Abstract
The large-bore magnets in the injection system of a high-intensity proton synchrotron are placed close to each other as compared to their bore sizes. In such cases, the magnetic cores interfere with the fringe fields of adjacent magnets. Moreover, the incoming beam passes through several kinds of time-varying fields along the injection line and the nonlinear field region of the ring quadrupole magnet. The beam behavior under these conditions is analyzed by using the Runge-Kutta method. Although the interference of the magnetic fields does not result in emittance growth, it produces a closed-orbit distortion. Field fluctuations of the time-varying field cause an emittance growth and the nonlinear field deforms the beam profile in phase space of the incoming beam. These effects lead to the modification of the injection scheme. This study focuses on the particle tracking with magnetic field interferences during the early stage of beam commissioning, when the space charge force is not important.
Highlights
The rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) [1] is designed to have a very large transverse acceptance of 324 mm mrad in order to achieve beam power in the order of megawatts
Test particles were generated at 10.0895 m upstream of the stripping foil, s 72:0235 m; three emittance ellipses of 216, 162, and 108 mm mrad were used, where the emittance of 216 mm mrad corresponds to the painting size of an injected beam for both phase-space planes
A beam-injection process with field interferences was simulated by a three-dimensional particle tracker without taking into account the space charge force
Summary
The rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) [1] is designed to have a very large transverse acceptance of 324 mm mrad in order to achieve beam power in the order of megawatts. The injected beam passes through the regions where the linearity of the magnetic field is not preserved. These contributions to the painting beam injection of the J-PARC RCS were investigated. The beam from the LINAC is injected into the ring by using the charge exchange and phase-space painting methods in order to accumulate the high-intensity protons. One is the shift-bump system to form an orbit offset of x 90 mm at the carbonstripping foil, and the other is the paint-bump system for the beam painting. The paint-bump system has a time dependence for painting the RCS beam in the phase space of 216 mm mrad with an injected beam of 6 mm mrad.
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