The <i>q</i>-profile effect on high-order harmonic <i>q</i> = 1 tearing mode generation during sawtooth crashes

Wang, Jialei; Lai, W.; Wang, Xiaogang

doi:10.1063/1.4731720

Cited by 14 publications

(13 citation statements)

References 49 publications

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“…The profile peaks around r/a = 0.3 close to two of the q = 1 surfaces. A similar instability with n > 1 was also found for plasma profiles with relatively high magnetic shear at the q = 1 surface [21]. The initial and final beta profiles of the energetic particles are compared in Fig.…”

Section: Mhd Instability In Monotonic Shear Plasma With 15 Ma Plasma mentioning

confidence: 60%

Large-Scale Simulation of Energetic Particle Driven Magnetohydrodynamic Instabilities in ITER Plasmas

Todo

Bierwage

2014

Plasma and Fusion Research

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Magnetohydrodynamic (MHD) instabilities driven by energetic alpha particles and beam deuterium particles are investigated for ITER operation scenarios using a hybrid simulation code for energetic particles interacting with an MHD fluid. The particle simulation method with finite Larmor radius effects is applied to both alpha and beam deuterium particles. For the steady-state scenario with 9 MA plasma current, beta-induced Alfvén eigenmodes (BAE modes) with low toroidal mode number (n = 3, 5) were found to become dominant in the nonlinear phase although many toroidal Alfvén eigenmodes (TAE modes) with n ∼ 15 are most unstable in the linear phase. The redistribution of energetic particles with δβ α ∼ δβ beam ∼ 0.07%, which respectively correspond to 6% and 8% of the central values, occurs in the nonlinear phase. When the toroidal mode number of the fluctuations is restricted to n ≤ 8, the redistribution is substantially reduced, thus, suggesting that the resonance overlap between the n ∼ 15 TAE and low-n BAE modes enhances the energetic particle transport in the run with full toroidal mode numbers. For the ITER scenario with 15 MA plasma current, an MHD instability with n = 3 that peaks around the q = 1 (q is the safety factor) magnetic surfaces is driven by bulk plasma current and bulk pressure, and results in significant redistribution of alpha particles with δβ α ∼ 0.3%. For the equilibrium profile with the safety factor profile uniformly raised by 0.1 to remove the q = 1 surfaces, only a benign MHD instability occurs and the energetic particle transport is negligible.

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Section: Mhd Instability In Monotonic Shear Plasma With 15 Ma Plasma mentioning

confidence: 60%

Large-Scale Simulation of Energetic Particle Driven Magnetohydrodynamic Instabilities in ITER Plasmas

Todo

Bierwage

2014

Plasma and Fusion Research

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“…When q ≈ m/n, the plasma response is entirely determined by resistive dissipation and the source. This is also the reason for why the spectrum of unstable modes becomes broader in m when the q profile is flattened around a q = 1 surface (as observed in [8]) and this effect may also play a role for the broad spectra found for multiple q = 1 surfaces separated by short distances [7,19]. The role of the safety factor profile is demonstrated by simulation results presented in section 4.1.…”

Section: Role Of the Safety Factor Profilementioning

confidence: 77%

“…An ECCD mechanism produces a corresponding current sheet and reduces the safety factor q. When q drops below 1, MHD instabilities with dominant poloidal mode numbers m > 1 may occur [7,8] and contribute to the structures observed in the ECE images.…”

Section: Interpretation and Hypothetical Frameworkmentioning

confidence: 99%

Dynamics of multiple flux tubes in sawtoothing KSTAR plasmas heated by electron cyclotron waves: II. Theoretical and numerical analysis

et al. 2014

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The dynamics of multiple closed flux tubes in the core of a sawtoothing tokamak plasma are studied using nonlinear simulations. This is motivated by recent observations of long-lived hot spots in the electron cyclotron emission (ECE) images of KSTAR plasmas with electron cyclotron heating (ECH) (Yun et al 2012 Phys. Rev. Lett. 109 145003). Using an empirical source term in a reduced set of MHD equations, it is shown that flux tubes with helicity h = 1 are easily produced and survive for the observed time intervals only if the safety factor is close to unity (|q − 1| 0.5%) and the magnetic shear is small (|s| 1). This suggests that sawteeth in KSTAR leave behind wide regions where q ≈ 1. On the basis of the relevant time scales, we discuss how this magnetic geometry and the spatial localization of the EC resonance may allow ECH to actively induce the formation of flux tubes. Using simulations with q profiles that possess a wide q = 1 region inside the sawtooth inversion radius, we examine how the flux tubes merge and annihilate, and how their dynamics depend on the strength of the drive. The phenomena seen in the simulations and experiments lead us to conclude that, during the sawtooth ramp phase, there is a dynamic competition between sources and sinks of thermal and magnetic energy, where the flux tubes may play an important role; both as carriers of and channels for energy. The development of self-consistent simulation models is motivated and directions for future experiments are given.

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“…[9] The simulation re-035201-2 sult also confirms that the prevailing harmonic modes are ascribed to the weakly reversed shear or broad low shear. [10,11] In this study, for the internal region, we use a simple analytic model [12] for 𝑞 profile construction in terms of the positions of the double 𝑚 = 1 mode, which are obtained from the soft-x ray array. For the edge region, the 𝑞 profile is from the EFIT code.…”

mentioning

confidence: 99%

“…Furthermore, the absence of the 2𝑓 2 harmonic mode is due to the larger magnetic shear in the second 𝑞 = 1 surface, which is consistent with the numerical calculations. [10,11] The larger amount of impurity accuracy in the plasma core region is the reason for snake excitation. It is no doubt that impurity accumulation is due to the abnormal particle transport.…”

mentioning

confidence: 99%

Transient Appearance of Double Spontaneous-Snakes in EAST H Mode Plasma

Xu¹,

Hu²,

Zhang³

2014

Chinese Phys. Lett.

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Transient lasting of double spontaneous snakes is observed in energy confinement improved plasma on the EAST tokamak. The destabilization of snakes with superb particle confinement can lower plasma energy confinement and slow plasma toroidal rotation. The non-monotonic 𝑞 profile with double 𝑞 = 1 surface, slightly above unity in central, is constructed. The prevailing harmonic modes are susceptible to the nearly zero magnetic shear. Finally, the role of anomalous particle transport and the formation of off-axis peaking electron profile on the excitation of double snakes are discussed.

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The q-profile effect on high-order harmonic q = 1 tearing mode generation during sawtooth crashes

Cited by 14 publications

References 49 publications

Large-Scale Simulation of Energetic Particle Driven Magnetohydrodynamic Instabilities in ITER Plasmas

Large-Scale Simulation of Energetic Particle Driven Magnetohydrodynamic Instabilities in ITER Plasmas

Dynamics of multiple flux tubes in sawtoothing KSTAR plasmas heated by electron cyclotron waves: II. Theoretical and numerical analysis

Transient Appearance of Double Spontaneous-Snakes in EAST H Mode Plasma

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