Possible Mechanisms of String Formation in Complex Plasmas at Elevated Pressures

Area of Science:

• Complex plasma physics
• Microparticle dynamics
• Space plasma research

Background:

• Formation of field-aligned microparticle strings is observed in complex plasmas.
• Understanding particle attraction mechanisms is key for interpreting experiments like Plasmakristall-4 (PK-4) on the ISS.
• Elevated gas pressures influence microparticle behavior in plasma.

Purpose of the Study:

• To theoretically investigate mechanisms responsible for microparticle attraction and string formation in complex plasmas.
• To compare two distinct theoretical approaches for calculating particle interaction energy.
• To reconcile theoretical predictions with experimental observations from the PK-4 experiment.

Main Methods:

• Theoretical investigation of particle interaction energy using two approaches.
• Approach 1: Dynamically screened wake potential for small Mach numbers.
• Approach 2: Effect of trapped ion cloud polarization by discharge electric fields.

Main Results:

• Both investigated approaches yield particle interaction energy independent of the discharge mode.
• The wake potential approach predicts particle attraction only at gas pressures > 40-45 Pa.
• The trapped ion polarization mechanism predicts attraction in the 20-40 Pa range, aligning with experiments.

Conclusions:

• The trapped ion polarization mechanism is crucial for explaining microparticle attraction in the experimentally relevant pressure range.
• This mechanism helps reconcile theoretical models with observations from complex plasma experiments.
• Further research can refine understanding of microparticle string formation in space-based plasma.