Ricardo Galvao | University of Sao Paulo (original) (raw)
Papers by Ricardo Galvao
Nuclear Fusion, 2004
Edge polarization experiments were carried out on ISTTOK using an emissive electrode. The depende... more Edge polarization experiments were carried out on ISTTOK using an emissive electrode. The dependence of the bias current on the radial electric field, measured by a radial array of Langmuir probes, is in qualitative agreement with the expression derived by Stringer for the transitional region between plateau and collisional transport regimes (Stringer T.E. 1993 Nucl. Fusion 33 1249). Improved particle
Computer Physics Communications, 2012
SCTE intends to provide a simple, yet powerful, framework for building data acquisition and equip... more SCTE intends to provide a simple, yet powerful, framework for building data acquisition and equipment control systems for experimental Physics, and correlated areas. Via its SCTE::Instrument module, RS-232, USB, and LAN buses are supported, and the intricacies of hardware communication are encapsulated underneath an object oriented abstraction layer. Written in Perl, and using the SCPI protocol, enabled instruments can be easily programmed to perform a wide variety of tasks. While this work presents general aspects of the development of data acquisition systems using the SCTE framework, it is illustrated by particular applications designed for the calibration of several in-house developed devices for power measurement in the tokamak TCABR Alfvén Waves Excitement System.
Physics of Plasmas, 2005
Recent results obtained in TCABR (Tokamak Chauffage Alfvén Brésilien) [J. H. F. Severo, I. C. Nas... more Recent results obtained in TCABR (Tokamak Chauffage Alfvén Brésilien) [J. H. F. Severo, I. C. Nascimento, V. S. Tsypin, and R. M. O. Galva~o, Nucl. Fusion 43, 1047 (2003)] show a nonmonotonic variation of the poloidal rotation velocity at the position of major magnetic islands. In this paper, the associated effect of the magnetic islands on the radial profile of
Brazilian Journal of Physics, 2002
Results of experiments performed at the Institute for Space Research (INPE) are reported. An enri... more Results of experiments performed at the Institute for Space Research (INPE) are reported. An enrichment of 390 percent of carbon isotopes was achieved in the plasma centrifuge. The role of ion-acoustic turbulence in the formation of double layers was experimentally investigated. The turbulent spectrum was measured and agrees quite well with the prediction of the modified Kadomtsev renormalized theory. The
Plasma Physics and Controlled Fusion, 2001
... The primary rate of runaway generation is given by a well known expression and depends critic... more ... The primary rate of runaway generation is given by a well known expression and depends critically on the value of the parameter α = E/ED, where ED is Dreicer critical field [3]. The secondary rate, on the other hand, is given by S2 = nb/τav, with the avalanche time estimated as ...
Plasma Physics and Controlled Fusion, 2019
The effect of fast ions on turbulent particle transport, driven by ion temperature gradient (ITG)... more The effect of fast ions on turbulent particle transport, driven by ion temperature gradient (ITG)/trapped electron mode turbulence, is studied. Two neutral beam injection (NBI) heated JET discharges in different regimes are analyzed at the radial position ρ t = 0.6, one of them an L-mode and the other one an H-mode discharge. Results obtained from the computationally efficient fluid model EDWM and the gyro-fluid model TGLF are compared to linear and nonlinear gyrokinetic GENE simulations as well as the experimentally obtained density peaking. In these models, the fast ions are treated as a dynamic species with a Maxwellian background distribution. The dependence of the zero particle flux density gradient (peaking factor) on fast ion density, temperature and corresponding gradients, is investigated. The simulations show that the inclusion of a fast ion species has a stabilizing influence on the ITG mode and reduces the peaking of the main ion and electron density profiles in the abs...
Preliminary results of the design of a small compact tokamak are presented. The design incorporat... more Preliminary results of the design of a small compact tokamak are presented. The design incorporates advanced concepts as start-up and current drive by electron cyclotron and lower hybrid waves, plasma heating by intense ion beams, and achievement of high beta by decreasing the aspect ratio.
