Francesco Pegoraro - Academia.edu (original) (raw)

Papers by Francesco Pegoraro

Physics Letters A, 1989

The extended variable ("ballooning") representation, commonly used for the study of short wavelen... more The extended variable ("ballooning") representation, commonly used for the study of short wavelength plasma modes in a toroidal magnetic equilibrium, is generalised to include: (i) the effect of a differential toroidal rotation; (ii) non-linar terms in the mode amplitude. These results are obtained by relating this representation to the irreducible representations of the relevant invariance group, which is shown to be a discrete Abelian subgroup of the Heisenberg group.

Physics of Plasmas, 2001

The effect of the pulse polarization and of the accelerated fast electrons on the propagation ano... more The effect of the pulse polarization and of the accelerated fast electrons on the propagation anomalies (“hosing” and “snaking”) of a high-intensity laser pulse in an underdense plasma is investigated with two dimensional particle in cell simulations. The pulse deflection and the type of plasma modes (solitons, vortices) into which the laser pulse energy is eventually deposited, are shown to depend on the pulse polarization.

Physics Letters, Section A: General, Atomic and Solid State Physics, 2002

Coherent magnetic structures comprising a magnetic vortex and an electron hole have been shown to... more Coherent magnetic structures comprising a magnetic vortex and an electron hole have been shown to be created by a Weibeltype, anisotropy driven instability. These structures arise from the electric and magnetic trapping of resonant electrons in the growing fields of the instability. The results of two dimensional Vlasov simulations of the nonlinear development of the instability are compared with a novel analytical model of a stationary propagating phase space structure which includes the depletion of the trapped electrons corresponding to the electron holes.

Plasma Physics and Controlled Fusion, 1995

The characteristic time of (incompressible) resistive modes in the neighbourhood of an X-point in... more The characteristic time of (incompressible) resistive modes in the neighbourhood of an X-point in the absence of external forcing is found to scale, when normalized on the Alfven time, as ( epsilon mod ln epsilon mod )-1 with epsilon the ratio between the Alfven and the resistive time. In X-point configurations with oblique separatrices, the mode time-scale becomes faster as

AIP Conference Proceedings, 2009

ABSTRACT

Physical Review Letters, 1996

A novel type of turbulence, which arises in 2D electron magnetohydrodynamics, is studied by numer... more A novel type of turbulence, which arises in 2D electron magnetohydrodynamics, is studied by numerical simulation. Energy dissipation rates are found to be independent of the dissipation coefficients. The energy spectrum E k follows the basic Kolmogorov-type predictions, k 25͞3 for kd e. 1 and k 27͞3 for kd e , 1 (d e is the electron inertial length) and is hence independent of the linear wave properties. Results are compared with other 2D turbulent systems.

The European Physical Journal D

Journal of Plasma Physics, 2018

A family of Lorentz invariant scalar functions of the magnetic field is defined in an ideal relat... more A family of Lorentz invariant scalar functions of the magnetic field is defined in an ideal relativistic plasma. These invariants are advected by the plasma fluid motion and play the role of the potential magnetic field introduced by Hide in (Ann. Geophys., vol. 1, 1983, 59) along the lines of Ertel’s theorem. From these invariants we recover the Cauchy conditions for the magnetic field components in the mapping from Eulerian to Lagrangian variables. In addition, the adopted procedure allows us to formulate, in a Lorentz invariant form, the Alfvén theorem for the conservation of the magnetic flux through a surface comoving with the plasma.

