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  • 1
    ISSN: 1572-9591
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3698-3705 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation, breakup, and temporal compression of strong solitons in a lumped circuit (dispersive) nonlinear LC-transmission line is treated. The strong lumped circuit solitons are characterized by the condition that almost all the signal charges may instantaneously appear on a simple circuit stage and travel much faster than the linear circuit signal speed. Under these conditions, the usual nonlinear Korteweg–de Vries theory of lumped nonlinear transmission lines does not apply. Properties of the soliton structure are derived; in particular, the rate at which energy is radiated for nonuniform parameters (i.e., temporal compression) is calculated and compared with numerical simulation.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4555-4562 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fast and efficient numerical algorithm using energy conservation is developed to study the interaction of high-energy particles with a toroidicity-induced Alfvén eigenmode (TAE). A Hamiltonian guiding center code is used to simulate the alpha particle motion and a nonlinear δf scheme is employed to calculate the wave-particle energy exchange. The code is benchmarked using the bump-on-tail problem and simulation results agree with analytical estimates. For a single TAE mode, the particle radial excursion is much less than the spacing between the resonances produced by the poloidal harmonics for International Thermonuclear Experimental Reactor parameters. Resonant particles that lose their energy to the wave can become trapped poloidally, but transfer to a loss orbit through this mechanism does not occur. Modification of the particle distribution leading to mode saturation is observed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2206-2214 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general method is developed for calculating boundary plasma fluctuations across a magnetic separatrix in a tokamak with a divertor or a limiter. The slab model, which assumes a periodic plasma in the edge reaching the divertor or limiter plate in the scrape-off layer (SOL), should provide a good estimate, if the radial extent of the fluctuation quantities across the separatrix to the edge is small compared to that given by finite particle banana orbit. The Laplace transform is used for solving the initial value problem. The electron-temperature-gradient (ETG)-driven instability is found to grow like t−1/2eγmt.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2402-2413 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear theory of the sonic ion-temperature-gradient-driven mode in the presence of sheared poloidal rotation is discussed in the context of a hydrodynamic model. Analytical and numerical calculations show that the growth rate increases for weak shear, but then decreases when the shearing frequency exceeds the mode frequency. This trend is a consequence of the coupling of radial eigenmodes induced by the asymmetric effective potential and the absorption and damping due to resonance between the wave frequency and shearing frequency. The former dominates at weak shear, resulting in destabilization, while the latter dominates for strong shear, resulting in stabilization. Mixing length estimates of the turbulent diffusivity are given, and a novel bifurcation scenario for the L→H transition is discussed.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1807-1817 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A unified theory of temperature gradient-driven trapped ion modes and ballooning instabilities is developed using kinetic theory in banana regimes. All known results such as electrostatic and purely magnetic trapped particle modes and ideal magnetohydrodynamic ballooning modes (or shear Alfvén waves) are readily derived from the present single general dispersion relation. Several new results from ion–ion collision, finite beta stabilization of ion temperature gradient-driven trapped particle modes, and trapped particle modification of ballooning modes are derived and discussed. The interrelationship between these modes is established.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 68-86 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A kinetic theory of collisionless and dissipative trapped-electron-driven drift wave turbulence in a sheared magnetic field is presented. Weak turbulence theory is employed to calculate the nonlinear electron and ion responses and to derive a wave kinetic equation that determines the nonlinear evolution of trapped-electron mode turbulence. The saturated fluctuation spectrum is calculated using the condition of nonlinear saturation. The turbulent transport coefficients (D, χi, χe), are, in turn, calculated using the saturated fluctuation spectrum. Because of the disparity in the three different radial scale lengths of the slab-like eigenmode: Δ (trapped-electron layer width), xt (turning point width), and xi (Landau