A Faraday cup structure for use with a processing tool. The cup structure has a conductive strike plate coupled to a circuit for monitoring ions striking the strike plate to obtain an indication of the ion beam current. The electrically conductive strike plate is fronted by a mask for dividing an ion beam intercepting cross section into regions or segments. The mask including walls extending to the strike plate for impeding ions reaching the sensor and particles dislodged from the sensor from entering into the evacuated region of the processing tool.