Development of a quad-channel high-resolution digital picoammeter for beam diagnostics

Abstract

In synchrotron light source applications, the photon beam interaction with various materials can produce electric charge which can be measured as current and be used to diagnose particle trajectories, beam intensity, beam profile, position, and stability. Sirius, a 4th-generation Brazilian synchrotron light source, will make use of hundreds of low-intensity measurement instruments. This work aims to show and discuss the design details, challenges, and test results of an Ethernet four-channel high-performance digital ammeter, applied for general-purpose beam diagnostics. The device is based on low-noise and extremely low input bias bipolar transimpedance amplifiers with eight selectable ranges (full scales from pA to mA). Characterization results show that the achieved gain, accuracy, and noise performance are on the same order of magnitude as those of expensive commercial benchtop equipment. In low bandwidth applications, the device was able to measure amplitudes of hundreds of picoampere with intrinsic noise of units of femtoampere (RMS). The designed device is a cost-effective solution.