Kolinko S. Features of ion beam formation in quadrupole lens systems with distorted magnetic fields structure

The thesis contains theoretical and experimental studies of influence of magnetic field distortions caused by misalignments of quadrupole lenses in the probe-forming systems on the ion beam formation processes. An experimental technique and a diagnostic device for precise centering and determination of the multipole field structure of the magnetic quadrupole lenses were developed and tested. The lenses tilts and shifts were found to cause probe shifts on a target, degradation of the probe current density at the distribution peaks, and growth of the probe size. The first lens in the "Russian quadruplet" and the second lens in the triplet along the beam are the most sensitive to the misalignments. Sustaining axial position of the probe during the lens alignment processes was shown to allow minimizing the field distortions negative affect. The experiments show that the developed diagnostic device determines attitude of lens physical axis with a 2 um accuracy and parasitic field components with a 10 % accuracy for a sextupole and a 20 % accuracy for an octupole. A quantitative dependence of the axis position, multipole field structure of the magnetic quadrupole lens on the power supply parameters, core temperature, and residual magnetization was experimentally determined. A number of applied studies were performed.