Scientific reports, Jan 11, 2017

Matter can be transferred into energy and the opposite transformation is also possible by use of ... more Matter can be transferred into energy and the opposite transformation is also possible by use of high-power lasers. A laser pulse in plasma can convert its energy into γ-rays and then e - e + pairs via the multi-photon Breit-Wheeler process. Production of dense positrons at GeV energies is very challenging since extremely high laser intensity ~1024 Wcm-2 is required. Here we propose an all-optical scheme for ultra-bright γ-ray emission and dense positron production with lasers at intensity of 1022-23 Wcm-2. By irradiating two colliding elliptically-polarized lasers onto two diamondlike carbon foils, electrons in the focal region of one foil are rapidly accelerated by the laser radiation pressure and interact with the other intense laser pulse which penetrates through the second foil due to relativistically induced foil transparency. This symmetric configuration enables efficient Compton back-scattering and results in ultra-bright γ-photon emission with brightness of ~1025 photons/s/...

Physics of Fluids, 1981

Low-frequency waves with high toroidal mode numbers in an axisymmetric toroidal configuration are... more Low-frequency waves with high toroidal mode numbers in an axisymmetric toroidal configuration are studied. In particular, the relationship between the periodicity constraints imposed by the geometry, magnetic shear, and the spatial structure of eigenmodes is investigated. By exploiting the radial translational invariance and the poloidal periodicity of the gyro-kinetic and Maxwell equations, the two-dimensional problem can be converted into a one-dimensional one, and the mode structure can be expressed in terms of a single extended poloidal variable. This representation is used in the description of electromagnetic modes with phase velocities larger than the ion thermal velocity and with frequencies below the ion gyro-frequency. Trapped particle, curvature, and compressional effects are retained. The dispersion equations for drift modes and Alfven-type modes are given in general geometry and simplified solutions are presented in the configuration of a double periodic plane slab.

Journal of Plasma Physics, 2016

In the single fluid, non-relativistic, ideal magnetohydrodynamic (MHD) plasma description, magnet... more In the single fluid, non-relativistic, ideal magnetohydrodynamic (MHD) plasma description, magnetic field lines play a fundamental role by defining dynamically preserved ‘magnetic connections’ between plasma elements. Here we show how the concept of magnetic connection needs to be generalized in the case of a relativistic MHD description where we require covariance under arbitrary Lorentz transformations. This is performed by defining 2-D magnetic connection hypersurfaces in the 4-D Minkowski space. This generalization accounts for the loss of simultaneity between spatially separated events in different frames and is expected to provide a powerful insight into the 4-D geometry of electromagnetic fields when boldsymbolEboldsymbolcdotboldsymbolB=0\boldsymbol{E}\boldsymbol{\cdot }\boldsymbol{B}=0boldsymbolEboldsymbolcdotboldsymbolB=0 .

AIP Conference Proceedings, 2002

Some recent developments in the analytical and numerical study of the interaction of ultra-intens... more Some recent developments in the analytical and numerical study of the interaction of ultra-intense ultra-short laser pulses with relativistic plasmas are reviewed. Special attention is given to the subject of ion acceleration in view of its applications which range from proton imaging to the acceleration of collimated ion bunches and to the effect of fast magnetic field line reconnection on the evolution of the self-generated magnetic field. CP634, Science of Superstrong Field Inter actions, edited by K. Nakajima and M. Deguchi

Muon-Catalyzed Fusion and Fusion with Polarized Nuclei, 1987

A magnetically confined, fusing plasma with coherently polarized spin nuclei can be subject to in... more A magnetically confined, fusing plasma with coherently polarized spin nuclei can be subject to instabilities due to the anisotropy in velocity space of the distribution function of the charged products of the fusion reactions. This anisotropy results from the polarization of the fusing nuclei. The characteristics of these instabilities depend strongly on the spatial inhomogeneity of the plasma.

Journal of Fusion Energy, 1995

Since the symposium was basically an assessment, it required two components:(1) presentation of r... more Since the symposium was basically an assessment, it required two components:(1) presentation of results, and (2) evaluation of the results. For the presentation of results, the selection of the speakers was guided by the criterion that the leading exponents of the various fusion programs had to be invited. And indeed, the leaders of all major fusion programs in the US, Japan, Russia, Europe, China, India,

Ignitor is a compact high magnetic field machine with tight aspect ratio and shaped cross section... more Ignitor is a compact high magnetic field machine with tight aspect ratio and shaped cross section, where large plasma currents can be produced. High plasma densities, strong Ohmic heating, good confinement of particles and energy, adequate plasma purity, and stability against MHD modes are expected on the basis of the machine characteristics.

