Collisional Merging of Field-Reversed Configurations in the FAT-CM Device Form Targets for the Excitation of Low-Frequency Waves

Abstract

We have conducted collisional merging of field-reversed-configuration (FRC) plasmas in the FAT-CM (FRC Amplification via Translation-Collisional Merging) device to generate merged FRCs as targets for the excitation of low-frequency waves. Because of the high-beta nature of an FRC, the confining magnetic field is highest at the wall of the device and decreases toward a magnetic null inside the separatrix. We therefore find that the frequencies of the waves produced in this experiment must be lower than the ion cyclotron frequency or higher than the electron plasma frequency, because waves outside this band are reflected or resonant outside the separatrix of the FRC. We have therefore developed loop antennas and power supplies to apply low-frequency, oscillatory magnetic fields and have installed them in the FAT-CM device. The parameters characterizing the equilibrium phase of the merged FRC (lifetime ∼250 µs, radius ∼0.2 m, length ∼1.8 m, electron density ∼1.0 × 10 20 m −3 , and total temperature ∼100 eV) are sufficient to enable studies of the propagation of low-frequency waves in the core regions of FAT-CM FRCs. We have also performed an initial experiment in which an oscillatory magnetic field has been applied to a merged FRC.

Collisional merging formation of a field-reversed configuration in the FAT-CM device

“…According to the simulation, almost all of the kinetic energy is converted back into the internal energy of the merged FRC plasma. Reduced expansion at the mirror enables us to install in vessel antennas for wave excitation [18].…”