Simulation of energetic particle driven geodesic acoustic modes and the energy channeling in the Large Helical Device plasmas

Abstract

Energetic particle driven geodesic acoustic modes (EGAMs) in the Large Helical Device (LHD) plasmas are investigated using MEGA code. MEGA is a hybrid simulation code for energetic particles interacting with a magnetohydrodynamic (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 EGAM. The EGAM channeling is reproduced by simulation with realistic parameters for the first time. The heating power to bulk ions is 3.4 kW/m 3 . It is found that the 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.

Nonlinear dynamics of energetic-particle driven geodesic acoustic modes in ASDEX Upgrade

“…One of these modes, called energetic-particle-driven geodesic acoustic mode (EGAM) 1,2 , can have a significant influence on the EP dynamics and on the plasma confinement. First of all, being excited, this mode provides an additional mechanism of the energy exchange between the energetic particles and the thermal plasma [3][4][5][6] due to the wave-particle interaction. Moreover, because of its interaction with the turbulence 7,8 , this mode might be used as an additional knob in the turbulence regulation.…”

The systematic investigation of energetic-particle-driven geodesic acoustic mode channeling using MEGA code

“…This simplification is valid as shown in Ref. [44,51], and the simplification saves a considerable amount of computational resources and time. The numbers of grid points of this pitch in the (R, φ, z) directions are (128, 64, 128), respectively.…”

“…4 of Ref. [51]. In the frequency chirping phase, energetic particles lose energy continuously, and the bulk ions absorb energy continuously.…”

“…[57] and Ref. [51]. This kinetic description of bulk ions is very important for EGAM channeling simulation, because the Landau damping process is a kind of wave-particle interaction process, and this process can be well simulated by the kinetic thermal ions model.…”

Hybrid simulation of NBI fast-ion losses due to the Alfvén eigenmode bursts in the Large Helical Device and the comparison with the fast-ion loss detector measurements

“…The energy channelling from fast ions to thermal ions through the interaction with the EGAM was demonstrated for the first time (Wang et al. 2019), and the kinetic stabilizing effect of trapped thermal ions was found on the ballooning modes in LHD (Sato & Todo 2019). The stabilizing effect of fast ions was also found on interchange modes in LHD if the initial total pressure profile is assumed to be the same for different fast ion pressure (Pinon, Todo & Wang 2018).…”