Design and Metrological Characterization of a Digitizer for the Highest Precision Magnet Powering in the High Luminosity Large Hadron Collider

A new digitizer, the HPM7177, which is a fundamental component of the signal chain for high precision measurement of particle accelerator magnet currents, is presented. It was designed to meet the unprecedented performance requirements for new 14 kA and 18 kA power converters (PCs) for the High Luminosity Large Hadron Collider (HL-LHC) project at CERN, particularly in terms of low-frequency noise and stability. To determine accurately the performance of the digitizer, which is on a similar level as state-of-the-art classical metrological equipment, we carried out a thorough characterization using the programmable Josephson voltage standard (PJVS) at PTB-Braunschweig. At its nominal full scale of 10 V, the digitizer has a white noise level of <175 nV Hz−1/2, 1/f noise floor ≈7 × 10-8V, and a 12-h peak-to-peak stability better than 2 μV or 0.2 parts per million (ppm). The static non-linearity from 0 V to +10 V is <1 ppm and remains stable to ≈ 10−7 level in 12 months. The digitizer operates at a fixed rate of 10 kSamples/s and can be synchronized externally. Besides qualifying HPM7177 for its application, the characterization reveals important aspects of its operation, as well as some performance limitations.