode] is assessed. The equilibrium conditions for an ERS mode plasma are estimated by solving the plasma transport equations using the thermal and particle diffusivities measured in a short duration ERS mode discharge in the Tokamak Fusion Test Reactor [F. M. Levinton et al., Phys. Rev. Lett. 75, 4417 (1995)]. The plasma performance depends strongly on Zeff and neutral beam penetration to the core. The steady-state projections typically have a central electron density of ∼2.5×1020 m−3 and nearly equal central electron and ion temperatures of ∼10 keV. In time-dependent simulations the peak fusion power, ∼ 25 MW, is twice the steady-state level. Peak performance occurs during the density rise when the central ion temperature is close to the optimal value of ∼15 keV. The simulated pressure profiles can be stable to ideal magnetohydrodynamic instabilities with toroidal mode number n=1,2,3,4 and ∞ for βnorm up to 2.5; the simulations have βnorm≤2.1. The enhanced reversed shear mode may thus provide an opportunity to conduct alpha physics experiments in conditions similar to those proposed for advanced tokamak reactors. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1348-1355 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conjecture that the safety factor profile, q(r), controls the improvement in tokamak plasmas from poor confinement in the Low- (L-) mode regime to improved confinement in the supershot regime has been tested in two experiments on the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Nucl. Fusion Res. 1, 51 (1987)]. First, helium was puffed into the beam-heated phase of a supershot discharge, which induced a degradation from supershot to L-mode confinement in about 100 ms, far less than the current relaxation time. The q and shear profiles measured by a motional Stark effect polarimeter showed little change during the confinement degradation. Second, rapid current ramps in supershot plasmas altered the q profile, but were observed not to change significantly the energy confinement. Thus, enhanced confinement in supershot plasmas is not due to a particular q profile, which has enhanced stability or transport properties. The discharges making a continuous transition between supershot and L-mode confinement were also used to test the critical-electron-temperature-gradient transport model. It was found that this model could not reproduce the large changes in electron and ion temperature caused by the change in confinement. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The first experiments utilizing high-power radio waves in the ion cyclotron range of frequencies to heat deuterium–tritium (D–T) plasmas have been completed on the Tokamak Fusion Test Reactor [Fusion Technol. 21, 13 (1992)]. Results from the initial series of experiments have demonstrated efficient core second harmonic tritium (2ΩT) heating in parameter regimes approaching those anticipated for the International Thermonuclear Experimental Reactor [D. E. Post, Plasma Physics and Controlled Nuclear Fusion Research, Proceedings of the 13th International Conference, Washington, DC, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239]. Observations are consistent with modeling predictions for these plasmas. Efficient electron heating via mode conversion of fast waves to ion Bernstein waves has been observed in D–T, deuterium-deuterium (D–D), and deuterium–helium-4 (D–4He) plasmas with high concentrations of minority helium-3 (3He) (n3He/ne(approximately-greater-than)10%). Mode conversion current drive in D–T plasmas was simulated with experiments conducted in D–3He–4He plasmas. Results show a directed propagation of the mode converted ion Bernstein waves, in correlation with the antenna phasing. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3509-3520 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hamiltonian coordinate, guiding center code calculations of the confinement of suprathermal ions in quasi-axisymmetric stellarator (QAS) designs have been carried out to evaluate the attractiveness of compact configurations which are optimized for ballooning stability. A new stellarator particle following code is used to predict the confinement of thermal and neutral beam ions in a small experiment with R=145 cm, B=1–2 T and for alpha particles in a reactor size device. As for tokamaks, collisional pitch angle scattering drives ions into ripple wells and stochastic field regions, where they are quickly lost. In contrast, however, such losses are enhanced in QAS so that high edge poloidal flux has limited value in improving ion confinement. The necessity for reduced stellarator ripple fields is emphasized. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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