Tuning of LANSCE 805-MHz High-Energy Linear Accelerator with Reduced Beam Losses

Abstract: Suppression of beam losses is essential for successful operation of high-intensity linac. Historically, the values of the field amplitudes and phases of the side-coupled, 805-MHz LANSCE linac modules are maintained using a well-known delta-t tuning procedure. Transverse matching of the beam with accelerator is performed through adjustments of beam ellipses in 4D phase space with accelerator lattice using matching quadrupoles. Control of the beam-energy ramp along the length of a proton linear accelerator is required to improve tune of accelerator and decrease beam losses. Time-of-flight measurements of the H- beam energy are now being used to confirm and improve the overall control of the energy ramp along the linac. The time-of-flight method utilizes absolute measurements of beam energy using direct signals from beam at an oscilloscope, as well as the difference in RF phases measured as the beam passes installed delta-t pickup loops. A newly developed BPPM data acquisition system is used. Beam energy measurement along accelerator together with phase scans, klystrons output power control, and delta-t method, allow tuning of accelerator much more close to original design and reduce losses generated by linac. Details of the upgraded tuning procedure and results of tuning and operation are presented.