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Specificities for High-resolution beam lines

In order to deliver very small-sized ion beam, the combining of slits, collimators and electromagnetic lenses (Q-poles) are used. They allow the shaping and the beam focusing so as to have micronic beam size.


Vue interieure


The object chamber


The object chamber is constituted of two consecutive sets of slits used to cut off most of the beam delivered by the accelerator. Indeed, to avoid an overheating of the system, a first stage of tungsten slits, equipped with a cooling system, had to be introduced to reduce the beam current. It is followed by a second stage of precisely polished slits made of tantalum carbide used to define the beam geometry. Finally, when a very precise object size is needed, a third motorized stage can be used to position a circular shape Platinum–Iridium collimator of calibrated size in the beam path. [1]



The focusing devices


The focusing is possible by using electromagnetic lenses (Q-poles) which are associated at least by two in order to focalised the beam according to both x- and y-axis.


For the microbeam line, a "triplet" system is used to obtain micron and sub-micron beam size (i.e. from 5 µm to 300 nm) depending on the size of the object (collimator) selected in the object chamber. To come down in resolution, two supplementary Q-poles ("doublets") are added to the "triplet" system so as to be in a "quintuplet" mode. This quintuplet mode will allow to reach a resolution around 150 nm with the smallest collimator.


For the micro-irradiation cell beam line, the focusing is provided by the use of a "quadruplet" system which allows to reach beam sizes between 10 to 1 µm according to the size of the object selected in the object chamber.




[1] Barberet P. et al. 2009 Nuc Instr Meth Phys Res B 267, 2003