Device for quantitative display of the current density within a charged-particle beam

A device for displaying the distribution of current density within a beam of electrically charged particles, said device comprising a support plate of electrically insulating material having a surface area at least equal to the cross-sectional area of the beam, m.times.n=q electrically conducting elements fixed on the support plate being so arranged as to form a lattice of elements which consist of m lines and n columns and are intended to intercept the charged particles of the beam to a partial extent, said elements being electrically connected to systems which serve to process electrical signals collected by said elements and to display the density of the beam at m.times.n points of its cross-section, said device having a screen plate provided with m.times.n holes, said screen plate being placed above said support plate, each of said m.times.n holes being placed directly above one of said elements, said screen plate which is of electrically conducting material is positively biaised, said charged particle beam being an ion beam.