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Non equilibrium plasmas produced by Dielectric Barrier Discharges (DBD) have been proposed long ago as one of the most promising tools for technological applications of plasmas [1]. Using a suitable electrode geometry the discharge could be confined to the surface of the dielectric barrier (SDBD) and interact only in a mediate way with the target of the plasma treatment. DBDs and SDBD driven by high voltage signals applied to electrodes happen generally in short bursts of activity. There are several tricky aspects, including the geometry of the electrodes and the charging of the dielectric material surface facing the discharge region. The production of reactive species and the capability to dissociate or dispose of harmful or unwanted compounds also depend on the interplay between the energy transferred to the discharge and their repetition and respect to the incoming flow. Here we present the results of an experimental campaign aimed to the disposal of Volatile Organic Compounds (VOC) in a gas-phase exposed to our SDBD plasma device. We also present the results of an experimental characterization of the discharge and of the plasma gas-phase, based on spectroscopy and time resolved imaging [2]. We discuss briefly also modelling of the plasma gas-phase the prospect of using suitable pulsed discharge operation to improve the dissociation efficiency of VOCs [3].

Plasma actuators have been proposed as a tool to produce hydrodynamical effects in the boundary layer of aerodynamical flows. We have analyzed some properties of these systems using suitable plasma diagnostics based on the emissivity characteristics of such plasmas. The direction and the velocity of propagation of the ionizing wave spreading on the dielectric surface were measured (in the 100–200 km/s range), and it was demonstrated that it behaves like a cathode-directed streamer. The averaged electron temperature (4–5 eV) and the reduced field strength (E/N ≈ 6 × 1019 V·m2) of the ionizing wave switching the discharges on were measured, too.

Blob and hole dynamics is investigated in the sheared rotating plasma column of a simple magnetised torus using two-dimensional time-averaged measurements and conditional averaging analysis. Experiments are performed in open field line configuration by adding a vertical magnetic field component to the toroidal one, resulting in a quasistationary equilibrium characterised by vertically elongated profiles. The combined effect of plasma rotation with the vertical field leads to a poloidally asymmetric sheared E × B flow in the electron diamagnetic direction, pointing downward and upward in the low and high field side of the midplane, respectively, on both sides of the shear layer. Statistical analysis indicates that density fluctuations are dominated by non-Gaussian positive intermittent blob events in the low-density edge region, and negative hole events in the core plasma, whereas the intermediate shear layer corresponds to the blob birth zone featuring Gaussian statistics. Conditional averaging analysis reveals that, in the course of its propagation, a blob breaks off from a structure elongated in the direction of the flow due to the differential stretching in the vicinity of the shear layer. Blobs are convected out of the potential contour and ejected by the fluctuating field to the limiter, while holes stay inside and propagate back into the main plasma. Blobs move poloidally with velocities up to 3.7 km / s and radially up to 2.6 km / s. These observations confirm the picture where persistent structures provide a means for a net convection of the charged particles to the limiter, across the magnetic field and beyond the edge region of the magnetised plasmas.

Featured Application: Control or at least prediction of the gas-phase composition in atmospheric pressure cold plasmas is very important to evaluate the potential of plasma treatments, which could be considered in several applications, from health and environmental processes targeting hazard agents to the production of advanced materials through suitable surface functionalization. We present results obtained from the numerical simulation of the gas-phase chemical kinetics in atmospheric pressure air non-equilibrium plasmas. In particular, we addressed the effect of the pulsed operation mode of a planar dielectric barrier discharge. As conjectured, the large difference in the time scales involved in the fast dissociation of molecules in plasmas and their subsequent reactions to produce stable chemical species makes the presence of a continuously repeated plasma production stage unnecessary and a waste of electrical power and efficiency. The results on NOx remediation, ozone production, water vapor and ammonia dissociation are discussed. A few comparisons with experimental findings in a dielectric barrier discharge reactor already used for applications are also briefly addressed. Our results clearly indicate a pattern for the optimization of the discharge using a carefully designed repetition rate and duty cycle.

