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 33 fA within 15 ms or a maximal resolution of 1.8 fA with a measurement time of 12.4 s. 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 ELBE positron beam (EPOS) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), achieving the nominal maximum resolution with high reproducibility. We then exploited the capabilities of the detector to resolve the 2-D 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 prompt optimization of beam transport.