Ion-temperature determination with a baffled Langmuir probe

Area of Science:

• Plasma Physics
• Diagnostic Techniques

Background:

• Langmuir probes are essential for plasma characterization.
• Measuring plasma parameters in magnetized environments presents challenges.
• Existing methods may lack real-time capabilities or accuracy.

Purpose of the Study:

• To develop and validate a modified Langmuir probe for enhanced plasma measurements.
• To enable real-time determination of space potential and ion temperature.
• To investigate the effect of probe geometry on plasma current collection.

Main Methods:

• Utilized a tungsten wire Langmuir probe with adjustable ceramic baffles in a barium Q-machine plasma.
• Oriented the probe perpendicular to the magnetic field (B).
• Varied the azimuthal orientation of baffle slots to control electron and ion access to the sensor.

Main Results:

• Adjustable electron (I_e^sat) and ion (I_i^sat) saturation currents achieved by altering baffle orientation without changing probe bias voltage (V_b).
• Accurate real-time space potential (V_s) measurements obtained with optimal shielding (I_e^sat/I_i^sat=1).
• Accurate real-time ion temperature (T_i) measurements obtained with maximal shielding (I_e^sat/I_i^sat≪1).

Conclusions:

• The baffled Langmuir probe provides a versatile tool for real-time plasma diagnostics.
• Differential floating potential measurements between optimally and maximally shielded configurations yield ion temperature and fluctuation phase.
• This technique enhances the capability for in-situ plasma parameter determination.