Optimization of space-charge dominated injection beam line of high current proton RFQ

Abstract

Design of a space charge dominated proton beam-line from an ECR ion source to a high current RFQ has been carried out using analytical formulation. The parameters of the beam-line consisting of two solenoids, a slit for selecting H+ and rejecting H2+, and buncher are optimized to match the proton beam with the acceptance of RFQ . Analytical formulation for multispecies beam instead of conventional optical code has helped in simultaneously achieving different objectives within a compact but optimum length. Disc model having finite input energy width for longitudinal calculations and K-V transverse envelope equations for individual macro-discs including the bunching effect has been used. Selected parameters have been further corroborated by particle tracking using the 3D field of buncher and RFQ . Efficient selection/rejection of species has been verified with different type of input particle distributions in particle tracking. Finally the transmitted H+ and remaining H2+ has been tracked through the RFQ . The ratio of H+ to H2+, which is roughly 7:3 at exit of ECRIS could be reduced to 32:1 after the slit, while through RFQ remaining H2+ gets only transmitted but without any acceleration.