Optimization of the probe-forming system for a scanning nuclear microprobe based on the ÉGP-10 electrostatic tandem accelerator

The probe-forming system of a nuclear scanning microprobe based on the parametric multiplets of quadrupole lenses is optimized. The optimization is aimed at creating an ion probe with energy of several MeV that produces a micrometer spot on the target at a current of ∼100 pA. The influence of different geometric and physical parameters on the ion-optical properties of the probe-forming systems considered is determined. The optimization is carried out by varying the parameters specifying a given parametric multiplet, and its efficiency is found from a quality criterion that takes into account the beam current for given sizes of the spot and target. The beam parameters at the entrance to and at the exit from the éGP-10 electrostatic tandem accelerator (produced by the VNIIéF) are involved in the optimizing calculations. These are the maximal energy, normalized brightness, transport conditions, and chromatic inhomogeneity of the beam (i.e., the energy straggling of beam particles). Allowance is also made for the parasitic components of the magnetic quadrupole lens field, which arise because of quadrupole symmetry breaking by technological and physical reasons.