Computer simulation of the space charge dominated beam dynamics for external injection into the JINR Phasotron
A project of increasing the beam intensity of the 660 MeV JINR proton Phasotron up to 50 µA by an external injection of the H − beam with energy of 5 MeV is now under design. Computer simulation of the space charge dominated beam dynamics in Phasotron is reported. As follows from the simulation, the capture efficiency does not change too much when the beam space charge is taken into account.
EXTERNAL INJECTION INTO PHASOTRON ( COMPUTER SIMULATION )
The paper summarizes the computer simulation data of the beam capture in acceleration at the external injection into the JINR Phasotron (Fig.1) for the injection energies 1.5, 3.0 and 5.0 MeV. The simulation takes into account the particle starting phase and injection time, the horizontal and axial beam emittances and the influence of the particle scattering by foil on the increase in the axial emittance. Simulation is fullfilled for the experimental magnetic field and RF program. Calculation shows the 15% capture efficiency for the injection energy 1.5 MeV and 24% for 5.0 MeV (the particle injection time of 80 µs).
Center-region geometry of the Berkeley 88-inch cyclotron†
In order to determine the proper position of the dee edge, ion source, puller, and beam-defining clipper with respect to the magnet center, measurements of the structure of the electric field in the surroundings of the ion source were made with a half-scale model in an electrolytic tank. The acceleration process during the first three revolutions was studied for different geometries and starting phases, by a graphical approximation method for orbit plotting. A more detailed study was then made to determine initial conditions—such as orbit-center distribution, energy spread, axial focusing, and energy bunching—as functions of the center geometry and starting phase. By increasing the particle path length during the first half revolution approximately 20 deg—achieved by azimuthal displacement of the source—good results were obtained. The ion-start location was finally determined so as to bring the beam close to an equilibrium orbit at 10 in. radius. This was done with an orbit code, modified to take account of the increased transit time through the acceleration gap of smaller radii. Some experimental results of changes in the cyclotron beam quality, caused by changes in the ion-starting conditions, are presented.