Advanced Real-Time Plasma Diagnostics Based on the Floating Harmonic Probe with a High-Speed FPGA-Based Acquisition System

Electrical diagnostic techniques using Langmuir probes have been widely employed to characterize plasma sources and investigate plasma physics. However, since this method relies on DC biasing, it faces limitations in deposition gas environments where dielectric films tend to form on the probe surface, resulting in unreliable measurements. To overcome this limitation, the Floating Harmonic Probe (FHP) has been proposed. It applies a small-amplitude AC voltage to a floating probe and analyzes the resulting current collected by the probe. This technique enables real-time plasma diagnostics even in dielectric deposition environments. In this study, we developed a high-speed plasma diagnostic system with a 100 MHz sampling rate based on FHM. The system features an FPGA-based data acquisition module capable of capturing current signals in real time. It is designed to accurately measure and analyze probe current signals over a wide frequency range. We analyzed the changes in electron temperature and electron density, confirming that high-speed sampling allows precise tracking of rapidly changing plasma characteristics. The developed system is applicable to plasma diagnostics in environments where high temporal resolution is required, such as pulsed discharges and the early detection of arcing phenomena, offering a promising platform for advanced diagnostic technologies.