Resonant Cavity Plasma Electron Source

A microwave plasma electron source in the form of a resonant cavity is described. Plasma density, electron temperature, and plasma potential were measured with a triple Langmuir probe along the cavity axis with and without electron current extraction to a keeper electrode and anode. Throughout most of the cavity, electron temperatures were low (1-2 eV) but rose sharply to ~10 eV, adjacent to an alumina window that separated the plasma from the microwave source. Those hot electrons generated a region of heavily overdense ( ~10¹⁹ m^-3) plasma that dominated the cavity current extraction capability. A maximum of 2.1 A was extracted to a flat plate anode biased 50 V above the cavity at a xenon flow rate of 0.75 mg/s and 60 W of absorbed microwave power.