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A high resolution IR/visible imaging system for the W7-X limiter.
G A Wurden1, L A Stephey2, C Biedermann3
1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
The Review of Scientific Instruments
|December 3, 2016
Summary
A new high-resolution imaging system with mid-infrared and visible cameras was used on the W7-X stellarator. This system monitored graphite limiters, measuring heat loads and particle fluxes for fusion energy research.
Area of Science:
- Plasma physics
- Fusion energy research
- Materials science
Background:
- The Wendelstein 7-X (W7-X) stellarator requires advanced diagnostics to monitor plasma-facing components.
- Graphite limiters are crucial for plasma confinement but are susceptible to heat loads and particle erosion.
- Understanding limiter behavior is essential for optimizing stellarator performance and longevity.
Purpose of the Study:
- To deploy and operate a novel high-resolution imaging system for analyzing W7-X inboard graphite limiters.
- To measure surface temperature, heat loads, and particle fluxes on the limiter tiles.
- To correlate infrared (IR) and visible light emissions with plasma conditions and limiter performance.
Main Methods:
- Utilized a synchronized mid-infrared (IR) and visible light camera system with sub-millimeter resolution.
- Acquired IR data at frame rates from 125 Hz to 1.25 kHz to capture transient thermal events.
- Employed narrow bandpass filters (C-III, H-alpha) on the visible camera for specific impurity analysis.
Main Results:
- Observed surface temperature increases exceeding 350°C on limiter tiles, particularly at leading edges and defect hotspots.
- Inferred plasma power fluxes in the range of 1-4.5 MW/m² during electron cyclotron resonance heating (ECRH).
- Measured equilibrated bulk tile temperatures and tile energy inputs (approx. 30 kJ/tile) using calorimetric IR data.
- Tracked small unipolar-arcing (UFO) events and correlated IR hotspots with C-III light emissions.
Conclusions:
- The high-resolution IR and visible imaging system is effective for diagnosing W7-X limiter performance.
- The system provides crucial data for understanding heat and particle loads on plasma-facing components.
- This diagnostic capability aids in optimizing stellarator operation and material protection strategies.
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