Disclosed is a radio-frequency plasma generating system including a radio-frequency generator and a plasma source, the radio-frequency generator being inductively or capacitively coupled to the plasma source through a resonant electric circuit, the radio-frequency generator being adapted to receive direct current power from a direct current power supply and for generating radio-frequency power at a frequency f, the radio-frequency power including a reactive radio-frequency power oscillating in the resonant electric circuit and an active radio-frequency power absorbed by the plasma. The radio-frequency plasma generating system includes a unit for measuring an efficiency of conversion E of direct-current power to active radio-frequency power absorbed by the plasma and a unit for adjusting the frequency f as a function of the measured efficiency of conversion E to maintain the efficiency of conversion E in a predetermined range within a RF plasma operational range.