A measurement system for a plasma processing system includes a detector and an ion current meter coupled to the ion current collector and configured to provide a signal based on the measurements from the ion current collector. The detector includes an insulating substrate including a cavity, an ion angle selection grid configured to be exposed to a bulk plasma disposed in an upper portion of the cavity, and an ion current collector disposed within the cavity at an opposite side of the cavity below the ion angle selection grid. The ion angle selection grid includes an ion angle selection substrate and a plurality of through openings extending through the ion angle selection substrate, where each of the plurality of through openings has a depth into the ion angle selection substrate and a width orthogonal to the depth, where a ratio of the depth to the width is greater than or equal to 40.