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The ion source comprises a cathode, an intermediate electrode and an anode with two ionization chambers between these electrodes, means for producing an axial magnetic field, means for applying a DC voltage between an intermediate electrode and the anode, ion extraction means and an alternating volt

The ion source comprises a cathode, an intermediate electrode and an anode with two ionization chambers between these electrodes, means for producing an axial magnetic field, means for applying a DC voltage between an intermediate electrode and the anode, ion extraction means and an alternating voltage generator between the cathode and the intermediate electrode.

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An ion source having at least two ionization chambers and at least three electrodes, comprising successively along a longitudinal direction a cathode, an intermediate electrode with a first aperature at its center and an anode with a second aperature at its center, the first ionization chamber being

An ion source having at least two ionization chambers and at least three electrodes, comprising successively along a longitudinal direction a cathode, an intermediate electrode with a first aperature at its center and an anode with a second aperature at its center, the first ionization chamber being disposed between said cathode and said intermediate electrode and the second ionization chamber being disposed between said intermediate electrode and said anode, comprising: means for introducing an ionizable medium in said first ionization chamber in the vicinity of said cathode; means for permanently applying, in operation, an A.C. voltage, at a frequency between about 20 and about 50 kHz, between said cathode and said intermediate electrode, thereby producing, in said first ionization chamber, a first plasma which remains ignited in a steady state; means for applying, between said intermediate electrode and said anode, a D.C. voltage of a polarity such that said anode is maintained positive relative to said intermediate electrode, thereby extracting essentially electrons from said first ionization chamber into said second ionization chamber through said first aperature in said intermediate electrode, said electrons producing a second plasma in said second ionization chamber; means for producing a longitudinal magnetic field between said intermediate electrode and said anode, thereby constricting said second plasma in said second ionization chamber; and means for extracting ions from said second ionization chamber through said second aperature in said anode.