Nonlocal theory of energetic-particle-induced geodesic acoustic mode

Qiu, Zhiyong; Zonca, F.; Chen, Liu

doi:10.1088/0741-3335/52/9/095003

Cited by 81 publications

(235 citation statements)

References 32 publications

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“…The EP-driven GAMs are called EGAMs. These modes have been predicted theoretically 7,8 , observed experimentally 9,10 and reported very recently numerically in the absence of turbulence 11 in gyrokinetic simulations with the 5D Gysela code 12 . The motivation of the present work relies upon fluid simulations where the turbulence level was controlled by GAMs in the core/edge transitional regime 13 .…”

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confidence: 56%

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Impact of Energetic-Particle-Driven Geodesic Acoustic Modes on Turbulence

et al. 2013

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The impact on turbulent transport of geodesic acoustic modes excited by energetic particles is evidenced for the first time in flux-driven 5D gyrokinetic simulations using the Gysela code. Energetic geodesic acoustic modes (EGAMs) are excited in a regime with a transport barrier in the outer radial region. The interaction between EGAMs and turbulence is such that turbulent transport can be enhanced in the presence of EGAMs, with the subsequent destruction of the transport barrier. This scenario could be particularly critical in those plasmas, such as burning plasmas, exhibiting a rich population of suprathermal particles capable of exciting energetic modes.Understanding turbulent transport is crucial in numerous plasma physics frameworks, ranging from plasma laboratories such as nuclear fusion devices 1 to astrophysical systems such as the solar tachocline 2 or the atmospheres 3 . In this letter, we focus on the turbulent transport in toroidal nuclear fusion devices (tokamaks), where accurate predictions are essential on the route towards the steady-state production of energy. Together with turbulence, energetic particles (EPs) constitute a ubiquitous component of current and future tokamaks, due to both nuclear reactions and heating systems. EPs are characterized by energies larger than the thermal energy. Whereas the impact of turbulence on EP transport has been analyzed and found to be weak 4 , the effect of EPs on turbulence has not been much studied so far (see e.g. Ref. 5) and represents the aim of our study. This analysis is done via the excitation by EPs of a class of modes naturally existing in tokamaks: the geodesic acoustic modes (GAMs) 6 , which are the oscillatory component of large scale E × B zonal flows. The EP-driven GAMs are called EGAMs. These modes have been predicted theoretically 7,8 , observed experimentally 9,10 and reported very recently numerically in the absence of turbulence 11 in gyrokinetic simulations with the 5D Gysela code 12 . The motivation of the present work relies upon fluid simulations where the turbulence level was controlled by GAMs in the core/edge transitional regime 13 . In addition, experimental evidence of the role of GAMs in the edgeturbulence suppression has been reported for the first time during the analysis of the L-H transition in the AS-DEX Upgrade tokamak 14 . However, in the context of core-turbulence suppression, the role of GAMs is less evident for several reasons. First, these modes are Landau damped in the core plasma. Second, since they are nonlinearly generated by turbulence, their external control a) Electronic mail:david.zarzoso-fernandez@polytechnique.org; Current address: Max-Planck-Institut für Plasmaphysik, EU-RATOM Association, Boltzmannstr. 2, Garching D-85748, Germany has proven difficult. Last, their frequency ω GAM is close to the characteristic turbulence frequency ω turb , which means that the shearing rate provided by GAMs might be large compared to the autocorrelation time. In that respect, theoretical predictions of the shearing effect ...

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confidence: 56%

“…In figure 2b we plot the time evolution of the slope of the distribution function at the resonant velocity v res = qω EGAM R, with ω EGAM the frequency of the EP mode 7,8,11 . After the introduction of S EP , the slope is clearly inverted, mainly in the region ρ > 0.5.…”

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confidence: 99%

Impact of Energetic-Particle-Driven Geodesic Acoustic Modes on Turbulence

et al. 2013

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“…2T th /m th (2) with n eq the total concentration and n EP the concentration of energetic particles. The choice of a double shifted Maxwellian is made so that no parallel momentum is injected in the system.…”

Section: Dispersion Relation Of Egamsmentioning

confidence: 99%

Analytic dispersion relation of energetic particle driven geodesic acoustic modes and simulations with NEMORB

et al. 2014

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Abstract. Recent progress regarding the excitation of energetic-particle driven geodesic acoustic modes (EGAMs) in particle-in-cell simulations is presented in this paper. The exact dispersion relation with adiabatic electrons is derived and solved. The origin of the so-called EGAM is briefly analysed and we show that its nature changes, at least, with the safety factor. A simple expression for the GAM frequency modified in the presence of a small concentration of energetic particles is given in the fluid limit. We show that gyrokinetic simulations with Nemorb in the presence of adiabatic electrons are able to reproduce the analytic predictions. Also, different energy channels are analysed by means of dedicated energy diagnostics characterizing the wave-particle interaction. Finite Larmor radius and finite orbit width effects are studied regarding the excitation of geodesic acoustic modes, showing that these effects are likely to be negligible for sufficiently high concentration of energetic particles, but significant when approaching the threshold of excitation.

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“…GAMs are linearly damped via Landau damping 9 , and thus exist mainly near the edge region, in a standard tokamak. They may be excited by non-linear Reynolds stresses [10][11][12][13][14][15][16] , poloidally asymmetric particle flux 10 and heat fluxes 17 and linearly by energetic particles [18][19][20][21][22][23][24] .…”

Section: Introductionmentioning

confidence: 99%

Geodesic acoustic modes with poloidal mode couplings ad infinitum

Singh

Gürcan

2017

Physics of Plasmas

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Geodesic acoustic modes (GAMs) are studied, for the first time, including all poloidal mode (m) couplings using drift reduced fluid equations. The nearest neighbor coupling pattern, due to geodesic curvature, leads to a semi-infinite chain model of the GAM with the mode-mode coupling matrix elements proportional to the radial wave number k r . The infinite chain can be reduced to a renormalized bi-nodal chain with a matrix continued fractions. Convergence study of linear GAM dispersion with respect to k r and the m-spectra confirms that high m couplings become increasingly important with k r . The radially sorted roots overlap with experimentally measured GAM frequency profile in low collisionality shots in Tore Supra thus explaining the reduced frequency of GAM in Tore Supra.

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Nonlocal theory of energetic-particle-induced geodesic acoustic mode

Cited by 81 publications

References 32 publications

Impact of Energetic-Particle-Driven Geodesic Acoustic Modes on Turbulence

Impact of Energetic-Particle-Driven Geodesic Acoustic Modes on Turbulence

Analytic dispersion relation of energetic particle driven geodesic acoustic modes and simulations with NEMORB

Geodesic acoustic modes with poloidal mode couplings ad infinitum

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