Plasma, Volume 5, Issue 2 (June 2022) – 8 articles

In recent years, one of the fastest growing technological applications in the field of nonthermal plasmas is the degradation of organic contaminants of water. In this work, the degradation of indigo carmine (IC) in water induced by a pulsed positive corona discharge operating in ambient air is reported. Degradation levels in different volumes of IC in solution with distilled water treated with different plasma exposure times immediately after discharge (0 h), and in the postdischarge up to 24 h were examined. To explain the IC discoloration in the postdischarge phase, a chemical model was developed. The stability of the reactive species in solution nitrate (NO₃⁻), nitrite (NO₂⁻) and hydrogen peroxide (H₂O₂), as well as the properties of the solution (electrical conductivity, pH) were also measured. The results suggest that the hydroxyl radical (OH˙) as well as ozone (O₃) are the main oxidizing species during the discharge phase, being primarily formed in the gas phase through plasma-mediated reactions and then transferred to the liquid by diffusion, while the OH˙ production in the bulk liquid through the decomposition of peroxinitrous acid (O=NOOH) plays a major role in the IC degradation during the postdischarge. These results are associated with a noticeably increase in the energy-yield values observed at 24 h post-treatment. Full article

We describe our investigations of a plasma-cathode electron source designed for the deposition of oxide coatings by the electron-beam evaporation of dielectric materials. Tests carried out using oxygen as the working gas showed that the source is operable without a change in parameters for at least ten hours of continuous operation. The current–voltage characteristics of the hollow-cathode plasma source in oxygen displayed a monotonically increasing character, and the voltage dependence of the discharge current was exponential. At the same time, for argon, nitrogen, and helium, the discharge voltage remained unchanged over a current ranging from 0.1 A to 1 A. A possible reason for these differences is the formation of oxides on the electrode surfaces for operation in the oxygen, impeding the discharge operation and requiring higher voltages for the same current as the other gases. The dependencies of the electron beam current on the accelerating voltage were monotonically increasing curves for all the gases except for helium, for which the beam current remained unchanged with increasing voltage over a range from two to ten kilovolts. Full article

Traditionally, spherical tokamak (ST) reactors are considered to operate in a steady state. This paper analyses the advantages of a pulsed ST reactor. The methodology developed for conventional tokamak (CT) reactors is used and it is shown that advantages of a pulsed operation are even more pronounced in an ST reactor because of its ability to operate at a higher beta, therefore achieving a higher bootstrap current fraction, which, together with a lower inductance, reduces requirements for magnetic flux from the central solenoid for the plasma current ramp-up and sustainment. Full article

Current methods used to treat non-muscle invasive bladder cancer are inadequate due to a high recurrence rate after surgery and the occurrence of adverse events such as interstitial pneumonia following intravesical instillation therapy. Low-temperature plasma is a new form of physical therapy that provides a rich source of reactive oxygen species (ROS). Oxidative solutions, created by pre-treatment of aqueous media with plasma before application to target cells, lead to the destruction of cancer cells through oxidative stress pathways. This study focuses on the effects of plasma-activated media (PAM) in bladder cancer cells. PAM treatment increases oxidative stress that leads to cell cycle arrest and concomitantly depolarises the mitochondrial membrane leading to increased mitochondrial ROS production. Cell cycle arrest and increased mitochondrial ROS production led to an increase in caspase 3/cytochrome c activity, which might explain the induction of apoptosis in bladder cancer cells in vitro and in a bladder cancer tumour in vivo. These observations highlight the potential of plasma activated solutions as a new adjuvant therapy in the clinical treatment of bladder cancer. Full article

