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  • 1
    Online Resource
    Online Resource
    Saturation of energetic-particle-driven geodesic acoustic modes due to wave–particle nonlinearity
    Cambridge University Press (CUP) ; 2017
    In:  Journal of Plasma Physics Vol. 83, No. 6 ( 2017-12)
    Details
    In: Journal of Plasma Physics, Cambridge University Press (CUP), Vol. 83, No. 6 ( 2017-12)
    Abstract: The nonlinear dynamics of energetic-particle (EP) driven geodesic acoustic modes (EGAM) is investigated here. A numerical analysis with the global gyrokinetic particle-in-cell code ORB5 is performed, and the results are interpreted with the analytical theory, in close comparison with the theory of the beam-plasma instability. Only axisymmetric modes are considered, with a nonlinear dynamics determined by wave–particle interaction. Quadratic scalings of the saturated electric field with respect to the linear growth rate are found for the case of interest. As a main result, the formula for the saturation level is provided. Near the saturation, we observe a transition from adiabatic to non-adiabatic dynamics, i.e. the frequency chirping rate becomes comparable to the resonant EP bounce frequency. The numerical analysis is performed here with electrostatic simulations with circular flux surfaces, and kinetic effects of the electrons are neglected.
    Type of Medium: Online Resource
    ISSN: 0022-3778 , 1469-7807
    URL: Article
    DOI: 10.1017/S0022377817000976
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2017
    detail.hit.zdb_id: 2004297-8
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  • 2
    Online Resource
    Online Resource
    Linear dispersion relation of geodesic acoustic modes driven by trapped and circulating energetic particles – CORRIGENDUM
    Cambridge University Press (CUP) ; 2021
    In:  Journal of Plasma Physics Vol. 87, No. 6 ( 2021-12)
    Details
    In: Journal of Plasma Physics, Cambridge University Press (CUP), Vol. 87, No. 6 ( 2021-12)
    Type of Medium: Online Resource
    ISSN: 0022-3778 , 1469-7807
    URL: Article
    DOI: 10.1017/S0022377821001197
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2021
    detail.hit.zdb_id: 2004297-8
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  • 3
    Online Resource
    Online Resource
    Linear dispersion relation of geodesic acoustic modes driven by trapped and circulating energetic particles
    Cambridge University Press (CUP) ; 2021
    In:  Journal of Plasma Physics Vol. 87, No. 4 ( 2021-08)
    Details
    In: Journal of Plasma Physics, Cambridge University Press (CUP), Vol. 87, No. 4 ( 2021-08)
    Abstract: We derive the local dispersion relation of energetic-particle-induced geodesic acoustic modes (EGAMs) for both trapped and circulating ion beams with single pitch angle slowing-down and Maxwellian distributions, as well as a bump-on-tail distribution in tokamak plasmas. For slowing-down and Maxwellian particles, the solutions of the local dispersion relation give the spectrum, growth rate and thresholds of excitation as functions of the pitch angle, beam density and frequency of the energetic particles bounce motion. For circulating ions there is only one unstable branch with frequency below the GAM continuum and a threshold of excitation in the pitch angle, for both the slowing-down and single pitch Maxwellian distributions. Trapped particles cause no excitation of a mode for neither slowing-down nor Maxwellian ion beams, but they can excite a mode with a bump-on-tail distribution when the mean velocity of the beam is larger than the threshold and the energetic particle bounce frequency is high enough.
    Type of Medium: Online Resource
    ISSN: 0022-3778 , 1469-7807
    URL: Article
    DOI: 10.1017/S0022377821000751
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2021
    detail.hit.zdb_id: 2004297-8
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  • 4
    Online Resource
    Online Resource
    Overview of KSTAR initial operation
    IOP Publishing ; 2011
    In:  Nuclear Fusion Vol. 51, No. 9 ( 2011-09-01), p. 094006-
    Details
    In: Nuclear Fusion, IOP Publishing, Vol. 51, No. 9 ( 2011-09-01), p. 094006-
    Abstract: Since the successful first plasma generation in the middle of 2008, three experimental campaigns were successfully made for the KSTAR device, accompanied with a necessary upgrade in the power supply, heating, wall-conditioning and diagnostic systems. KSTAR was operated with the toroidal magnetic field up to 3.6 T and the circular and shaped plasmas with current up to 700 kA and pulse length of 7 s, have been achieved with limited capacity of PF magnet power supplies. The mission of the KSTAR experimental program is to achieve steady-state operations with high performance plasmas relevant to ITER and future reactors. The first phase (2008–2012) of operation of KSTAR is dedicated to the development of operational capabilities for a super-conducting device with relatively short pulse. Development of start-up scenario for a super-conducting tokamak and the understanding of magnetic field errors on start-up are one of the important issues to be resolved. Some specific operation techniques for a super-conducting device are also developed and tested. The second harmonic pre-ionization with 84 and 110 GHz gyrotrons is an example. Various parameters have been scanned to optimize the pre-ionization. Another example is the ICRF wall conditioning (ICWC), which was routinely applied during the shot to shot interval. The plasma operation window has been extended in terms of plasma beta and stability boundary. The achievement of high confinement mode was made in the last campaign with the first neutral beam injector and good wall conditioning. Plasma control has been applied in shape and position control and now a preliminary kinetic control scheme is being applied including plasma current and density. Advanced control schemes will be developed and tested in future operations including active profiles, heating and current drives and control coil-driven magnetic perturbation.