An experimental study of the plasma gas phase in low pressure radiofrequency discharges of oxygen is presented. The plasma phase has been studied by means of mass spectroscopy of the neutral and of the charged species, directly sampling the plasma gas phase. We also measured the ion energy distributions. We have studied the influence of the operating conditions on the plasma gas-phase composition. Ion density and energy have been measured as a function of discharge parameters. In particular, we have identified operating conditions in low pressure discharges allowing the extraction of ions from the plasma state with energies exceeding 50 eV. This makes plasma processing with energetic oxygen ions feasible in our device.

We discuss the effects of air atmospheric plasma interaction with the surface of a textile. We studied how plasma can promote changes in its texture and roughness at nano- and micro-meter scales, having an impact on the improvement of such macroscopic properties as hydro/oleo-repellency and pilling, without altering the hand assessment quality of the textile. These results are obtained by analyzing images taken using electron microscopy. We studied both the fluctuations of the image intensity at the fiber surfaces and their Fourier transforms at the sub-micrometer scales. As a case study, we have analyzed the modifications of a cashmere fabric and the improvement of finishing using resin spray coating. We observe a better efficiency when resin is applied to a plasma-treated sample. This result has been traced to the modifications that plasma induces on the surface at the nanoscale. This opens up wide perspectives to the use of plasma technology for the whole textile industrial sector.

Optical emission spectroscopy was used to characterize the gas phase in a gliding arc tornado reactor used for plasma applications. Results concerning the transition between spark and fully developed arc regimes are presented, by comparing with the electrical characteristics of the discharge. An extended analysis of spectra of air and helium discharges mixed with water and hexamethyldisiloxane vapors was performed, with the identification of active radical species involved in the surface functionalization of polymeric nanoparticles.

A noninvasive diagnostic technique relying on optical emission spectroscopy is used for studying plasma confined in a purely toroidal magnetic field. Visible emission lines of molecular hydrogen were specifically targeted. Bi-dimensional structures and poloidal plasma profiles were reconstructed from the emissivity distribution of hydrogen Fulcher system using a tomographic method. A few details concerning the methods employed to capture different emission viewlines, data reduction and tomographic reconstruction techniques are also addressed. We report also the first measurement of the excitation temperature of the H 2 [3c] level in the center of the plasma column, Texc= 0.67 ± 0.11 eV. Graphic Abstract: [Figure not available: see fulltext.]

We have analyzed the electrical characteristics of a plug probe as a function of the orientation relative to the local magnetic field. Our aim was to demonstrate that the probe characteristic, besides a better evaluation of the plasma potential, retains the capability to reliably estimate the electron temperature and density. This feature could be exploited with a multi-pin probe to measure simultaneously the fluctuations of all plasma parameters.

The Gliding Arc Tornado (GAT) is a device operating a near atmospheric pressure discharge with optimized hydrodynamical properties compared to those of gliding arcs reactors. The name points to the reverse vortex flow configuration, a tornado, of the gas-phase in the discharge region. In practice, this is implemented through a tangential gas injection from the lateral surface of a cylinder hosting the process chamber. This ensures an optimal mixing and much longer residence times respect to an axial laminar flow [1]. It provides also, normally a better insulation of the device walls from the discharge. It was also observed that a higher level of non-equilibrium characterizes the plasma gas-phase than in arcs. We have developed and used a kind of these devices for the treatment of lignin by plasmas [2]. Particles in powder, such as lignin, can be easily injected in the gas flow, separated and exposed to the plasma gas-phase while they are transported by the hydrodynamical flow. So optimal interaction with the discharge gas-phase could be achieved. Here we will present some results concerning the characterization of the discharge and of the plasma gas-phase. We discuss briefly also the prospect of plasma processing and its optimization, we have studied during a dedicated application, the POLISTE project [3].

