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  • 1
    Electronic Resource
    Electronic Resource
    Hybrid magnetohydrodynamic-particle simulation of linear and nonlinear evolution of Alfvén modes in tokamaks (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 3287-3301 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Linear and nonlinear properties of moderate-toroidal-number (n) shear-Alfvén modes in tokamaks are investigated by using a hybrid MHD-particle simulation code, which solves the coupled set of MHD (magnetohydrodynamic) equations for the electromagnetic fields and gyrocenter Vlasov equation for a population of energetic ions. The existence of unstable toroidal Alfvén eigenmodes (TAE's) and their kinetic counterpart is shown for low values of the energetic-ion pressure gradient. Above a certain threshold value, the energetic particle continuum mode (EPM) is destabilized, with growth rate fast increasing with increasing energetic-particle pressure gradient. The threshold shows an inverse dependence on n. High-n EPM's could then be unstable in realistic plasma conditions. Neglecting MHD nonlinearities, for the sake of simplicity, it is shown that nonlinear TAE saturation appears to be due to the trapping of resonant energetic ions in the potential well of the wave. Saturation of the EPM occurs instead because of a macroscopic outward displacement of the energetic-ion population, with potentially dramatic consequences on α-particle confinement; such conclusions are not modified by the inclusion of MHD nonlinearities. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872997
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  • 2
    Electronic Resource
    Electronic Resource
    Reduction of the electron thermal conductivity produced by ion Bernstein waves on the Frascati Tokamak Upgrade tokamak (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4721-4724 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Operating with a high frequency and a wave guide antenna, the ion Bernstein wave (IBW) experiment on the Frascati Tokamak Upgrade is not dominated, as expected, by nonlinear plasma edge phenomena. By coupling IBW power, a simultaneous increase of plasma density and central electron temperature (≥2 keV) is produced when the confinement magnetic field is adjusted to set an ion cyclotron resonant layer in the plasma bulk. Transport analysis indicates a reduction of the electron thermal transport inside the internal resonant layer larger than a factor of 2. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1408912
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  • 3
    Electronic Resource
    Electronic Resource
    Role of Alfvén instabilities in energetic ion transport : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1880-1884 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments with plasma heating by waves at the ion cyclotron resonance of a minority species have shown that the heating efficiency degrades above a certain power threshold. It is found that this threshold is due to the destabilization of a branch of shear Alfvén waves, the Energetic Particle Modes, which causes a diffusive loss of fast ions. These modes not only play a fundamental role in the transport of the fast ions, but appear closely related to the formation of giant sawteeth. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873446
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  • 4
    Electronic Resource
    Electronic Resource
    Linear and nonlinear dynamics of Alfvén eigenmodes in tokamaks (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 418-441 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Linear and nonlinear dynamics of various toroidicity induced global Alfvén eigenmodes is investigated by means of an initial value numerical code. The code uses the reduced magnetohydrodynamic (MHD) model expanded to the third order in the inverse aspect ratio parameter ε (ε ≡ a/R0, with a the minor radius of the plasma column and R0 the major radius of the vacuum chamber). Nonlinear saturation is shown to occur due to the excitation of a perturbation to the nonlinear mode structure, which dissipates energy on very short scales. In particular, the nonlinear saturation of the Toroidal Alfvén Eigenmodes (TAE) and of the Resistive Periodic Shear Alfvén Eigenmodes (RPSAE) due to MHD nonlinearities is investigated and compared with analytical predictions. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870968
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  • 5
    Electronic Resource
    Electronic Resource
    Hybrid magnetohydrodynamic-gyrokinetic simulation of toroidal Alfvén modes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3711-3723 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Resonant energetic particles play a major role in determining the stability of toroidal Alfvén eigenmodes (TAE's) by yielding the well-known driving mechanism for the instability and by producing an effective dissipation, which removes the singular character of local oscillations of the shear-Alfvén continuum and gives discrete kinetic Alfvén waves (KAW's). Toroidal coupling of two counterpropagating KAW's generates the kinetic analog of the TAE, the KTAE (kinetic TAE). The nonperturbative character of this phenomenon and of the coupling between TAE and KAW's, and the relevance of finite drift-orbit effects limit the effectiveness of the analytical approach to asymptotic regimes, which are difficult to compare with realistic situations. A three-dimensional hybrid fluid-particle initial-value code for the numerical simulation of the linear and nonlinear evolution of toroidal modes of the Alfvén branch has been developed. It is shown that for typical parameters the KTAE is, indeed, more unstable than the TAE. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871071
