Ruggero Barni - Profile on Academia.edu (original) (raw)

Papers by Ruggero Barni

Research paper thumbnail of Current-voltage analysis in SDBD plasma discharge

Current-voltage analysis in SDBD plasma discharge

46th European Physical Society Conference on Plasma Physics, EPS 2019, 2019

Research paper thumbnail of Structure dynamics associated with temperature fluctuations in the magnetised plasma of the Thorello device

Experimental investigation of magnetised plasma turbulence is actively pursued in fusion aimed as... more Experimental investigation of magnetised plasma turbulence is actively pursued in fusion aimed as well as in basic plasma physics toroidal devices. The experimental study of the

Research paper thumbnail of Bohm like particle transport in a toroidal magnetoplasma in absence of longitudinal current

Bohm like particle transport in a toroidal magnetoplasma in absence of longitudinal current

Research paper thumbnail of Experimental Characterization of a new Plasma Source for Controlled Deposition of Thin Films

Thin films find several applications depending on both their morphology and chemistry. We have re... more Thin films find several applications depending on both their morphology and chemistry. We have recently implemented a double step deposition process in which film chemistry can be controlled separately from film growth. The molecules of the substance chosen for the deposit are obtained by dissociating an appropriate precursor into an inductively coupled plasma (ICP) obtained from an argon-oxygen mixture. Molecules formed during this first phase are then extracted through a nozzle into a lower pressure deposition chamber. A supersonic freely expanding jet is thus produced, until recompression occurs through a shock wave. Before and after the latter, the flow properties and the degree of molecule clusterization are different. Consequently, film growth can be controlled by changing the substrate location. We will present the design and properties of this new versatile plasma source for thin film deposition. It is well know that ICP discharges work in the inductive regime (H) only after...

Research paper thumbnail of Surface Dielectric Barrier Discharge Plasma MATLAB simulation

Surface Dielectric Barrier Discharge Plasma MATLAB simulation

Research paper thumbnail of A plug-probe diagnostics for the measurement of electric field fluctuations in the turbulent state of the simply magnetised toroidal plasma device THORELLO

Experimental investigation of magnetised plasma turbulence is actively pursued in fusion aimed as... more Experimental investigation of magnetised plasma turbulence is actively pursued in fusion aimed as well as in basic plasma physics toroidal devices. In particular the understanding of turbulent transport mechanisms has a great interest for the improvement of the magnetic confinement. Here we discuss the use of plug-probes, a suitable modification of traditional Langmuir electrostatic probes, for an experimental investigation of plasma parameters fluctuations of a turbulent, low beta, low temperature plasma in a simply magnetised toroidal configuration. The experiments have been executed on the Thorello device, operating at the University of Milano-Bicocca [1]. In this device, a low temperature, high density plasma can be produced in a steady configuration by driving a hot cathode discharge in low pressure hydrogen gas. In particular, in toroidal magnetised plasmas a large fraction of anomalous particles and energy transport is attributed to the propagation of coherent structures [2]....

Research paper thumbnail of A multiple pin Langmuir probe for the measurement of the electric field drift and its spatial derivatives

A multiple pin Langmuir probe for the measurement of the electric field drift and its spatial derivatives

Review of Scientific Instruments, 2021

We discuss the measurement of the electric field drift (E→xB→ velocity) and its spatial derivativ... more 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.

Research paper thumbnail of Characterization of the electrical and optical properties of a gliding arc tornado device

The European Physical Journal D

Optical emission spectroscopy was used to characterize the gas phase in a gliding arc tornado rea... more 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. Graphic abstract

Research paper thumbnail of Intermittent structures and quasi-stationary equilibrium in a simple magnetized torus in open field line configuration

Intermittent structures and quasi-stationary equilibrium in a simple magnetized torus in open field line configuration

