Analyzing The Design and Manufacturing Challenges of Water-Cooled Langmuir Probes for NSTX-U Neutral Beam Ion Sources.

Neutral Beam Injection (NBI) is used as an auxiliary heating method on the NSTX-U magnetic fusion device. NBI is crucial for increasing plasma temperatures by introducing high-energy atoms into a magnetically confined plasma, where they become ionized and trapped. The Langmuir probes used within the NBI sources were designed by Lawrence Berkeley National Laboratory. The probes play an essential role in this process by monitoring plasma density and providing arc spot protection. These probes consist of a probe body assembly and a Molybdenum tip. However, the design of the probes incorporates the use of multiple vacuum brazing steps that present challenges in fabrication and ultimately result in high failure rates — either unusable components or shorter-than-expected operational lifespans. Finite element analysis is intended to provide supporting evidence of the effectiveness of a revised design of the probe geometry and enhance its performance using SOLIDWORKS and ANSYS. Simulations, including static structural, steady-state thermal, and fluid flow analyses, are applied to evaluate mechanical stability and thermal performance. Water flow pathway modeling is performed to optimize cooling efficiency and verify heat load limits. This research seeks to improve probe reliability and performance for more efficient NBI operations in the NSTX-U.