NOVELTY - The ozone generator device (4) comprises a microwave source, a microwave resonant structure comprising a plasma generator, a unit (39) for transmitting the microwaves from microwave source to the resonant structure, a reaction chamber introducing the plasma generator, a unit (10) for introducing the fluid in the reaction chamber, and a unit (12) for extracting the chemical species from the reaction chamber. The resonant structure comprises a wired resonant element of quarter wave antenna type, and a mass surface in the form of plane or truncated cone.    USE - The ozone generator device is useful for the production of a chemical species from a fluid e.g. air comprising dioxygen (all claimed).    ADVANTAGE - The ozone generator device is compact, and ensures energy efficient production of the chemical species from air without preliminary drying of the air.    DETAILED DESCRIPTION - The ozone generator device (4) comprises a microwave source, a microwave resonant structure comprising a plasma generator, a unit (39) for transmitting the microwaves from microwave source to the resonant structure, a reaction chamber introducing the plasma generator, a unit (10) for introducing the fluid in the reaction chamber, and a unit (12) for extracting the chemical species from the reaction chamber. The resonant structure comprises a wired resonant element of quarter wave antenna type, and a mass surface in the form of plane or truncated cone. The quarter wave antenna type element comprises a main cone, and first and second ends connected to the main cone. The first end of the element is connected to the mass surface. The main cone is parallel to the mass surface. The second end of the element is free and projected towards the mass surface from the main cone, and has an antenna electrode parallel to the mass surface. The mass surface has a mass electrode corresponding to the antenna electrode, where the antenna electrode and the mass electrode form a set of plasma generator. A cylindrical sheath made of a dielectric material is defined in the reaction chamber. A chamber is arranged for introducing the fluid in the resonant structure and fluid evacuation chamber. The reaction chamber provides a fluid connection between the fluid chamber and the evacuation chamber. The microwave source is adapted to generate microwaves at a frequency of 630 MHz. A unit comprising nitrogen is arranged for dissociating the dioxygen made of oxygen atoms in the presence of microwaves INDEPENDENT CLAIMS are included for:    (1) an installation for treatment of a fluid in a closed circuit; and    (2) a process for production of a chemical species.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic sectional view of a device for the production of a chemical species from a fluid.    Ozone generator device (4)    Unit for introduction of fluid (10)    Unit for extraction of species (12)    Wall (34)    Transmission unit (39)    Three holes. (46)