A purification apparatus (100, 500) comprising: a radio frequency, RF, signal source (270, 520) configured to generate an RF signal; a first electrode (240, 540) electrically coupled to the RF signal source, wherein the first electrode is configured to receive the RF signal and to convert the RF signal into electromagnetic energy that is radiated by the first electrode; a second electrode (250, 550); a conduit (160, 530) that includes an input port (166, 566), an output port (168, 568), and a chamber (260, 560), wherein the input port (166, 566) and the output port (168,568) are in fluid communication with the chamber (260, 560) and the chamber (260, 560) is configured to receive an electrodeless bulb (280, 580), and wherein the chamber (260, 560) is defined by first and second boundaries that are separated by a distance that is less than the wavelength of the RF signal so that the chamber (260, 560) is sub-resonant, wherein the first electrode (240, 540) is physically positioned at the first boundary, wherein the second electrode (250, 550) is physically positioned at the second boundary, and wherein the first electrode (240, 540), the second electrode (250, 550), and the chamber (260, 560) form a structure that is configured to capacitively couple the electromagnetic energy into the electrodeless bulb when the electrodeless bulb (280, 580) is positioned within the chamber; chamber (260, 560); a variable resonant circuit (590, 600) electrically coupled between an output of the RF signal source and the first electrode (240, 540); a system controller configured to establish and modify a resonant frequency of the variable resonant circuit (590, 600) through control signals that the system controller sends to the variable resonant circuit (590, 600); and one or more of an electric field sensor, a radiation intensity sensor, a luminous intensity sensor and a contamination sensor, respectively configured to sense an electromagnetic field intensity within the chamber, a radiation intensity within the chamber, a luminous intensity within the chamber and a contamination level within the chamber and to send a sensor signal to the system controller indicating, respectively, the electromagnetic field intensity, the radiation intensity, the luminous intensity and the contamination intensity, wherein the system controller is configured to modify the resonant frequency of the variable resonant circuit (590, 600) based on the sensor signal. a radio frequency, RF, signal source (270, 520) configured to generate an RF signal; a first electrode (240, 540) electrically coupled to the RF signal source, wherein the first electrode is configured to receive the RF signal and to convert the RF signal into electromagnetic energy that is radiated by the first electrode; a second electrode (250, 550); a conduit (160, 530) that includes an input port (166, 566), an output port (168, 568), and a chamber (260, 560), wherein the input port (166, 566) and the output port (168,568) are in fluid communication with the chamber (260, 560) and the chamber (260, 560) is configured to receive an electrodeless bulb (280, 580), and wherein the chamber (260, 560) is defined by first and second boundaries that are separated by a distance that is less than the wavelength of the RF signal so that the chamber (260, 560) is sub-resonant, wherein the first electrode (240, 540) is physically positioned at the first boundary, wherein the second electrode (250, 550) is physically positioned at the second boundary, and wherein the first electrode (240, 540), the second electrode (250, 550), and the chamber (260, 560) form a structure that is configured to capacitively couple the electromagnetic energy into the electrodeless bulb when the electrodeless bulb (280, 580) is positioned within the chamber; chamber (260, 560); a variable resonant circuit (590, 600) electrically coupled between an output of the RF signal source and the first electrode (240, 540); a system controller configured to establish and modify a resonant frequency of the variable resonant circuit (590, 600) through control signals that the system controller sends to the variable resonant circuit (590, 600); and one or more of an electric field sensor, a radiation intensity sensor, a luminous intensity sensor and a contamination sensor, respectively configured to sense an electromagnetic field intensity within the chamber, a radiation intensity within the chamber, a luminous intensity within the chamber and a contamination level within the chamber and to send a sensor signal to the system controller indicating, respectively, the electromagnetic field intensity, the radiation intensity, the luminous intensity and the contamination intensity, wherein the system controller is configured to modify the resonant frequency of the variable resonant circuit (590, 600) based on the sensor signal.