Laser absorption spectroscopy diagnostics of helium metastable atoms generated in dielectric barrier discharge cryoplasmas

Abstract

Cryoplasmas, which are plasmas whose gas temperatures are below room temperature (RT), have shown dynamic changes in their physical and chemical characteristics when the gas temperature in the plasmas (T gp ) was decreased from RT. In this study, we measured the temporal behavior of helium metastable (He m ) atoms generated in a parallel-plate dielectric barrier discharge at ambient gas temperatures (T ga ) of 300, 100, and 14 K and with a gas density similar to atmospheric conditions by laser absorption spectroscopy. The increments of T gp to T ga were less than 20 K. We found from the results that the He m lifetime and maximum density become longer and larger over one order of magnitude for lower T ga . The reasons for the long He m lifetime at low T ga are decreases in the rate coefficients of three-body He m quenching reactions and in the amounts of molecular impurities with boiling points higher than that of He.

Perspectives on functional nitrogen science and plasma-based in situ functionalization

“…Stable, high-density plasmas can be generated at both low and high pressures and temperatures. [28][29][30][31] As an example, Ito et al reported that a micrometer-scale plasma discharge was successfully generated in supercritical CO 2 . 32) Thereafter, Meneoka et al demonstrated a dielectric barrier discharge between carbon nanotube electrodes in high-density N 2 .…”

Oxygen atoms and nitrogen molecules as spectroscopic probes for the temperature determination in non-equilibrium cryogenic helium plasma jets

“…One exception only for cryogenic plasmas was reported in the literature for the He 2 excimer solvated in the liquid helium [11]: the lowest allowed rotational quantum state of the d 3 Σ u + state was exclusively populated. The presence of impurities in helium gas changes the emission spectra observed in different plasmas initiated by radiofrequency (RF), dielectric barrier discharge (DBD), corona, direct current (DC) discharges or by highly energetic particles [12,13,14,15,16,17,18,19,20]. Lowering the temperature of the helium gas usually causes decreasing of the impurity emission intensities accompanied by increasing of the emission intensity from the helium atoms and molecules [14,15].…”

“…The presence of impurities in helium gas changes the emission spectra observed in different plasmas initiated by radiofrequency (RF), dielectric barrier discharge (DBD), corona, direct current (DC) discharges or by highly energetic particles [12,13,14,15,16,17,18,19,20]. Lowering the temperature of the helium gas usually causes decreasing of the impurity emission intensities accompanied by increasing of the emission intensity from the helium atoms and molecules [14,15]. Nevertheless, fast cooling (for T ≈ 100 K within time ~ 0.1 ms) of the helium plasma jet allows observation of intense emission from impurity species at temperatures ~ 10 K [12,16,18,21,22].…”

Laser absorption spectroscopy for measurement of He metastable atoms of a microhollow cathode plasma

“…18,22) Laser absorption spectroscopy has been used as a standard technique for the measurement of metastable 2 3 S atoms. [23][24][25][26][27] Millard et al evaluated the metastable atom density in a plasma generated by a stationary glow discharge. 23) The electrodes in their device had a parallel-plate configuration, with electrodes of 38 mm diameter spaced 18 mm apart.…”

“…In this study, we performed laser absorption spectroscopy measurements for the helium 2 3 S 1 -2 3 P 0,1,2 transitions [23][24][25][26][27] in a micro-hollow-cathode helium plasma to investigate the behavior of the metastable 2 3 S 1 atoms. The experimental technique adopted in this study is based on a previous study 28) of the 2 1 P-3 1 D transition, wherein two-dimensional spatial distributions of the electric fields, 2 1 P atomic density, gas temperature, and electron density were evaluated at a gas pressure of 10 kPa.…”