Erdinc Karakas

Experimental Studies on the Plasma Bullet Propagation and Its Inhibition

Plasma bullets generated by atmospheric pressure low temperature plasma jets have recently been an active research topic due to their unique properties and their enhanced plasma chemistry. In this paper, experimental insights into the plasma bullet lifetime and its velocity are reported. Data obtained from intensified charge-coupled device camera and time-resolved optical emission spectroscopy (OES) elucidated the existence of a weakly ionized channel between the plasma bullet and its source (such as the plasma pencil). Factors responsible for the inhibition of the propagation of the bullet, such as low helium mole fraction, the magnitude of the applied voltage, and the secondary discharge ignition time, are also revealed. A new technique is discussed to accurately measure the plasma bullet velocity, using time-resolved OES. This new technique shows that during its lifetime the plasma bullet goes through launching, propagation, and ending phases. In addition, it is noted that the plasma bullet exhibits an unstable behavior at the early beginning and late ending of the propagation.

The evolution of atmospheric-pressure low-temperature plasma jets: jet current measurements

In this study, we report insights into the dynamics of atmospheric-pressure low-temperature plasma jets (APLTPJs). The plasma jet current was measured by a Pearson current monitor for different operating conditions. These jet current measurements confirmed a proposed photo-ionization model based on streamer theory. Our results are supported by intensified charged-couple device camera observations. It was found that a secondary discharge ignition, arising from the positive high-voltage electrode, causes the inhibition of plasma bullet propagation. Our observations also showed the existence of an ionization channel between the APLTPJ reactor and the plasma bullet. In addition, the maximum electron density along the plasma jet was estimated using Ohms law, and an empirical relationship was derived between the plasma bullet velocity and the plasma bullet area.

Destruction of α-synuclein based amyloid fibrils by a low temperature plasma jet

Amyloid fibrils are ordered beta-sheet aggregates that are associated with a number of neurodegenerative diseases such as Alzheimer and Parkinson. At present, there is no cure for these progressive and debilitating diseases. Here we report initial studies that indicate that low temperature atmospheric pressure plasma can break amyloid fibrils into smaller units in vitro. The plasma was generated by the “plasma pencil,” a device capable of emitting a long, low temperature plasma plume/jet. This avenue of research may facilitate the development of a plasma-based medical treatment.

Propagation Phases of Plasma Bullets

Plasma bullets have recently been used in novel applications in biology and medicine, which spurred interesting developments in the new interdisciplinary field of “Plasma Medicine.” In this paper, using high speed ICCD camera images we show that during their lifetime, plasma bullets undergo three distinctive phases: a launching phase during which the bullet velocity increases rapidly, a propagation phase during which the bullet velocity is temporarily maintained but later steadily decreases, and an ending phase during which the bullet collapses.

Optical emission spectroscopy and Langmuir probe diagnostics of CH3F/O2 inductively coupled plasmas

A CH3F:O2 (50%:50%) inductively coupled discharge, sustained in a compact plasma reactor, was investigated as a function of power (20–400 W) and pressure (9–30 mTorr), using optical emission spectroscopy and Langmuir probe measurements. The electron density increased linearly with power but only weakly with pressure. The effective electron temperature was nearly independent of power and pressure. The gas temperature, obtained from the rotational structure of N2 (C → B) optical emission, increased from 400 to 900 K as a function of inductive mode power between 75 and 400 W at 10 mTorr. For constant feed gas flow, the absolute H, F, and O atom densities, estimated by optical emission rare gas actinometry, increased linearly with power. The absolute number density ratios H/Ar, F/Ar, and O/Ar, increased, decreased, and remained constant, respectively, with pressure. The H-atom density was estimated to be 5.4 × 1013 cm−3 at 400 W and 10 mTorr (gas temperature = 900 K), implying a high degree of dissociation of...

Influence of Cell Type, Initial Concentration, and Medium on the Inactivation Efficiency of Low-Temperature Plasma

It is now well known that low-temperature plasmas can inactivate bacteria effectively. At low doses, these plasmas can also help in the proliferation of healthy fibroblasts and detach damaged cells without causing necrosis. The combination of these characteristics leads to the possibility of using plasmas in biomedical applications such as wound healing. Although only limited understanding is available as to the mechanisms whereby plasmas interact with cells (prokaryotic or eukaryotic), it is now well established that the effects of plasmas on biological cells depend on the cell type, the cell concentration, and the medium supporting them. In this paper, we present clear visual evidence of these dependencies in the case of bacteria. Through simple imaging, we show that the size and shape of the inactivation zone depend on the type of bacteria, their initial concentrations, and the medium supporting the cells.

A Positive Corona-Based Ion Wind Generator

Using an electrical discharge to control airflow has recently been an active area of research. This is mostly because of the interest in the manipulation of free airflow for aerodynamic applications. Corona discharges are well suited for these applications. In this paper, we present photographs illustrating the ion wind effect in a clear visual manner. The device used is a positive corona discharge between the end of sharp wires and a grounded mesh electrode. Measurements of the average wind speed as a function of the applied voltage for two different gap distances are presented.

Abrupt transitions in species number densities and plasma parameters in a CH3F/O2 inductively coupled plasma

Measured relative densities as a function of O2 addition in a CH3F/O2 inductively coupled plasma changed abruptly for H, O, and particularly F atoms (factor of 4) at 48% O2. A corresponding transition was observed in electron density, effective electron temperature, and gas temperature, as well as in C, CF, and CH optical emission. These abrupt transitions were attributed to the reactor wall reactivity, changing from a polymer-coated surface to a polymer-free surface and vice-versa, as the O2 content in the feed gas crossed 48%.

Effects of fluid flow on the characteristics of an atmospheric pressure low temperature plasma jet

Recently interest in low temperature atmospheric pressure plasma jets has increased due to their unique capabilities and novel applications [1], such as biomedicine. Prior experimental results showed that low temperature plasma jets are in fact trains of plasma bullets/packets traveling at supersonic velocities. This is especially interesting because the plasma bullets travel in a region free of any external electric field. Although Lu and Laroussi [2] explained this phenomenon by photoionization, how the bullets form and how they reach such high velocities are still not well-understood issues. Additionally, some properties of the plasma jets, such as the plasma plume length, homogeneity, bullets shape etc., are directly affected by the fluid flow, the geometry of the electrodes, and the characteristics of the applied high voltage pulse. In this paper, the fluid dynamics and electrostatic simulations of the plasma pencil are performed by a commercially available, partial differential equation solver based on Finite Element Method. We found that if the fluid velocity value is more than 10 m/s, the plasma plume starts to fluctuate and becomes unstable. In addition, the length and homogeneity of the plasma plume are directly related to the applied high voltage (magnitude and pulse width) and the fluid velocity values. These numerical simulations contribute some insights for future theoretical explanations and allow us to determine the optimum operation conditions of the plasma pencil.

Guest Editorial Special Issue on Atmospheric Pressure Plasma Jets and Their Applications

The 25 papers in this special issue focus on atmospheric pressure jets and their applications.