Hybrid simulation study on ion heating by low-frequency wave excited in a field-reversed configuration

In this paper, we use hybrid simulation to elucidate the plasma heating mechanism due to waves excited in Field-Reversed Configuration (FRC) plasma. The plasma parameters are a separatrix radius of 0.16 m and a separatrix length of 1.16 m (x-point position is z = ± 0.57 m). The wave excitation antenna consists of two loop antennas with a radius of 0.3 m and is placed at a position of z = ± 0.5 m. The current waveform of the antenna is a sine wave with a maximum current value of 30 kA and a frequency of 160 kHz. The simulation results showed that the excited waves caused compression/expansion of the plasma, and at the same time, the temperature of the plasma increased or decreased at the compressed/expanded position. When waves are applied, a 23% increase in the volume-averaged ion temperature in the separatrix is observed compared to the case without waves applied. On the other hand, no increase in electron temperature is observed. For the electron fluid, the adiabatic condition is well established, and temperature changes are observed as the plasma compressed and expanded. On the other hand, for ions, kinetic energy perpendicular to the magnetic field lines increases during compression, and part of this energy is transferred to the energy of the parallel component by collisionless pitch angle scattering, resulting in heating due to the so-called magnetic pumping.