In this study, the electrocatalytic activity of nickel foam, which is activated by cobalt, molybdenum, and nickel phosphide nanostructures, is prepared by the plasma hydrothermal method for use in the release of hydrogen and oxygen. The morphology and crystallographic structure of the synthesized phosphide specimens were examined by means of scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. Moreover, the electrolysis activity for these sets of specimens was investigated using the Tafel polarization curve or linear sweep voltammetry, cyclic voltammetry, as well as by means of the electrochemical impedance spectroscopy technique. Preliminary results show that nickel phosphide presents the highest electrocatalytic activity than the other phosphides developed in this research. In this regard, it presents an electrocatalytic activity to release hydrogen and oxygen of around −1.7 and 0.82 mV, which is measured at a current density of 100 mA·cm⁻², respectively. Full article

A non-thermal plasma, air purification device (PlasmaShield^®, MD250, Keswick, SA, Australia), was investigated using spatially resolved optical emission spectroscopy. The emission spectra were measured with two spatial dimensions to analyze and identify the transition lines of excited NO–γ (A²Σ–X²Π), N₂ (C³Π–B³Π), and N₂⁺ (B²Σ–X²Σ) systems. The N₂ emission band at 337 and 316 nm were used to determine the spatially resolved vibrational temperature of N₂ molecules, $T_{vib}^{N_2}$. It was found that the average N₂ vibrational temperatures in the x and y directions are almost the same. Two key operating parameters, supplied power and air flow, influence the N₂ vibrational temperature. The results demonstrate that applying higher supplied power increases the vibrational temperature, while changes in air flow velocity do not affect the vibrational temperature values. The phenomenological plasma temperature (PPT) was also estimated from the N₂ vibrational temperature. It was observed that PlasmaShield^® generates excited N₂ and NO only within a narrow region around the discharge electrode tip (with peak intensity below 100 µm from the tip). The study also shows no presence of excited OH*, O*, and other radicals. Full article

A vibrational analysis of various poly(o-aminophenol) structures has been undertaken using first principles methods. It is shown that a mixture of quinoid and keto forms of poly(o-aminophenol) gives rise to a simulated spectrum that replicates the experimental infrared spectra of plasma-produced poly(o-aminophenol) better than either the quinoid or keto poly(o-aminophenol) spectra alone. An unassigned peak in the spectrum is attributed to hydrogen bonding to the silica substrate. Full article

The measured current traces of alow energy AECS PF-1 plasma focus device are used for studying of the formed plasma, and the produced ion and electron beams. Anadapted version of the Lee model (RADPFV5.15FIB&REB) is applied, taking into account the fitting procedures between the measured and computed current waveforms for each shot. The experiments on AECSPF-1 were performed with three different gases—helium, nitrogen, and argon—for studying the effect of the atomic number on the properties of the generated beams. For numerical experiments using the Lee model, 36 successful shots for each gas were selected. The peak values of the total discharge current I_peak were 50–55 kA, the pinch currents I_pinchwere34–36 kA, and the final pinch radius reached a minimum value of 0.03 cm for argon. The ion mean energy ranged from 35 keV (for He) to 223 keV (for Ar). The beam energy also had an extreme value of 1.34 J (0.05%E₀) for argon. The results presented the highest values of 2.4 × 10¹⁴Wm⁻² for the power flow density, and adamage factor of around 3.1 × 10¹⁰ Wm⁻²s^0.5 for argon. For electron beams, the results also showed that the fluence and flux increased with the higher atomic number and reached a peak of 9.7 × 10²² m⁻² and 5.9 × 10³⁰ m⁻² s⁻¹ for argon, respectively. The results presented the highest values of 2.2 × 10¹⁶Wm⁻² for the power flow density (heat flux), and adamage factor of around 3 × 10¹² Wm⁻²s^0.5 for argon. The kinetic energy of the relativistic electrons was found to be within the range of 18–23 keV. The results show that the ion and electron beam properties (energy, flux, fluence, ion and electron numbers, current, power flow density, and damage factor) emitted from the plasma focus had wide ranges based on the operational plasma focus parameters. Thus, these results could be used for selection of the suitable plasma focus parameters for desired material processing applications. Full article