NOVELTY - The slipping plasma arc generator comprises a reactor (10) internally delimits a closed enclosure (12) having reactive gas and two removable electrodes that are connected to a source of voltage to start and maintain the reactive gas discharge. The removable electrodes are axially mounted to other electrodes to vary the distance between the electrodes (20). The reactor wall (18) constitutes one of the electrodes, where the other electrode is arranged in the form of a central electrode in an axially removable point into the reactor.    USE - Useful for motor vehicles equipped with a fuel cell system.    ADVANTAGE - The plasma generator controls the operation of plasma in order to free from variations of parameters such as temperature and pressure.    DETAILED DESCRIPTION - The slipping plasma arc generator comprises a reactor (10) internally delimits a closed enclosure (12) having reactive gas and two removable electrodes that are connected to a source of voltage to start and maintain the reactive gas discharge. The removable electrodes are axially mounted to other electrodes to vary the distance between the electrodes (20). The reactor wall (18) constitutes one of the electrodes, where the other electrode is arranged in the form of a central electrode in an axially removable point into the reactor. The reactor comprises a localized shrinking section to reduce inter-electrodes distance. The reactor is placed at the vicinity of the free end of the electrode. The central electrode is assembled on a support connected to the reactor wall by an endless mechanical system. The shrinking section comprise zones of regularly varying sections. INDEPENDENT CLAIMS are included for:    (1) a system;    (2) a device of reforming hydrocarbon or its mixture for the production of hydrogen; and    (3) a pollution control device fixed to a board of a vehicle.    DESCRIPTION OF DRAWING(S) - The diagram shows a plasma generator:    Reactor; (10)    Closed enclosure; (12)    Openings; (14, 16)    Reactor wall; (18)    Electrode point. (20)