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, 2000

The long-time evolution of nonlinear Landau damping in collisionless plasmas is analyzed by solvi... more The long-time evolution of nonlinear Landau damping in collisionless plasmas is analyzed by solving the Vlasov-Poisson system numerically. The value of the parameter marking the transition between Landau's and O'Neil's regimes is determined and compared with analytical results. The long-time evolution of a finiteamplitude electric field with wavelength equal to the length of the simulation box L is given by a superposition of two counterpropagating ''averaged'' Bernstein-Greene-Kruskal ͑BGK͒ waves. When LϾ and longer wavelength modes can be excited, the BGK waves correspond to an intermediate regime that is eventually modified by the excitation of the sideband instability. Ions dynamics is found not to affect these behaviors significantly.

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 2002

A linearized analysis is presented of the stability of a shell which accretes mass as it expands ... more A linearized analysis is presented of the stability of a shell which accretes mass as it expands in a plasma under the push of the electromagnetic radiation trapped inside it. The interaction with the radiation is described in terms of a ponderomotive force and the shell dynamics is treated within the snowplow approximation. The mass accretion and the radiation expansion are shown to affect the stability of planar, cylindrical, and spherical shells differently.

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 2002

The relativistic self-focusing of high-intensity laser pulses in underdense plasmas is investigat... more The relativistic self-focusing of high-intensity laser pulses in underdense plasmas is investigated with three-dimensional particle in cell simulations. The different behavior of a linearly polarized pulse in the two transverse directions is interpreted as a combination of two two-dimensional responses with different polarizations. In the polarization plane a high density sheet is formed, which separates the two regions of oppositely directed quasistatic magnetic field.

Physics Letters A, 1989

The extended variable ("ballooning") representation, commonly used for the study of short wavelen... more The extended variable ("ballooning") representation, commonly used for the study of short wavelength plasma modes in a toroidal magnetic equilibrium, is generalised to include: (i) the effect of a differential toroidal rotation; (ii) non-linar terms in the mode amplitude. These results are obtained by relating this representation to the irreducible representations of the relevant invariance group, which is shown to be a discrete Abelian subgroup of the Heisenberg group.

Physics of Plasmas, 2001

The effect of the pulse polarization and of the accelerated fast electrons on the propagation ano... more The effect of the pulse polarization and of the accelerated fast electrons on the propagation anomalies (“hosing” and “snaking”) of a high-intensity laser pulse in an underdense plasma is investigated with two dimensional particle in cell simulations. The pulse deflection and the type of plasma modes (solitons, vortices) into which the laser pulse energy is eventually deposited, are shown to depend on the pulse polarization.

Physics Letters, Section A: General, Atomic and Solid State Physics, 2002

Coherent magnetic structures comprising a magnetic vortex and an electron hole have been shown to... more Coherent magnetic structures comprising a magnetic vortex and an electron hole have been shown to be created by a Weibeltype, anisotropy driven instability. These structures arise from the electric and magnetic trapping of resonant electrons in the growing fields of the instability. The results of two dimensional Vlasov simulations of the nonlinear development of the instability are compared with a novel analytical model of a stationary propagating phase space structure which includes the depletion of the trapped electrons corresponding to the electron holes.

