High density Langmuir probe array for NSTX scrape-off layer measurements under lithiated divertor conditions

Area of Science:

• Plasma Physics
• Fusion Energy Engineering

Background:

• Understanding plasma behavior in the scrape-off layer is crucial for magnetic confinement fusion.
• The edge plasma region significantly impacts overall fusion device performance and material integrity.

Purpose of the Study:

• To develop and implement a high-density Langmuir probe array for detailed scrape-off layer measurements in the National Spherical Torus Experiment (NSTX).
• To characterize heat and particle fluxes and transient edge plasma events within the NSTX divertor region.

Main Methods:

• Designed and deployed a 99-electrode Langmuir probe array in three parallel radial rows.
• Configured the array for both swept and triple-probe operation.
• Mounted the array within a carbon tile in the lower outer divertor of NSTX, adjacent to the liquid lithium divertor.

Main Results:

• Successfully developed a high-density Langmuir probe array for NSTX.
• Collected initial data using swept probe operation to track the outer strike point.
• Measured relevant scale lengths for heat and particle fluxes (1-5 cm) and observed transient events on millisecond timescales.

Conclusions:

• The developed Langmuir probe array is a viable tool for detailed scrape-off layer diagnostics in NSTX.
• Initial measurements provide valuable insights into plasma transport and event dynamics in the divertor region.
• Further analysis will refine understanding of plasma-material interactions and optimize fusion device operation.