Methods and systems for generating a plasma using an external plasma system are described. The plasma system may include an energy coupling device (e.g., an electromagnetic coil or capacitor) that is submersed within a liquid coolant and powered by an RF source. In some embodiments, a C-shaped magnetic core may be submersed within the liquid coolant and one or more plasma tubes may be arranged within an opening of the C-shaped magnetic core between the ends of the C-shaped magnetic core. To generate a plasma in a first tube of the one or more plasma tubes, a gas may be inserted into the first tube while the RF source drives a coil surrounding a portion of the C-shaped magnetic core to couple electromagnetic energy into the gas within the first tube.