Journal of Physics Communications, 2022

A steady regime dominated by intermittent blob and hole structures is identified in the plasma st... more A steady regime dominated by intermittent blob and hole structures is identified in the plasma state of a simple magnetized torus by achieving a quasi-stationary equilibrium using an open magnetic field line configuration. The open helical field line configuration is characterized by a connection length, L_c=2a(B_φ/B_z )≳1750 cm, and pitch ratio, r_B=B_z/B_φ ≲0.01. This is realized by superposing a vertical magnetic fied, B_z, to the toroidal field, B_φ, and the regime is achieved for B_z≤0.4 mT. The combined effect of plasma rotation, arising from a substantial radial electric field, together with an open field line, results in vertically elongated plasma profiles and an asymmetric sheared poloidal flow. The analysis shows the existence of density fluctuations exhibiting universal statistical properties, dominated by non-Gaussian blob events in the edge region and holes in the core plasma, separated by a region ascribed as blob birth zone corresponding to a velocity shear layer. Tw...

Research paper thumbnail of Intermittent structures and quasi-stationary equilibrium in a simple magnetized torus in open field line configuration

Intermittent structures and quasi-stationary equilibrium in a simple magnetized torus in open field line configuration

Journal of Physics Communications, 2022

A steady regime dominated by intermittent blob and hole structures is identified in the plasma st... more A steady regime dominated by intermittent blob and hole structures is identified in the plasma state of a simple magnetized torus by achieving a quasi-stationary equilibrium using an open magnetic field line configuration. The open helical field line configuration is characterized by a connection length, L_c=2a(B_φ/B_z )≳1750 cm, and pitch ratio, r_B=B_z/B_φ ≲0.01. This is realized by superposing a vertical magnetic fied, B_z, to the toroidal field, B_φ, and the regime is achieved for B_z≤0.4 mT. The combined effect of plasma rotation, arising from a substantial radial electric field, together with an open field line, results in vertically elongated plasma profiles and an asymmetric sheared poloidal flow. The analysis shows the existence of density fluctuations exhibiting universal statistical properties, dominated by non-Gaussian blob events in the edge region and holes in the core plasma, separated by a region ascribed as blob birth zone corresponding to a velocity shear layer. Tw...

Research paper thumbnail of 15+ MILLION TOP 1% MOST CITED SCIENTIST 12.2% AUTHORS AND EDITORS FROM TOP 500 UNIVERSITIES Chemical Kinetics in Air Plasmas at Atmospheric Pressure

Research paper thumbnail of 1 Coherent structures in sheared velocity flow

1 Coherent structures in sheared velocity flow

Research paper thumbnail of Current Filaments in Asymmetric Surface Dielectric Barrier Discharge

Applied Sciences

In this study, we examine the statistical properties of asymmetric surface dielectric barrier dis... more In this study, we examine the statistical properties of asymmetric surface dielectric barrier discharges (SDBD) produced by applying a periodic high voltage between two conducting displaced electrodes, located at the opposite sides of a flat dielectric panel. Here, the asymmetry refers to the fact that the lower electrode is fully covered with an insulating material, while the upper one, glued onto the dielectric surface, is otherwise left exposed to the air. Such a configuration allows the formation of a thin layer of plasma above the insulating surface. A single cycle signal consists of two well-separated half-cycle patterns, denoted as forward and backward strokes, corresponding to positive and negative voltages, respectively. They display a quite complex discharge pattern constituted by a sequence of individual peaks (bursts) of varying current and time duration. Specifically, we find that backward stroke bursts carry a positive mean charge Q≃0.3 nC and mean current I≃35 mA, wit...