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  • 6
    Electronic Resource
    Electronic Resource
    The radial structure of the ion-temperature-gradient-driven mode (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 4081-4089 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analysis of the radial structure of the ion-temperature-gradient-driven mode is presented and the dependence of the radial correlation length Lr on parameters such as magnetic shear is discussed. It is found that Lr decreases algebraically with increasing shear for moderate to large shear values, and it decreases exponentially with decreasing shear for low shear values. These results seem in qualitative agreement with several experiments which observe strong reduction of the transport coefficients close to the magnetic axis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860576
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  • 7
    Electronic Resource
    Electronic Resource
    On resonant destabilization of toroidal Alfvén eigenmodes by circulating and trapped energetic ions/alpha particles in tokamaks (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2385-2388 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Toroidal Alfvén eigenmodes are shown to be resonantly destabilized by both circulating and trapped energetic ions/alpha particles. In particular, the energetic circulating ions are shown to resonate with the mode not only at the Alfvén speed (vA), but also at one-third of this speed, while for trapped ions, the dominant instability mechanism is shown to be due to the resonance between the precessional magnetic drift and the wave. Implications of the theory for present and future tokamaks are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860208
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  • 8
    Electronic Resource
    Electronic Resource
    An instrument for measuring the momentum flux from atomic and charged particle jets (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3586-3591 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have developed an instrument to measure the momentum flux from an intense plasma stream for which the standard techniques used for low-pressure gases (〈10 Torr) at room temperature are unsuitable. With a response time of 〈 50 ms, this device, a plasma momentum meter, can measure forces of 10−5–103 N onto surfaces of different materials immersed in dense plasmas (n(approximately-greater-than)1012cm−3). Such forces are transmitted predominantly by ionic and neutral species, with 10's of eV's of kinetic energy, are accompanied by high heat fluxes, and are pulsed. The momentum flux onto a biasable target plate is transferred via a suspended quartz tube onto a sensitive force transducer, a capacitance-type pressure gauge. This protects the transducer from thermal damage, arcing, and sputtering. An absolute force calibration of the PMM to 1% accuracy has been made and is described. A flat carbon target has been used in measurements of the momentum flux of He, Ne, Ar, and Kr plasmas produced in a magnetized linear plasma device.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141575
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  • 9
    Electronic Resource
    Electronic Resource
    Instrument for measuring the momentum flux from atomic and charged particle jets (abstract) : Eighth topical conference on high—temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 3148-3148 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have developed an instrument to measure the momentum flux from an intense plasma stream for which the standard techniques used for low-pressure gases (〈10 Torr) at room temperature are unsuitable. This device, a plasma momentum meter, can measure forces of 10−5–103 Newtons with a response time of 〈50 ms onto surfaces of different materials immersed in dense plasmas (n(approximately-greater-than)1012 cm−3). Such forces are transmitted predominantly by ionic and neutral species, with 10's of eV's of kinetic energy, are accompanied by high heat fluxes, and are pulsed. The momentum flux onto a biasable target plate is transferred via a suspended quartz tube onto a sensitive force transducer, a capacitance-type pressure gauge. This protects the transducer from thermal damage, arcing, and sputtering. An absolute force calibration of the PMM to 1% accuracy has been made and is described. A flat carbon target has been used in measurements of the momentum flux of He, Ne, Ar, and Kr plasmas produced in a magnetized linear plasma device.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141666
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  • 10
    Electronic Resource
    Electronic Resource
    Longitudinal oscillations in a classical Yang-Mills plasma (2000)
    Springer
    The European physical journal 8 (2000), S. 131-143 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 12.38.Mh Quark-gluon plasma - 52.35.Mw Nonlinear waves and nonlinear wave propagation (including parametric effects, mode coupling, ponderomotive effects, etc.)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: An analytical approach to the non linear system describing classical 1D longitudinal oscillations in an SU(2) plasma is proposed. A physical interpretation is given for two distinct “Abelian” and “non-Abelian” phases of the non-linear oscillations. Numerical estimates of meaningful physical quantities are made. Analytical results are extended to the physically more relevant SU(3) case, for which numerical simulations have been also carried out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050017
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