A nozzle for a plasma generator. The nozzle comprises a body (1) defining a plasma generating chamber (25) having a gas inlet (12) at one end and plasma outlet (10) at the opposite end defining a flow direction from the inlet to the outlet. An inner electrode (20) is positioned around an inner wall of the body. An outer earthed electrode (22) is provided around an outer wall of the body. The inner (20) and outer (22) electrodes overlap one another in the flow direction.