Time- and spatially resolved emission spectroscopy of the dielectric barrier discharge for soft ionization sustained by a quasi-sinusoidal high voltage

Abstract

A helium capillary dielectric barrier discharge was investigated by means of time-resolved optical emission spectroscopy with the aim of elucidating the process of the formation of the plasma jet. The helium emission line at 706 nm was utilized to monitor spatial and temporal propagation of the excitation of helium atoms. The discharge was sustained with quasi-sinusoidal high voltage, and the temporal evolution of the helium atomic emission was measured simultaneously with the discharge current. The spatial development of the plasma was investigated along the discharge axis in the whole region, which covers the positions in the capillary between the electrodes as well as the plasma jet outside the capillary. The high voltage electrode was placed 2 mm from the capillary orifice, and the distance between the ground and high voltage electrode was 10 mm. The complete spatiotemporal grid of the development of the helium excitation has shown that during the positive half-period of the applied voltage, two independent plasmas, separated in time, are formed. First, the early plasma that constitutes the plasma jet is formed, while the discharge in the capillary follows subsequently. In the early plasma, the helium atom excitation propagation starts in the vicinity of the high voltage electrode and departs from the capillary towards the ground electrode as well as several millimeters outside of the capillary in the form of the plasma jet. After relatively slow propagation of the early plasma in the capillary and the jet, the second plasma starts between the electrodes. During the negative voltage period, only the plasma in the capillary between the electrodes occurs.

Time-resolved spectroscopy of a homogeneous dielectric barrier discharge for soft ionization driven by square wave high voltage

“…3. In the picture, the position-dependent times at which the emission line intensity maxima occur (henceforth referred to as times of occurrence or occurrence times) are correlated with the plasma current signals in the same manner as in previous paper [22]. In both left and right part of Fig.…”

“…The transient emission intensities measured at three x positions inside and three positions outside the capillary are shown in Fig. 2b, c. As in the case of a sinusoidal-like driving voltage [22], during the positive voltage period, two emission signals Fig. 2b).…”

“…1. All the elements of the experimental arrangement, including one and the same capillary DBD, were the same as in the previous experiment [22], except the generator for supplying HV to the DBD electrodes. In order to get a reliable ionization source with no jumps from the homogeneous into the filamentary mode, a homemade generator was developed which produces square wave voltages with a rise time within 0.1 μs and the peak-to-peak voltages up to 3.5 kV.…”

“…The operation of DBD was investigated by time and spatially resolved OES measurements of the helium 706 and 501 nm lines intensities, with square wave high voltage applied to the electrodes. The comparison with recent results [22] obtained by using sinusoidal-like HV generator to operate the DBD is made. In both cases, the spatiotemporal behavior of the measured emission was found to be generally very similar.…”

“…Recently [22], an extensive investigation of the helium capillary dielectric barrier discharge sustained by a quasi-sinusoidal high voltage has been reported. The spectrally, spatially, and temporally resolved emission from the discharge was measured simultaneously with plasma current.…”