Stripping Foil Displacement Unit Control for H⁻ Injection in PSB at CERN

For CERN's Linac4 (L4) Proton Synchrotron Booster (PSB) injection scheme, slices of the 160 MeV H⁻ beam will be distributed to the 4 superposed synchrotron rings of the PSB. The beam will then be injected horizontally into the PSB by means of an H⁻ charge-exchange injection system using a graphite stripping foil to strip the electrons from the H⁻ ions. The foil and its positioning mechanism will be housed under vacuum inside a stripping foil unit, containing a set of six foils that can be mechanically rotated into the beam aperture. The band with mounted foils is controlled by a stepping motor while a resolver, micro-switches and a membrane potentiometer provide foil position feedback. The vicinity of the ionizing beam and vacuum requirements have constrained the selection of the above mentioned control system parts. The positioning and interlocking logic is implemented in an industrial Programmable Logic Controller (PLC). This paper describes the design of the stripping foil unit electronics and controls and presents the first results obtained from a test bench unit which will be installed in the Linac4 transfer line by the end of the 2015 for foil tests with beam.