    Type of Medium: Online Resource
    ISSN: 0029-5515 , 1741-4326
    URL: Article
    DOI: 10.1088/0029-5515/51/9/094006
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2011
    detail.hit.zdb_id: 2037980-8
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  • 5
    Online Resource
    Online Resource
    Overview of FTU results
    IOP Publishing ; 2011
    In:  Nuclear Fusion Vol. 51, No. 9 ( 2011-09-01), p. 094015-
    Details
    In: Nuclear Fusion, IOP Publishing, Vol. 51, No. 9 ( 2011-09-01), p. 094015-
    Abstract: New FTU ohmic discharges with a liquid lithium limiter at I P = 0.7–0.75 MA, B T = 7 T and n e0 ⩾ 5 × 10 20  m −3 confirm the spontaneous transition to an enhanced confinement regime, 1.3–1.4 times ITER-97-L, when the density peaking factor is above a threshold value of 1.7–1.8. The improved confinement derives from a reduction of electron thermal conductivity (χ e ) as density increases, while ion thermal conductivity (χ i ) remains close to neoclassical values. Linear microstability reveals the importance of lithium in triggering a turbulent inward flux for electrons and deuterium by changing the growth rates and phase of the ion-driven turbulence, while lithium flux is always directed outwards. A particle diffusion coefficient, D ∼ 0.07 m 2  s −1 , and an inward pinch velocity, V ∼ 0.27 m s −1 , in qualitative agreement with Bohm–gyro-Bohm predictions are inferred in pellet fuelled lithized discharges. Radio frequency heated plasmas benefit from cleaner plasmas with edge optimized conditions. Lower hybrid waves penetration and current drive effects are clearly demonstrated at and above ITER densities thanks to a good control of edge parameters obtained by plasma operations with the external poloidal limiter, lithized walls and pellet fuelling. The electron cyclotron (EC) heating system is extensively exploited in FTU for contributing to ITER-relevant issues such as MHD control: sawtooth crash is actively controlled and density limit disruptions are avoided by central and off-axis deposition of 0.3 MW of EC power at 140 GHz. Fourier analysis shows that the density drop and the temperature rise, stimulated by modulated EC power in low collisionality plasmas are synchronous, implying that the heating method is the common cause of both the electron heating and the density drop. Perpendicularly injected electron cyclotron resonance heating is demonstrated to be more efficient than the obliquely injected one, reducing the minimum electric field required at breakdown by a factor of 3. Theoretical activity further develops the model to interpret high-frequency fishbones on FTU and other experiments as well as to characterize beta-induced Alfvén eigenmodes induced by magnetic islands in ohmic discharges. The theoretical framework of the general fishbone-like dispersion relation is used for implementing an extended version of the HMGC hybrid MHD gyrokinetic code. The upgraded version of HMGC will be able to handle fully compressible non-linear gyrokinetic equations and 3D MHD.
