Self-Organized Stationary States of Tokamaks

Jardin, S.C.; Ferraro, N.M.; Krebs, I.

doi:10.1103/physrevlett.115.215001

Cited by 66 publications

(97 citation statements)

References 28 publications

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“…All other parameters are held fixed as described in [18]. To keep the Spitzer resistivity similar between simulations with different values of β, it is rescaled accordingly.…”

Section: Simulation Set-upmentioning

confidence: 99%

“…This paper aims at broadening the understanding of the flux pumping mechanism based on the explanation given in [18]. We present the asymptotic states of 3D nonlinear resistive MHD simulations that can be classified into two basic types: Sawtoothing cases where q 0 decreases to values significantly below unity and q 0 ≈ 1 is periodically restored by a change of the magnetic topology, and steady-state sawtooth-free cases with a helically perturbed core, low magnetic shear in the center and a central safety factor profile that stays close to unity.…”

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confidence: 99%

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Magnetic flux pumping in 3D nonlinear magnetohydrodynamic simulations

et al. 2017

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A self-regulating magnetic flux pumping mechanism in tokamaks that maintains the core safety factor at $q\approx 1$, thus preventing sawteeth, is analyzed in nonlinear 3D magnetohydrodynamic simulations using the M3D-C$^1$ code. In these simulations, the most important mechanism responsible for the flux pumping is that a saturated $(m=1,n=1)$ quasi-interchange instability generates an effective negative loop voltage in the plasma center via a dynamo effect. It is shown that sawtoothing is prevented in the simulations if $\beta$ is sufficiently high to provide the necessary drive for the $(m=1,n=1)$ instability that generates the dynamo loop voltage. The necessary amount of dynamo loop voltage is determined by the tendency of the current density profile to centrally peak which, in our simulations, is controlled by the peakedness of the applied heat source profile.Comment: submitted to Physics of Plasmas (23 pages, 15 Figures

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“…All other parameters are held fixed as described in [18]. To keep the Spitzer resistivity similar between simulations with different values of β, it is rescaled accordingly.…”

Section: Simulation Set-upmentioning

confidence: 99%

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confidence: 99%

Magnetic flux pumping in 3D nonlinear magnetohydrodynamic simulations

et al. 2017

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“…Bonfiglio et al [3] presented simulation evidence to prove that during the flux conversion and dynamo processes involved in the formation of the reversed field pinche (RFP) equilibria, it is electrostatic and not inductive electric fields that play the most important role in plasma motions. More recently, Jardin et al [4] used the same electrostatic dynamo idea to explain the 'magnetic flux pumping' enabling stationary nonsawtoothing 'hybrid' discharges in the tokamak [5].…”

Section: Introductionmentioning

confidence: 99%

Role of electric fields in the MHD evolution of the kink instability

Lapenta

Skender

2017

New J. Phys.

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The discovery (Bonfiglio et al 2005 Phys. Rev. Lett. 94 145001) of electrostatic fields playing a crucial role in establishing plasma motion in the flux conversion and dynamo processes in reversed field pinches is revisited. In order to further elucidate the role of the electrostatic fields, a flux rope configuration susceptible to the kink instability is numerically studied with an MHD code. Simulated nonlinear evolution of the kink instability is found to confirm the crucial role of the electrostatic fields.A new insight is gained on the special function of the electrostatic fields: they lead the plasma towards the reconnection site at the mode resonant surface. Without this step the plasma column could not relax to its nonlinear state, since no other agent is present to perform this role. While the inductive field generated directly by the kink instability is the dominant flow driver, the electrostatic field is found to allow the motion in the vicinity of the reconnection region.

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“…In a simulation using M3D-C1 (3D resistive MHD) code [40], the q-profile is raised via generation of an interchange mode at the axis that adjusts the loop voltage through dynamo. Steady state turbulence, which to some degree is always present in tokamaks can co-exist with other modes and hence, not contradicting any of the previously mentioned works, can explain why there is a stationary non-sawtooting state over resistive time scales.…”

Section: L-mode Type Profilesmentioning

confidence: 99%

Turbulent contributions to Ohm's law in axisymmetric magnetized plasmas

Chavdarovski

Gatto

2017

Physics of Plasmas

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Abstract.The effect of magnetic turbulence in shaping the current density in axisymmetric magnetized plasma is analyzed using a turbulent extension of Ohm's law derived from the self-consistent action-angle transport theory. Besides the well-known hyperresistive (helicity-conserving) contribution, the generalized Ohm's law contains an anomalous resistivity term, and a turbulent bootstrap-like term proportional to the current density derivative. The numerical solution of the equation for equilibrium and turbulence profiles characteristic of conventional and advanced scenarios shows that, trough "turbulent bootstrap" effect and anomalous resistivity turbulence can generate power and parallel current which are a sizable portion (about 20 − 25 %) of the corresponding effects associated with the neoclassical bootstrap effect. The degree of alignment of the turbulence peak and the pressure gradient plays an important role in defining the steady-state regime. In fully bootstrapped tokamak, the hyper-resistivity is essential in overcoming the intrinsic limitation of the hollow current profile.

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Self-Organized Stationary States of Tokamaks

Cited by 66 publications

References 28 publications

Magnetic flux pumping in 3D nonlinear magnetohydrodynamic simulations

Magnetic flux pumping in 3D nonlinear magnetohydrodynamic simulations

Role of electric fields in the MHD evolution of the kink instability

Turbulent contributions to Ohm's law in axisymmetric magnetized plasmas

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