Transitions to improved confinement regimes induced by changes in heating in zero-dimensional models for tokamak plasmas

Zhu, Hao; Chapman, Sandra C.; Dendy, R. O.; Itoh, K.

doi:10.1063/1.4884126

Cited by 4 publications

(5 citation statements)

References 33 publications

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“…11 and 30 and followed up by theoretical development and improved models. [31][32][33] A further advance of the 0D model was its 1D, five-field extension 10 which, in addition to the drift wave (DW) intensity and zonal flow (ZF) energy, also evolved the mean flow (MF), pressure, and density. Using this model, important new signatures of the transition were recovered and documented in Refs.…”

Section: Introductionmentioning

confidence: 99%

Linking the micro and macro: L-H transition dynamics and threshold physics

Malkov

Diamond

Miki³

et al. 2015

Physics of Plasmas

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The links between the microscopic dynamics and macroscopic threshold physics of the L → H transition are elucidated. Emphasis is placed on understanding the physics of power threshold scalings, and especially on understanding the minimum in the power threshold as a function of density Pthr (n). By extending a numerical 1D model to evolve both electron and ion temperatures, including collisional coupling, we find that the decrease in Pthr (n) along the low-density branch is due to the combination of an increase in collisional electron-to-ion energy transfer and an increase in the heating fraction coupled to the ions. Both processes strengthen the edge diamagnetic electric field needed to lock in the mean electric field shear for the L→H transition. The increase in Pthr (n) along the high-density branch is due to the increase with ion collisionality of damping of turbulence-driven shear flows. Turbulence driven shear flows are needed to trigger the transition by extracting energy from the turbulence. Thus, we identify the critical transition physics components of the separatrix ion heat flux and the zonal flow excitation. The model reveals a power threshold minimum in density scans as a crossover between the threshold decrease supported by an increase in heat fraction received by ions (directly or indirectly, from electrons) and a threshold increase, supported by the rise in shear flow damping. The electron/ion heating mix emerges as important to the transition, in that it, together with electron-ion coupling, regulates the edge diamagnetic electric field shear. The importance of possible collisionless electron-ion heat transfer processes is explained.

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Section: Introductionmentioning

confidence: 99%

Linking the micro and macro: L-H transition dynamics and threshold physics

Malkov

Diamond

Miki³

et al. 2015

Physics of Plasmas

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“…The model (12) for the L-state reduces to the model (11) for the s-state when N = 0 as intended. In (12a) three additional terms have been added when compared with (11).…”

Section: B Modeling the L-statementioning

confidence: 99%

“…The creation of an edge transport barrier formed by a sheared zonal flow is closely related to the L-H transition 3 . Ordinary differential equation (ODE) models for the L-H transition are based on the predator-prey relationship between zonal flow and turbulent flow, and incorporate a potential energy related to the pressure profile as an additional state variable [4][5][6][7][8][9][10][11][12] . Miki et al 13 and Wu et al 14 have both suggested 1D partial differential equation (PDE) models for the L-H transition based on this predator-prey relationship.…”

Section: Introductionmentioning

confidence: 99%

Sparse identification of a predator-prey system from simulation data of a convection model

et al. 2017

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The use of low-dimensional dynamical systems as reduced models for plasma dynamics is useful as solving an initial value problem requires much less computational resources than fluid simulations. We utilize a data-driven modeling approach to identify a reduced model from simulation data of a convection problem. A convection model with a pressure source centered at the inner boundary models the edge dynamics of a magnetically confined plasma. The convection problem undergoes a sequence of bifurcations as the strength of the pressure source increases. The time evolution of the energies of the pressure profile, the turbulent flow, and the zonal flow capture the fundamental dynamic behavior of the full system. By applying the Sparse Identification of Nonlinear Dynamics (SINDy) method we identify a predator-prey type dynamical system that approximates the underlying dynamics of the three energy state variables. A bifurcation analysis of the system reveals consistency between the bifurcation structures, observed for the simulation data, and the identified underlying system.

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“…These model has been very successful during the last years [20][21][22]. The aim of this paper is to report on the interesting effect of a stepwise increase of the different heating powers on turbulence and confinement by extending [21].…”

Section: Introductionmentioning

confidence: 99%

“…The bifurcation occurs when zonal flow causes a transport barrier (steep temperature gradient) [2][3][4][5][6], to be produced at the edge of the plasma, improving plasma confinement. Zero-dimensional models [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] [7], called MD model, which has one fewer variable for which oscillatory heating was studied in [21]. This distinctive phenomenology may offer a path to future experimental testing of the assumptions of zero-dimensional models, and perhaps distinguishing between them.…”

Section: Introductionmentioning

confidence: 99%

Study of improved confinement by a stepwise increase of the input heating power for tokamak plasmas

2016

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The article is an extension of the brief study by [Sarah Douglas et al., Phys. Plasmas 20, 114504 (2013)], where in the study a sinusoidal perturbation of the heating power has been studied. In this paper a stepwise increase of the heating power and its influence on the L-H transition are studied. Using a function,for the transition of input heating power for tokamak plasmas i.e. the addition of the perturbation, ) / tanh( T t A , to constant power q 0 is shown to promote the confinement, leading to the L-H transition at a lower value of q 0 , as compared to the case of constant q 0 without the ) / tanh( T t A perturbation. It is seen that the input heating power Q that consists of constant part q 0 in addition to a function ) / tanh( T t A provides the L-H transition for relatively small A and much wider range values of 1/T as compare to [Sarah Douglas et al., Phys. Plasmas 20, 114504 (2013)].

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Transitions to improved confinement regimes induced by changes in heating in zero-dimensional models for tokamak plasmas

Abstract: It is shown that rapid substantial changes in heating rate can induce transitions to improved energy confinement regimes in zero-dimensional models for tokamak plasma phenomenology. We examine for the first time the effect of step changes in heating rate in the models of E-

Cited by 4 publications

References 33 publications

Linking the micro and macro: L-H transition dynamics and threshold physics

Linking the micro and macro: L-H transition dynamics and threshold physics

Sparse identification of a predator-prey system from simulation data of a convection model

Study of improved confinement by a stepwise increase of the input heating power for tokamak plasmas

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