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Ramesh Narayan - One of the best experts on this subject based on the ideXlab platform.
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Electron heating by the ion cyclotron instability in collisionless accretion flows i compression driven instabilities and the Electron heating mechanism
The Astrophysical Journal, 2015Co-Authors: Lorenzo Sironi, Ramesh NarayanAbstract:In systems accreting well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the innermost regions of the disk is believed to be collisionless and have two temperatures, with the ions substantially hotter than the Electrons. However, whether a collisionless faster-than-Coulomb energy transfer mechanism exists in two-temperature accretion flows is still an open question. We study the physics of Electron heating during the growth of ion velocity-space instabilities by means of multidimensional, fully kinetic, particle-in-cell (PIC) simulations. A background large-scale compression—embedded in a novel form of the PIC equations—continuously amplifies the field. This constantly drives a pressure anisotropy P ⊥ > P ∥ because of the adiabatic invariance of the particle magnetic moments. We find that, for ion plasma beta values β0i ~ 5-30 appropriate for the midplane of low-luminosity accretion flows (here, β0i is the ratio of ion thermal pressure to magnetic pressure), mirror modes dominate if the Electron-to-proton temperature ratio is T 0e /T 0i 0.2, whereas for T 0e /T 0i 0.2 the ion cyclotron instability triggers the growth of strong Alfven-like waves, which pitch-angle scatter the ions to maintain marginal stability. We develop an analytical model of Electron heating during the growth of the ion cyclotron instability, which we validate with PIC simulations. We find that for cold Electrons (β0e 2 me /mi , where β0e is the ratio of Electron thermal pressure to magnetic pressure), the Electron energy gain is controlled by the magnitude of the E-cross-B velocity induced by the ion cyclotron waves. This term is independent of the Initial Electron temperature, so it provides a solid energy floor even for Electrons starting with extremely low temperatures. On the other hand, the Electron energy gain for β0e 2 me /mi —governed by the conservation of the particle magnetic moment in the growing fields of the instability—is proportional to the Initial Electron temperature, and it scales with the magnetic energy of ion cyclotron waves. Our results have implications for two-temperature accretion flows as well as for solar wind and intracluster plasmas.
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Electron heating by the ion cyclotron instability in collisionless accretion flows i compression driven instabilities and the Electron heating mechanism
The Astrophysical Journal, 2015Co-Authors: Lorenzo Sironi, Ramesh NarayanAbstract:In systems accreting well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the innermost regions of the disk is believed to be collisionless and have two temperatures, with the ions substantially hotter than the Electrons. However, whether a collisionless faster-than-Coulomb energy transfer mechanism exists in two-temperature accretion flows is still an open question. We study the physics of Electron heating during the growth of ion velocity-space instabilities by means of multidimensional, fully kinetic, particle-in-cell (PIC) simulations. A background large-scale compression—embedded in a novel form of the PIC equations—continuously amplifies the field. This constantly drives a pressure anisotropy P ⊥ > P ∥ because of the adiabatic invariance of the particle magnetic moments. We find that, for ion plasma beta values β0i ~ 5-30 appropriate for the midplane of low-luminosity accretion flows (here, β0i is the ratio of ion thermal pressure to magnetic pressure), mirror modes dominate if the Electron-to-proton temperature ratio is T 0e /T 0i 0.2, whereas for T 0e /T 0i 0.2 the ion cyclotron instability triggers the growth of strong Alfven-like waves, which pitch-angle scatter the ions to maintain marginal stability. We develop an analytical model of Electron heating during the growth of the ion cyclotron instability, which we validate with PIC simulations. We find that for cold Electrons (β0e 2 me /mi , where β0e is the ratio of Electron thermal pressure to magnetic pressure), the Electron energy gain is controlled by the magnitude of the E-cross-B velocity induced by the ion cyclotron waves. This term is independent of the Initial Electron temperature, so it provides a solid energy floor even for Electrons starting with extremely low temperatures. On the other hand, the Electron energy gain for β0e 2 me /mi —governed by the conservation of the particle magnetic moment in the growing fields of the instability—is proportional to the Initial Electron temperature, and it scales with the magnetic energy of ion cyclotron waves. Our results have implications for two-temperature accretion flows as well as for solar wind and intracluster plasmas.
N Sonmez - One of the best experts on this subject based on the ideXlab platform.
