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  • 1
    Electronic Resource
    Electronic Resource
    Gyrokinetic simulations in general geometry and applications to collisional damping of zonal flows : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1857-1862 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fully three-dimensional gyrokinetic particle code using magnetic coordinates for general geometry has been developed and applied to the investigation of zonal flows dynamics in toroidal ion-temperature-gradient turbulence. Full torus simulation results support the important conclusion that turbulence-driven zonal flows significantly reduce the turbulent transport. Linear collisionless simulations for damping of an initial poloidal flow perturbation exhibit an asymptotic residual flow. The collisional damping of this residual causes the dependence of ion thermal transport on the ion–ion collision frequency, even in regimes where the instabilities are collisionless. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874008
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  • 2
    Electronic Resource
    Electronic Resource
    Alpha-driven magnetohydrodynamics (MHD) and MHD-induced alpha loss in the Tokamak Fusion Test Reactor : 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. 1610-1616 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Alpha-driven toroidal Alfvén eigenmodes (TAEs) are observed as predicted by theory in the post-neutral beam phase in high central q (safety factor) deuterium–tritium (D–T) plasmas in the Tokamak Fusion Test Reactor (TFTR) [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)]. The mode location, poloidal structure, and the importance of q profile for TAE instability are discussed. So far no alpha particle loss due to these modes was detected due to the small mode amplitude. However, alpha loss induced by kinetic ballooning modes (KBMs) was observed in high-confinement D–T discharges. Particle orbit simulation demonstrates that the wave–particle resonant interaction can explain the observed correlation between the increase in alpha loss and appearance of multiple high-n (n≥6, n is the toroidal mode number) modes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872363
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  • 3
    Electronic Resource
    Electronic Resource
    Ripple-induced energetic particle loss in tokamaks (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3043-3054 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The threshold for stochastic transport of high energy trapped particles in a tokamak due to toroidal field ripple is calculated by explicit construction of primary resonances, and a numerical examination of the route to chaos. Critical field ripple amplitude is determined for loss. The expression is given in magnetic coordinates and makes no assumptions regarding shape or up-down symmetry. An algorithm is developed including the effects of prompt axisymmetic orbit loss, ripple trapping, convective banana flow, and stochastic ripple loss, which gives accurate ripple loss predictions for representative Tokamak Fusion Test Reactor [R. Hawryluk, Plasma Phys. Controlled Fusion 33, 1509 (1991)] and International Thermonuclear Experimental Reactor [K. Tomabechi, Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1989), Vol. 3, p. 214] equilibria. The algorithm is extended to include the effects of collisions and drag, allowing rapid estimation of alpha particle loss in tokamaks. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871641
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  • 4
    Electronic Resource
    Electronic Resource
    Effective temperatures, sawtooth mixing, and stochastic diffusion ripple loss of fast H+ minority ions driven by ion cyclotron heating in the Tokamak Fusion Test Reactor (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2430-2436 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper presents studies of the H+ minority ions driven by Ion Cyclotron Radio Frequency (ICRF) heating in the Tokamak Fusion Test Reactor (TFTR) [R. J. Hawryluk et al., Phys. Plasmas 5, 1577 (1998)] deuterium plasmas using primarily passive H° flux detection in the energy range of 0.2–1.0 MeV. The measured passive H+ energy spectra are compared with active (Li pellet charge exchange) results. It is shown that in the passive mode the main donors for the neutralization of H+ ions in this energy range are C5+ ions. The measured effective H+ tail temperatures range from 0.15 MeV at an ICRF power of 2 MW to 0.35 MeV at 6 MW. Radial redistribution of ICRF-driven H+ ions was detected when giant sawtooth crashes occurred during the ICRF heating. The redistribution affected ions with energy below 0.7–0.8 MeV. The sawtooth crashes displaces H+ ions outward along the plasma major radius into the stochastic ripple diffusion domain where those ions are lost in ∼10 msec. These observations are consistent with the model of the redistribution of energetic particles developed previously to explain the results of deuterium-tritium (DT) alpha-particle redistribution due to sawtooth oscillations observed in TFTR. The experimental data are also consistent with numerical simulations of H+ stochastic ripple diffusion losses.© 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873539
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  • 5
    Electronic Resource
    Electronic Resource
    Quasi-helical magnetohydrodynamic equilibria in the presence of flow (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2653-2663 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By investigating the conservation laws of guiding-center mechanics, an extension of quasi-helical static magnetohydrodynamic equilibria to incorporate strong flow is obtained, subject to suitable ordering assumptions. Such equilibria correspond to self-consistent Fokker-Planck kinetic equilibria in the presence of a quasi-helical magnetic field. The effect of small symmetry-breaking contributions in the magnetic field is investigated. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871522
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  • 6
    Electronic Resource
    Electronic Resource
    Toroidal Alfvén eigenmode-induced ripple trapping (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2871-2873 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Toroidal Alfvén eigenmodes are shown to be capable of inducing ripple trapping of high-energy particles in tokamaks, causing intense localized particle loss. The effect has been observed in TFTR [R. Hawryluk, Plasma Phys. Controlled Fusion 33, 1509 (1991)]. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871452
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  • 7
    Electronic Resource
    Electronic Resource
    Near threshold anomalous transport in the standard map (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 8 (1998), S. 757-767 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Anomalous transport is investigated near threshold in the standard map. Very long time flights, and a large anomaly in the transport, are shown to be associated with a new form of multi-island structures causing orbit sticking. The phase space structure of these traps, and the exponents of the characteristic long time tails associated with them are determined. In general these structures are very complex, but some cases, consisting of layers of islands, allow simple modeling. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.166361
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  • 8
    Electronic Resource
    Electronic Resource
    Energetic particle transport in compact quasi-axisymmetric stellarators (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3509-3520 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.873611
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  • 9
    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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  • 10
    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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