Optimization and analysis of a low-energy injector for high-intensity proton beam

Abstract

Nanjing University and local government are pushing ahead with a high-intensity proton linac project called Nanjing Proton Source (NPS). At the first stage, a low-energy injector including an ion source and a low-energy beam transport (LEBT) will be set up to provide 65 keV, 28 mA proton beam. A duoplasmatron source with triode electrodes and a two-solenoid magnetic focusing LEBT is our favorable choice. As we know, the most important role of the LEBT is to minimize the emittance growth and optimize the Twiss parameters into radio frequency quadrupole (RFQ). This paper clearly introduces the optimization procedure that sets effective solenoid fields as two free parameters to search for the minimum rms emittance and the best-matched Twiss parameters by plotting contour maps. The detailed LEBT layout and solenoids design are completed based on the optimization. The robustness and stability of the LEBT are also analyzed in the end. The beam phase-space distribution and beam qualities are discussed under a range of space charge compensation degrees and different initial beam distribution types. Besides, the LEBT is designed to eliminate the vast majority of beam contaminants by using two collimators.