Description
Active plasma resonance spectroscopy (APRS) exploits plasmas' resonance at the electron plasma frequency to diagnose key parameters like electron density. The Curling probe, pioneered by Sugai et al., is a compact APRS variant: a conductive spiral on a dielectric substrate whose resonant frequency shift with surrounding permittivity, enabling local plasma density measurement. Its small size allows non-intrusive integration into chamber walls for process monitoring and control. However, detectable density ranges are limited by the probe's design frequency. This study introduces the CP1300 Curling probe (Fig. 1a) and characterizes it experimentally in a hot tungsten cathode DC plasma system at low-pressure argon. We compare electron densities measured by CP1300 and Langmuir probe under identical spatial and experimental conditions (Fig. 1b), focusing on low-pressure regimes, probe behaviour near dielectrics, and non-reactive plasmas. These measurements are conducted in argon gas at a low pressure of 2.1 Pa, with electron density evaluated as a function of discharge current. The results are subsequently compared with those obtained using a Langmuir probe. These results show CP1300 densities (ne) closely matching Langmuir probe values across discharge currents, confirming reliability within the probe's frequency-limited range. For example, at 100 mA discharge current, both probes yield ne≈1010 cm-3, with <10% deviation. These findings validate CP1300 for robust, non-intrusive ne monitoring in DC discharges, with implications for plasma process optimization.