Metastable helium atom density in a single electrode atmospheric plasma jet during sample treatment

Abstract

The metastable He atoms play an important role in atmospheric pressure plasma jet (APPJ) chemistry processes and in the plasma generation. This work presents cavity ringdown spectroscopy (CRDS) investigation of metastable helium atom (2 S 3 1 ) densities in a single electrode APPJ during sample treatment. A spatially resolved density distribution of a free jet (without sample) was measured at a He flow rate of 2 slm. The maximum measured density of a free jet was around × 7 10 11 cm −3 . With the insertion of a sample the densities increased up to 10 times. Helium metastable atoms, in a single electrode helium APPJ (2 slm, ≈2.5 kV, pulsed DC, 10 kHz repetition rate), decayed exponentially with a mean lifetime of ± 0.27 0.03 μs. Eight different samples of the same sizes but different conductivities were used to investigate the influence of a sample material on the He metastable densities. The correlation between sample conductivities and metastable He densities above the sample surface was found. Metastable He density can also be further increased with decreasing sample distance, increasing conductive sample surface area and by increasing He flow.

Plasma‐activated water to improve the stress tolerance of barley

“…The atmospheric plasma jet is generated in open air by using a quartz tube with the outer and inner diameters of 1.5 and 1 mm, respectively (Figure ). A copper wire of 100‐μm diameter is inserted into the capillary serving as the powered electrode . The powered electrode is connected to a high‐voltage supply with a sinus drive (28 kHz, 12 kV).…”

“…A copper wire of 100-μm diameter is inserted into the capillary serving as the powered electrode. [50] The powered electrode is connected to a high-voltage supply with a sinus drive (28 kHz, 12 kV). N 2 gas (99.996% purity) is supplied into the capillary, typically with a flow rate of 0.5 slm (standard liter per min).…”

Ar(1s5) absolute radial densities in a ns‐pulsed argon plasma jet impinging on dielectric targets at floating potential – plasma action on organic molecules

“…APPJs can be obtained through the excitation/ionization of a noble gas (usually argon or helium) by means of rf, kHz‐sinusoidal and ‐pulsed high voltages (HV) . Besides, they exhibit interesting properties for applications in biomedicine, agriculture, and interactions with inert targets . In the latter applications, the plasma impinges on different liquid and solid surfaces.…”

“…The role of metastable atoms in APPJs is particularly significant . They have relatively high energies, and act as energy reservoirs, contributing significantly to the plasma chemistry.…”

“…In what concerns He APPJs, numerous works have been devoted to the reliable measurement of He m densities. Helium plasma jets are generally stable and diffuse, and He m can be easily quantified via TDLAS (Tunable Diode Laser Absorption Spectroscopy) . This has been achieved both in the free‐jet case (i.e.…”