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exploring the prominent channel charged higgs pair production in supersymmetric two parameter non universal higgs model
Nuclear Physics, 2020Co-Authors: N SonmezAbstract:Abstract In this study, the charged Higgs pair production is calculated in the context of the supersymmetry at a γγ-collider. The channel is explored in Two-parameter Non-Universal Higgs Model where the model provides relatively light neutral and charged Higgs bosons. The computation is extended to one loop-level, and the divergence arising in the loop-diagrams are cured with the radiative photon correction. The production rate of the charged Higgs pair reaches up to σ ˆ UU LO+NLO = 121 fb at s ˆ = 635 GeV . The analysis of the cross-section is also given varying the parameters m A and tan β . The total convoluted cross-section with the photon luminosity in an e + e − machine is calculated as a function of the center-of-mass energy up to 1 TeV , and it gets up to 42 fb at s = 900 GeV depending on the polarization of the Initial Electron and laser photon.
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exploring the prominent channel charged higgs pair production in supersymmetric two parameter non universal higgs model
arXiv: High Energy Physics - Phenomenology, 2018Co-Authors: N SonmezAbstract:In this study, the charged Higgs pair production is calculated in the context of the supersymmetry at a $\gamma\gamma$-collider. The channel is explored in Two-parameter Non-Universal Higgs Model where the model provides relatively light neutral and charged Higgs bosons. The computation is extended to one loop-level, and the divergence arising in the loop-diagrams are cured with the radiative photon correction. The production rate of the charged Higgs pair reaches up to $\hat{\sigma}_\text{UU}^\text{LO+NLO}=0.121\text{ fb}$ at $\sqrt{\hat{s}}=635\text{ GeV}$. The analysis of the cross-section is also given varying the parameters $m_A$ and $\tan\beta$. The total convoluted cross-section with the photon luminosity in an $e^+e^-$ machine is calculated as a function of the center-of-mass energy up to $1\text{ TeV}$, and it gets up to $0.42\text{ fb}$ at $\sqrt{s}=900 \text{ GeV}$ depending on the polarization of the Initial Electron and laser photon.
Jiashi Yang - One of the best experts on this subject based on the ideXlab platform.
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an analysis of the extension of a zno piezoelectric semiconductor nanofiber under an axial force
Smart Materials and Structures, 2017Co-Authors: Chunli Zhang, Weiqiu Chen, Xiaoyuan Wang, Jiashi YangAbstract:This paper presents a theoretical analysis on the axial extension of an n-type ZnO piezoelectric semiconductor nanofiber under an axial force. The phenomenological theory of piezoelectric semiconductors consisting of Newton's second law of motion, the charge equation of electrostatics and the conservation of charge was used. The equations were linearized for small axial force and hence small Electron concentration perturbation, and were reduced to one-dimensional equations for thin fibers. Simple and analytical expressions for the electromechanical fields and Electron concentration in the fiber were obtained. The fields are either totally or partially described by hyperbolic functions relatively large near the ends of the fiber and change rapidly there. The behavior of the fields is sensitive to the Initial Electron concentration and the applied axial force. For higher Initial Electron concentrations the fields are larger near the ends and change more rapidly there.
Christoph H Keitel - One of the best experts on this subject based on the ideXlab platform.
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single shot carrier envelope phase determination of long superintense laser pulses
Physical Review Letters, 2018Co-Authors: Yueyue Chen, Karen Zaven Hatsagortsyan, Christoph H KeitelAbstract:The impact of the carrier-envelope phase (CEP) of an intense multicycle laser pulse on the radiation of an Electron beam during nonlinear Compton scattering is investigated. We have identified a CEP effect specific to the ultrarelativistic regime. When the Electron beam counterpropagates with the laser pulse, pronounced high-energy x-ray double peaks emerge near the backward direction relative to the Initial Electron motion. This is achieved in the relativistic interaction domain, where both the Electron energy is required to be lower than for the Electron reflection condition at the laser peak and the stochasticity effects in the photon emission need to be weak. The asymmetry parameter of the double peaks in the angular radiation distribution is shown to serve as a sensitive measure for the CEP of up to 10-cycle long laser pulses and can be applied for the characterization of extremely strong laser pulses in present and near future laser facilities.
