  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.
