Beam optics transport and fundamental processes involving a charge breeder in the upgraded SPIRAL1 facility

The thesis describes with a great deal of details the efforts done to understand the physical processes inside the SPIRAL1 ECR charge breeder. This device accepts the mono-charged ion beams of different masses and charge bred them to higher charge states. In the framework of the SPIRAL1 upgrade, the R and D of charge breeding technique is of primary interest for optimizing the yields of radioactive ion beams (RIBs). In this context, the thesis begins with a theoretical discussion dealing with the different Target Ion Sources (TIS) at upgraded SPIRAL1 facility, Low Energy Beam Transport system and fundamentals of plasma physics relevant for the production of highly charged ions in ECR ion source plasmas. This is followed by description of the technological issues affecting the 1⁺/N⁺ charge breeding technique. In the final chapter, the effect of axial magnetic field gradient, position of deceleration tube and 1⁺ beam emittance were studied to understand their influence on the performance of the SP1 CB (charge breeding efficiency). The optimization of axial magnetic field gradient shows that the charge breeding efficiency is strongly influenced by the variation of the two soft iron rings positions around the permanent magnet hexapole. It has been deduced from the observations that the charge breeding efficiency improves when the emittance of 1⁺ beam is smaller and the position of deceleration tube is close to the entrance of SP1 CB. At the same time, the charge breeding times of K charge states (1⁺, 2⁺, 4⁺ and 9⁺) were estimated by pulsing the injected K¹⁺ beam. The results from these investigations revealed the optimum SP1 CB tuning parameters that can minimize the value of charge breeding time and maximize the charge breeding efficiency of the high charge states of K.In order to investigate the 1⁺ ion beam transport (shooting through mode) through the SP1 ECR charge breeder and the fundamental physical mechanisms involved in charge breeding process, several experiments were carried out in the framework of this thesis (the interaction of 1⁺ ion beam of different masses (Na⁺ and K⁺) in different background plasma species (He and O₂)). The data from these experiments (potentials, emittance of 1⁺ beam, deceleration tube position, magnetic field and pressures) were collected and given as inputs to the numerical simulation tools (SIMION, TraceWin and MCBC). The simulations were performed in three steps: i) simulation of the 1⁺ beam transmission through the breeder to verify the ion losses and showed good agreement with the experimental results. ii) simulation of 1⁺ beam transmission through a potential map that reflects the presence of the ECR plasma (without collisions) and reproduced the DeltaV curves of 1⁺ and 2⁺. It also revealed the role of Coulomb collisions in the charge breeding process leading to a necessary detailed analysis using Monte-Carlo Charge Breeding code (MCBC). iii) MCBC models Coulomb collisions of the injected 1⁺ ion beam in an ECR plasma and atomic processes which includes ionization and charge exchange. The code finally able to reproduce the low charge state (1⁺ and 2⁺) experimental trends by varying each plasma parameter (plasma density, ion temperature and electron temperature) independently. A novel simulation strategy has been developed to estimate the plasma parameters from charge breeding simulations. Finally, Simulations demonstrated that the ion temperature, the plasma density and 1⁺ ion beam quality as critical parameters influencing the 1⁺ ion capture and the reasons for the difference in charge breeding efficiencies between Na (in Helium plasma) and K (in Helium and Oxygen plasma) species were discussed. (author)