A model of GAM intermittency near critical gradient in toroidal plasmas

Miki, K.; Kishimoto, Y.; Miyato, N.; Li, J Q

doi:10.1088/1742-6596/123/1/012028

Cited by 4 publications

(6 citation statements)

References 17 publications

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“…Regarding the coexistence state, the stability conditions are estimated from both the physical limitation of the positive ZF and GAM energy population and the Routh-Hurwitz stability criterion. Here the criterion can be reduced to the condition of a 0 > 0 in equation (20).…”

Section: Stability Analysis Bistability and Its Implementationmentioning

confidence: 99%

“…In this vein, [18] discussed a multiple shearing predator-prey model, consisting of turbulence, ZF and mean flow shear V E as well. References [19,20] discussed a predator-prey model associated with residual ZFs and GAMs. This present model is an expansion of the previous one, including weights for the frequency spectrum of the shearing field.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Novel states of pre-transition edge turbulence emerging from shearing mode competition

Miki¹,

Diamond²

2011

Nucl. Fusion

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A novel model handling zonal flow, geodesic acoustic mode (GAM), and turbulence self-consistently as a predator-prey system with multiple frequency shearings is introduced. ZF with finite frequency has different shearing relation from that with zero frequency depending to their auto-correlation times. Splitting ZF broadband spectrum into the two modes of wave populations enables us to state different shearing weights to the turbulence contributions of the ZFs. We define states with no ZF and GAM states as L-mode-like state, with ZF and without GAM as ZF-only state, with GAM and without ZF as GAM-only state, and both with ZF and GAM as the coexisting state. Since the coexisting state does not appear in the minimal model, mode-competition effects are introduced. We introduce one which originates from higher order perturbation of wave actions. The model exhibits a sequence of transition between various roots as the driving flux increases. In some chosen parameters, bi-stability is evident, which suggests the origin of the hysteretic behavior in the turbulence intensity field during power ramp up/down studies. In the presence of noise due to ambient turbulence offers a novel and interesting mechanism to explain the bursts and pulsations observed in the turbulence field prior to the L-H transition.

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Section: Stability Analysis Bistability and Its Implementationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Novel states of pre-transition edge turbulence emerging from shearing mode competition

Miki¹,

Diamond²

2011

Nucl. Fusion

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“…Then we will investigate the stability around each of the fixed points to understand the comprehensive behavior of the solution trajectories for the system. 19,22 Note that the group propagation terms vanish in the limit of a stable state, hence we neglect the radiative dissipation terms in the stability analysis. We expand Eqs.…”

Section: B Analysis Of Modelmentioning

confidence: 99%

Role of the geodesic acoustic mode shearing feedback loop in transport bifurcations and turbulence spreading

Miki

Diamond

2010

Physics of Plasmas

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A theory of the effect of the geodesic acoustic mode ͑GAM͒ on turbulence is presented. Two synergistic issues are elucidated: namely, the physics of the zonal flow modulation and its role in the L-H transition, and the role of the GAM wave group propagation in turbulence spreading. Using a wavekinetic modulational analysis, the response of the turbulence intensity field to the GAM is calculated. This analysis differs from previous studies of zero-frequency zonal flows since it accounts for resonance between the drift wave group speed and the GAM strain field, which induces secularity. This mechanism is referred to as secular stochastic shearing. Finite real frequency and radial group velocity are intrinsic to the GAM, so its propagation can induce nonlocal phenomena at the edge and pedestal regions. To understand the effect of the GAM on turbulence and transition dynamics, a predator-prey model incorporating the dynamics of both turbulence and the GAMs is constructed and analyzed for stability around fixed points. Three possible states are identified, namely, an L-modelike stationary state, a reduced turbulence state, and a GAM limit-cycle state. The system is attracted to the state with the minimum turbulence level.

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“…GAM's frequency and damping rate as functions of q are studied by specifying = 0.3 and locating q in the range [1,7] as shown in Figs.1 and 2. GAM's frequency is a decreasing function of q as shown in Fig.…”

Section: The Effect Of Q On Gam's Dispersionmentioning

confidence: 99%

Damping of Geodesic Acoustic Mode by Trapped Electrons

Zhang¹,

Gao²,

Wu³

et al. 2014

Plasma Sci. Technol.

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We study the Landau resonance between geodesic acoustic mode (GAM) and trapped electrons as a GAM's collisionless damping. The assumption ofω de ω be is adopted. The damping rate induced by trapped electrons is found to be an increasing function of q. In low q range, circulating-ion-induced damping rate is larger than that induced by trapped electrons. As q increases, the latter becomes larger than the former. The reason is that trapped electrons' resonant velocity is close to vte from the lower side, whiles circulating ions' resonant velocity gets bigger further from vti. So the number of resonant trapped electrons increases, whiles the number of resonant circulating ions decreases. The amplitude of damping rate induced by trapped electrons in the edge plasma can be comparable to that induced by circulating ions in the low q range. Another phenomenon we found is that in the chosen range of , the damping caused by trapped electrons has a maximum value at point q for different q. The reason is that as is close to q , trapped electorns' resonant velocity is close to vte.

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A model of GAM intermittency near critical gradient in toroidal plasmas

Cited by 4 publications

References 17 publications

Novel states of pre-transition edge turbulence emerging from shearing mode competition

Novel states of pre-transition edge turbulence emerging from shearing mode competition

Role of the geodesic acoustic mode shearing feedback loop in transport bifurcations and turbulence spreading

Damping of Geodesic Acoustic Mode by Trapped Electrons

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