Physical design of the neutralizer for CFETR negative ion based neutral beam injection prototype

•A 3D model of the beamline of CFETR NNBI prototype has been developed to study the gas flow and the beam transport in the beamline.•The gas density profiles and consequent gas target thickness in either neutralizer design of single channel or two narrow channels were compared via Monte Carlo method at different gas flow rate.•The power load on different components of the neutralizer were estimated via Monte Carlo method at different beamlets divergence and misalignment.