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Description
During the 2023 KSTAR experimental campaign, the lower divertor was replaced with tungsten monoblock plasma-facing components. The transition from carbon to tungsten is expected to substantially modify impurity sources and transport in the divertor plasma. However, prior to this upgrade, KSTAR lacked a dedicated diagnostic for measuring D-alpha emission in the divertor region, limiting detailed investigation of divertor impurity behavior and plasma–wall interactions.
A divertor D-alpha diagnostic system has been designed, fabricated, and installed to enable localized measurements in the KSTAR divertor. The system consists of nine lines-of-sight, with five channels viewing the central divertor and four channels viewing the X-point region. Each channel employs a 0.25-inch collimator, resulting in a spot diameter of approximately 4 mm, constrained by the narrow gaps between divertor blocks. Two identical nine-channel modules were installed at the K-port and G-port, providing toroidally separated measurements with a separation of 90 degrees. Channel alignment and absolute intensity calibration were performed using laser-based alignment and a calibrated integrating sphere, respectively.
The diagnostic utilizes interchangeable narrowband optical filters, allowing flexible measurements of D-alpha emission as well as other impurity line radiation. This system provides a new capability for systematic studies of impurity behavior and divertor plasma characteristics in KSTAR under tungsten wall conditions.
This paper presents the design, fabrication, installation, and initial operational results of the divertor D-alpha diagnostic system.