The software application described in this work aims to help with one of the main issues in exper... more The software application described in this work aims to help with one of the main issues in experimental physics, the automation of data acquisition and equipment control. This software application, designated as SCTE, was written in Perl and uses the SCPI language to communicate with test instruments. The communication goes through RS-232 port, also known as serial port, vastly available in current generation PCs and testing equipment. Although the RS-232 port has been used here, SCTE may be easily adapted to work with USB or other kind of ports. SCTE enables the simultaneous control of several test equipment of different kinds, like oscilloscopes and signal generators, in order to automate an entire experiment. This program has been used to calibrate a new set of devices for power determination, part of the Alfven wave heating system of the tokamak TCABR.
Fusion Engineering and Design, 2006
ABSTRACT The ICANT code computes self-consistently the surface current distribution on a 3D anten... more ABSTRACT The ICANT code computes self-consistently the surface current distribution on a 3D antenna model radiating in a plasma or vacuum and has been used to analyze the coupling properties of various antenna models. In this work it is used to assess near-fields generated by different versions of the TCABR (Tokamak Chauffage Alfvén wave heating experiment in Brazil) antenna as well as coupling properties of the TEXTOR tokamak in Forshungszentrum Jülich. Two different strap models planned for the TCABR antenna are shown to be practically equivalent in terms of maximum electric field. Textor coupling calculations are close to experimental values.
Physics of Plasmas, 2004
... JHF Severo, IC Nascimento, VS Tsypin, YK Kuznetsov, EA Saettone, A. Vannucci, RMO Galvão, M. ... more ... JHF Severo, IC Nascimento, VS Tsypin, YK Kuznetsov, EA Saettone, A. Vannucci, RMO Galvão, M. Tendler, AB Mikhailovskii. ... ED Taylor, C. Cates, ME Mauel, DA Maurer, D. Nadle, GA Navratil, and M. Shilov, Effect of magnetic islands on the local plasma behavior in a tokamak ...
Journal of Plasma Physics, 2002
Absorption by trapped particles is supposed to seriously hinder current drive by Alfvén waves. Ho... more Absorption by trapped particles is supposed to seriously hinder current drive by Alfvén waves. However, it is shown in this paper that the same effect is rather beneficial for the emergence of the radial electric field induced by these waves, which is important for creating and maintaining transport barriers in tokamaks.
arXiv: Plasma Physics, 2018
In this work we introduce, for the first time, as far as we know, a complete self-consist kinetic... more In this work we introduce, for the first time, as far as we know, a complete self-consist kinetic model for collisional transport in the nonextensive statistics, i.e., the generalization of the ordinary Maxwell-Boltmzann statistics according to the Tsallis entropy. Starting only from the definition of this entropy, we derive the kinetic model, find its solutions for the electrons in a strongly magnetized plasmas, and calculate the respective transport coefficients in order to set the closed fluid equations. The results are further applied to model heat transport in space plasmas and the cold pulse phenomenon in magnetic confined plasmas.
Physical Review E
The modulational instability of a linearly polarized, strong, electromagnetic wave in a ͑unmagnet... more The modulational instability of a linearly polarized, strong, electromagnetic wave in a ͑unmagnetized͒ positron-electron plasma is analyzed using relativistic two-fluid hydrodynamics to properly account for physical regimes of very high temperatures. The effect of phonon damping is also included in the treatment. The theory can be reduced to a pair of extended Zakharov equations. The envelope modulation is then studied by deriving the corresponding nonlinear Schrödinger ͑NLS͒ equation, using multiscale perturbation analysis. According to the intensity of the damping three different types of NLS are obtained. The main results are ͑a͒ that relativistic temperatures modify the stability result found in the literature for low temperature, zero damping, e ϩ-e Ϫ plasmas, and ͑b͒ that phonon damping also produces substantial changes in the NLS, which then predict unstable envelopes. This work extends previous analyses, showing that if the phonon damping is O͑⑀ 0 ͒ or O͑⑀ 1 ͒ ͑⑀ is the perturbation parameter͒, a modulational instability appears in the electron-positron case in all ranges of temperature and wave frequencies. Thus presence of some amount of sound absorption helps to produce an envelope decay. When the phonon damping is very small ͓O͑⑀ 2 ͔͒ the self-modulational instability occurs in a finite band near the reduced plasma frequency, for ultrarelativistic temperatures.
