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Issue Date: 24-Jan-2019
Authors: D'Agostino, Grazia
Title: Orbit dynamics studies of injection, acceleration and extraction of high-intensity beams for the upgrade of the INFN-LNS Superconducting Cyclotron
Abstract: The nuclear research carried out at the LNS laboratory in Catania is mainly allowed by the ion beams delivered by two ion accelerators, a 15 MV Tandem and a k800 Superconducting Cyclotron (the so-called CS). These accelerators deliver to the INFN-LNS scientific community a large variety of stable ion beams with energies ranging from a few MeV/amu to 80 MeV/amu. NUMEN, a nuclear physics project born recently at INFN-LNS, proposes the use of the heavy ion induced double charge exchange reactions as a tool to access quantitative information relevant for nuclear matrix elements for neutrinoless double beta decay. The pilot experiment carried out by the NUMEN team at LNS in Catania has already demonstrated that beam power of the order of 1-10 kW of Carbon, Oxigen and Neon with energies in the range 15-70 MeV/amu are mandatory for the NUMEN reaction study. An additional requirement is that the beam energy resolution should not overcome 1/1000 FWHM. Currently, the maximum CS beam power does not exceed 100 W, so a substantial upgrade of the CS is needed to fulfil the NUMEN requirements. In the frame of the CS upgrade, this thesis is devoted to the simulations of beam dynamics in the LNS cyclotron, with the aim to overcome the current CS limitations and to propose innovative solutions for achieving the beam characteristics in terms of beam power and energy resolution required by the NUMEN project. In this thesis, one of the main topic is the stripping extraction from the CS. The study has allowed to individuate: i) the stripper foil position for each ion to be extracted by stripping, ii) the transverse dimension and direction of the new extraction channel in the CS to be used for all the ions to be extracted by stripping and iii) the features of the magnetic channels to be installed inside the new extraction channel. The second subject of this thesis is the beam injection and acceleration up to the extraction in the LNS cyclotron. This study has been possible thanks to the development of the beam tracking model of the INFN-LNS Superconducting Cyclotron, performed in collaboration with the Ion Beam Applications company. This work has shown that the total transmission efficiency from the CS bore injection up to the extraction system, simulating also a process of energy selection outside the CS according to the NUMEN requirement, is only around the 2.7%, a low value compared to the expected value of 15%. The energy selection process is the main cause of the low total efficiency. We demonstrated that the major contribution to the beam energy spread at the extraction in the LNS cyclotron is due to the large emittance circulating in the LNS cyclotron. The energy gain per turn contributes only partially to the energy spread at the extraction but, in any case, it sets an inferior limit on the minimum energy spread obtainable in the CS cyclotron. This value stays around 0.2%, about the twice of the NUMEN requirement. This thesis allows also to establish a roadmap of the goals and milestones to be achieved in next months/years. According to the simulation results, the goal of reduction of the beam energy spread at the extraction can be achieved only paying attention on the ion beam production and transport to the CS, since these processes determine the emittance in the horizontal and vertical phase spaces of the beam entering the CS central region. Also a good quality of the accelerated beam will be necessary since an initial beam offset in the central region implies a further increase of the beam energy spread at the extraction. This work has also shown that an increase of the injection efficiency is possible by applying higher dee voltages than the nominal one and modifying slightly the existing central region design. These changes have allowed to increase the injection efficiency up to a factor of about 1.7.
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