A Highly Efficient Microwave Plasma Jet Based on Evanescent-Mode Cavity Resonator Technology

This article introduces a novel low-power and highly efficient atmospheric pressure microwave plasma jet (APPJ). Specifically, a capillary tube passing through the critical gap area of a high-
$Q$
evanescent-mode (EVA) cavity resonator provides a controlled gas flow rate to realize microwave gas breakdown and plasma jet formation even with milliwatts range input power. The theory, simulation, fabrication, and characterization of the introduced plasma jet technology are discussed. A prototype 2.45 GHz device can operate at powers as low as 400 mW with >80% power efficiency and provides up to a 6-mm-long plasma jet with electron density in the range of
$10^{15}$
cm
$^{-3}$
in a 1 to 7 slpm helium flow rate. Considering its high plasma density as well as low operating power and jet temperature, this device is a viable and safe solution for a wide range of applications, including emerging plasma medicine needs.