The growing demand in the field of discovering and investigating exotic nuclei by means of fragment separators yields challenging restrictions on future facilities. The main task of a fragment separator is the in-flight separation of many different species of nuclides, produced with an ion beam on a target. To achieve the best resolution and capture of rare nuclei, maximal beam illumination of the apertures of the ion-optical elements is required. Many fragment separators have a wide operation range of the magnetic rigidity Brho. Moreover, frequent changes of Brho are required during experiments. Often magnets are operated in the saturation region of the iron yokes, leading to local changes of the magnetic field (B-field) distributions and the corresponding particle trajectories. In such cases it is important to have a fast ion-optical model with good predictability, which considers the real field distributions and the saturation.
This thesis describes the development of a general approach to provide a fast and accurate ion-optical model (Taylor transfer map) of large aperture magnets starting from simulated or measured 3D B-field distributions. To produce highly accurate transfer map, a B-field has to be represented by 3D polynomials. It is crucial that the whole transversal aperture is described by a single polynomial, whereas many polynomials might be used in the longitudinal direction. High non-uniformity of the B-field makes this problem more complicated, especially for the regions near the pole shoe ends. The problem was solved by means of a combination of the Surface Integration Helmholtz Method (SIHM) and the Least Squares (LS) method. The approach was extended further for obtaining the B-field polynomial representation dependent on both: the coordinates and the excitation current. This representation allows to produce Brho dependent transfer maps, which can be useful for the optimization of the separator settings for different experiments.
The method was tested using the analytical field model, based on a configuration of thin wires and a Biot-Savart law, resulting in a high stability against the errors in the input B-field. The rigidity dependent transfer maps were generated for the normal conducting dipole of the Super-FRS preseparator. The ion-optical study of the preseparator in the separator as well as in the spectrometer modes were conducted