Optical emission spectroscopy was used to characterize the gas-phase in a gliding arc tornado reactor used for plasma applications. Results concerning the transition between spark and fully developed arc regimes are presented.

Plasma process is a promising physical method for sterilization. Due to the lack of suitable plasma diagnostics, installed in the reactors, a general lack of knowledge happens about the gas-phase chemical composition and the influence of operating parameters. The same lack of knowledge happens in case of gas plasma generated from different gases, candidates for sterilization purposes. The aim of this work is to understand the role of different agents acting in the sterilization process, evaluate the effectiveness of different precursor gases and validate the plasma reactor dedicated. A plasma reactor, equipped with an extended set of plasma diagnostics is dedicated to the understanding the role of different agents of gas plasma sterilization process. A microbiological investigation is carried out to evaluate the efficiency of the steps of the process on cultures of Escherichia coli, using both hydrogen peroxide and argon. The effects on the colonies of Escherichia Coli are assessed in terms of species present in the chamber, acquiring the spectra resulting from the exposure of the Petri dish to sterilization. With regard to the sterilization action of Peroxide and Argon plasma, CFUs are counted for each significant point of the cycle and survival curves are provided. Differences emerge between Peroxide and Argon plasma, for action mechanisms and sterilization time. The survival curves show a more effective sterilizing action of Argon plasma. A validation is necessary by an appropriate statistic and by considering more resistant microorganisms. Reactor will be used to evaluate different precursor gases and microorganisms. The use of non-corrosive and non-irritating gas, such as argon, for sterilization purpose implies a simplification of the plant equipment. It would be possible to remove the components for the vaporization and concentration of peroxide, and to eliminate the management of the boxes containing discarded peroxide, managed to date as hazardous wastes an

We discuss the measurement of the electric field drift (E→xB→ velocity) and its spatial derivatives in a low temperature magnetized plasma by means of a suitably arranged multi-pin Langmuir probe. Results are presented relating the properties of the velocity field and its electrostatic fluctuations. In particular, we have measured components of the non-linear terms in the fluid magnetohydrodynamics equation.

Simple toroidal devices or simply magnetized torus (SMT) are considered as ideal testbed for studying physics of turbulence and associated heat and particle transport relevant to fusion devices since the magnetic field lines and parallel boundary conditions of SMTs are very similar to that of scrape of layer (SOL) of tokamaks. Previously it was reported that by increasing the toroidal field a transition from coherent to turbulent mode was observed. But the conventional stable equilibrium does not exist in SMTs due to the lack of rotational transform. Whereas some studies suggested the possible existence of 2D quasi stationary equilibrium as a function of connection length which can be realized in SMTs by applying a finite vertical field to the toroidal magnetic field [1]. In the present study, experiments were performed in an SMT device ‘Thorello’ by varying finite vertical field between -8 Gauss and +8 Gauss to a toroidal field of 400 Gauss. A hydrogen plasma is produced in the system using filamentary discharge by applying -80 V to the cathode with respect to the chamber for a working pressure of 4x10-4 mbar. 1D radial profile of plasma parameters obtained by Langmuir probe showed the variation in the depth of the potential well with varying vertical field. The mean radial density profile also indicated the shrinking of plasma column towards the centre as the vertical field is increased. Since it is known that this potential can gives rise to fluctuating electric field and which in turn result in a poloidal flow. Further studies have been carried out to obtain 2D plasma profile and using conditional sampling to explore the possible effect of vertical field on density intermittent structures (blobs/voids) which are localized density enhanced/depleted regions [2]. [1] K. Rypdal, E. Gronvoll, F. Oynes, A. Fredriksen, R. J. Armstrong, and J. Trulsen, Plasma Phys. Controlled Fusion 36, 1099 (1994). [2] R. Barni, S. Caldirola, L. Fattorini, and C. Riccardi, Physics of P