Modeling of the ECCD injection effect on the Heliotron J and LHD plasma stability

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The interaction between energetic particles (EPs) and EP-driven magnetohydrodynamic (MHD) instabilities in Heliotron J, a low-shear helical axis stellarator/heliotron, is investigated with MEGA, a hybrid MHD-EP simulation code with the free boundary condition, on the last closed flux surface. The n/m = 1/2 energetic particle mode (EPM) and the n/m = 2/4 global Alfvén eigenmode (GAE) in the peripheral plasma region of Heliotron J are successfully modeled with the free boundary condition. The free boundary condition affects the EP driving rate of the n/m = 1/2 EPM and the n/m = 2/4 GAE through the changes in the mode spatial profile. Under the fixed boundary condition, the linear growth rate of the EP-driven MHD mode with low mode numbers is underestimated. The interaction between EP and these experimentally-observed modes is kinetically analyzed. It is found that the strongest EP–shear Alfvén wave interactions arise from the toroidicity-induced resonances in the high-velocity region. These high-velocity EPs can efficiently interact with the peripheral EP-driven mode. The additional toroidally-asymmetric resonances are localized in the low-velocity region; therefore, their effects are weak for the bump-on-tail EP velocity distribution function.

Section: Simulation Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Numerical investigation into the peripheral energetic-particle-driven MHD modes in Heliotron J with free boundary hybrid simulation

Adulsiriswad¹,

Todo²,

Kado³

et al. 2021

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“…The FAR3d code was already validated with respect to gyro-kinetic and hybrid codes in dedicated benchmarking studies [41]. In addition, the linear simulation performed by the code shows a reasonable agreement with respect to observational data, reproducing the AE stability in LHD [42][43][44][45], DIII-D [46][47][48][49][50], TJ-II [33,51,52] and Heliotron J [53,54] plasma. In addition, the nonlinear version of the code succeeded in analyzing the sawtooth-like internal collapse events and energetic-ion-driven resistive interchange mode (EIC) burst observed in LHD plasma [39,[55][56][57][58] and the AE saturation in DIII-D plasma [59].…”

Section: Numerical Schemementioning

confidence: 78%

Simulation of the TAEs’ saturation phase in the Large Helical Device: MHD burst

Varela¹,

Spong²,

Todo³

et al. 2022

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The aim of the present study is to analyze the saturation regime of the Toroidal Alfven Eigenmodes (TAE) in the LHD plasma, particularly the MHD burst. The linear and non linear evolution of the TAEs are simulated by the FAR3d code that uses a reduced MHD model for the thermal plasma coupled with a gyrofluid model for the energetic particles (EP) species. The linear simulations indicate the overlapping of $1/2-1/1$, $2/3-2/4$ and $3/5-3/6$ TAEs in the inner-middle plasma region and frequency range of $45-75$ kHz, triggered by EPs with an energy of $T_{f} = 45$ keV and EP $\beta = 0.022 $. The non linear simulations show that $2/3-2/4$ and $3/4-3/5$ TAEs are further destabilized due to the energy transfer from $1/1-1/2$ TAE, leading to a broad TAEs radial overlapping and the MHD burst triggering. The energy of $1/1-1/2$ TAE is also non linearly transferred to the thermal plasma destabilizing the $0/0$ and $0/1$ modes, inducing the generation of shear flows and zonal currents as well as large deformations in the thermal pressure and EP density radial profiles. The non linear simulation reproduces the same succession of instabilities and the same frequency range with respect to the experiment. The instability propagates outward during the bursting phase, showing a large decrease of the EP density profile between the middle-outer plasma, pointing out the loss of part of the EP population that explains the decrease of the plasma heating efficiency observed during the MHD burst.

“…Destabilization of shear Alfvén waves depends on the precise magnetic configuration (rotational transform profile) and the balance between the fast particle drive and damping mechanisms. The impact of ECRH and ECCD has been investigated in stellarator devices [20] demonstrating a clear effect of ECCD on the observed mode spectrum (figure 4). For the case illustrated in the figure, adding counter-ECCD decreases the rotational transform in the core.…”

Section: Characterization and Control Of Alfvén Eigenmodesmentioning

confidence: 99%

Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas

Hidalgo¹,

Ascasíbar²,

Alegre³

et al. 2022

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TJ-II stellarator results on modelling and validation of plasma flow asymmetries due to on-surface potential variations, plasma fuelling physics, Alfvén eigenmodes (AEs) control and stability, the interplay between turbulence and neoclassical (NC) mechanisms and liquid metals are reported. Regarding the validation of the neoclassically predicted potential asymmetries, its impact on the radial electric field along the flux surface has been successfully validated against Doppler reflectometry measurements. Research on the physics and modelling of plasma core fuelling with pellets and tracer encapsulated solid pellet injection has shown that, although post-injection particle radial redistributions can be understood qualitatively from NC mechanisms, turbulence and fluctuations are strongly affected during the ablation process. Advanced analysis tools based on transfer entropy have shown that radial electric fields do not only affect the radial turbulence correlation length but are also capable of reducing the propagation of turbulence from the edge into the scrape-off layer. Direct experimental observation of long range correlated structures show that zonal flow structures are ubiquitous in the whole plasma cross-section in the TJ-II stellarator. Alfvénic activity control strategies using ECRH and ECCD as well as the relation between zonal structures and AEs are reported. Finally, the behaviour of liquid metals exposed to hot and cold plasmas in a capillary porous system container was investigated.