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  • 1995-1999  (12)
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  • 1
    Electronic Resource
    Electronic Resource
    The role of the neutral beam fueling profile in the performance of the Tokamak Fusion Test Reactor and other tokamak plasmas : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1699-1706 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scalings for the stored energy and neutron yield, determined from experimental data, are applied to both deuterium-only and deuterium–tritium plasmas in different neutral-beam-heated operational domains in the Tokamak Fusion Test Reactor [Nucl. Fusion 25, 1167 (1985)]. The domain of the data considered includes the Supershot, high poloidal beta, low-mode, and limiter high-mode operational regimes, as well as discharges with a reversed magnetic shear configuration. The new important parameter in the present scaling is the peakedness of the heating beam fueling profile shape. Ion energy confinement and neutron production are relatively insensitive to other plasma parameters compared to the beam fueling peakedness parameter and the heating beam power when considering plasmas that are stable to magnetohydrodynamic modes. However, the stored energy of the electrons is independent of the beam fueling peakedness. The implication of the scalings based on this parameter is related to theoretical transport models such as radial electric field shear and ion temperature gradient marginality models. Similar physics interpretation is provided for beam heated discharges on other major tokamaks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872272
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  • 2
    Electronic Resource
    Electronic Resource
    Isotopic scaling of confinement in deuterium–tritium plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2299-2307 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The confinement and heating of supershot plasmas are significantly enhanced with tritium beam injection relative to deuterium injection in the Tokamak Fusion Test Reactor [Plasma Phys. Controlled Fusion 26, 11 (1984)]. The global energy confinement and local thermal transport are analyzed for deuterium and tritium fueled plasmas to quantify their dependence on the average mass of the hydrogenic ions. Radial profiles of the deuterium and tritium densities are determined from the D–T fusion neutron emission profile. The inferred scalings with average isotopic mass are quite strong, with τE∝〈A〉0.85±0.20, τEthermal∝〈A〉0.89±0.20, χitot∝〈A〉−2.6±0.5, and De∝〈A〉−1.4±0.2 at fixed Pinj. For fixed local plasma parameters χitot∝〈A〉−1.8±0.4 is obtained. The quoted 2σ uncertainties include contributions from both diagnostic errors and shot irreproducibility, and are conservatively constructed to attribute the entire scatter in the regressed parameters to uncertainties in the exponent on plasma mass. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871253
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  • 3
    Electronic Resource
    Electronic Resource
    Fusion performance analysis of plasmas with reversed magnetic shear in the Tokamak Fusion Test Reactor (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3247-3262 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A case for substantial loss of fast ions degrading the performance of tokamak fusion test reactor plasmas [Phys. Plasmas 2, 2176 (1995)] with reversed magnetic shear (RS) is presented. The principal evidence is obtained from an experiment with short (40–70 ms) tritium beam pulses injected into deuterium beam heated RS plasmas [Phys. Rev. Lett. 82, 924 (1999)]. Modeling of this experiment indicates that up to 40% beam power is lost on a time scale much shorter than the beam–ion slowing down time. Critical parameters which connect modeling and experiment are: The total 14 MeV neutron emission, its radial profile, and the transverse stored energy. The fusion performance of some plasmas with internal transport barriers is further deteriorated by impurity accumulation in the plasma core. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873565
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  • 4
    Electronic Resource
    Electronic Resource
    Neoclassical simulations of fusion alpha particles in pellet charge exchange experiments on the Tokamak Fusion Test Reactor (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2826-2833 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.873717
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of particle transport barriers in reverse shear plasmas on the Tokamak Fusion Test Reactor : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1832-1838 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.872853
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  • 6
    Electronic Resource
    Electronic Resource
    Calculations of alpha particle loss for reversed magnetic shear in the Tokamak Fusion Test Reactor (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4001-4008 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hamiltonian coordinate, guiding center code calculations of the toroidal field ripple loss of alpha particles from a reversed shear plasma in the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)] predict 40% total alpha losses and 20% ripple diffusion losses. This is about double the loss rate of a comparable non-reversed magnetic shear plasma. High central q is found to increase alpha ripple losses as well as first orbit losses of alphas in the reversed shear simulations. Alpha ripple transport on TFTR affects ions within r/a=0.5, not at the plasma edge. The entire plasma is above threshold for stochastic ripple loss of alpha particles at birth energy in the reversed shear case simulated, so that all trapped 3.5 MeV alphas are lost stochastically or through prompt losses. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872519
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  • 7
    Electronic Resource
    Electronic Resource
