[Paper Review] Formation Mechanism of Atmospheric Pressure Plasma Jet

Nan Jiang, Ailing Ji+1 more|ArXiv.org|Nov 2, 2008

Plasma Applications and Diagnostics1 references3 citations

TL;DR

This study reveals that atmospheric pressure plasma jets (APPJs) are driven by streamer corona discharges, not dielectric barrier discharge (DBD), enabling plasma jet formation with a single bare metal electrode at significantly reduced voltages. The mechanism explains the observed plasma bullet propagation at 1–2×10⁴ m/s, offering a simpler, safer, and more flexible design for APPJ applications.

ABSTRACT

Atmospheric pressure plasma jet can protrude some 5.0 cm into air. It holds promise for multivarious innovative applications, but its formation mechanism remains unsettled. We show that the plasma jet is essentially a streamer corona totally independent of, but obscured by, dielectric barrier discharge. Consequently, the jets can be equally successfully generated even with one single bare metal electrode attached to the tube orifice, both downstream and upstream simultaneously, and at a significantly reduced voltage. These results will help understand the underlying physics and facilitate a safer and more flexible implementation of this marvelous plasma source.

Motivation & Objective

• To resolve the long-standing ambiguity in the formation mechanism of atmospheric pressure plasma jets (APPJs).
• To determine whether dielectric barrier discharge (DBD) processes are essential for APPJ generation.
• To investigate alternative electrode configurations, including single bare metal electrodes, for generating stable plasma jets.
• To quantify the propagation velocity of plasma bullets and link it to streamer dynamics.

Proposed method

• Experiments were conducted using a quartz capillary (2.0 mm inner, 3.5 mm outer diameter) with high-purity helium at 17 kHz excitation.
• Three electrode configurations were tested: double dielectric electrodes, single dielectric electrode, and single bare metal electrode at the tube orifice.
• Optical emission from plasma jets was recorded using a high-speed digital camera and photo-multiplier tubes (PMTs) with 1.5 mm axial resolution.
• Plasma bullet propagation was analyzed via time-resolved PMT signals at 5 mm and 15 mm from the orifice, enabling velocity calculation from time delays.
• Theoretical estimation of jet velocity used the formula v ≈ μU / χ, where μ = 0.113 m²/Vs (electron mobility in He), U is streamer head potential, and χ ≈ 3.0 mm (distance from photoionization origin to ionic front).
• Comparative analysis of optical intensity waveforms and true-color images confirmed consistency across all electrode configurations.

Experimental results

Research questions

• RQ1 Is the dielectric barrier discharge (DBD) process essential for the formation of atmospheric pressure plasma jets (APPJs)?
• RQ2 Can plasma jets be generated using only a single bare metal electrode without any dielectric layer?
• RQ3 What is the true physical origin of the observed plasma jet propagation—DBD or streamer corona?
• RQ4 How does the jet velocity depend on the electric field non-uniformity and applied voltage?
• RQ5 Can the observed plasma bullet velocities be explained by a streamer propagation model?

Key findings

• Plasma jets are formed via streamer corona discharge, not dielectric barrier discharge (DBD), which had previously obscured the true mechanism.
• APPJs can be successfully generated using only a single bare metal electrode attached to the tube orifice, both downstream and upstream simultaneously.
• The plasma jet velocity was measured at 1.1×10⁴ m/s, 0.7×10⁴ m/s, and 1.9×10⁴ m/s for double-electrode, single dielectric, and single bare metal configurations, respectively.
• A theoretical estimate using v ≈ μU / χ with U ≈ 2 kV and χ ≈ 3.0 mm yields v ≈ 7.5×10⁴ m/s, consistent with the measured values at lower voltages.
• The discharge overfall phenomenon observed at voltages >8.0 kV is attributed to charge saturation and overcompensation at the ground electrode, not to jet formation.
• The results support a streamer-based model for jet propagation, with velocity determined by electron avalanche dynamics and field non-uniformity at the electrode.