Research paper thumbnail of Atmospheric Pressure Plasma Discharge for Polysiloxane Thin Films Deposition and Comparison with Low Pressure Process

Plasma Chemistry and Plasma Processing, 2011

An atmospheric pressure dielectric barrier plasma discharge has been used to study a thin film de... more An atmospheric pressure dielectric barrier plasma discharge has been used to study a thin film deposition process. The DBD device is enclosed in a vacuum chamber and one of the electrodes is a rotating cylinder. Thus, this device is able to simulate continuous processing in arbitrary deposition condition of pressure and atmosphere composition. A deposition process of thin organosilicon films has been studied reproducing a nitrogen atmosphere with small admixtures of hexamethyldisiloxane (HMDSO) vapours. The plasma discharge has been characterized with optical emission spectroscopy and voltagecurrent measurements. Thin films chemical composition and morphology have been characterized with FTIR spectroscopy, atomic force microscopy (AFM) and contact angle measurements. A strong dependency of deposit character from the HMDSO concentration has been found and then compared with the same dependency of a typical low pressure plasma enhanced chemical vapour deposition process.

Research paper thumbnail of Diagnostics of reactive RF plasmas

Vacuum, 2007

Experimental characterization of the plasma state as well as the neutral gas phase in a low press... more Experimental characterization of the plasma state as well as the neutral gas phase in a low pressure discharge is presented. A radiofrequency supply produces plasma driving an electrical discharge in a gas mixture through a resonant inductive coupling. The plasma state has been characterized by means of electrostatic probes, optical emission spectroscopy. Mass spectroscopy of the neutral and of the charged species has been performed too, sampling the gas phase inside the discharge. Results on Ar/SF 6 plasmas are presented to study the effect of argon doping on the production of reactive atomic fluorine in the discharge. More efficient application of Ar/SF 6 plasmas to surface fluorination of polymers could be expected in view of these results.

Research paper thumbnail of Radial Convection of Plasma Structures in a Turbulent Rotating Magnetized-Plasma Column

Physical Review Letters, 2004

The turbulent regime of a rotating magnetized plasma column has been studied. The detection and t... more The turbulent regime of a rotating magnetized plasma column has been studied. The detection and the spatiotemporal analysis of structures by means of conditional sampling techniques is performed. Because of the overall rotation and centrifugal effects, the structures inside the turbulence move on average along a spiral trajectory leading to a net radial convection of the charged particles to the walls. The development of a poloidal electric field inside the structures has been measured. It leads to the observed outwards radial E B drift in agreement with the expectations of recent theoretical works.

Research paper thumbnail of Characterization of the Chemical Kinetics in an O2/HMDSO RF Plasma for Material Processing

Advances in Physical Chemistry, 2012

Experimental study of the plasma gas phase in low-pressure radiofrequency discharges of oxygen an... more Experimental study of the plasma gas phase in low-pressure radiofrequency discharges of oxygen and hexamethyldisiloxane is presented. The plasma phase has been studied by means of optical emission spectroscopy. Mass spectroscopy of the neutral and of the charged species has been performed too, directly sampling the plasma gas phase, by a dedicated spectrometer. We also measured the ion energy distribution. We have studied the influence of the operating conditions on the plasma gas-phase composition which plays a primary role in the formation process of SiO2films, which are known for their important applicative uses.

Research paper thumbnail of Formation of spiral structures and radial convection in the edge region of a magnetized rotating plasma

New Journal of Physics, 2005

The rotation of a cylindrical plasma column in a magnetic field has been studied in the linear se... more The rotation of a cylindrical plasma column in a magnetic field has been studied in the linear section of the new plasma device Mistral. Under suitable conditions we observe a transition to a turbulent regime characterized by strong, bursty fluctuations at the edge of the column. The detection and the study of the spatio-temporal evolution of structures in the turbulent regime have been performed by means of a new enhanced conditional sampling technique. We have collected evidence of the development of a bent tail emanating from the plasma column. The charged particles inside the structure move along a spiral trajectory resulting in a net radial convection of the plasma to the walls. We show experimentally that a poloidal electric field is present inside the structures leading to the observed outwards radial E × B drift, in agreement with the expectations of recent and past theoretical works.

