Time-dependence of the electron energy distribution function in the nitrogen afterglow

Abstract

In this paper, we present an investigation of the timerelaxation of the electron energy distribution function (EEDF) in the nitrogen afterglow of an 2 = 433 MHz flowing discharge at = 3 3 torr, in a tube with inner radius = 1 9 cm. We solve the time-dependent Boltzmann equation, including the term for creation of new electrons in associative/Penning reactions, coupled to a system of rate balance equations for the heavy-particles. The EEDFs are also obtained experimentally, from second derivatives of digitized probe characteristics measured using a triple probe technique, and compared with the calculations. It is shown that an equilibrium between the vibrational distribution function of ground-state molecules N 2 (1 6 +) and low-energy electrons is rapidly established, in times 10 7 s. In these early instants of the postdischarge, a dip is formed in the EEDF around 4 eV. The EEDF finally reaches a quasi-stationary state for 10 6 s, although the electron density still continues to decrease beyond this instant. Collisions of highly excited N 2 (1 6 + 35) molecules with N(4) atoms are in the origin of a maximum in the electron density occurring downstream from the discharge at 2 10 2 s. These reactions create locally the metastable states N 2 (3 6 +) and N 2 (1 6), which in turn ionize the gas in associative/Penning processes. Slow electrons remain for very long times in the postdischarge and can be involved in electron stepwise processes with energy thresholds smaller than 2-3 eV.

Non-equilibrium vibrational and electron energy distributions functions in atmospheric nitrogen ns pulsed discharges and μs post-discharges: the role of electron molecule vibrational excitation scaling-laws

“…A number of theoretical calculations of the vdf and eedf are available which are generally characterized by the use of different data sets for the key cross sections. In this context interesting results were reported for the low pressure nitrogen afterglow by Guerra et al by coupling eedf and electronically excited state kinetics to reproduce the experimental eedf from second derivatives of digitized probe characteristics measured using a triple probe technique [30].…”

Depolymerization of inulin in the highly reactive gas phase of a non thermal plasma at atmospheric pressure

“…The formation oxygen active species such as radicals • OH or metastable O 2 −, O* depends on the oxygen/helium or oxygen/nitrogen ratio. It is known in the literature as penning effect: oxygen acts as a quenching gas and helium or nitrogen transfer their energy via collisions to ionize oxygen . The formation of nitric acid under N 2 /O 2 plasma discharge would not only explain the complete conversion of inulin (which remains incomplete under He/O 2 ) but also the degradation into HMF under high nitrogen content (80% N 2 /20% O 2 ).…”

“…It is known in the literature as penning effect: oxygen acts as a quenching gas and helium or nitrogen transfer their energy via collisions to ionize oxygen. [19][20][21] The formation of nitric acid under N 2 /O 2 plasma discharge would not only explain the complete conversion of inulin (which remains incomplete under He/O 2 ) but also the degradation into HMF under high nitrogen content (80% N 2 /20% O 2 ). The increase of temperature, from excited species relaxation, would also take part in the depolymerization process as it forms an energy reservoir [22] altering the plasma discharge.…”

Shockwave Propagation in Nonequilibrium Air Plasma

“…Recent work has concentrated on the decay of the electron density and excited states 20,21 and these investigations show lifetimes of both the relevant excited states and decay times of the electron density to be in the order of msec. The electron density decay is dominated for 10 -5 to 10 -4 s at 2 Torr and 10 -5 to 10 -3 s at 10 Torr by the slow ambipolar diffusion, before switching to free diffusion 22 .…”