SNS HEBT momentum scraper, H+ ray trace simulation and vacuum chamber design

In the 1 MW Spallation Neutron Source (SNS), the High-Energy Beam Transfer line (HEBT) connects the LINAC to the accumulator ring. A major requirement of the SNS complex is to have low uncontrolled beam loss (InA/m), to allow hands on maintenance. The vacuum requirement for the HEBT is 5×10^-8 Torr. Excessive H^- stripping will occur above this pressure and increase losses in the machine. The HEBT is also equipped with three sets of beam halo scrapers, one for momentum arid two for transverse collimation. The momentum scraper is located at a maximum dispersion point, between the 3^rd dipole magnet (DD3) of HEBT and the 14^th quadrupole (Q14) of the HEBT line. The momentum scraper uses movable foils that strip the H^- beam that has momentum spread (0.2%<δp/p<0.6%) into H⁺, and the H⁺ ions are then directed out of the HEBT beam line to a beam dump by the next bending magnet DD4 (4^th dipole of HEBT). In order to ensure that the extracted H ⁺ beam travels inside the extraction chamber to minimize the radiation in the beam dump station region, we performed H⁺ particle tracking to determine the outer boundaries and the angle of the Y-type vacuum chamber that will contain the H⁺ beam. The development and design of the special HEBT momentum scraper extraction and exit chamber, and the relevant H⁺ trajectories are presented in this paper