Search

The multiphase simulations are conducted with the kinetic-magnetohydrodynamics hybrid code MEGA to investigate the spatial and the velocity distributions of lost fast ions due to the Alfvén eigenmode (AE) bursts in the Large Helical Device plasmas. It is found that fast ions are lost along the divertor region with helical symmetry both before and during the AE burst except for the promptly lost particles. On the other hand, several peaks are present in the spatial distribution of lost fast ions along the divertor region. These peaks along the divertor region can be attributed to the deviation of the fast-ion orbits from the magnetic surfaces due to the grad-B and the curvature drifts. For comparison with the velocity distribution of lost fast ions measured by the fast-ion loss detector (FILD), the ‘numerical FILD’ which solves the Newton–Lorentz equation is constructed in the MEGA code. The velocity distribution of lost fast ions detected by the numerical FILD during AE burst is in good qualitative agreement with the experimental FILD measurements. During the AE burst, fast ions with high energy (100–180 keV) are detected by the numerical FILD, while co-going fast ions lost to the divertor region are the particles with energy lower than 50 keV.

We have developed a 2½-dimensional open boundary particle simulation model and have studied the current-driven electrostatic ion-cyclotron instability and related d.c. potential difference. Fresh streaming electrons are injected smoothly from the boundaries at each time step, avoiding unphysical accumulation of charged particles in front of the boundaries. As a current-driven electrostatic ion cyclotron instability grows, a d.c. potential difference along the magnetic field lines is created.

The drift model is an extention of magnetohydrodynamics (MHD) with the ion finite Larmor radius effects. It is demostrated with a one-dimensional simulation code that the dispersion relation of the kinetic Alfven wave is reproduced with the drift model. The simulation code for MHD and energetic alpha particles (MEGA) has been extended with the drift model and an extended Ohm's law where the electron Landau damping is taken into account with the Landau fluid model. The linear stability of the alpha-particle driven Alfven eigenmode in the Tokamak Fusion Test Reactor (TFTR) deuterium-tritium (D-T) plasma was investigated with the extended MKGA code. The nonlinear simulation results of an ITER-like plasma with a weak negative shear are presented.