An Efficient Ionization Method for Pressure Up To Thousands of Pascals

A novel radio-frequency antenna consisting of isolated solenoids is reported to generate plasma for pressure up to thousands of pascals. The underlying mechanism involves capacitive coupling, inductive coupling and axial confinement from magnetic mirrors. It can ionize the air reliably with pressure up to $2500$~Pa for the $1$~kW-$13.56$~MHz power supply employed, and maintain the discharge steadily from tens of minutes to hours. This ionization method is particularly useful for plasma propulsion in near space and other low-temperature plasma applications where sub-atmospheric pressure is required.