3D simulation of electric field in the inflector of CC-12 cyclotron

Abstract

The inflector is intended to inject the beam formed by the external injection system into the central area of the cyclotron along the helical trajectory. The quality of the inflector simulation significantly affects the characteristics of the accelerated beam. Different geometrical models describing field-forming elements of the inflector are given in the paper. The results of the field computations with the ANSYS and ISFEL3D codes are given.The CC-12 compact cyclotron has been designed and manufactured in the JSC "NIIEFA" to be used for production of medical radioisotopes [1]. A part of this cyclotron is an external injection system comprising a multipole source of H − ions, two focusing electrostatic lenses, two electromagnetic correctors and inflector [2]. The inflector transfers the beam from the horizontal injection channel to the vertically located median plane of the cyclotron. The electric field of the inflector jointly with the magnetic field of the cyclotron forces the beam particles to follow a helical trajectory.Similar to a field of an ordinary capacitor, the field in the inflector is formed by a pair of spiral-twisted electrodes. The electrode twist angle non-linearly changes from zero at the inflector beam input to a maximum value at its output. The gap between electrodes decreases, on the contrary. Electrodes are made on an NC machine-tool and then are fixed onto an insulator inside an earthed shield. Equal potentials of opposite sign are applied to electrodes. The inflector provides 3D centering of the beam and plays an important role in matching the emittance to the acceptance of the cyclotron. The quality of the inflector calculation significantly affects the intensity of the extracted beam.Computer designing of a helical inflector is an iterative process, and it usually consists of the following stages: 1) choice and variation of parameters specifying the reference trajectory (the beam axis) and the shape of electrodes; 2) simplified analysis of the beam characteristics in paraxial fields neglecting edge effects; 3) complete 3D simulation of the field and analysis of the beam dynamics in it. The results presented in the report were obtained by using the ANSYS program package [3]. To calculate the field, three geometrical models were developed, in particular, models N 1, 1A and 2.In model 1 all the details of the inflector assembly, which have a weak affect on the field in the beam area, are neglected. Inflector electrodes are replaced with a pair of spiral-twisted plates of a finite thickness, Fig.1. The shape of the plate is reconstructed by the SolidWorks code [4] from an ordered set Figure 1. Inflector geometry in the Model 1 Figure 2. Inflector geometry in the Model 2 of points and then is exported to the ANSYS.Model 1A is a parametric one. It is intended for electrodes with piecewise-plate surface, Fig.3, which can be reconstructed by the ANSYS integrated tools. Model 2 operates with an actual shape of electrodes and accounts for all necessary details reconstructed by the SolidWorks.978-1...