West, MichaelCharles, ChristineBoswell, Roderick2015-12-070093-3813http://hdl.handle.net/1885/22582A prototype of the helicon double-layer thruster (HDLT) has been tested and characterized when immersed inside a space simulation vacuum chamber. When operating with xenon and increasing the applied radio-frequency power, a new high-density "blue" mode has been observed. This mode occurs when the plasma source transitions from a capacitively coupled mode to a probable helicon-wave-sustained mode. Images of the HDLT prototype operating in xenon are presented and show the appearance of a bright white/blue plasma once the mode transition occurs. This is accompanied by a significant increase in the plasma density inside the plasma source of the HDLT.Keywords: Capacitively coupled; Double layers; High-density; Mode transitions; plasma thruster; Radio-frequency power; Space simulations; Space technologies; Vacuum chambers; Electric propulsion; Plasma density; Plasma sources; Xenon; Helicons Double-layer; electric propulsion; helicon; plasma thruster; space technology; xenon201110.1109/TPS.2011.21585892016-02-24