Uniform-beam irradiation technique using multipole magnets
A technique of high-quality uniform-beam irradiation has been developed using multipole magnets for materials science and life science. This irradiation technique based on uniformization of the transverse beam intensity distribution by the nonlinear focusing forces enables to perform uniform irradiation at any point over the whole area of a large sample at a constant low particle fluence rate.
Two couples of sextupole and octupole magnets have been installed in a beam line of the cyclotron, as shown in Fig. A. To form a high-quality uniform beam, various kinds of experimental and theoretical R and D's are in progress such as beam conditioning by multiple scattering, 2D beam profile measurement, beam intensity attenuation for a wide-ranging change of the fluence rate, and theoretical/numerical studies on beam dynamics of ion beams under the nonlinear focusing forces.
Figure B shows a numerical result of 2D beam intensity distribution on the target when the Gaussian beam tail is folded by the octupole forces.
Fig. A : Beam line for uniform-beam formation.
An experimental chamber will be installed at the end of the beam line
Fig. B : Numerical simulation result of tail-folding of the beam by octupole magnets.
(a) 2D intensity distribution and (b) 1D intensity distribution on the target.
A uniform area of about 10 cm x 10 cm can be formed.