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Updated: Jun 10, 2026
08:10
Building Langmuir Probes and Emissive Probes for Plasma Potential Measurements in Low Pressure, Low Temperature Plasmas
Published on: May 25, 2021
High-speed dual Langmuir probe
Robert B Lobbia1, Alec D Gallimore
1Department of Aerospace Engineering, Plasmadynamics and Electric Propulsion Laboratory, The University of Michigan, Ann Arbor, Michigan 48109, USA.
The Review of Scientific Instruments
|August 7, 2010
Summary
A new high-speed dual Langmuir probe (HDLP) enables microsecond-timescale measurements of turbulent plasma properties. This advanced probe reveals significant fluctuations in electron density, temperature, and plasma potential within Hall thruster plumes, correlating with discharge instabilities.
Area of Science:
- Plasma Physics
- Space Propulsion Engineering
Background:
- Turbulent plasma discharges are crucial in applications like Hall effect thrusters.
- Traditional Langmuir probes lack the temporal resolution to capture rapid plasma dynamics.
- Understanding plasma fluctuations is key to optimizing thruster performance and stability.
Purpose of the Study:
- To develop and validate a high-speed dual Langmuir probe (HDLP) for temporally resolved measurements of turbulent plasma.
- To investigate the spatio-temporal characteristics of plasma properties in Hall thruster plumes.
- To correlate plasma fluctuations with thruster discharge instabilities.
Main Methods:
- A novel HDLP system was designed, integrating a swept Langmuir probe with a shielded null probe for microsecond-timescale bias sweeps.
- Traditional thin-sheath Langmuir probe theory was applied for data interpretation.
- The HDLP system was used for near- and far-field plume measurements downstream of a Hall effect thruster, collecting extensive spatial and temporal data.
Main Results:
- The HDLP system achieved bias sweep rates up to 1 MHz, enabling detailed analysis of plasma properties.
- Measurements in the Hall thruster plume showed electron densities of (1x10^15)-(5x10^16) m⁻³, electron temperatures of 1–3.5 eV, and plasma potentials of 5–15 V.
- Significant 19 kHz fluctuations in electron density, temperature, and plasma potential were observed throughout the plume, synchronized with thruster discharge current oscillations (breathing mode).
- Observed plasma wave propagation velocities exceeded 10 km/s, consistent with ion transit times.
Conclusions:
- The developed HDLP system provides unprecedented temporal resolution for studying turbulent plasmas.
- The study demonstrates a strong link between Hall thruster discharge instabilities and plasma property fluctuations within the plume.
- The findings offer insights into plasma wave propagation and energy transfer mechanisms in Hall thrusters.
