PCT No. PCT / FR97 / 00906 Sec. 371 Date Jan. 21, 1999 Sec. 102(e) Date Jan. 21, 1999 PCT Filed May 23, 1997 PCT Pub. No. WO98 / 53201 PCT Pub. Date Nov. 26, 1998The
ion beam concentration apparatus for a
plasma thruster having closed
electron drift comprises: a) an essentially frustoconical flared magnetic
pole piece (63) open at both ends and designed to be situated downstream from the outlet plane of a
plasma thruster having an annular
ionization and acceleration channel (1) and
peripheral and central pole pieces (3, 4) disposed on either side of the annular channel (1) to produce an essentially radial
magnetic field in an outlet plane (14) perpendicularly to the axis of the annular channel (1); and b) an additional
peripheral magnetic circuit (60; 80) connecting the downstream end of the flared magnetic
pole piece (63) to said
peripheral pole piece (3), the flared magnetic pole piece (63) co-operating with the additional peripheral
magnetic circuit (60; 80) and with the peripheral and central pole pieces (3, 4) to define the shape of the
magnetic field downstream from the annular channel (1) in such a manner as to constrain the
ion beam emitted by the annular channel (1) to remain within an essentially conical zone whose predetermined angle at the apex is defined by the angle at the apex of the flared magnetic pole piece (63).