Ruggero Barni - Academia.edu (original) (raw)
Papers by Ruggero Barni
46th European Physical Society Conference on Plasma Physics, EPS 2019, 2019
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
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...
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]....
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.
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
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...
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...
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...
Plasma Chemistry and Plasma Processing, 2011
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.
Physical Review Letters, 2004
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.
New Journal of Physics, 2005
46th European Physical Society Conference on Plasma Physics, EPS 2019, 2019
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
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...
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]....
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.
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
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...
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...
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...
Plasma Chemistry and Plasma Processing, 2011
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.
Physical Review Letters, 2004
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.
New Journal of Physics, 2005