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. When a threshold in the plasma discharge current is exceeded, selective amplification produces a highly coherent, large amplitude shear 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 [1]. The discharge current threshold for maser action increases as background magnetic field strength B0 increases; this threshold influences the maser behaviors, including amplitude modulations. This maser with LaB6 source has only m $=$ 1 mode, while the maser with BaO source has a mode transition from m $=$ 0 to m $=$ 1 mode. The LaB6 maser wavelength is insensitive to parameters except for discharge voltage, which is under investigation. The experimental results will motivate future Alfv\'{e}n wave study in laboratory device and thus help better understand space plasma physics such as testing the theory of Alfv\'{e}n-wave-induced heating of stellar atmosphere. \\[4pt] [1] J. E. Maggs and G. J. Morales and T.A. Carter, Phys. Plasmas. 12, 013103 (2005)