Research paper thumbnail of Trends in plasma applications

Trends in plasma applications

Research paper thumbnail of Chemical Kinetics of the Plasma Gas-hase in Humid Air Non-thermal Atmospheric Pressure Discharges

Chemical Kinetics of the Plasma Gas-hase in Humid Air Non-thermal Atmospheric Pressure Discharges

Research paper thumbnail of Current-voltage analysis in SDBD plasma discharge

Current-voltage analysis in SDBD plasma discharge

46th European Physical Society Conference on Plasma Physics, EPS 2019, 2019

Research paper thumbnail of Structure dynamics associated with temperature fluctuations in the magnetised plasma of the Thorello device

Experimental investigation of magnetised plasma turbulence is actively pursued in fusion aimed as... more Experimental investigation of magnetised plasma turbulence is actively pursued in fusion aimed as well as in basic plasma physics toroidal devices. The experimental study of the

Research paper thumbnail of Bohm like particle transport in a toroidal magnetoplasma in absence of longitudinal current

Bohm like particle transport in a toroidal magnetoplasma in absence of longitudinal current

Research paper thumbnail of Experimental Characterization of a new Plasma Source for Controlled Deposition of Thin Films

Thin films find several applications depending on both their morphology and chemistry. We have re... more Thin films find several applications depending on both their morphology and chemistry. We have recently implemented a double step deposition process in which film chemistry can be controlled separately from film growth. The molecules of the substance chosen for the deposit are obtained by dissociating an appropriate precursor into an inductively coupled plasma (ICP) obtained from an argon-oxygen mixture. Molecules formed during this first phase are then extracted through a nozzle into a lower pressure deposition chamber. A supersonic freely expanding jet is thus produced, until recompression occurs through a shock wave. Before and after the latter, the flow properties and the degree of molecule clusterization are different. Consequently, film growth can be controlled by changing the substrate location. We will present the design and properties of this new versatile plasma source for thin film deposition. It is well know that ICP discharges work in the inductive regime (H) only after...

Research paper thumbnail of Surface Dielectric Barrier Discharge Plasma MATLAB simulation

Surface Dielectric Barrier Discharge Plasma MATLAB simulation

Research paper thumbnail of A plug-probe diagnostics for the measurement of electric field fluctuations in the turbulent state of the simply magnetised toroidal plasma device THORELLO

Experimental investigation of magnetised plasma turbulence is actively pursued in fusion aimed as... more Experimental investigation of magnetised plasma turbulence is actively pursued in fusion aimed as well as in basic plasma physics toroidal devices. In particular the understanding of turbulent transport mechanisms has a great interest for the improvement of the magnetic confinement. Here we discuss the use of plug-probes, a suitable modification of traditional Langmuir electrostatic probes, for an experimental investigation of plasma parameters fluctuations of a turbulent, low beta, low temperature plasma in a simply magnetised toroidal configuration. The experiments have been executed on the Thorello device, operating at the University of Milano-Bicocca [1]. In this device, a low temperature, high density plasma can be produced in a steady configuration by driving a hot cathode discharge in low pressure hydrogen gas. In particular, in toroidal magnetised plasmas a large fraction of anomalous particles and energy transport is attributed to the propagation of coherent structures [2]....

Research paper thumbnail of A multiple pin Langmuir probe for the measurement of the electric field drift and its spatial derivatives

A multiple pin Langmuir probe for the measurement of the electric field drift and its spatial derivatives

Review of Scientific Instruments, 2021

We discuss the measurement of the electric field drift (E→xB→ velocity) and its spatial derivativ... more 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.

Research paper thumbnail of Characterization of the electrical and optical properties of a gliding arc tornado device

The European Physical Journal D

Optical emission spectroscopy was used to characterize the gas phase in a gliding arc tornado rea... more 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. Graphic abstract

Research paper thumbnail of Intermittent structures and quasi-stationary equilibrium in a simple magnetized torus in open field line configuration

Intermittent structures and quasi-stationary equilibrium in a simple magnetized torus in open field line configuration

