Isochronous cyclotron and method of extraction of charged particles from such cyclotron

Superconducting or non-superconducting isochronous sector-focused cyclotron, comprising an electromagnet with at least an upper pole and at least a lower pole that constitute the magnetic circuit, the poles together being made of at least three pairs of sectors (3, 4) called “pairs of hill sectors” and separated from each other by a pair of sectors (3, 4) called “pair of valley sectors”, each pair of hill sectors and each pair of valley sectors comprising an upper sector and a lower sector located symmetrically with respect to the symmetry plane of the cyclotron called the median plane (100) with a vertical gap therebetween which is small for the pairs of hill sectors and which is large for the pairs of valley sectors, said cyclotron being energised by at least one pair of main coils (6), characterised in that:

• (i) at least one pair of hill sectors is significantly longer in the radial direction of the cyclotron than the remaining pairs of hill sectors in order to have at least one pair of extended hill sectors (3) and at least one pair of non-extended hill sectors (4);
• (ii) at the radial extremity of said pair of extended hill sectors (3) is present a groove (7), said groove (7) or said plateau (7′) following the shape of the extracted orbit and the vertical gap at said groove (7) or at said plateau (7′) increasing stepwise in order to have a very steep fall-off or dip (200) in the magnetic field in the extended part of the hill sector.