Journal of Physics C: Solid State Physics
The influence of a laser field on the scattering rate for the electron-phonon interaction in semi... more The influence of a laser field on the scattering rate for the electron-phonon interaction in semiconductor layered heterojunction structures is discussed. It is found that for a laser beam polarised in the layer plane and with a frequency w such that ut > 1, where r is the carrier relaxation time, the phonon-limited mobility increases with increasing laser field strength.
Journal of Physics B: Atomic and Molecular Physics
... We note that the ionisation probability exhibits an initial linear increase with time and eve... more ... We note that the ionisation probability exhibits an initial linear increase with time and eventually reaches a saturation, similar to what has been observed by Leopold and Percival(l979) in the atomic problem. ... Page 9. 3842 IL Mayer, L C M Miranda, BY Tong and RM 0 Galvao ...
Physical Review E
We study the parametric decays of a large amplitude, linearly polarized electromagnetic wave in a... more We study the parametric decays of a large amplitude, linearly polarized electromagnetic wave in an electronpositron plasma. We include harmonic generation, the ponderomotive force, and weakly relativistic effects. It is shown that when v s /cϽc/v p ͑v s is the electroacoustic velocity, c is the speed of light, and v p is the phase velocity of the electromagnetic wave͒, there are two instabilities. One is an ordinary decay instability, in which the pump wave decays into a sideband wave, propagating backward relative to the pump wave, and an electroacoustic mode propagating forward. The other is an essentially electromagnetic nonresonant modulational instability ͑which is due to higher order effects of the pump wave amplitude͒, in which the pump wave decays into two sideband waves. When v s /cуc/v p , there is a modulational nonresonant instability, and an ordinary modulational instability, in which the pump wave decays into a sideband wave and a forward propagating electroacoustic mode. ͓S1063-651X͑97͒03709-4͔
Nuclear Fusion, 2004
Edge polarization experiments were carried out on ISTTOK using an emissive electrode. The depende... more Edge polarization experiments were carried out on ISTTOK using an emissive electrode. The dependence of the bias current on the radial electric field, measured by a radial array of Langmuir probes, is in qualitative agreement with the expression derived by Stringer for the transitional region between plateau and collisional transport regimes (Stringer T.E. 1993 Nucl. Fusion 33 1249). Improved particle
Computer Physics Communications, 2012
SCTE intends to provide a simple, yet powerful, framework for building data acquisition and equip... more SCTE intends to provide a simple, yet powerful, framework for building data acquisition and equipment control systems for experimental Physics, and correlated areas. Via its SCTE::Instrument module, RS-232, USB, and LAN buses are supported, and the intricacies of hardware communication are encapsulated underneath an object oriented abstraction layer. Written in Perl, and using the SCPI protocol, enabled instruments can be easily programmed to perform a wide variety of tasks. While this work presents general aspects of the development of data acquisition systems using the SCTE framework, it is illustrated by particular applications designed for the calibration of several in-house developed devices for power measurement in the tokamak TCABR Alfvén Waves Excitement System.
Physics of Plasmas, 2005
Recent results obtained in TCABR (Tokamak Chauffage Alfvén Brésilien) [J. H. F. Severo, I. C. Nas... more Recent results obtained in TCABR (Tokamak Chauffage Alfvén Brésilien) [J. H. F. Severo, I. C. Nascimento, V. S. Tsypin, and R. M. O. Galva~o, Nucl. Fusion 43, 1047 (2003)] show a nonmonotonic variation of the poloidal rotation velocity at the position of major magnetic islands. In this paper, the associated effect of the magnetic islands on the radial profile of
Brazilian Journal of Physics, 2002
Results of experiments performed at the Institute for Space Research (INPE) are reported. An enri... more Results of experiments performed at the Institute for Space Research (INPE) are reported. An enrichment of 390 percent of carbon isotopes was achieved in the plasma centrifuge. The role of ion-acoustic turbulence in the formation of double layers was experimentally investigated. The turbulent spectrum was measured and agrees quite well with the prediction of the modified Kadomtsev renormalized theory. The
Plasma Physics and Controlled Fusion, 2001
... The primary rate of runaway generation is given by a well known expression and depends critic... more ... The primary rate of runaway generation is given by a well known expression and depends critically on the value of the parameter α = E/ED, where ED is Dreicer critical field [3]. The secondary rate, on the other hand, is given by S2 = nb/τav, with the avalanche time estimated as ...
