Spatially-resolved charge detectors for particle beam optimization with femtoampere resolution achieved by in-vacuum signal preamplification

We present the design of a Faraday cup-like charged particle detector in a four quadrant configuration aimed at facilitating the alignment of low-intensity beams of exotic particles. The device is capable of assessing the current on the electrodes with a resolution of 33fA within 15ms or a maximal resolution of 1.8fA with a measurement time of 12.4s. This performance is achieved by minimizing the noise through a preamplification circuit installed in vacuum, as close as possible to the electrodes. We tested the detector with the positron beam of ELBE, achieving the nominal maximum resolution with high reproducibility. We then exploited the capabilities of the detector to resolve the two-dimensional shape of the beam, and revealed the presence of a weak electron beam being transported alongside the positrons. Characterization of the detector performance showed that in a variety of scenarios it can be used to quickly center positron beams thus allowing for the prompt optimization of beam transport.