Plasma accelerator of short length with closed electron drift

A plasma accelerator of short length with closed electron drift, comprising a main annular channel for ionization and acceleration (24) delimited by parts (22) of insulating material and open at its downstream end (225), at least one hollow cathode (40) disposed outside the main annular channel (24) adjacent to the downstream portion thereof, an annular anode (25) concentric with the main annular channel (24) and disposed at a distance from the open downstream end (225) thereof, first and second means (41, 26) for feeding ionizable gas and respectively associated with the hollow cathode (40) and with the annular anode (25), magnetic means (31 to 33, 34 to 38) for creating a magnetic field in the main annular channel (24), and an annular buffer chamber (23) whose size in the radial direction is at least equal to that of the main annular channel (24) and which extends upstream therefrom beyond the zone in which the annular anode (25) is placed, the second means (26) for feeding an ionizable gas opening out in the annular buffer chamber (23) upstream from the anode (25) into a zone that is distinct from the zone including the anode (25),

• characterized in that the means (31 to 33, 34 to 38) for creating a magnetic field in the main channel (24) are adapted to produce a magnetic field in said main channel (24) that is essentially radial at the downstream end (225) of the channel (24) and has a maximum induction at this level, this magnetic field having a minimum induction in the transition zone situated in the vicinity of the anode (25), the absolute value of the induction of this magnetic field increasing again upstream from the anode (25), at the level of the buffer chamber (23) to produce a magnetic mirror effect, the magnetic field having, between the anode (25) and the downstream end (225) of the channel 24), a concavity which is orientated downwards and produces a focussing of the ions, a region located downstream from the anode (25) having a maximum ionisation density, in that the means for creating a magnetic field comprise a plurality of distinct magnetic field creation means (31 to 33) and inner and outer plane radial pole pieces (35, 34) disposed level with the outlet face on either side of the main channel (24) and interconnected by a central core (38), a yoke (36), and a peripheral magnetic circuit (37) disposed axially outside the main channel (24), the yoke (36) being made up of radial elements situated in the immediate vicinity of the anode (25) and penetrating into the annular buffer chamber (23), communication spaces (13) between the annular buffer chamber (23) and the main channel (24) being left between the radial elements.