Plasma Physics and Controlled Fusion, 2019
The effect of fast ions on turbulent particle transport, driven by ion temperature gradient (ITG)... more The effect of fast ions on turbulent particle transport, driven by ion temperature gradient (ITG)/trapped electron mode turbulence, is studied. Two neutral beam injection (NBI) heated JET discharges in different regimes are analyzed at the radial position ρ t = 0.6, one of them an L-mode and the other one an H-mode discharge. Results obtained from the computationally efficient fluid model EDWM and the gyro-fluid model TGLF are compared to linear and nonlinear gyrokinetic GENE simulations as well as the experimentally obtained density peaking. In these models, the fast ions are treated as a dynamic species with a Maxwellian background distribution. The dependence of the zero particle flux density gradient (peaking factor) on fast ion density, temperature and corresponding gradients, is investigated. The simulations show that the inclusion of a fast ion species has a stabilizing influence on the ITG mode and reduces the peaking of the main ion and electron density profiles in the abs...
Preliminary results of the design of a small compact tokamak are presented. The design incorporat... more Preliminary results of the design of a small compact tokamak are presented. The design incorporates advanced concepts as start-up and current drive by electron cyclotron and lower hybrid waves, plasma heating by intense ion beams, and achievement of high beta by decreasing the aspect ratio.
The software application described in this work aims to help with one of the main issues in exper... more The software application described in this work aims to help with one of the main issues in experimental physics, the automation of data acquisition and equipment control. This software application, designated as SCTE, was written in Perl and uses the SCPI language to communicate with test instruments. The communication goes through RS-232 port, also known as serial port, vastly available in current generation PCs and testing equipment. Although the RS-232 port has been used here, SCTE may be easily adapted to work with USB or other kind of ports. SCTE enables the simultaneous control of several test equipment of different kinds, like oscilloscopes and signal generators, in order to automate an entire experiment. This program has been used to calibrate a new set of devices for power determination, part of the Alfven wave heating system of the tokamak TCABR.
Fusion Engineering and Design, 2006
ABSTRACT The ICANT code computes self-consistently the surface current distribution on a 3D anten... more ABSTRACT The ICANT code computes self-consistently the surface current distribution on a 3D antenna model radiating in a plasma or vacuum and has been used to analyze the coupling properties of various antenna models. In this work it is used to assess near-fields generated by different versions of the TCABR (Tokamak Chauffage Alfvén wave heating experiment in Brazil) antenna as well as coupling properties of the TEXTOR tokamak in Forshungszentrum Jülich. Two different strap models planned for the TCABR antenna are shown to be practically equivalent in terms of maximum electric field. Textor coupling calculations are close to experimental values.
Physics of Plasmas, 2004
... JHF Severo, IC Nascimento, VS Tsypin, YK Kuznetsov, EA Saettone, A. Vannucci, RMO Galvão, M. ... more ... JHF Severo, IC Nascimento, VS Tsypin, YK Kuznetsov, EA Saettone, A. Vannucci, RMO Galvão, M. Tendler, AB Mikhailovskii. ... ED Taylor, C. Cates, ME Mauel, DA Maurer, D. Nadle, GA Navratil, and M. Shilov, Effect of magnetic islands on the local plasma behavior in a tokamak ...
