Direct two-dimensional goniometric steering of vacuum electrospray ion beams for angular time-of-flight studies

Area of Science:

• Spacecraft propulsion
• Plasma physics
• Materials science

Background:

• Vacuum electrospray ionization (ESI) thrusters are promising electric propulsion (EP) technologies offering high efficiency and precise thrust control.
• The angular characteristics of ESI ion plumes, including molecular composition and droplet behavior, are not fully understood, posing challenges for thruster reliability.

Purpose of the Study:

• To develop and demonstrate a novel method for two-dimensional steering of vacuum ESI beams.
• To investigate the angular properties and molecular composition of ESI plumes with high precision.

Main Methods:

• Utilized an externally wetted tungsten needle with 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) ionic liquid.
• Employed a dual-axis goniometer for in-vacuo beam steering in pitch and yaw.
• Conducted angular-dependent time-of-flight measurements of molecular species within the ESI plume.

Main Results:

• Demonstrated precise two-dimensional steering of vacuum ESI beams.
• Observed significant variations in the relative abundance of monomers, dimers, trimers, and heavy species across different plume angles.
• Found monomers to be at a relative minimum, while fragments, trimers, and heavy species were at a relative maximum at the beam center.

Conclusions:

• The developed steering method significantly enhances signal-to-noise ratios for diagnostic tools.
• Provides a robust framework for detailed characterization of ESI plume dynamics and composition.
• Critical for optimizing ESI-based propulsion systems and enabling new laboratory applications.