The Behavior of Edge Instabilities and Turbulence in Gas-Puff-Fueled LAPD Discharges

The recent upgrade of the main plasma source of the Large Plasma Device (LAPD) [1] from Barium Oxide to Lanthanum Hexaboride has motivated a new fueling procedure to support higher-density operation. Piezoelectric valves near the anode puff gas during the discharge, and the chamber is evacuated between shots. This mode of operation can achieve higher densities and better axial density uniformity than the previous fueling procedure but also has revealed interesting new plasma behaviors. A transition from broadband edge turbulence to a single coherent mode is observed with increased neutral fueling via gas puffing. We will present experimental data demonstrating this behavior and discuss future experiments to understand the nature of this transition.

References

[1] W. Gekelman, et al., Rev. Sci. Instrum., 87, 025105 (2016).