Spatially resolved collision network in glow discharge via voltage-space-energy mapping

Spatial evolution of microscopic collision mechanisms in non-equilibrium plasmas is a key challenge in energy transfer research. This work introduces a diagnostic method: By mapping probe bias voltage, spatial position, electron energy, and collision type, we reconstruct the spatial gradient of the collision network in the negative glow region using a single Langmuir probe. Key aspects of this approach include converting voltage scans into axial movement coordinates and correlating EEDF peak energies to specific collision “fingerprints” (e.g., 9.4 eV for Penning ionization of H₂S by metastable He, 19.8 eV for superelastic collisions between metastable He and fast electrons). Experiments in helium glow discharges reveal enhanced metastable helium excitation near the cathode sheath and low-energy electron de-excitation at the center, intensifying atom-atom collisions. This method allows in situ, calibration-free identification of impurities like H₂S, CH₄, and air components. EEDF evolution under discharge perturbations provides a comprehensive view of collision kinetics, revealing complex interactions between energy transfer, collision cross sections, and particle transport. This approach overcomes the spatial limitations of traditional point measurements, offering a high-resolution tool for plasma micro-kinetics research.