Practical solutions for reliable triple probe measurements in magnetized plasmas

Area of Science:

• Plasma physics
• Fluid dynamics
• Turbulence research

Background:

• Accurate local, time-resolved plasma measurements are crucial for understanding complex plasma phenomena.
• Traditional diagnostic techniques face challenges with accuracy and reliability.

Purpose of the Study:

• To investigate and refine the triple probe method for precise plasma diagnostics.
• To address and overcome limitations in triple probe measurements, such as phase delay and stray capacitance.
• To validate the improved triple probe technique in a turbulent plasma environment.

Main Methods:

• Detailed investigation of the triple probe technique, focusing on error sources like phase delay, ion sheath expansion, and stray capacitance.
• Development of a novel electronic circuit to minimize stray capacitance.
• Experimental validation using the TORPEX device with interchange-driven turbulence.
• Cross-checking results with established Langmuir probe techniques.

Main Results:

• Successfully overcame common difficulties in triple probe measurements, enhancing reliability.
• Demonstrated good agreement between triple probe data and other Langmuir probe methods.
• Revealed significant electron temperature fluctuations, indicating that plasma potential fluctuations cannot be approximated by floating potential fluctuations.
• Showed that time-averaged, fluctuation-induced particle flux can be determined from floating potential alone in specific radial regions.

Conclusions:

• The refined triple probe method provides reliable, time-resolved measurements of plasma parameters.
• Electron temperature fluctuations significantly impact plasma potential measurements.
• Floating potential measurements are sufficient for deducing time-averaged particle flux in certain turbulent plasma conditions, simplifying analysis.