damping point), Δ〈xt〈xi, it is found that ion Compton scattering rather than trapped-electron Compton scattering is the dominant nonlinear saturation mechanism. Ion Compton scattering transfers wave energy from short to long wavelengths where the wave energy is shear damped. As a consequence, a saturated fluctuation spectrum ||φ||2(kθ)∼k−αθ (α=2 and 3 for the dissipative and collisionless regimes, respectively) occurs for kθ ρs〈1 and is heavily damped for kθ ρs〉1. The predicted fluctuation level and transport coefficients are well below the "mixing length'' estimate. This is due to the contribution of radial wave numbers x−1t〈kr≤ρ−1i to the nonlinear couplings, the effect of radial localization of the trapped-electron response to a layer of width Δ, and the weak turbulence factor 〈γle/ωk〉k〈1, which enters the saturation level.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 3083-3092 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A nonlinear system of equations is derived for drift waves in a high-beta plasma (β(very-much-greater-than)1). The magnetic field pressure is taken small compared to the particle pressure. Pressure balance is established by having a uniform particle pressure with the density and temperature gradients in opposite directions. The primary purpose of the magnetic field is to inhibit radial heat flux. This is the principle of such plasma fusion systems as the wall sustained multiple mirror, compressed liner, and magnetic-insulated inertial fusion, where the heat is contained over a relatively short radial scale length and a long axial scale length. The nonlinear equations for the mathematical model contain drift instabilities that give rise to radial heat and particle fluxes that can enhance the losses expected from classical collisional effects. The linear and nonlinear evolution of the model is studied here.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Runaway electrons are calculated to be produced during the rapid plasma cooling resulting from "killer pellet" injection experiments, in general agreement with observations in the DIII-D [J. L. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] tokamak. The time-dependent dynamics of the kinetic runaway distributions are obtained with the CQL3D [R. W. Harvey and M. G. McCoy, "The CQL3D Code," in Proceedings of the IAEA Technical Committee Meeting on Numerical Modeling, Montreal, 1992 (International Atomic Energy Agency, Vienna, 1992), p. 489] collisional Fokker–Planck code, including the effect of small and large angle collisions and stochastic magnetic field transport losses. The background density, temperature, and Zeff are evolved according to the KPRAD [D. G. Whyte and T. E. Evans et al., in Proceedings of the 24th European Conference on Controlled Fusion and Plasma Physics, Berchtesgaden, Germany (European Physical Society, Petit-Lancy, 1997), Vol. 21A, p. 1137] deposition and radiation model of pellet–plasma interactions. Three distinct runway mechanisms are apparent: (1) prompt "hot-tail runaways" due to the residual hot electron tail remaining from the pre-cooling phase, (2) "knock-on" runaways produced by large-angle Coulomb collisions on existing high energy electrons, and (3) Dreicer "drizzle" runaway electrons due to diffusion of electrons up to the critical velocity for electron runaway. For electron densities below (approximate)1×1015 cm−3, the hot-tail runaways dominate the early time evolution, and provide the seed population for late time knock-on runaway avalanche. For small enough stochastic magnetic field transport losses, the knock-on production of electrons balances the losses at late times. For losses due to radial magnetic field perturbations in excess of (approximate)0.1% of the background field, i.e., δBr/B≥0.001, the losses prevent late-time electron runaway. © 2000 American Institute of Physics.
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  • 10
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We propose a new method of measuring the fast confined α-particle distribution in a reacting plasma. The presence of α particles in a D-T plasma will create a high-energy tail on the deuterium and tritium ion energy distributions. A 3.5 MeV alpha can transfer 3.4 MeV to a tritium ion in a single elastic scattering interaction. Calculations of the size of these knock-on tails in tokamaks such as TFTR, JET, and ITER show that it may be possible to measure these tails and provide information on the fast confined alphas. The knock-on tail ions will produce D-T neutrons with energies up to 20.7 MeV, so that D-T neutron spectroscopy can be used to monitor the alpha population. Neutron spectroscopy looks especially attractive for ITER. A collimated array of threshold neutron activation detectors could be used to deduce the confined alpha density profile. Tests of this diagnostic can also be done on TFTR and JET. Existing high-energy neutral particle analyzers may allow observation of the ion tails directly via passive and/or active charge exchange. © 1995 American Institute of Physics.
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