Design, fabrication new structures of thin-film probes for plasma magnetic field diagnostics.

Abstract

Accurate magnetic field diagnostics are critical for understanding plasma behavior in magnetically confined fusion devices. While conventional inductive probes are widely used, their hand winding construction leads to limitations in mechanical stability and measurement reproducibility. This study presents the design, fabrication, and characterization of advanced thin-film magnetic probes utilizing microfabrication techniques to overcome these limitations. Through systematic electromagnetic simulations in Computer Simulation Technology, we evaluated three coil geometries and identified the circular configuration as optimal, exhibiting superior frequency response characteristics. Based on these results, we developed three innovative probe architectures: differential, parallel, and three-dimensional array configurations. The probes were fabricated via magnetron sputtering on alumina ceramic substrates. Extensive calibration experiments demonstrated remarkable agreement (<5% deviation) between simulation predictions and measurements obtained from both vector network analysis and impedance analysis, which validates our simulations. The differential configuration exhibited superior performance with ±1% accuracy in magnetic fields exceeding 0.003 T. This precision is maintained toward the 0.01-0.1 T range, which is relevant for measuring the poloidal magnetic field and its fluctuations in the HL-3 tokamak. These results demonstrate that the thin-film probes offer significant advantages in spatial resolution, measurement reproducibility, and frequency bandwidth compared to the conventional designs, making them particularly suitable for advanced plasma diagnostics in fusion research.