Explanation of the JET<i>n</i>= 0 chirping mode

Berk, H. L.; Boswell, C.; Borba, D.; Figueiredo, A.; Johnson, T.; Nave, M. F. F.; Pinches, S. D.; Sharapov, S. E.; Contributors, Jet

doi:10.1088/0029-5515/46/10/s04

Cited by 154 publications

(217 citation statements)

References 32 publications

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“…It is noteworthy that these hooks resemble experimentally observed chirping patterns. 23 These behaviors can be understood by recognizing the competition that now exists between the sink in the drag collision operator that acts to deepen the hole and the diffusion that acts to fill the hole. This competition can be modeled using Eqs.…”

Section: Drag and Diffusionmentioning

confidence: 99%

Effect of dynamical friction on nonlinear energetic particle modes

Lilley¹,

Breǐzman²,

Sharapov³

2010

Physics of Plasmas

106

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A fully nonlinear model is developed for the bump-on-tail instability including the effects of dynamical friction ͑drag͒ and velocity space diffusion on the energetic particles driving the wave. The results show that drag provides a destabilizing effect on the nonlinear evolution of waves. Specifically, in the early nonlinear phase of the instability, the drag facilitates the explosive scenario of the wave evolution, leading to the creation of phase space holes and clumps that move away from the original eigenfrequency. Later in time, the electric field associated with a hole is found to be enhanced by the drag, whereas for a clump it is reduced. This leads to an asymmetry of the frequency evolution between holes and clumps. The combined effect of drag and diffusion produces a diverse range of nonlinear behaviors including hooked frequency chirping, undulating, and steady state regimes. An analytical model is presented, which explains the aforementioned diversity. A continuous production of hole-clump pairs in the absence of collisions is also observed.

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Section: Drag and Diffusionmentioning

confidence: 99%

Effect of dynamical friction on nonlinear energetic particle modes

Lilley¹,

Breǐzman²,

Sharapov³

2010

Physics of Plasmas

106

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“…In thermal plasma, those modes are damped. It was found, in a JET experiment with Ion Cyclotron Resonant Heating (ICRH), that n=0 modes identified 5,6 as Global GAMs could be driven unstable by trapped energetic ions. This observation led to the idea of controlling the GAMs, and perhaps plasma turbulence coupled to the GAMs, with energetic particles.…”

Section: Introductionmentioning

confidence: 99%

Relation between energetic and standard geodesic acoustic modes

et al. 2014

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Geodesic Acoustic Modes (GAMs) are electrostatic, axisymmetric modes which are non-linearly excited by turbulence. They can also be excited linearly by fast-particles; they are then called Energetic-particle-driven GAMs (EGAMs). Do GAMs and EGAMs belong to the same mode branch? Through a linear, analytical model, in which the fast particles are represented by a Maxwellian bump-on-tail distribution function, we find that the answer depends on several parameters. For low values of the safety factor q and for high values of the fast ion energy, the EGAM originates from the GAM. On the contrary, for high values of q and for low values of the fast ion energy, the GAM is not the mode which becomes unstable when fast particles are added: the EGAM then originates from a distinct mode, which is strongly damped in the absence of fast particles. The impact of other parameters is further explored: ratio of the ion temperature to the electron temperature, width of the fast particle distribution, mass and charge of the fast ions. The ratio between the EGAM and the GAM frequencies was found in experiments (DIII-D) and in non-linear numerical simulations (code GYSELA) to be close to 1/2: the present analytical study allows one to recover this ratio.

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“…2 > 1/q 2 , another well known root is described by equation (1), which is the geodesic acoustic mode (GAM) with a frequency 2 = 2(1+1/2q 2 ) [8][9][10]. The same branch was found in [11,12] and [4], but was called the BAE branch.…”

Section: Low Frequency Alfvén-acoustic Continuummentioning

confidence: 93%

Predications and Observations of Global Beta-induced Alfven-acoustic Modes in JET and NSTX

Gorelenkov¹

2008

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In this paper we report on observations and interpretations of a new class of global MHD eigenmode solutions arising in gaps in the low frequency Alfvén-acoustic continuum below the geodesic acoustic mode frequency. These modes have been just reported (Gorelenkov et al 2007 Phys. Lett. 370 70-7) where preliminary comparisons indicate qualitative agreement between theory and experiment. Here we show a more quantitative comparison emphasizing recent NSTX experiments on the observations of the global eigenmodes, referred to as beta-induced Alfvén-acoustic eigenmodes (BAAEs), which exist near the extrema of the Alfvén-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes may shift as the safety factor, q, profile relaxes. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta <2% as well as in NSTX plasmas at relatively high beta >20%. In NSTX plasma observed magnetic activity has the same properties as predicted by theory for the mode structure and the frequency. Found numerically in NOVA simulations BAAEs are used to explain the observed properties of relatively low frequency experimental signals seen in NSTX and JET tokamaks.

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Explanation of the JETn= 0 chirping mode

Cited by 154 publications

References 32 publications

Effect of dynamical friction on nonlinear energetic particle modes

Effect of dynamical friction on nonlinear energetic particle modes

Relation between energetic and standard geodesic acoustic modes

Predications and Observations of Global Beta-induced Alfven-acoustic Modes in JET and NSTX

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