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Energetic-particle-driven geodesic acoustic modes (EGAMs) channeling in the Large Helical Device (LHD) plasmas are systematically investigated for the first time using MEGA code. MEGA is a hybrid simulation code for energetic particles interacting with a magnetohydrodynamic (MHD) fluid. In the present work, both the energetic particles and the bulk ions are described kinetically. The EGAM profiles in the three-dimensional form is illustrated. Then, EGAM channeling behaviors are analyzed under different conditions. During the EGAM activities without frequency chirping, EGAM channeling occurs in the linear growth stage but terminates in the decay stage after the saturation. During the EGAM activities with frequency chirping, EGAM channeling occurs continuously. Also, low-frequency EGAM makes the energy transfer efficiency () higher, and this is confirmed by changing the energetic particle pressure, energetic particle beam velocity, and energetic particle pitch angle. Moreover, higher bulk ion temperature makes the energy transfer efficiency higher. In addition, under a certain condition, the energy transfer efficiency in the deuterium plasma is lower than that in the hydrogen plasma. [ABSTRACT FROM AUTHOR]

Energetic particle driven geodesic acoustic modes (EGAMs) in Large Helical Device plasmas are investigated using MEGA code. MEGA is a hybrid simulation code for energetic particles interacting with a magneto-hydrodynamic (MHD) fluid and in the present work, both the energetic particles and bulk ions are described by the kinetic equations. The low frequency EGAMs are reproduced. Also, the energy transfer is analyzed and the bulk ion heating during the EGAM activity is observed. The ions obtain energy when the energetic particles lose energy, and this indicates that an energy channel is established by the EGAM. EGAM channeling is reproduced by simulation with realistic parameters for the first time. The heating power to bulk ions is 3.4 . It is found that sideband resonance is dominant during the energy transfer from EGAM to the bulk ions, and the transit frequencies of resonant bulk ions are one-half of the EGAM frequency. [ABSTRACT FROM AUTHOR]

Effects of fast ions on the magnetohydrodynamic (MHD) instabilities in a Large Helical Device (LHD) plasma with the central beta value (=pressure normalized by the magnetic pressure) 4% have been investigated with hybrid simulations for energetic particles interacting with an MHD fluid. When fast ions are neglected, it is found that the dominant instability is an ideal interchange mode with the dominant harmonic m/n = 2/1, where m, n are respectively the poloidal and toroidal numbers. The spatial peak location of the m/n = 2/1 harmonic is close to the ι = 1/2 magnetic surface located at r/a = 0.29, where ι is the rotational transform and r/a is the normalized radius. The second unstable mode is a resistive interchange mode with m/n =3/2 that peaks at r/a = 0.65 nearby the ι = 2/3 surface, which grows more slowly than the m/n = 2/1 mode. The nonlinear coupling of the m/n = 3/2 and 2/1 mode results in the growth of the m/n = 5/3 mode and other modes leading to the global reduction and flattening of the pressure profile. When fast ions are considered with the central beta value 0.2% and the total pressure profile is kept the same, the ideal interchange mode with m/n = 2/1 located close to the plasma center is stabilized while the resistive interchange mode with m/n = 3/2 located far from the plasma center is less affected. The stabilization is attributed to the reduction of bulk pressure gradient, which is the dilution of the free energy source, because the energy transfer between the fast ions and the interchange modes is found to be negligible. For higher fast-ion pressure, Alfvén eigenmodes are destabilized by fast ions. [ABSTRACT FROM AUTHOR]

Energetic-particle-driven geodesic acoustic modes (EGAMs) observed in a Large Helical Device experiment are investigated using a hybrid simulation code for energetic particles interacting with a magnetohydrodynamic (MHD) fluid. The frequency chirping of the primary mode and the sudden excitation of the half-frequency secondary mode are reproduced for the first time with the hybrid simulation using the realistic physical condition and the three-dimensional equilibrium. Both EGAMs have global spatial profiles which are consistent with the experimental measurements. For the secondary mode, the bulk pressure perturbation and the energetic particle pressure perturbation cancel each other out, and thus the frequency is lower than the primary mode. It is found that the excitation of the secondary mode does not depend on the nonlinear MHD coupling. The secondary mode is excited by energetic particles that satisfy the linear and nonlinear resonance conditions, respectively, for the primary and secondary modes. [ABSTRACT FROM AUTHOR]