Journal of Physics Communications, 2022

A steady regime dominated by intermittent blob and hole structures is identified in the plasma st... more A steady regime dominated by intermittent blob and hole structures is identified in the plasma state of a simple magnetized torus by achieving a quasi-stationary equilibrium using an open magnetic field line configuration. The open helical field line configuration is characterized by a connection length, L_c=2a(B_φ/B_z )≳1750 cm, and pitch ratio, r_B=B_z/B_φ ≲0.01. This is realized by superposing a vertical magnetic fied, B_z, to the toroidal field, B_φ, and the regime is achieved for B_z≤0.4 mT. The combined effect of plasma rotation, arising from a substantial radial electric field, together with an open field line, results in vertically elongated plasma profiles and an asymmetric sheared poloidal flow. The analysis shows the existence of density fluctuations exhibiting universal statistical properties, dominated by non-Gaussian blob events in the edge region and holes in the core plasma, separated by a region ascribed as blob birth zone corresponding to a velocity shear layer. Tw...

Research paper thumbnail of Intermittent structures and quasi-stationary equilibrium in a simple magnetized torus in open field line configuration

Intermittent structures and quasi-stationary equilibrium in a simple magnetized torus in open field line configuration

Journal of Physics Communications, 2022

A steady regime dominated by intermittent blob and hole structures is identified in the plasma st... more A steady regime dominated by intermittent blob and hole structures is identified in the plasma state of a simple magnetized torus by achieving a quasi-stationary equilibrium using an open magnetic field line configuration. The open helical field line configuration is characterized by a connection length, L_c=2a(B_φ/B_z )≳1750 cm, and pitch ratio, r_B=B_z/B_φ ≲0.01. This is realized by superposing a vertical magnetic fied, B_z, to the toroidal field, B_φ, and the regime is achieved for B_z≤0.4 mT. The combined effect of plasma rotation, arising from a substantial radial electric field, together with an open field line, results in vertically elongated plasma profiles and an asymmetric sheared poloidal flow. The analysis shows the existence of density fluctuations exhibiting universal statistical properties, dominated by non-Gaussian blob events in the edge region and holes in the core plasma, separated by a region ascribed as blob birth zone corresponding to a velocity shear layer. Tw...

Research paper thumbnail of 15+ MILLION TOP 1% MOST CITED SCIENTIST 12.2% AUTHORS AND EDITORS FROM TOP 500 UNIVERSITIES Chemical Kinetics in Air Plasmas at Atmospheric Pressure

Research paper thumbnail of 1 Coherent structures in sheared velocity flow

1 Coherent structures in sheared velocity flow

Research paper thumbnail of Current Filaments in Asymmetric Surface Dielectric Barrier Discharge

Applied Sciences

In this study, we examine the statistical properties of asymmetric surface dielectric barrier dis... more In this study, we examine the statistical properties of asymmetric surface dielectric barrier discharges (SDBD) produced by applying a periodic high voltage between two conducting displaced electrodes, located at the opposite sides of a flat dielectric panel. Here, the asymmetry refers to the fact that the lower electrode is fully covered with an insulating material, while the upper one, glued onto the dielectric surface, is otherwise left exposed to the air. Such a configuration allows the formation of a thin layer of plasma above the insulating surface. A single cycle signal consists of two well-separated half-cycle patterns, denoted as forward and backward strokes, corresponding to positive and negative voltages, respectively. They display a quite complex discharge pattern constituted by a sequence of individual peaks (bursts) of varying current and time duration. Specifically, we find that backward stroke bursts carry a positive mean charge Q≃0.3 nC and mean current I≃35 mA, wit...

Research paper thumbnail of Atmospheric Pressure Plasma Discharge for Polysiloxane Thin Films Deposition and Comparison with Low Pressure Process

Plasma Chemistry and Plasma Processing, 2011

An atmospheric pressure dielectric barrier plasma discharge has been used to study a thin film de... more An atmospheric pressure dielectric barrier plasma discharge has been used to study a thin film deposition process. The DBD device is enclosed in a vacuum chamber and one of the electrodes is a rotating cylinder. Thus, this device is able to simulate continuous processing in arbitrary deposition condition of pressure and atmosphere composition. A deposition process of thin organosilicon films has been studied reproducing a nitrogen atmosphere with small admixtures of hexamethyldisiloxane (HMDSO) vapours. The plasma discharge has been characterized with optical emission spectroscopy and voltagecurrent measurements. Thin films chemical composition and morphology have been characterized with FTIR spectroscopy, atomic force microscopy (AFM) and contact angle measurements. A strong dependency of deposit character from the HMDSO concentration has been found and then compared with the same dependency of a typical low pressure plasma enhanced chemical vapour deposition process.

