Registration of gas impurities in nonlocal plasma of helium microdischarge by an additional electrode — sensor

Abstract

Identification of gas impurities in helium by selective registration of groups of fast electrons created in Penning ionization of impurities atoms or molecules by metastable helium atoms at pressures of 7-40 Torr is realized. The collisional electron spectroscopy (CES) method is applied and is experimentally verified. Identification of impurities atoms and molecules is accomplished in collisional regime of movement of the particles, where the different groups of electrons have no time to relax in energy by collisions in the volume and behave independently of each other. An original design of microplasma gas analyzer is proposed, containing only nonlocal negative glow plasma of a short dc microdischarge. Registration of the energy spectra of penning electrons by means of an additional electrode-sensor, located at the boundary of the discharge volume is performed. The sensor has large collecting area compared to classical Langmuir probes, contributing to significant enhancement in the measurements sensitivity. Maxima in the EEDF are recorded in helium with small admixtures of krypton, argon and air. The obtained maxima appear at low discharge currents and at characteristic energies corresponding exactly to the expected maxima for penning electrons of the known gas impurities used. The gas analyser is compact, simple in technical performance, has high sensitivity and its size is dramatically reduced compared to the existing devices for gas analysis. This work is an approach to the development of microdischarge gas analyzers for gas impurities detection like poison gases, gas pollutions in the atmosphere or in the industry etc.

Energy spectra of Penning electrons in non-local plasma at middle and high pressures

“…The energy spectra of the Penning electrons recorded at high pressures of the main gas are similar to those obtained in our earlier papers [5,6] and 5.3×10 -16 cm 2 , respectively [9]), differ by about a factor of three, one can conclude that, at the particular discharge conditions, the density of singlet metastable He atoms is about three times as low as the density of triplet metastable He atoms.…”

“…A maximum appears at about 4.2 eV due to a Penning reaction between N 2 molecules present in the plasma as residual air impurities and triplet metastable He atoms leading to the formation of molecular nitrogen ions in ground state [1,5,6]: (5) and (6)) is seen in figure 4 as well. It is weak and appears only at discharge currents over 8 mA.…”

“…The so-called "modulation method" [8] was used. The recording system is typical for the probe measurements [5].…”

“…In this work we used the new collisional electron spectroscopy (CES) method, whose basic principles were presented in [4][5][6]. The CES method is based on measuring the energy spectra R(ε) of fast non-local electrons released in Penning ionization of the impurities atoms or molecules by the metastable atoms of the main gas:…”

A new hybrid scheme for simulations of highly collisional RF-driven plasmas

“…Whereas this popular approach is suitable for studying most atmospheric pressure discharges, there are situations where it turns out to be inadequate even in such highly collisional plasmas (e.g., [5][6][7][8]). In [5] it was shown that one of the indispensable ingredients in the mechanism of striation generation in an atmospheric dielectric barrier discharge is the non-local energy transport of the electrons.…”