An ion thruster internal discharge chamber electrostatic probe diagnostic technique using a high-speed probe...

Area of Science:

• Space Propulsion
• Plasma Physics
• Materials Science

Background:

• Gridded ion thrusters are vital for deep space missions, but their lifetime is limited by component erosion.
• While grid erosion is well-studied, discharge cathode erosion is increasingly recognized as a critical factor in ring-cusp ion thrusters.
• Characterizing the plasma environment near the discharge cathode is essential for mitigating erosion.

Purpose of the Study:

• To develop and demonstrate a novel method for in-situ plasma characterization within the discharge chamber of an operating ion thruster.
• To investigate the near-cathode plasma parameters, specifically electron temperature and number density.
• To provide data that can elucidate discharge cathode erosion mechanisms and their dependence on thruster operating conditions.

Main Methods:

• A high-speed axial reciprocating probe positioning system was employed to minimize thruster perturbation and probe heating.
• Symmetric double Langmuir probes were utilized for electrostatic measurements.
• Measurements were taken over a two-dimensional spatial array within the near-discharge cathode region of a 30-cm-diameter ring-cusp ion thruster.

Main Results:

• Successfully demonstrated a 2D interrogation method for the discharge chamber plasma.
• Measured electron temperatures ranging from 2-5 eV.
• Obtained number density contours with a peak of 8 x 10^12 cm^-3 on the centerline.

Conclusions:

• The developed method allows for detailed characterization of near-cathode plasma parameters in operational ion thrusters.
• The obtained electron temperature and density data provide insights into plasma behavior relevant to discharge cathode erosion.
• This research offers a pathway to better understand and potentially reduce erosion rates, thereby extending ion thruster lifetime.