A divertor scraper observation system for the Wendelstein 7-X stellarator

Area of Science:

• Fusion Energy Research
• Plasma Physics
• Materials Science

Background:

• The Wendelstein 7-X stellarator utilizes graphite divertor elements, known as scrapers, to manage plasma-wall interactions.
• Understanding heat loads and plasma interactions on these scrapers is crucial for stellarator operation and material integrity.

Purpose of the Study:

• To design, build, calibrate, and install a novel infrared/visible imaging endoscope system.
• To enable detailed, in-situ diagnostics of plasma interactions and heat loads on a specific scraper element and adjacent divertor surfaces.

Main Methods:

• The system employs a shuttered pinhole-protected pair of off-axis parabolic mirrors and flat turning mirrors to relay light.
• Infrared (FLIR SC8303HD) and visible (PCO 5.5 edge) cameras, along with a spectrometer, are used for data acquisition.
• The optical path extends 1.6 meters to a vacuum window, allowing commercial optics to be used outside the vessel.

Main Results:

• The endoscope system successfully captures infrared and visible light from the scraper's 700 mm length.
• The system's field of view encompasses areas monitored by embedded thermocouples and Langmuir probes.
• A comparison between predicted and actual optical test performances of the system is presented.

Conclusions:

• The developed imaging endoscope system is a valuable diagnostic tool for studying plasma-facing components in stellarators.
• This technology enhances the understanding of heat loads and plasma-material interactions, contributing to fusion energy advancement.