Plasma Physics and Controlled Fusion, 1995

The characteristic time of (incompressible) resistive modes in the neighbourhood of an X-point in... more The characteristic time of (incompressible) resistive modes in the neighbourhood of an X-point in the absence of external forcing is found to scale, when normalized on the Alfven time, as ( epsilon mod ln epsilon mod )-1 with epsilon the ratio between the Alfven and the resistive time. In X-point configurations with oblique separatrices, the mode time-scale becomes faster as

AIP Conference Proceedings, 2009

ABSTRACT

Physical Review Letters, 1996

A novel type of turbulence, which arises in 2D electron magnetohydrodynamics, is studied by numer... more A novel type of turbulence, which arises in 2D electron magnetohydrodynamics, is studied by numerical simulation. Energy dissipation rates are found to be independent of the dissipation coefficients. The energy spectrum E k follows the basic Kolmogorov-type predictions, k 25͞3 for kd e. 1 and k 27͞3 for kd e , 1 (d e is the electron inertial length) and is hence independent of the linear wave properties. Results are compared with other 2D turbulent systems.

The European Physical Journal D

Journal of Plasma Physics, 2018

A family of Lorentz invariant scalar functions of the magnetic field is defined in an ideal relat... more A family of Lorentz invariant scalar functions of the magnetic field is defined in an ideal relativistic plasma. These invariants are advected by the plasma fluid motion and play the role of the potential magnetic field introduced by Hide in (Ann. Geophys., vol. 1, 1983, 59) along the lines of Ertel’s theorem. From these invariants we recover the Cauchy conditions for the magnetic field components in the mapping from Eulerian to Lagrangian variables. In addition, the adopted procedure allows us to formulate, in a Lorentz invariant form, the Alfvén theorem for the conservation of the magnetic flux through a surface comoving with the plasma.

Scientific reports, Jan 11, 2017

Matter can be transferred into energy and the opposite transformation is also possible by use of ... more Matter can be transferred into energy and the opposite transformation is also possible by use of high-power lasers. A laser pulse in plasma can convert its energy into γ-rays and then e - e + pairs via the multi-photon Breit-Wheeler process. Production of dense positrons at GeV energies is very challenging since extremely high laser intensity ~1024 Wcm-2 is required. Here we propose an all-optical scheme for ultra-bright γ-ray emission and dense positron production with lasers at intensity of 1022-23 Wcm-2. By irradiating two colliding elliptically-polarized lasers onto two diamondlike carbon foils, electrons in the focal region of one foil are rapidly accelerated by the laser radiation pressure and interact with the other intense laser pulse which penetrates through the second foil due to relativistically induced foil transparency. This symmetric configuration enables efficient Compton back-scattering and results in ultra-bright γ-photon emission with brightness of ~1025 photons/s/...

Physics of Fluids, 1981

Low-frequency waves with high toroidal mode numbers in an axisymmetric toroidal configuration are... more Low-frequency waves with high toroidal mode numbers in an axisymmetric toroidal configuration are studied. In particular, the relationship between the periodicity constraints imposed by the geometry, magnetic shear, and the spatial structure of eigenmodes is investigated. By exploiting the radial translational invariance and the poloidal periodicity of the gyro-kinetic and Maxwell equations, the two-dimensional problem can be converted into a one-dimensional one, and the mode structure can be expressed in terms of a single extended poloidal variable. This representation is used in the description of electromagnetic modes with phase velocities larger than the ion thermal velocity and with frequencies below the ion gyro-frequency. Trapped particle, curvature, and compressional effects are retained. The dispersion equations for drift modes and Alfven-type modes are given in general geometry and simplified solutions are presented in the configuration of a double periodic plane slab.

Journal of Plasma Physics, 2016

In the single fluid, non-relativistic, ideal magnetohydrodynamic (MHD) plasma description, magnet... more In the single fluid, non-relativistic, ideal magnetohydrodynamic (MHD) plasma description, magnetic field lines play a fundamental role by defining dynamically preserved ‘magnetic connections’ between plasma elements. Here we show how the concept of magnetic connection needs to be generalized in the case of a relativistic MHD description where we require covariance under arbitrary Lorentz transformations. This is performed by defining 2-D magnetic connection hypersurfaces in the 4-D Minkowski space. This generalization accounts for the loss of simultaneity between spatially separated events in different frames and is expected to provide a powerful insight into the 4-D geometry of electromagnetic fields when boldsymbolEboldsymbolcdotboldsymbolB=0\boldsymbol{E}\boldsymbol{\cdot }\boldsymbol{B}=0boldsymbolEboldsymbolcdotboldsymbolB=0 .

