Gyrokinetic turbulence simulations at high plasma beta

Pueschel, M. J.; Kammerer, Matthias; Jenko, F.

doi:10.1063/1.3005380

Cited by 145 publications

(244 citation statements)

References 33 publications

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“…On the other hand, the heat flux at β i = 0.6% is one-half of that at β i = 0.2%. One of the reasons is the beta dependence of zonal flow production (Pueschel et al 2008). The zonal flow shearing decreases with beta slower than the linear growth rate.…”

Section: Microturbulence At Finite Beta (Nonlinear Simulations)mentioning

confidence: 99%

“…10(b). It is reported that the transport due to the magnetic flutter is proportional to the square of beta β 2 in ITG turbulence (Pueschel et al 2008), and that is explained by the production of a stochastic magnetic field. The violation of magnetic surface is caused by the production of the tearing parity, as explained in Sec.…”

Section: Impact Of Magnetic Perturbation On Turbulent Transportmentioning

confidence: 99%

“…In addition, the kinetic electron effect elongates the mode structure along the field line, and thus a large simulation domain along the field line is required. Large computational resources which meet the requirements are the reason why numerical simulations of turbulence based on the electromagnetic gyrokinetic model (Antonsen and Lane 1980;Frieman and Chen 1982;Hahm et al 1988;Hazeltine and Meiss 2003;Brizard and Hahm 2007) are mainly carried out in the flux-tube geometry (Kotschenreuther et al 1995;Jenko 2000;Jenko et al 2000;Jenko and Dorland 2001;Candy and Waltz 2003a,b;Candy 2005;Pueschel et al 2008;Peeters et al 2009;Pueschel and Jenko 2010;Waltz 2010;Hatch et al 2012;Pueschel et al 2013a,b) which is along a magnetic field line and is localized in the radial direction to reduce computational cost (Beer et al 1995). Although, there are some gyrokinetic simulations on electromagnetic turbulence in global domain covering a whole torus plasma and also some electromagnetic gyrokinetic studies on space plasmas (Schekochihin et al 2009), we focus on gyrokinetic simulations in local flux-tube domain in this review.…”

Section: Introductionmentioning

confidence: 99%

“…Electromagnetic gyrokinetic simulations are applied to the studies of turbulent transport in finite-beta tokamak plasmas and the beta-scan is carried out (Candy 2005;Pueschel et al 2008;Pueschel and Jenko 2010). In finite-beta tokamak plasmas, the growth rate of the ITG instability is suppressed by magnetic field line bending as plasma beta increases (Kim et al 1993) (Sec.…”

Section: Introductionmentioning

confidence: 99%

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Electromagnetic gyrokinetic simulation of turbulence in torus plasmas

et al. 2015

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Gyrokinetic simulations of electromagnetic turbulence in magnetically confined torus plasmas including tokamak and heliotron/stellarator are reviewed. Numerical simulation of turbulence in finite beta plasmas is an important task for predicting the performance of fusion reactors and a great challenge in computational science due to multiple spatio-temporal scales related to electromagnetic ion and electron dynamics. The simulation becomes further challenging in non-axisymmetric plasmas. In finite beta plasmas, magnetic perturbation appears and influences some key mechanisms of turbulent transport, which include linear instability and zonal flow production. Linear analysis shows that the ion-temperature gradient (ITG) instability, which is essentially an electrostatic instability, is unstable at low beta and its growth rate is reduced by magnetic field line bending at finite beta. On the other hand, the kinetic ballooning mode (KBM), which is an electromagnetic instability, is destabilized at high beta. In addition, trapped electron modes (TEMs), electron temperature gradient (ETG) modes, and micro-tearing modes (MTMs) can be destabilized. These instabilities are classified into two categories: ballooning parity and tearing parity modes. These parities are mixed by nonlinear interactions, so that, for instance, the ITG mode excites tearing parity modes. In the nonlinear evolution, the zonal flow shear acts to regulate the ITG driven turbulence at low beta. On the other hand, at finite beta, interplay between the turbulence and zonal flows becomes complicated because the production of zonal flow is influenced by the finite beta effects. When the zonal flows are too weak, turbulence continues to grow beyond a physically relevant level of saturation in finite-beta tokamaks. Nonlinear mode coupling to stable modes can play a role in the saturation of finite beta ITG mode and KBM. Since there is a quadratic conserved quantity, evaluating nonlinear transfer of the conserved quantity from unstable modes to stable modes is useful for understanding the saturation mechanism of turbulence.

