Imaging of two-dimensional ion-beam profiles using a scanning Faraday cup array combined with a 128-channel...

A two-dimensional beam-profile monitor has been constructed based on a scanning Faraday cup array, a 128-channel picoammeter system, and a LabVIEW-based data acquisition system. The Faraday cup array consists of 128 small Faraday cups, while each is connected to an independent picoammeter of the picoammeter system. It is driven across the ion beam by a servo motor and images the two-dimensional beam profile by directly measuring the absolute electric current distribution. The benefit from the avoidance of readout switching between different Faraday cups is that the crosstalk is negligible during a beam scanning. Typically, this monitor scans a beam cross section of 76.8 × 76.8 mm2 within 18-420 seconds. Tests with 50-keV O5+ and 1.8-MeV Xe25+ beams show that an ion beam with beam flux greater than ∼1 pA/mm2 can be clearly distinguished and a spatial resolution of ∼0.6 mm can be achieved. The total beam current measured by this device was calibrated using a Faraday cup, showing a systematic negative deviation of ∼6%-8% relative to the reference current, which is mainly attributed to inlet diameter tolerance and alignment errors.