A study of helium atmospheric-pressure guided streamers for potential biological applications

Abstract

The origin of differences in the rotational temperatures of various molecules and ions (N + 2 (B), OH(A) and N 2 (C)) is studied in helium atmospheric-pressure guided streamers. The rotational temperature of N + 2 (B) is room temperature. It is estimated from the emission band of the first negative system at 391.4 nm, and it is governed by the temperature of N 2 (X) in the surrounding air. N 2 (X) is ionized by direct electron impact in the outer part of the plasma. N + 2 (B) is deactivated by collisions with N 2 and O 2 . The rotational temperature of OH(A), estimated from the OH band at 306.4 nm, is slightly higher than that of N + 2 (B). OH(A) is excited by electron impact with H 2 O during the first 100 ns of the applied voltage pulse. Next, OH(A) is produced by electron impact with OH(X) created by the quenching of OH(A) by N 2 and O 2 . H 2 O diffuses deeper than N 2 into the plasma ring and the rotational temperature of OH(A) is slightly higher than that of N + 2 (B). The rotational temperature of N 2 (C), estimated from the emission of the second positive system at 315.9 nm, is governed by its collisions with helium. The gas temperature of helium at the beginning of the pulse is predicted to be several hundred kelvin higher than room temperature.

Electrical, Thermal and Optical Parametric Study of Guided Ionization Waves Produced with a Compact μs-Pulsed DBD-Based Reactor

“…T rot was obtained as the value giving the best fit between these two spectra based on the least squares method. The fitting gives T rot = T gas = 344 K. The error on the measured value is estimated to be ±40 K [14]. Any influence on the measured value due to the spectral response of the optical system is excluded, since the latter is expected to be nearly constant within such a small wavelength interval (6 nm).…”

“…Analogous behavior has been observed by other groups in similar [24,25,31] and different [42] μs-pulsed driven GIWs; it could be related with the (a) Since many of the plasma-based DBD systems are meant to be used in biomedicine, the notion of temperature is very important. Different groups have proposed biocompatible reactors in terms of gas temperature [14][15][16]24], for which the temperature modification of the reactor mechanical parts is not considered. The effect of V p on the dielectric tube temperature (T sat , see Figure 2) is thoroughly studied herein.…”

“…Furthermore, OH(A) molecules are produced via dissociation (through collisions with electrons) of H2O molecules (present in the form of vapors) and electron impact excitation of the OH(X) [14]. N2(C) is produced through the electron impact excitation of N2(X) species, later forming N2(SPS) through radiative relaxation to the N2(B) state.…”

“…T exc was found to be about 1.2 eV at 12 kV, while it increased with the voltage amplitude. Besides, the electron density (n e ), calculated via the Stark broadening of two emission lines (i.e., He at 447.1 and H β at 486.1 nm), increased with the applied voltage and varied between~10 14 (center of the discharge) and~10 15 cm −3 (edge of the discharge). In another example, Jõgi et al [20] investigated a helium linear-field "micro-plasma jet" that was generated within microtubes (diameter−D tube : 80-500 µm) and biased by sinusoidal high voltage at 6 kHz.…”

“…In our case, OH(A-X) emission was detected in the emission spectrum of GIWs (see Figure 11). A representative experimental rotational structure of this molecule is given in Figure 13 (black color), which was fitted with the corresponding synthetic rotational spectrum (red dots) that was produced with a home-made code [6,14,15,51]. T rot was obtained as the value giving the best fit between these two spectra based on the least squares method.…”