Biasing, acquisition, and interpretation of a dense Langmuir probe array in NSTX

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Langmuir Probe Diagnostics

Background:

• The lower divertor region of fusion devices is critical for managing heat and particle exhaust.
• Accurate plasma characterization in the divertor is essential for optimizing fusion reactor performance.
• Langmuir probes are standard tools for measuring plasma parameters, but interpretation can be challenging.

Purpose of the Study:

• To deploy and utilize a dense array of 99 Langmuir probes in the NSTX lower divertor.
• To overcome interpretation challenges of probe measurements in time-dependent scrape-off-layer (SOL) plasmas.
• To determine plasma electron temperature and density at the probe locations.

Main Methods:

• Installation of a 99-probe Langmuir probe array in the NSTX lower divertor.
• Flexible electronic system enabling various probe biasing and measurement types (swept, single, triple probe).
• Complementary use of single- and triple-Langmuir probe signals for robust plasma parameter determination.

Main Results:

• Successful deployment and operation of the dense Langmuir probe array.
• Demonstrated ability to determine plasma temperature and density using complementary probe techniques.
• Comparison of divertor measurements with midplane diagnostics provided valuable insights.

Conclusions:

• The dense Langmuir probe array provides a powerful diagnostic capability for the NSTX lower divertor.
• Complementary single and triple probe measurements offer a reliable method for characterizing SOL plasma parameters.
• The results contribute to a better understanding of plasma behavior in fusion device divertors.