Correcting Faraday Cup Measurements with Rutherford Backscattering Spectroscopy

Faraday cups are devices that can measure the intensity of an ion beam by collecting its charged particles. In many accelerator-based studies, the beam intensity must be accurately determined. This requires that a Faraday cup captures all incoming ions and secondary emitted electrons. Instead of constructing a complicated, electrically suppressed Faraday cup, the authors have opted to quantify the systematic error in cup readings with Rutherford scattering at large angles (which is well understood). A proton beam of 3.4 MeV, incident upon a copper target, generated backscattered ions that were captured by a silicon surface barrier detector. This detector measured the energy distribution of the backscattered ions, and the spectrum obtained was used to calculate the current of the ion beam, which could be compared to the simple Faraday cup readings. This comparison produced a correction factor that was used to scale the Faraday cup’s measurements to minimize this systematic error.