Afterglow conductivity measurements of air and N₂following intense electron-beam excitation

Abstract

We have developed a new method of applying the microwave cavity perturbation technique that allows us to measure simultaneously real and imaginary conductivity decays. We report here results of afterglow decay measurements for air and N2 excited by an intense e-beam pulse. From these data, we calculate electron densities arid electron temperatures using exact expressions for the conductivities. The electron density decays for laboratory and synthetic air are approximately 10 and 40 times longer than predicted based on electron attachment for humid and dry air, respectively. Ambipolar diffusion coefficients and dissociative recombination rates measured at low pressures are inconsistent with previous results because our deduced electron temperatures are much higher than values used in previous studies. The decays in humid air appear to be dominated by ion conductivity.

Nonequilibrium Plasma Research

“…The inferred electron temperatures are consistent with experimental and numerical data reported by Spencer et al [22] and Guerra et al [27]. At 1 Torr, Spencer et al [22] indirectly measured an electron temperature of 0.6 eV in the afterglow using a microwave cavity resonator. At 3.3 Torr, Guerra et al [27] calculated an electron temperature of 0.7 eV in the near afterglow (1 μs < t < 100 μs).…”

“…We compared the measured decay of the electron number density to the theoretical decay by ambipolar diffusion to the wall and determined that the electron temperature in the near afterglow stays between 0.4 eV and 0.7 eV, depending on gas pressure. This confirms previous work by Spencer et al [22] and Guerra et al [27]. Many practical high pressure Dielectric Barrier Discharge (DBD) applications [30] require large electrode areas to achieve large surface area processing while maintaining high plasma-chemical and electrical efficiency.…”

“…Since the decrease in maximum signal is greater at higher pressure, we infer that electron-neutral collisions are causing the decrease. Spencer et al [22] found similar absorption in microwave signal at pressures of 1 Torr or greater.…”

“…Introduction Since Stenzel [14] introduced the hairpin resonator in 1976, this diagnostic tool has been used by Hebner et al [15], Piejak et al [16,17] and Haas et al [18] to measure the electron number density in low pressure RF discharges (10 mTorr < p < 300 mTorr). The hairpin resonator is just one of a wide range of available microwave diagnostics for measuring electron number density [19][20][21][22]. This paper only briefly describes the theory and experimental set up of the hairpin resonator for measuring the steady-state electron number density since more detailed information can be found in the previously referenced papers [14][15][16][17][18].…”

Characterization of electrostatic discharge induced plasmas in dielectrics irradiated by multi-MeV electron beam

“…The interaction of microwaves with plasmas and, more specifically, transmission, reflection, interferometry, and resonant cavity analysis are used to determine electric conductivity, and with some assumptions, the electron density and collision frequency of the plasma. [20][21][22][23] When a plasma is created in a cavity, the modification of its quality factor considering an oscillating electric field E r ð Þ is given by the following equation:…”