A sterilisation or disinfecting system in which non-thermal plasma is generated in pulses, in which pulses of microwave frequency energy are used to sustain each plasma pulse, and a detectable characteristic of each pulse of microwave energy is used to trigger a radiofrequency strike pulse which strikes the plasma. The system includes a strike signal generation circuit arranged to condition and/or process the signal from the microwave signal coupler to form a control signal based on the detectable characteristic, which may be the rising edge or amplitude of the pulse.
