Ivan B Krstić

Spectroscopic measurement of electric field in atmospheric-pressure plasma jet operating in bullet mode

Atmospheric-pressure helium plasma jet operating in the bullet/streamer mode has been studied using optical emission spectroscopy. Electric field strength distribution is measured using Stark polarization spectroscopy of He I 492.19 nm line. It is shown that the electric field is almost constant along the jet axis. Measured electric field distribution is in agreement with theoretical predictions of streamer propagation in helium jets at atmospheric pressure. Obtained radial distribution of the axial electric field shows that the ring-shaped structure of the light emission is a consequence of such electric field distribution.

Spatio-temporally resolved electric field measurements in helium plasma jet

The focus of this paper is on the spatially and temporally resolved measurements of the electric field in atmospheric-pressure plasma jets operating in helium. Using the Stark polarization spectroscopy method, temporal development of the electric field was observed in steps which were in range of 20–500 ns. Such temporal resolution was complemented by the spatial resolution of 0.025 mm. Depending on the plasma jet configuration, the maximal electric field strength in the bullet/streamer head was between 10 and 20 kV cm−1. Electric field measurements are accompanied by the electrical and spectroscopic diagnostics of the discharge evolution. It was found that without the grounded electrode downstream from the nozzle, the jet develops as the cathode directed streamer. Contrarily, when a grounded electrode is present, development of the plasma jet is very similar to the evolution of the single microdischarge in air. Finally, the direct relation between electric field strength and the velocity of the plasma bullet is demonstrated.

Spectroscopic Study of Low-Frequency Helium DBD Plasma Jet

Atmospheric-pressure helium plasma jet has been studied by optical emission spectroscopy and electrical measurements. Streamer/bullet properties of the plasma jet are observed in the positive voltage half cycle, whereas in the negative jet, they operate more as a glowlike atmospheric-pressure discharge. This is revealed by spatially resolved measurements of intensity distribution of typical excited species and by electric field measurements based on Stark polarization spectroscopy. Obtained radial distribution of the axial electric field of the bullet shows that the ring-shaped structure of the light emission is a consequence of such electric field distribution. Gas temperature distribution over the jet is obtained by Boltzmann plot of rotational lines of N2+ and OH bands. Gas temperature is found to be about 310 K, favorable for the biomedical applications.

Electric field measurements in a kHz-driven He jet - The influence of the gas flow speed

This report focuses on the dependence of electric field strength in the effluent of a vertically downwards-operated plasma jet freely expanding into room air as a function of the gas flow speed. A 30 kHz AC-driven He jet was used in a coaxial geometry, with an amplitude of 2 kV and gas flow between 700 sccm and 2000 SCCM. The electric field was measured by means of Stark polarization spectroscopy of the He line at 492.19 nm. While the minimum and the maximum measured electric fields remained unchanged, the effect of the gas flow speed is to cause stretching of the measured profile in space-the higher the flow, the longer and less steep the electric field profile. The portion of the effluent in which the electric field was measured showed an increase of electric field with increasing distance from the capillary, for which the probable cause is the contraction of the plasma bullet as it travels through space away from the capillary. There are strong indications that the stretching of the electric field profile with increase in the flow speed is caused by differences in gas mixing as a function of the gas flow speed. The simulated gas composition shows that the amount of air entrained into the gas flow behaves in a similar way to the observed behaviour of the electric field. In addition we have shown that the visible length of the plasma plume is associated with a 0.027 molar fraction of air in the He flow in this configuration, while the maximum electric field measured was associated with a 0.014 molar fraction of air at gas flow rates up to 1500 SCCM (4.9 m s(-1)). At higher flows vortices occur in the effluent of the jet, as seen in Schlieren visualization of the gas flow with and without the discharge.

The isolated head model of the plasma bullet/streamer propagation: electric field-velocity relation

A model of the isolated streamer head based on Meeks criterion of the avalanche to streamer transition is applied for description of the plasma bullet propagation in a helium/air admixture. According to the model previously proposed by Kulikovsky for streamers in air, along with the knowledge of one of three parameters: electric field, ionization integral or the width of the space charge layer, the other two parameters could be determined. Furthermore, using the streamer current or radius, it is possible to determine the electric field-streamer velocity functional dependence. Obtained results showed satisfactory agreement with both the results of the fluid model from the literature and the experimental results of plasma jet studies. Finally, for the sake of comparison, streamer velocity dependence on the electric field strength range of 10–250 kV cm−1 is determined for helium, argon and air.

Electric field measurement in the dielectric tube of helium atmospheric pressure plasma jet

The results of the electric field measurements in the capillary of the helium plasma jet are presented in this article. Distributions of the electric field for the streamers are determined for different gas flow rates. It is found that electric field strength in front of the ionization wave decreases as it approaches to the exit of the tube. The values obtained under presented experimental conditions are in the range of 5–11 kV/cm. It was found that the increase in gas flow above 1500 SCCM could induce substantial changes in the discharge operation. This is reflected through the formation of the brighter discharge region and appearance of the electric field maxima. Furthermore, using the measured values of the electric field strength in the streamer head, it was possible to estimate electron densities in the streamer channel. Maximal density of 4  × 1011 cm−3 is obtained in the vicinity of the grounded ring electrode. Similar behaviors of the electron density distributions to the distributions of the elec...

Correlation between measured voltage and observed wavelength in commercial AlGaInP laser diode

Temperature of a commercial AlGaInP/GaInP quantum well laser diode (LD) is measured using two methods: peak wavelength shift and the diode voltage drop caused by working current. Time evolutions of temperature obtained by the two methods during the LD self-heating are measured and compared. No significant difference between the thus obtained temperature evolutions is obtained. Correlation between the LD voltage drop and the laser radiation frequency is established using a simple four-level semiconductor laser scheme and the LD gap energy is estimated. The LD gap energy decreases from 1.66 eV to 1.56 eV for temperature increase of 21 K, at close to room temperature. It is found that LDs frequency decrease is caused by the gap energy decrease.

Electrochemical Behaviour of a Composite Rh/TiO2 Layer Formed Potentiodynamically on Titanium Surface

Potentiodynamic polarization of a mechanically polished titanium electrode in a diluted solution of Rhodium(III) chloride in 0.1 M perchloric acid was performed, resulting in simultaneous formation of both Rh and TiO2 films. The morphology of obtained Rh/TiO2 composite film followed the morphology of titanium support, as evidenced by SEM technique. This composite surface was examined by cyclic voltammetry in both acidic and alkaline solutions, in the potential region of both hydrogen and oxygen underpotential deposition. The charge related to hydrogen underpotential deposition corresponded to a surface roughness of 43. As a consequence of high surface roughness, the diffusion current of oxygen reduction in an oxygen saturated 0.1 M NaOH solution, measured by voltammetry on rotating disc electrode, was found to be comparable to the current of hydrogen underpotential deposition.