Magnetohydrodynamic hybrid simulation model with kinetic thermal ions and energetic particles

In this paper, we report the novel experimental observation of both unstable and stable Toroidicity-induced Alfvén Eigenmodes (TAEs) measured simultaneously in a JET tokamak plasma. The three-ion-heating scheme (D-DNBI-3He) is employed to accelerate deuterons to MeV energies, thereby destabilizing TAEs with toroidal mode numbers n = 3 - 5, each decreasing in mode amplitude. At the same time, the Alfvén Eigenmode Active Diagnostic resonantly excites a stable n = 6 TAE with total normalized damping rate -γ/ω0 ≈ 1% - 4%. Hybrid kinetic-MHD modeling with codes NOVA-K and MEGA both find eigenmodes with similar frequencies, mode structures, and radial locations as in experiment. NOVA-K demonstrates good agreement with the n = 3, 4, and 6 TAEs, matching the damping rate of the n = 6 mode within uncertainties and identifying radiative damping as the dominant contribution. Improved agreement is found with MEGA for all modes: the unstable n = 3 - 5 and stable n = 2, 6 modes, with the latter two stabilized by higher intrinsic damping and lower fast ion drive, respectively. While some discrepancies remain to be resolved, this unique validation effort gives us confidence in TAE stability predictions for future fusion devices.

Section: Hybrid Kinetic-mhd Simulations With Megamentioning

confidence: 99%

Simultaneous measurements of unstable and stable Alfvén eigenmodes in JET

Tinguely¹,

Gonzalez-Martin²,

Puglia³

et al. 2022

“…where ω φ and ω θ are measured following particle orbits in the equilibrium magnetic field for the linear resonance condition [31]. The magenta lines represent the resonance condition F (ω φ , ω θ ) = L where L is an integer and labeled in the figure.…”

Section: Distribution Function Analysismentioning

confidence: 99%

Simulation study of energetic-particle driven off-axis fishbone instabilities in tokamak plasmas

Li¹,

Todo²,

Wang³

et al. 2021

Self Cite

Kinetic-magnetohydrodynamic hybrid simulations were performed to investigate the linear growth and the nonlinear evolution of off-axis fishbone mode (OFM) destabilized by trapped energetic ions in tokamak plasmas. The spatial profile of OFM is mainly composed of m/n = 2/1 mode inside the q = 2 magnetic flux surface while the m/n = 3/1 mode is predominant outside the q = 2 surface, where m and n are the poloidal and toroidal mode numbers, respectively, and q is the safety factor. The spatial profile of the OFM is a strongly shearing shape on the poloidal plane, suggesting the nonperturbative effect of the interaction with energetic ions. The frequency of the OFM in the linear growth phase is in good agreement with the precession drift frequency of trapped energetic ions, and the frequency chirps down in the nonlinear phase. Two types of resonance conditions between trapped energetic ions and OFM are found. For the first type of resonance, the precession drift frequency matches the OFM frequency, while for the second type, the sum of the precession drift frequency and the bounce frequency matches the OFM frequency. The first type of resonance is the primary resonance for the destabilization of OFM. The resonance frequency which is defined based on precession drift frequency and bounce frequency of the nonlinear orbit for each resonant particle is analyzed to understand the frequency chirping. The resonance frequency of the particles that transfer energy to the OFM chirps down, which may result in the chirping down of the OFM frequency. A detailed analysis of the energetic ion distribution function in phase space shows that the gradient of the distribution function along the E′ = const. line drives or stabilizes the instability, where E′ is a combination of energy and toroidal canonical momentum and conserved during the wave-particle interaction. The distribution function is flattened along the E′ = const. line in the nonlinear phase leading to the saturation of the instability.

“…In this paper, the effect of the kinetic thermal ions on the instabilities have been investigated by using MEGA code based on the kinetic MHD model where the thermal ions are treated with the drift kinetic model [11,12]. The guiding-center velocity v of the thermal ions is given by…”

Section: Model Equationsmentioning

confidence: 99%

Kinetic thermal ion effects on maintaining high beta plasmas above the Mercier criterion in the Large Helical Device

Sato¹,

Todo²

2021

Self Cite

It is found that kinetic thermal ions have a significant stabilizing effect on Large Helical Device (LHD) plasmas from the kinetic magnetohydrodynamic (MHD) simulations. The simulation results for the LHD plasmas at high magnetic Reynolds number show that the high beta plasmas can be maintained since the saturation level of the pressure-driven MHD instabilities is significantly reduced by the kinetic thermal ions. This results from the fact that the response of the trapped ions to the instabilities is weakened by the precession drift motion in the three-dimensional magnetic field. Thus the supercritical stability of the LHD plasmas well above the Mercier criterion can be attributed to the precession drift motion of the trapped ions in the three-dimensional magnetic field.