Research paper thumbnail of Diagnostics of reactive RF plasmas

Vacuum, 2007

Experimental characterization of the plasma state as well as the neutral gas phase in a low press... more Experimental characterization of the plasma state as well as the neutral gas phase in a low pressure discharge is presented. A radiofrequency supply produces plasma driving an electrical discharge in a gas mixture through a resonant inductive coupling. The plasma state has been characterized by means of electrostatic probes, optical emission spectroscopy. Mass spectroscopy of the neutral and of the charged species has been performed too, sampling the gas phase inside the discharge. Results on Ar/SF 6 plasmas are presented to study the effect of argon doping on the production of reactive atomic fluorine in the discharge. More efficient application of Ar/SF 6 plasmas to surface fluorination of polymers could be expected in view of these results.

Research paper thumbnail of Radial Convection of Plasma Structures in a Turbulent Rotating Magnetized-Plasma Column

Physical Review Letters, 2004

The turbulent regime of a rotating magnetized plasma column has been studied. The detection and t... more The turbulent regime of a rotating magnetized plasma column has been studied. The detection and the spatiotemporal analysis of structures by means of conditional sampling techniques is performed. Because of the overall rotation and centrifugal effects, the structures inside the turbulence move on average along a spiral trajectory leading to a net radial convection of the charged particles to the walls. The development of a poloidal electric field inside the structures has been measured. It leads to the observed outwards radial E B drift in agreement with the expectations of recent theoretical works.

Research paper thumbnail of Characterization of the Chemical Kinetics in an O2/HMDSO RF Plasma for Material Processing

Advances in Physical Chemistry, 2012

Experimental study of the plasma gas phase in low-pressure radiofrequency discharges of oxygen an... more Experimental study of the plasma gas phase in low-pressure radiofrequency discharges of oxygen and hexamethyldisiloxane is presented. The plasma phase has been studied by means of optical emission spectroscopy. Mass spectroscopy of the neutral and of the charged species has been performed too, directly sampling the plasma gas phase, by a dedicated spectrometer. We also measured the ion energy distribution. We have studied the influence of the operating conditions on the plasma gas-phase composition which plays a primary role in the formation process of SiO2films, which are known for their important applicative uses.

Research paper thumbnail of Formation of spiral structures and radial convection in the edge region of a magnetized rotating plasma

New Journal of Physics, 2005

The rotation of a cylindrical plasma column in a magnetic field has been studied in the linear se... more The rotation of a cylindrical plasma column in a magnetic field has been studied in the linear section of the new plasma device Mistral. Under suitable conditions we observe a transition to a turbulent regime characterized by strong, bursty fluctuations at the edge of the column. The detection and the study of the spatio-temporal evolution of structures in the turbulent regime have been performed by means of a new enhanced conditional sampling technique. We have collected evidence of the development of a bent tail emanating from the plasma column. The charged particles inside the structure move along a spiral trajectory resulting in a net radial convection of the plasma to the walls. We show experimentally that a poloidal electric field is present inside the structures leading to the observed outwards radial E × B drift, in agreement with the expectations of recent and past theoretical works.

Research paper thumbnail of Trends in plasma applications

Trends in plasma applications

Research paper thumbnail of Chemical Kinetics of the Plasma Gas-hase in Humid Air Non-thermal Atmospheric Pressure Discharges

Chemical Kinetics of the Plasma Gas-hase in Humid Air Non-thermal Atmospheric Pressure Discharges