Journal of Plasma Physics, 2002
Absorption by trapped particles is supposed to seriously hinder current drive by Alfvén waves. Ho... more Absorption by trapped particles is supposed to seriously hinder current drive by Alfvén waves. However, it is shown in this paper that the same effect is rather beneficial for the emergence of the radial electric field induced by these waves, which is important for creating and maintaining transport barriers in tokamaks.
arXiv: Plasma Physics, 2018
In this work we introduce, for the first time, as far as we know, a complete self-consist kinetic... more In this work we introduce, for the first time, as far as we know, a complete self-consist kinetic model for collisional transport in the nonextensive statistics, i.e., the generalization of the ordinary Maxwell-Boltmzann statistics according to the Tsallis entropy. Starting only from the definition of this entropy, we derive the kinetic model, find its solutions for the electrons in a strongly magnetized plasmas, and calculate the respective transport coefficients in order to set the closed fluid equations. The results are further applied to model heat transport in space plasmas and the cold pulse phenomenon in magnetic confined plasmas.
Physical Review E
The modulational instability of a linearly polarized, strong, electromagnetic wave in a ͑unmagnet... more The modulational instability of a linearly polarized, strong, electromagnetic wave in a ͑unmagnetized͒ positron-electron plasma is analyzed using relativistic two-fluid hydrodynamics to properly account for physical regimes of very high temperatures. The effect of phonon damping is also included in the treatment. The theory can be reduced to a pair of extended Zakharov equations. The envelope modulation is then studied by deriving the corresponding nonlinear Schrödinger ͑NLS͒ equation, using multiscale perturbation analysis. According to the intensity of the damping three different types of NLS are obtained. The main results are ͑a͒ that relativistic temperatures modify the stability result found in the literature for low temperature, zero damping, e ϩ-e Ϫ plasmas, and ͑b͒ that phonon damping also produces substantial changes in the NLS, which then predict unstable envelopes. This work extends previous analyses, showing that if the phonon damping is O͑⑀ 0 ͒ or O͑⑀ 1 ͒ ͑⑀ is the perturbation parameter͒, a modulational instability appears in the electron-positron case in all ranges of temperature and wave frequencies. Thus presence of some amount of sound absorption helps to produce an envelope decay. When the phonon damping is very small ͓O͑⑀ 2 ͔͒ the self-modulational instability occurs in a finite band near the reduced plasma frequency, for ultrarelativistic temperatures.
Journal of Physics C: Solid State Physics
The influence of a laser field on the scattering rate for the electron-phonon interaction in semi... more The influence of a laser field on the scattering rate for the electron-phonon interaction in semiconductor layered heterojunction structures is discussed. It is found that for a laser beam polarised in the layer plane and with a frequency w such that ut > 1, where r is the carrier relaxation time, the phonon-limited mobility increases with increasing laser field strength.
Journal of Physics B: Atomic and Molecular Physics
... We note that the ionisation probability exhibits an initial linear increase with time and eve... more ... We note that the ionisation probability exhibits an initial linear increase with time and eventually reaches a saturation, similar to what has been observed by Leopold and Percival(l979) in the atomic problem. ... Page 9. 3842 IL Mayer, L C M Miranda, BY Tong and RM 0 Galvao ...
Physical Review E
We study the parametric decays of a large amplitude, linearly polarized electromagnetic wave in a... more We study the parametric decays of a large amplitude, linearly polarized electromagnetic wave in an electronpositron plasma. We include harmonic generation, the ponderomotive force, and weakly relativistic effects. It is shown that when v s /cϽc/v p ͑v s is the electroacoustic velocity, c is the speed of light, and v p is the phase velocity of the electromagnetic wave͒, there are two instabilities. One is an ordinary decay instability, in which the pump wave decays into a sideband wave, propagating backward relative to the pump wave, and an electroacoustic mode propagating forward. The other is an essentially electromagnetic nonresonant modulational instability ͑which is due to higher order effects of the pump wave amplitude͒, in which the pump wave decays into two sideband waves. When v s /cуc/v p , there is a modulational nonresonant instability, and an ordinary modulational instability, in which the pump wave decays into a sideband wave and a forward propagating electroacoustic mode. ͓S1063-651X͑97͒03709-4͔