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  • 11
    Electronic Resource
    Electronic Resource
    Alpha particle effects on the internal kink and fishbone modes (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3369-3377 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of alpha particles on the internal kink and fishbone modes are studied analytically. The nonadiabatic contribution from untrapped alpha particles is negligible. Finite inverse aspect ratio, plasma β, and plasma shaping effects can significantly enhance the trapped particle drift reversal domain in the pitch angle space and reduce the bounce-averaged magnetic drift frequency. The decrease of the drift magnitude and drift reversal effects on the ideal kink mode is small, but the βα threshold for the fishbone mode can be much lower than previously predicted [B. Coppi, S. Migliuolo, F. Pegoraro, and F. Porcelli, Phys. Fluids B 2, 927 (1990)]. Moreover, the fishbone mode could be excited by alpha particles, even when the plasma is stable in the ideal magnetohydrodynamic (MHD) limit. In addition, the ion diamagnetic drift frequency (finite ion Larmor radius effect) has a strong destabilizing effect on the fishbone mode when it is comparable with the trapped alpha-averaged precessional drift frequency, even though it stabilizes the plasma in the ideal MHD limit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870485
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  • 12
    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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  • 13
    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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  • 14
    Electronic Resource
    Electronic Resource
    Saturation of alpha particle driven instability in Tokamak Fusion Test Reactor (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 629-632 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A nonlinear theory of kinetic instabilities near threshold [Berk et al., Plasma Phys. Rep. 23, 842 (1997)] is applied to calculate the saturation level of toroidicity-induced Alfvén eigenmodes (TAE), and to be compared with the predictions of δf method calculations (Y. Chen, Ph.D. thesis, Princeton University, 1998). Good agreement is observed between the predictions of both methods and the predicted saturation levels are comparable to experimentally measured amplitudes of the TAE oscillations in Tokamak Fusion Test Reactor [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)]. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873216
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  • 15
    Electronic Resource
    Electronic Resource
    Toroidal Alfvén eigenmodes in TFTR deuterium–tritium plasmas : 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. 1703-1711 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Purely alpha-particle-driven toroidal Alfvén eigenmodes (TAEs) with toroidal mode numbers n=1–6 have been observed in deuterium–tritium (D–T) plasmas on the tokamak fusion test reactor [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)]. The appearance of mode activity following termination of neutral beam injection in plasmas with q(0)〉1 is generally consistent with theoretical predictions of TAE stability [G. Y. Fu et al. Phys. Plasmas 3, 4036 (1996)]. Internal reflectometer measurements of TAE activity is compared with theoretical calculations of the radial mode structure. Core localization of the modes to the region of reduced central magnetic shear is confirmed, however the mode structure can deviate significantly from theoretical estimates. The peak measured TAE amplitude of δn/n∼10−4 at r/a∼0.3−0.4 corresponds to δB/B∼10−5, while δB/B∼10−8 is measured at the plasma edge. Enhanced alpha particle loss associated with TAE activity has not been observed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872818
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  • 16
    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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  • 17
    Electronic Resource
    Electronic Resource
    Nonlinear self-sustainment of magnetic islands (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 977-979 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A mechanism is proposed for a nonlinear self-sustainment of magnetic islands that relies on the presence of a chaotic region. Particles diffusing in the stochastic magnetic field produce a local increase of current at X points on a rational surface, which in turn sustains the original perturbation if the equilibrium profile is concave. It is shown that the new equilibrium is stable. In a tokamak the mechanism is operative in the region outside the q=2 surface, in agreement with the observation of strong electron confinement degradation in this region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858985
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  • 18
    Electronic Resource
    Electronic Resource
    Alpha particle confinement in tokamaks (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 980-982 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An assessment of diffusive tokamak transport mechanisms of concern for alpha particles indicates that the "stochastic regime'' is the only one that appears to pose a real danger for adequate alpha confinement. This fact, in conjunction with the threshold character of that mechanism, allows one to decide whether an alpha born at a given location will be lost or confined, according to a very simple criterion. Implementing this criterion numerically results in a new code for the assessment of alpha confinement, which is orders of magnitude faster than earlier codes used for this purpose.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858986
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  • 19
    Electronic Resource
    Electronic Resource
    Trapped particle destabilization of the internal kink mode (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 278-286 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The internal kink mode is destabilized by trapped high-energy particles, leading to a new branch of the internal kink dispersion relation with a real frequency near the average trapped-particle precession frequency and a growth rate of the same magnitude. This trapped particle branch of the dispersion relation is investigated numerically for a variety of particle distributions. Mode growth rate and frequency is found as a function of plasma β, density, and trapped-particle energy and distribution. The high-energy trapped particle sources considered are neutral beam injection, ion-cyclotron heating, and fusion alpha particles. Relevance for various plasma heating schemes is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865198
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  • 20
    Electronic Resource
    Electronic Resource
    Mode–particle resonances during near-tangential neutral beam injection in the Tokamak Fusion Test Reactor (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1584-1588 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Coherent magnetohydrodynamic modes have been observed previously during neutral beam injection in the PDX tokamak [Phys. Rev. Lett. 50, 891 (1983)] and they have now been seen in the TFTR tokamak [Phys. Fluids 26, 2958 (1983)]. Periodic bursts of oscillations were detected with several plasma diagnostics, and Fokker–Planck calculations show that the populations of trapped particles in both tokamaks are sufficient to account for fishbone destabilization if a resonant interaction, between the mode and the beam ions, is assumed. Estimates of mode parameters are in reasonable agreement with the experiments, and they indicate that the fishbone mode may continue to affect the performance of intensely heated tokamaks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859483
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