| 摘要 |
The present invention relates to a cyclotron capable or producing a first beam of accelerated charged particles defined by a first <<charge-over-mass>> ratio (q/m) or a second beam of accelerated charged particles defined by a second <<charge-over-mass>> ratio (q/m)' less than said first <<charge-over-mass>> ratio (q/m), said cyclotron comprising: an electromagnet comprising two poles, preferably an upper pole and a lower pole, positioned symmetrically relatively to a middle plane perpendicular to the central axis of the cyclotron and separated by a gap provided for circulation of the charged particles, each of said poles comprising several sectors positioned so as to have an alternation of areas with a narrow gap called <<hills>> and areas with a wide gap called <<valleys>>; a main induction coil for generating an essentially constant main induction field in the gap between said poles and a means for modifying the magnetic field profile according to the <<charge-over-mass>> ratio of the particles to be accelerated, comprising a ferromagnetic part present in one of said valleys and extending radially from a region close to the center to the periphery of the cyclotron, said ferromagnetic part forming a magnetic circuit with the bottom of said valley, so as to generate a sufficiently large additional magnetic field for accelerating particles of said first beam having said first charge-over-mass ratio (q/m); characterized by: a secondary induction coil positioned around said ferromagnetic part so as to be able to induce a magnetic field opposing the magnetic field induced in said ferromagnetic part by said main induction coil and reduce the contribution of the additional magnetic field provided by said ferromagnetic part for accelerating the particles of said second beam having said second charge-over-mass ratio (q/m)'.
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