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 using commercial off-the-shelf (COTS) components capable of sampling essentially indefinitely (here ~10 seconds) at a rate of 10 billion samples per second and 8 bits per sample. The core of the system is a field-programmable gate array (FPGA), which receives data from a high-performance analogue-to-digital converter (ADC). The data are streamed in real time from the FPGA to a computer over optical fibre 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. In this paper we describe our digitisation system, demonstrate its capability, and then use it to acquire data from microwave diagnostics at the ASDEX Upgrade and Wendelstein 7-X fusion experiments.

Keywords: Fast digitizer, GHz bandwidth, FPGA, ADC, real-time