Development and application of an ion sensitive probe for helicon plasma diagnostics

This study focuses on the design and application of an Ion Sensitive Probe (ISP) for the PKU Plasma Test (PPT) device, marking the first implementation of the ISP in a large-diameter helicon plasma device with a single-loop antenna discharge. The strong influence of electrode material on ISP diagnostic performance is also observed for the first time, and tungsten is proven to be the optimal choice. Experimental results demonstrate that both ion and electron temperatures are at the order of 1 eV. This observation can be attributed to the electron-ion energy relaxation process, which allows electrons and ions to reach near thermal equilibrium through collisions. Comparative analyses with Langmuir probe diagnostics show maximum deviations of 8% and 12% in density and electron temperature measurements, respectively, confirming the high reliability of the ISP diagnostics. The radial profiles of plasma density and temperature in the PPT device are also systematically studied as functions of RF power and magnetic field strength. The findings demonstrate that increasing RF power significantly enhances plasma density, while ion and electron temperatures remain stable. The response of ion temperature to varying magnetic fields is more complex, necessitating further investigation. This study enhances the reliability of ion temperature diagnostics in helicon plasmas. Moreover, the ISP is also applicable to various magnetic confinement plasmas, including etching plasmas, mirror machines, tokamaks, and stellarators.