An ultrafast digitizer for continuous measurements from microwave fusion diagnostics

Abstract

Fast digitizers are employed in a variety of experimental contexts, including for microwave measurements from fusion plasma diagnostics. However, most existing commercial digitizers used for this purpose are severely limited by their onboard memory. Here we present a system developed from mostly commercially available hardware components capable of acquiring essentially indefinitely (here $\sim$10 s) while meeting the target performance of 5 GHz analog bandwidth with a rate of 10 billion samples per second and 8 bits per sample. At its core is a field-programmable gate array (FPGA) receiving data from a high-performance analog-to-digital converter (ADC). The data are continuously streamed with a maximum throughput of 120 Gb/s from the FPGA to a computer over optical fiber in the form of raw Ethernet packets, allowing the use of entirely standard networking hardware in the PC. Whilst this technology is transferable to a range of applications, we are motivated by the demands of microwave scattering measurements, for which the new digitizer increased the acquisition duty cycle from 6% to 100%. In this paper we describe our digitization system, demonstrate its capability, and then use it to acquire data from microwave diagnostics at the ASDEX Upgrade and Wendelstein 7-X fusion experiments.