The flush-mounted rail Langmuir probe array designed for the Alcator C-Mod vertical target plate divertor.

Area of Science:

• Plasma Physics
• Fusion Energy Engineering

Background:

• Langmuir probes are crucial for plasma diagnostics in fusion devices.
• Traditional probes face challenges with high heat fluxes and sheath expansion effects.
• Alcator C-Mod's divertor environment presents extreme conditions for diagnostic tools.

Purpose of the Study:

• To introduce and evaluate novel flush-mounted, toroidally elongated Langmuir probes (rail probes).
• To assess the durability and performance of rail probes under high heat flux conditions.
• To investigate the mitigation of sheath expansion effects in Langmuir probe measurements.

Main Methods:

• Designing and implementing an array of rail probes on the Alcator C-Mod vertical target plate.
• Operating the rail probes over multiple experimental campaigns (FY2015, FY2016).
• Comparing data from rail probes with traditional 'proud' probes to analyze sheath expansion.

Main Results:

• Rail probes demonstrated successful operation without damage, enduring heat flux densities exceeding 1 GW m^-2.
• The toroidally elongated geometry effectively reduced the influence of sheath expansion.
• Comparison data confirmed the mitigation of sheath expansion effects, enabling measurements at low magnetic field line angles (0.5°).

Conclusions:

• The developed rail probes are robust and suitable for high-heat-flux environments in fusion divertors.
• The rail probe design significantly improves the accuracy of Langmuir probe measurements by minimizing sheath expansion.
• These probes enhance the diagnostic capabilities for future fusion energy research.