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UBC Theses and Dissertations

Magnetic field study for a new generation high resolution mass separator Marchetto, Marco


The work presented in this thesis is part of the design of the high resolution mass separator for the ARIEL facility under construction at TRIUMF, located in the UBC campus. This new facility, together with the existing ISAC facility, will produce rare isotope beams for nuclear physics experiments and nuclear medicine. The delivery of such beams requires a stage of separation after production to select the isotope of interest. The required separation is expressed in terms of resolving power defined as the inverse of the relative mass difference between two isotopes that need to be separated. The higher the mass the greater the resolving power required. The challenge is the separation of two isobars rather than two isotopes that by definition require a much lower resolving power. A resolving power of twenty thousand is the minimum required to achieve isobaric separation up to the uranium mass. The state of the art for existing heavy ion mass separators is a resolving power in the order of ten thousand for a transmitted emittance of less than three micrometers. The more typical long term operational value is well below ten thousand for larger emittances. The main goal of this project is to develop a mass separator that maintains an operational resolving power of twenty thousand. Different aspects influence the performance of the mass separator; the two main ones are the optics design and the field quality of the magnetic dipole(s) that provides the core functionality of the mass separator. In this thesis we worked from the hypothesis that minimizing the magnetic field integral variation with respect to the design mass resolution is equivalent to minimizing the aberration of the optical system. During this work we investigated how certain geometric parameters influence the field quality, as for example the dependency of the field flatness on the magnet pole gap. We also developed a new technique to control the mesh in the finite element analysis to facilitate particle tracking calculations. Beyond demonstrating our hypothesis, we ultimately produced a final magnet design where the field integral variation is less than one part in one hundred thousand.

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