Transmission efficiency and beam reception of the SESRI 300 MeV synchrotron injection line

Abstract

SESRI300MeV synchrotron in Harbin Institute of Technology is now under construction and all the equipment have been installed and tested. Before beam commission beginning, beam transport through the injection line is simulated with a full dimension model by tracewin code. Field distribution of RF cavities are calculated with CST and results are substituted in to the tracewin code to generate accurate results. Envelop mode and multi-particles mode are used in the beam simulation with two typical beams (2H%2B and 209Bi32%2B, the lightest beam and the heaviest beam). Both beams are accelerated from 4keV/u to 2MeV/u by a RFQ cavity and two IH-DTL cavities. Then 2H%2B beam is stripped to proton beam by a carbon foil and accelerated to 5.6MeV with the third IH-DTL cavity. Simulation results show that the strength of the magnet and the acceleration field are proportional to the mass charge ratio. Beam transmission ratio and the injection line acceptance are inverse proportional to the beam transverse emittance. 209Bi32%2B beam transmission ratio and beam acceptance(energy spread less than ±0.2%) are 72.16% and 46.72% with transverse emittanceε=0.12πmm·mrad(ECR source output) and ε=0.4πmm·mrad(RFQ output). 2H%2B beam transmission ratio and beam acceptance are 24.19% and 17.89% with ε=0.2πmm·mrad (ECR source output) and ε=0.5ππmm·mrad (RFQ output). In order to obtain high transmission ratio and beam acceptance, transverse emittance should be limited to 0.1πmm·mrad after the RFQ. With this limitation, 209Bi32%2B beam transmission ratio and the acceptance are increased to 96.68% and 92.63%, 2H%2B beam transmission ratio and the acceptance are increased to 74.40% and 68.18%. If two additional quadrupole magnets are added, the 2H%2B beam transmission ratio and beam acceptance can be increased to 90.73% and 83.61%, which will fulfill the long-time operation request. Phase space change process shows that loss of 209Bi32%2B beam is mainly caused by longitudinal defocusing (energy spread and phase width spread), loss of proton beam is caused both by longitudinal defocusing and transverse defocusing (beam envelop spreading), that is why two additional focusing magnets should be added in proton beam acceleration. Results also show that by using field distribution calculation in the simulation process, more influences of the cavity design details can be confirmed, like beam off-axis caused by dipole field in the IH-DTL cavity and beam loss caused by unperfect field in the RFQ. Tracking with field distribution is shown to be a useful method to link the cavity design process, beam line design process, and beam commission process.