AIP Conference Proceedings, 2002

Some recent developments in the analytical and numerical study of the interaction of ultra-intens... more Some recent developments in the analytical and numerical study of the interaction of ultra-intense ultra-short laser pulses with relativistic plasmas are reviewed. Special attention is given to the subject of ion acceleration in view of its applications which range from proton imaging to the acceleration of collimated ion bunches and to the effect of fast magnetic field line reconnection on the evolution of the self-generated magnetic field. CP634, Science of Superstrong Field Inter actions, edited by K. Nakajima and M. Deguchi

Muon-Catalyzed Fusion and Fusion with Polarized Nuclei, 1987

A magnetically confined, fusing plasma with coherently polarized spin nuclei can be subject to in... more A magnetically confined, fusing plasma with coherently polarized spin nuclei can be subject to instabilities due to the anisotropy in velocity space of the distribution function of the charged products of the fusion reactions. This anisotropy results from the polarization of the fusing nuclei. The characteristics of these instabilities depend strongly on the spatial inhomogeneity of the plasma.

Journal of Fusion Energy, 1995

Since the symposium was basically an assessment, it required two components:(1) presentation of r... more Since the symposium was basically an assessment, it required two components:(1) presentation of results, and (2) evaluation of the results. For the presentation of results, the selection of the speakers was guided by the criterion that the leading exponents of the various fusion programs had to be invited. And indeed, the leaders of all major fusion programs in the US, Japan, Russia, Europe, China, India,

Ignitor is a compact high magnetic field machine with tight aspect ratio and shaped cross section... more Ignitor is a compact high magnetic field machine with tight aspect ratio and shaped cross section, where large plasma currents can be produced. High plasma densities, strong Ohmic heating, good confinement of particles and energy, adequate plasma purity, and stability against MHD modes are expected on the basis of the machine characteristics.

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, 2000

The long-time evolution of nonlinear Landau damping in collisionless plasmas is analyzed by solvi... more The long-time evolution of nonlinear Landau damping in collisionless plasmas is analyzed by solving the Vlasov-Poisson system numerically. The value of the parameter marking the transition between Landau's and O'Neil's regimes is determined and compared with analytical results. The long-time evolution of a finiteamplitude electric field with wavelength equal to the length of the simulation box L is given by a superposition of two counterpropagating ''averaged'' Bernstein-Greene-Kruskal ͑BGK͒ waves. When LϾ and longer wavelength modes can be excited, the BGK waves correspond to an intermediate regime that is eventually modified by the excitation of the sideband instability. Ions dynamics is found not to affect these behaviors significantly.

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 2002

A linearized analysis is presented of the stability of a shell which accretes mass as it expands ... more A linearized analysis is presented of the stability of a shell which accretes mass as it expands in a plasma under the push of the electromagnetic radiation trapped inside it. The interaction with the radiation is described in terms of a ponderomotive force and the shell dynamics is treated within the snowplow approximation. The mass accretion and the radiation expansion are shown to affect the stability of planar, cylindrical, and spherical shells differently.

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 2002

The relativistic self-focusing of high-intensity laser pulses in underdense plasmas is investigat... more The relativistic self-focusing of high-intensity laser pulses in underdense plasmas is investigated with three-dimensional particle in cell simulations. The different behavior of a linearly polarized pulse in the two transverse directions is interpreted as a combination of two two-dimensional responses with different polarizations. In the polarization plane a high density sheet is formed, which separates the two regions of oppositely directed quasistatic magnetic field.