    Energetic particle orbits in the National Spherical Tokamak Experiment (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3667-3675 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The trajectories of neutral beam injected energetic ions in spherical tokamaks are examined. The large poloidal magnetic field in the outboard region of spherical tokamaks causes neutral beam injected ions to be born on trapped orbits even with cotangential injection. Numerical solutions to the equations for particle motion and for guiding center drifts are compared in several magnetic equilibria for a range of particle initial conditions. Even when rL/a∼1/4 the guiding center orbits closely resemble the path of the instantaneous center of gyration of the particle motion; exceptions occur primarily for orbits near the trapped/passing boundary. Finite Larmor radius effects are included in guiding center simulations of prompt orbit loss in the National Spherical Tokamak Experiment (NSTX) [J. Spitzer et al., Fusion Technol. 30, 1337 (1996)]. Orbit loss in the NSTX is caused primarily by collisions with the close fitting conducting shell, and severe losses would be expected with counter directed injection. While most orbits are similar to those found in conventional tokamaks, additional orbit types are possible in spherical tokamaks. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872263
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  • 8
    Electronic Resource
    Electronic Resource
    Simulations of alpha particle ripple loss from the International Thermonuclear Experimental Reactor (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3037-3042 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Calculations of collisional stochastic ripple loss of alpha particles from the new 20 toroidal field (TF) coil International Thermonuclear Experimental Reactor (ITER) [Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239] predict small alpha ripple losses, less than 0.4%, close to the loss calculated for the full current operation of the earlier 24 TF coil design. An analytic fit is obtained to the ITER ripple data field demonstrating the nonlinear height dependence of the ripple minimum for D-shaped ripple contours. In contrast to alpha loss simulations for the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)], a simple Goldston, White, and Boozer stochastic loss criterion [Phys. Rev. Lett. 47, 647 (1981)] ripple loss model is found to require an increased renormalization of the stochastic threshold δs/δGWB(approximately-greater-than)1. Effects of collisions, sawtooth broadening, and reversal of the grad-B drift direction are included in the particle following simulations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871640
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  • 9
    Electronic Resource
    Electronic Resource
    TRANSP simulations of International Thermonuclear Experimental Reactor plasmas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 4583-4593 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The TRANSP code [R. V. Budny et al., Nucl. Fusion 35, 1497 (1995)] is used to construct comprehensive, self-consistent models for plasmas within the separatrix surface in the International Thermonuclear Experimental Reactor (ITER) [Technical Basis for the ITER Interim Design Report, Cost Review and Safety Analysis (International Atomic Energy Agency, Vienna, 1996)]. Steady state profiles of two plasmas from the ITER "Interim Design'' database are used. Effects of 1 MeV neutral beam injection, sawteeth mixing, toroidal field ripple, and helium ash transport are included. Results are given for the fusion rate profiles, and parameters describing effects such as the alpha particle heating of electrons and thermal ions, and the thermalization rates. The modeling indicates that the deposition of the neutral beam ions will peak in the plasma center, and the average beam ion energy will be half the injected energy. Sawtooth mixing will broaden the fast alpha profile. The toroidal ripple loss rate of alpha energy will be 3% before sawtooth crashes and will increase by a factor of 3 immediately following sawtooth crashes. Various assumptions for the thermal He transport and the He recycling coefficient at the separatrix Rrec are used. If the ratio of helium and energy confinement times, τ*He/τE is less than 15, the steady state fusion power is predicted to be 1.5 GW or greater. The values of the transport coefficients required for this fusion power depend on Rrec. If this is larger than about 0.5, and if the inward pinch is small the required He diffusivity must be much larger than that measured in tokamaks. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871584
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  • 10
    Electronic Resource
    Electronic Resource
    Deuterium–tritium high confinement (H-mode) studies in the Tokamak Fusion Test Reactor (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2366-2374 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High or enhanced confinement (H-mode) plasmas have been obtained for the first time with nearly equal concentrations of deuterium and tritium in high-temperature, high poloidal beta plasmas in the Tokamak Fusion Test Reactor (TFTR) [McGuire, Phys. Plasmas 2, 2176 (1995)]. Tritium fueling was provided mainly through high-power neutral beam injection (NBI) with powers up to 31 MW and beam energies of 90–110 keV. A transition to a circular limiter H-mode configuration has been obtained, following a programmed rapid decrease of the plasma current. Isotope effects, due to the presence of tritium, led to different behavior for deuterium–deuterium (DD) and deuterium–tritium (DT) H-modes relative to confinement, edge localized magnetohydrodynamic modes (ELMs), and ELM effects on fusion products. However, the threshold power for the H-mode transition was the same in DD and DT. Some of the highest values of the global energy confinement time, τE, have been achieved on TFTR during the ELM-free phase of DT H-mode plasmas. Enhancements of τE greater than four times the L-mode have been attained. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871490
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