A plasma source for generating a disinfecting and/or sterilizing gas mixture, including: - an ionization chamber having: - a dielectric tubular portion, - an inflow port for feeding a gas or gas mixture into the chamber, - an outflow port for exhausting the disinfecting and/or sterilizing gas mixture out of the chamber, - a first electrode positioned inside the dielectric tubular portion, and - a second electrode positioned outside the dielectric tubular portion; - a high voltage source having a high voltage output terminal (24, 26), wherein an electrical conductor (28, 30) connects the output terminal (24, 26) to the first or second electrode (16, 20); and - a forced gas cooling system for cooling the ionization chamber, characterized in that, the forced gas cooling system is arranged for forcing a cooling gas flow onto the dielectric tubular portion in a direction substantially orthogonal to a longitudinal axis of the tubular portion, wherein the forced gas cooling system comprises an elongate funnel having two sidewalls (36a, 36b) tapering towards the dielectric tubular portion and extending along the longitudinal axis, said forced gas cooling system further comprising at least one fan, wherein the funnel is arranged between at least one fan and the dielectric tubular portion and configured to force the cooling gas flow by the fan into the funnel towards its narrow end where the two sidewalls converge, wherein said narrow end has an elongate exit opening disposed adjacent the dielectric tubular portion and extending along the longitudinal axis, wherein the exit opening is arranged facing the dielectric tubular portion and configured to force the cooling gas flow exiting the opening to flow onto one side of the tubular portion in the direction substantially orthogonal to the longitudinal axis. - an ionization chamber having: - a dielectric tubular portion, - an inflow port for feeding a gas or gas mixture into the chamber, - an outflow port for exhausting the disinfecting and/or sterilizing gas mixture out of the chamber, - a first electrode positioned inside the dielectric tubular portion, and - a second electrode positioned outside the dielectric tubular portion; - a dielectric tubular portion, - an inflow port for feeding a gas or gas mixture into the chamber, - an outflow port for exhausting the disinfecting and/or sterilizing gas mixture out of the chamber, - a first electrode positioned inside the dielectric tubular portion, and - a second electrode positioned outside the dielectric tubular portion; - a high voltage source having a high voltage output terminal (24, 26), wherein an electrical conductor (28, 30) connects the output terminal (24, 26) to the first or second electrode (16, 20); and - a forced gas cooling system for cooling the ionization chamber, characterized in that, the forced gas cooling system is arranged for forcing a cooling gas flow onto the dielectric tubular portion in a direction substantially orthogonal to a longitudinal axis of the tubular portion, wherein the forced gas cooling system comprises an elongate funnel having two sidewalls (36a, 36b) tapering towards the dielectric tubular portion and extending along the longitudinal axis, said forced gas cooling system further comprising at least one fan, wherein the funnel is arranged between at least one fan and the dielectric tubular portion and configured to force the cooling gas flow by the fan into the funnel towards its narrow end where the two sidewalls converge, wherein said narrow end has an elongate exit opening disposed adjacent the dielectric tubular portion and extending along the longitudinal axis, wherein the exit opening is arranged facing the dielectric tubular portion and configured to force the cooling gas flow exiting the opening to flow onto one side of the tubular portion in the direction substantially orthogonal to the longitudinal axis.