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Design of an inflector for the triumf cyclotron Root, Laurence Wilbur

Abstract

This thesis is considered with the problem of the electrostatic inflection of an axially directed ion beam into the magnetic median plane at the center of a cyclotron. The analysis is applied to the case of the TRIUMF 500 MeV H cyclotron, where the beam from the ion source has an energy of 300 keV and the central magnetic field is approximately 3.0 kG. The properties of several inflector designs are briefly considered, and it is shown that the spiral inflector is most flexible, because it has two free parameters which may be varied to optimize the position and velocity of the ion beam at the entrance to the cyclotron injection gap. This type of inflector was therefore singled out for more detailed study. The first order optical properties of a spiral inflector operating in the presence of a homogeneous magnetic field were calculated using an analytic method similar to the one used by Belmont and Pabot. It was found that the accuracy of their calculation could be improved considerably by including an additional first order term in their electric field approximation. The origin of this additional term is studied in detail. Numerical results are presented for a typical spiral inflector design. The electric potential distribution inside a spiral inflector was calculated by solving Laplace's equation numerically in three dimensions. Trajectories were then numerically integrated through this potential distribution in the presence of a homogeneous magnetic field. The results obtained in these calculations were found to be in good agreement with the previous results obtained using the analytic approach. The characteristics of a spiral inflector operating in the presence of a non-homogeneous magnetic field similar to the one in the TRIUMF cyclotron is proposed. The optical properties of the proposed TRIUMF design have been calculated assuming an idealized electric field distribution within the body of the inflector. The spiral inflector has been constructed with the aid of a numerically controlled milling machine for cutting the electrode surfaces. A description is given of the milling procedure and of the computer program which was used to control the movement of the tool head.

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