Properties of Maser-generated Alfv\'{e}n wave in a Large Laboratory Device

This research is motivated by the investigations of the natural Alfv\'{e}n wave maser, which refers to the resonant amplification of Alfv\'{e}n wave in the earth-surrounding plasmas. A resonant cavity that results from applying a locally non-uniform magnetic field to a plasma source region between the anode and cathode of the Large Plasma Device creates the maser. In this research, a lanthanum hexaboride (LaB6)) cathode is used as the plasma source. Above an excitation threshold, selective amplification produces a highly coherent, large amplitude Alfv\'{e}n wave that propagates out of the resonator through a semitransparent mesh anode into the plasma column where the magnetic field is uniform. The excitation threshold depends on the discharge voltage, and it increases as background magnetic field strength increases; this threshold influences the maser behaviors, including amplitude modulations. The maser with LaB6 source has m $=$ 1 mode and exhibits a right-handed rotation, which is consistent with the electron diamagnetic drift rotation, supporting the possibility of a drift Alfv\'{e}n wave maser. To distinguish between drift and shear Alfv\'{e}n waves, a new experiment with the maser cavity excited by a driving circuit was performed. This allows us to access low frequencies (compared to $\omega $*) that cannot be spontaneously driven. The dispersion relation of this driven maser is under investigation. The experimental results will motivate future Alfv\'{e}n wave study in laboratory devices and thus help better understand space plasma physics such as testing the theory of Alfv\'{e}n-wave-induced heating of stellar atmosphere.