Abstract
The transverse impedance of eight extraction pulsed kicker magnets is a strong beam instability source in the 3-GeV rapid cycling synchrotron (RCS) at the Japan Proton Accelerator Research Complex. Significant beam instability occurs even at half of the designed 1 MW beam power when the chromaticity ($\ensuremath{\xi}$) is fully corrected for the entire acceleration cycle by using ac sextupole (SX) fields. However, if $\ensuremath{\xi}$ is fully corrected only at the injection energy by using dc SX fields, the beam is stable. In order to study realistic beam instability scenarios, including the effect of space charge and to determine practical measures to accomplish 1 MW beam power, we enhance the orbit particle tracking code to incorporate all realistic time-dependent machine parameters, including the time dependence of the impedance itself. The beam stability properties beyond 0.5 MW beam power are found to be very sensitive to a number of parameters in both simulations and measurements. In order to stabilize a beam at 1 MW beam power, two practical measures based on detailed and systematic simulation studies are determined, namely, (i) proper manipulation of the betatron tunes during acceleration and (ii) reduction of the dc SX field to reduce the $\ensuremath{\xi}$ correction even at injection. The simulation results are well reproduced by measurements, and, as a consequence, an acceleration to 1 MW beam power is successfully demonstrated. In this paper, details of the orbit simulation and the corresponding experimental results up to 1 MW of beam power are presented. To further increase the RCS beam power, beam stability issues and possible measures beyond 1 MW beam power are also considered.
Highlights
The 3-GeV rapid cycling synchrotron (RCS) in the Japan Proton Accelerator Research Complex (J-PARC) acts as a high-intensity proton beam source for the neutron and muon production targets in the Material and Life Science Experimental Facility (MLF), as well as the injector for the main ring synchrotron (MR) [1]
We studied with dynamic variations of the RCS parameters, injected beam parameters, and the beam intensity, which eventually give a scope to study in a wide range of the space charge regime or the above space charge parameter Δν/νs
We present a comparison between simulated and measured results of time-dependent beam survival studied in the presence of strong space charge at the previous injection energy of 0.181 GeV for a beam power of 0.375 MW
Summary
The 3-GeV rapid cycling synchrotron (RCS) in the Japan Proton Accelerator Research Complex (J-PARC) acts as a high-intensity proton beam source for the neutron and muon production targets in the Material and Life Science Experimental Facility (MLF), as well as the injector for the main ring synchrotron (MR) [1]. One can generally estimate the beam instability threshold by calculating the growth rate of the beam instability This depends on many parameters, of which the beam intensity, chromaticity, and betatron tunes are the most significant [11]. A precise numerical simulation that considers the details of these variations as well as the effects of space charge and other beam instability sources is required. The motivation of the present work was to study realistic beam instability scenarios in the J-PARC RCS while incorporating all relevant dynamics including the effect of the space charge. In order to perform realistic simulations of the RCS, we introduced numerous enhancements to the code to cope with all relevant time-dependent machine parameters and error sources, as well as realistic transverse and longitudinal injection painting. The simulation results were well reproduced by measurements, and an acceleration to 1 MW beam power has been successfully demonstrated
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