Dust measurements in tokamaks (invited)

Area of Science:

• Fusion energy research
• Plasma physics
• Materials science

Background:

• Dust production and accumulation are significant operational and safety concerns for the International Thermonuclear Experimental Reactor (ITER).
• Effective dust diagnostics are crucial for monitoring and mitigating these risks in both surface and plasma environments.
• Existing diagnostic techniques in tokamaks face challenges, especially in detecting dust in hidden areas and accurately determining particle size.

Purpose of the Study:

• To review current and developing dust diagnostic techniques for ITER.
• To highlight the challenges of dust accumulation in ITER's complex geometry.
• To introduce a novel electrostatic dust detector for monitoring dust in inaccessible regions.

Main Methods:

• Review of dust diagnostic categories: surface and plasma.
• Application of Mie scattering, visible imaging, and spectroscopy in the DIII-D tokamak.
• Development and testing of a novel electrostatic dust detector at PPPL.
• Controlled injection of pre-characterized carbon dust into the DIII-D lower divertor for calibration and benchmarking.

Main Results:

• Laser scattering successfully resolved dust particles from 0.16 to 1.6 micrometers, enabling quantification of dust content and production rates.
• Visible imaging with fast cameras detected individual dust particles of a few microns and larger, allowing for trajectory analysis.
• Spectroscopic diagnostics observed increased emissions from injected carbon dust, indicating potential for novel survey methods.

Conclusions:

• A combination of established and novel diagnostic approaches is necessary for comprehensive dust monitoring in ITER.
• The novel electrostatic dust detector shows promise for monitoring dust in previously inaccessible areas.
• Spectroscopic analysis of dust emissions offers a new avenue for developing advanced dust survey diagnostics.