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Section: Microturbulence At Finite Beta (Nonlinear Simulations)mentioning

confidence: 99%

Section: Impact Of Magnetic Perturbation On Turbulent Transportmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electromagnetic gyrokinetic simulation of turbulence in torus plasmas

et al. 2015

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“…Damped buffer regions of width Δ b =8 ρ s and damping rate ν b =1 c s /a are used at both radial boundaries to prevent profile relaxation [53] and the time-and flux-surface-averaged gradient contribution from the n=0 zonal moments is less than 1% of the equilibrium values. A unique feature of these simulations is that nearly all of the electron thermal transport (~98%) comes from the magnetic flutter contribution (~v ||,e ⋅δB r /B) in contrast to ITG/TEM turbulence, ETG turbulence, or even simulations that approach the ideal or kinetic ballooning mode limit (χ e,em /χ e,tot~5 0%) [55][56][57][58]. In addition there is negligible particle, ion thermal or momentum transport, consistent with strong magnetic flutter contribution and the fact that ions are much heavier than electrons (v ||,i <<v ||,e ).…”

Section: Numerical Gridsmentioning

confidence: 99%

Simulation Of Microtearing Turbulence In NSTX

Guttenfelder¹,

Kaye²,

Nevins³

et al. 2012

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Thermal energy confinement times in NSTX dimensionless parameter scans increase with decreasing collisionality. While ion thermal transport is neoclassical, the source of anomalous electron thermal transport in these discharges remains unclear, leading to considerable uncertainty when extrapolating to future ST devices at much lower collisionality.Linear gyrokinetic simulations find microtearing modes to be unstable in high collisionality discharges. First non-linear gyrokinetic simulations of microtearing turbulence in NSTX show they can yield experimental levels of transport. Magnetic flutter is responsible for almost all the transport (~98%), perturbed field line trajectories are globally stochastic, and a test particle stochastic transport model agrees to within 25% of the simulated transport. Most significantly, microtearing transport is predicted to increase with electron collisionality, consistent with the observed NSTX confinement scaling. While this suggests microtearing modes may be the source of electron thermal transport, the predictions are also very sensitive to electron temperature gradient, indicating the scaling of the instability threshold is important. In addition, microtearing turbulence is susceptible to suppression via sheared E×B flows as experimental values of E×B shear (comparable to the linear growth rates) dramatically reduce the transport below experimental values. Refinements in numerical resolution and physics model assumptions are expected to minimize the apparent discrepancy. In cases where the predicted transport is strong, calculations suggest that a proposed polarimetry diagnostic may be sensitive to the magnetic perturbations associated with the unique structure of microtearing turbulence.

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MHD Stability

Kikuchi¹,

Azumi²

2015

Frontiers in Fusion Research II

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Ideal, resistive and kinetic MHD instabilities are described. Since the birth of steady state tokamak research in 1990, there are number of important understandings of MHD modes related to steady state tokamak. In Sect. 8.1, we introduce the spectral property of MHD operator such as continuous spectrum and spectral gap, in brief. Marginal stability is discussed using the Newcomb equation in Sect. 8.2. Section 8.3 deals with flow effect on ideal MHD based on the Frieman-Rotenberg equation briefly. Localized MHD instabilities such as ELM, peeling/ballooning modes, infernal and barrier localized modes are discussed in Sect. 8.4. In Sect. 8.5, we introduce progress of resistive MHD such as the classical tearing mode (TM), the neoclassical tearing mode (NTM), the double tearing mode (DTM). Kinetic MHD equation is introduced in Sect. 8.6. In Sect. 8.7, Alfven eigenmode (AE) is introduced extensively. An important resistive/kinetic instability called the resistive wall mode (RWM) is introduced in Sect. 8.8. Control of ideal, resistive and kinetic MHD is essential element of fusion research. For three types of advanced tokamak operation (WS, NS, CH) to realize efficient steady state operation, ideal MHD modes such as peeling/ballooning modes for edge plasma, infernal modes for core plasma and BLM for ITB, resistive MHD modes such as NTM, DTM, RWM, kinetic MHD modes such as TAE, RSAE are understood well including control knob, while some kinetic MHD are still in progress in understanding. Key issue is that plasma profile does not match optimum profile for high beta advanced tokamak operation since profile is determined by the turbulent transport. Hence, combined understanding of MHD and turbulent transport is essential to optimize operation scenario for steady state tokamak operation.

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Gyrokinetic turbulence simulations at high plasma beta

Cited by 145 publications

References 33 publications

Electromagnetic gyrokinetic simulation of turbulence in torus plasmas

Electromagnetic gyrokinetic simulation of turbulence in torus plasmas

Simulation Of Microtearing Turbulence In NSTX

MHD Stability

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