Maser-like mode driven by flow shear in a heated magnetized plasma*

Results of a basic heat transport experiment at LAPD involving an off-axis heating source are presented. A ring-shaped electron beam source injects low energy electrons (below ionization energy) along a strong magnetic field into a pre-existing, large and cold plasma, resulting in a long, hollow, cylindrical region of elevated plasma pressure. Azimuthal and axial flows with shear are present as a consequence of the boundary conditions at the ring-source.  The source configuration allows for active control of the azimuthal flows and flow shear. At high flow shear the system suddenly transitions from broadband drift-wave fluctuations into a regime dominated by a single frequency (~ 0.04f_ci), maser-like mode with Alfvenic characteristics, which causes enhanced transport. The large mode amplitude (delta n / n > 0.5 ) peaks where the shear in the azimuthal flow is  largest. The mode remains active for times long compared to typical transport time scales. Results are presented on the mode structure, the threshold for mode growth and its dependence on the magnitude of the flow shear.