A high resolution multichannel acquisition system for magnetic measurements of fusion experiments

Magnetic fusion experiments rely heavily on coil loops as the primary type of magnetic sensors, offering the desired precision, reliability, and robustness. However, in order to obtain the magnetic field evolution, the signals from these sensors need to be time-integrated. Traditionally, analog integrators were employed due to their wide dynamic range, but they present challenges in terms of complexity and the need for a separate channel for the derivative (dB/dt) signals required to measure fast events, plasma instabilities, and magnetic turbulence accurately. In this work, we propose a novel system design based on high-resolution analog-to-digital converters (ADCs) that eliminates the need for analog integrators and the second acquisition channel, simplifying and compacting the overall system. The system utilizes a 1 MSamples/sec, 20-bit resolution ADC, providing a resolution comparable to that of good analog integrators. To ensure accurate measurements, each acquisition channel is electrically isolated individually, effectively eliminating the ground loops generated by the experiment's magnetic fields, which often hamper the measurements. The system architecture is implemented on 6U boards, with each board acting as an autonomous system housing 12 input channels and its own SOC-FPGA, with a total of 144 channels on a 6U sub-rack. Each board simultaneously provides three essential functionalities: a timing synchronization decoder, transient recording of full-speed ADC data, and continuous Ethernet UDP transmission of subsampled signals to the real-time control system. This comprehensive approach allows for efficient data acquisition, analysis, and integration into the experiment's control framework.