Mode Transitions in the Helicon Double-Layer Thruster Prototype Operating in Xenon

A 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.