Spatial and temporal profile monitor with nanosecond resolution for CERN's Linac4

Abstract

CERN's Linac4 will provide 160-MeV H− beams with an intensity of 2 × 1014 ions s−1. In the first section of Linac4, a beam chopper removes sequences of 500-ps-long micro-bunches from the H− beam. We developed a monitor to measure the time structure and spatial profile of this chopped beam with resolutions Δt ∼ 1 ns and Δx ∼ 2 mm. The large active area 40 mm × 40 mm and dynamic range of the detector also allows studies of beam halos. The H− beam first struck a carbon foil, and the resulting burst of secondary electrons were accelerated by a series of parallel grid electrodes. The electrons struck a phosphor screen, and the resulting image of the scintillation light was transported to a charge-coupled device camera. The time resolution was attained by applying high-voltage pulses of sub-nanosecond rise and fall times to the electrodes and phosphor screen.