Overview of the Langmuir probe and current shunt diagnostics on the SPARC tokamak.

To enable real-time control, explore high-field plasma physics, and validate the design of the ARC power plant, SPARC will be equipped with a comprehensive suite of plasma diagnostics. Among these are electrical probe diagnostics integrated into plasma-facing components and attached to the vacuum vessel, including 54 Langmuir probes and 44 current shunt sensors. Main chamber Langmuir probes are tightly integrated into the plasma-facing components and will measure edge plasma parameters at the midplane and at off-midplane limiters. Embedded halo current shunt sensors provide measurements of the halo current width along the off-midplane limiters and share many components with the off-midplane Langmuir probe designs to simplify the interface with the first wall. Divertor Langmuir probes are limited to the X-point target chamber to be used for the SPARC advanced divertor mission. Poloidal current shunts are mounted to the vacuum vessel wall around the divertor for dissipative divertor control. Verified designs are shown to ensure that the probes will contribute meaningful data and that the probe assemblies have a high chance of surviving SPARC's harsh electromagnetic and thermal environment, since the maintenance opportunities will be minimal due to limited personnel accessibility in later campaigns. The design of all in-vessel probe assemblies is complete; pre-assembly into the corresponding plasma-facing component assemblies is underway prior to installation into SPARC. This paper summarizes the final system design, describes relevant analysis completed through the final design stage and assembly considerations through first encounters with hardware, and highlights the diagnostic requirements, which motivate Langmuir probe measurements on SPARC.