A hand held plasma applicator for a plasma sterilisation system, the applicator comprising: an enclosed plasma generating region having: a gas inlet for receiving gas from a gas feed, an energy inlet for receiving microwave energy, and an outlet for delivering plasma out of the plasma generating region towards matter to be sterilised； a microwave connector for launching microwave power from a microwave cable into the energy inlet； and an impedance adjustor arranged to control the impedance within the plasma generating region beyond the microwave connector when gas and microwave energy are delivered thereto.