    Type of Medium: Online Resource
    ISSN: 0029-5515 , 1741-4326
    URL: Article
    DOI: 10.1088/0029-5515/51/9/094015
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2011
    detail.hit.zdb_id: 2037980-8
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  • 6
    Online Resource
    Online Resource
    Turbulent contributions to Ohm's law in axisymmetric magnetized plasmas
    AIP Publishing ; 2017
    In:  Physics of Plasmas Vol. 24, No. 7 ( 2017-07-01)
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 24, No. 7 ( 2017-07-01)
    Abstract: The effect of magnetic turbulence in shaping the current density in axisymmetric magnetized plasmas is analyzed using a turbulent extension of Ohm's law derived from the self-consistent action-angle transport theory. Besides the well-known hyper-resistive (helicity-conserving) contribution, the generalized Ohm's law contains an anomalous resistivity term and a turbulent bootstrap-like term proportional to the current density derivative. The numerical solution of the equation for equilibrium and turbulence profiles characteristic of conventional and advanced scenarios shows that, through the “turbulent bootstrap” effect and anomalous resistivity, power and parallel current can be generated which are a sizable portion (about 20%–25%) of the corresponding effects associated with the neoclassical bootstrap effect. The degree of alignment of the turbulence peak and the pressure gradient plays an important role in defining the steady-state regime. In a fully bootstrapped tokamak, the hyper-resistivity is essential in overcoming the intrinsic limitation of the hollow current profile.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.4993208
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2017
    detail.hit.zdb_id: 1472746-8
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  • 7
    Online Resource
    Online Resource
    Self-consistent electron transport in tokamaks
    AIP Publishing ; 2007
    In:  Physics of Plasmas Vol. 14, No. 9 ( 2007-09-01)
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 14, No. 9 ( 2007-09-01)
    Abstract: Electron particle, momentum, and energy fluxes in axisymmetric toroidal devices are derived from a version of the action-angle collision operator that includes both diffusion and drag in action-space [D. A. Hitchcock, R. D. Hazeltine, and S. M. Mahajan, Phys. Fluids 26, 2603 (1983); H. E. Mynick, J. Plasma Phys. 39, 303 (1988)]. A general result of the theory is that any contribution to transport originating directly from the toroidal frequency of the particle motion is constrained to be zero when the electron temperature is equal to the ion temperature. In particular, this constraint applies to those components of the particle and energy fluxes that are proportional to the magnetic shear, independent of the underlying turbulence and of whether the particles are trapped or untrapped. All the total fluxes describing collisionless transport of passing electrons in steady-state magnetic turbulence contain contributions proportional to the conventional thermodynamic drives, which are always outward, and contributions proportional to the magnetic shear, which have both magnitude and sign dependent on the ion-electron temperature ratio. The turbulent generalization of Ohm’s law includes a hyper-resistive term, which flattens the current density profile on a fast time scale, and a turbulent electric field, which can have both signs depending on the electron-ion temperature ratio.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.2768940
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2007
    detail.hit.zdb_id: 1472746-8
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  • 8
    Online Resource
    Online Resource
    Effect of temperature anisotropy on the dynamics of geodesic acoustic modes
    Cambridge University Press (CUP) ; 2023
    In:  Journal of Plasma Physics Vol. 89, No. 1 ( 2023-02)
    Details
    In: Journal of Plasma Physics, Cambridge University Press (CUP), Vol. 89, No. 1 ( 2023-02)
    Abstract: In this work, we revisit the linear gyro-kinetic theory of geodesic acoustic modes (GAMs) and derive a general dispersion relation for an arbitrary equilibrium distribution function of ions. A bi-Maxwellian distribution of ions is then used to study the effects of ion temperature anisotropy on GAM frequency and growth rate. We find that ion temperature anisotropy yields sensible modifications to both the GAM frequency and growth rate as both tend to increase with anisotropy and these results are strongly affected by the electron to ion temperature ratio.
    Type of Medium: Online Resource
    ISSN: 0022-3778 , 1469-7807
    URL: Article
    DOI: 10.1017/S0022377823000016
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2023
    detail.hit.zdb_id: 2004297-8
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  • 9
    Online Resource
    Online Resource
    Kinetic structures of shear Alfvén and acoustic wave spectra in burning plasmas
    IOP Publishing ; 2010
    In:  Journal of Physics: Conference Series Vol. 260 ( 2010-11-01), p. 012022-
    Details
    In: Journal of Physics: Conference Series, IOP Publishing, Vol. 260 ( 2010-11-01), p. 012022-
    Type of Medium: Online Resource
    ISSN: 1742-6596
    URL: Article
    DOI: 10.1088/1742-6596/260/1/012022
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2010
    detail.hit.zdb_id: 2166409-2
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  • 10
    Online Resource
    Online Resource
    Turbulent sources in axisymmetric plasmas
    IOP Publishing ; 2009
    In:  Plasma Physics and Controlled Fusion Vol. 51, No. 7 ( 2009-07-01), p. 075002-
    Details
    In: Plasma Physics and Controlled Fusion, IOP Publishing, Vol. 51, No. 7 ( 2009-07-01), p. 075002-
    Type of Medium: Online Resource
    ISSN: 0741-3335 , 1361-6587
    URL: Article
    DOI: 10.1088/0741-3335/51/7/075002
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2009
    detail.hit.zdb_id: 1473144-7
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