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attosecond gamma ray pulses via nonlinear compton scattering in the radiation dominated regime
Physical Review Letters, 2015Co-Authors: Karen Zaven Hatsagortsyan, Benjamin J Galow, Christoph H KeitelAbstract:The feasibility of the generation of bright ultrashort gamma-ray pulses is demonstrated in the interaction of a relativistic Electron bunch with a counterpropagating tightly focused superstrong laser beam in the radiation-dominated regime. The Compton scattering spectra of gamma radiation are investigated using a semiclassical description for the Electron dynamics in the laser field and a quantum electrodynamical description for the photon emission. We demonstrate the feasibility of ultrashort gamma-ray bursts of hundreds of attoseconds and of dozens of megaElectronvolt photon energies in the near-backwards direction of the Initial Electron motion. The tightly focused laser field structure and the radiation reaction are shown to be responsible for such short gamma-ray bursts, which are independent of the durations of the Electron bunch and of the laser pulse. The results are measurable with the laser technology available in the near future.
Lorenzo Sironi - One of the best experts on this subject based on the ideXlab platform.
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Electron heating by the ion cyclotron instability in collisionless accretion flows i compression driven instabilities and the Electron heating mechanism
The Astrophysical Journal, 2015Co-Authors: Lorenzo Sironi, Ramesh NarayanAbstract:In systems accreting well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the innermost regions of the disk is believed to be collisionless and have two temperatures, with the ions substantially hotter than the Electrons. However, whether a collisionless faster-than-Coulomb energy transfer mechanism exists in two-temperature accretion flows is still an open question. We study the physics of Electron heating during the growth of ion velocity-space instabilities by means of multidimensional, fully kinetic, particle-in-cell (PIC) simulations. A background large-scale compression—embedded in a novel form of the PIC equations—continuously amplifies the field. This constantly drives a pressure anisotropy P ⊥ > P ∥ because of the adiabatic invariance of the particle magnetic moments. We find that, for ion plasma beta values β0i ~ 5-30 appropriate for the midplane of low-luminosity accretion flows (here, β0i is the ratio of ion thermal pressure to magnetic pressure), mirror modes dominate if the Electron-to-proton temperature ratio is T 0e /T 0i 0.2, whereas for T 0e /T 0i 0.2 the ion cyclotron instability triggers the growth of strong Alfven-like waves, which pitch-angle scatter the ions to maintain marginal stability. We develop an analytical model of Electron heating during the growth of the ion cyclotron instability, which we validate with PIC simulations. We find that for cold Electrons (β0e 2 me /mi , where β0e is the ratio of Electron thermal pressure to magnetic pressure), the Electron energy gain is controlled by the magnitude of the E-cross-B velocity induced by the ion cyclotron waves. This term is independent of the Initial Electron temperature, so it provides a solid energy floor even for Electrons starting with extremely low temperatures. On the other hand, the Electron energy gain for β0e 2 me /mi —governed by the conservation of the particle magnetic moment in the growing fields of the instability—is proportional to the Initial Electron temperature, and it scales with the magnetic energy of ion cyclotron waves. Our results have implications for two-temperature accretion flows as well as for solar wind and intracluster plasmas.
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Electron heating by the ion cyclotron instability in collisionless accretion flows i compression driven instabilities and the Electron heating mechanism
The Astrophysical Journal, 2015Co-Authors: Lorenzo Sironi, Ramesh NarayanAbstract:In systems accreting well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the innermost regions of the disk is believed to be collisionless and have two temperatures, with the ions substantially hotter than the Electrons. However, whether a collisionless faster-than-Coulomb energy transfer mechanism exists in two-temperature accretion flows is still an open question. We study the physics of Electron heating during the growth of ion velocity-space instabilities by means of multidimensional, fully kinetic, particle-in-cell (PIC) simulations. A background large-scale compression—embedded in a novel form of the PIC equations—continuously amplifies the field. This constantly drives a pressure anisotropy P ⊥ > P ∥ because of the adiabatic invariance of the particle magnetic moments. We find that, for ion plasma beta values β0i ~ 5-30 appropriate for the midplane of low-luminosity accretion flows (here, β0i is the ratio of ion thermal pressure to magnetic pressure), mirror modes dominate if the Electron-to-proton temperature ratio is T 0e /T 0i 0.2, whereas for T 0e /T 0i 0.2 the ion cyclotron instability triggers the growth of strong Alfven-like waves, which pitch-angle scatter the ions to maintain marginal stability. We develop an analytical model of Electron heating during the growth of the ion cyclotron instability, which we validate with PIC simulations. We find that for cold Electrons (β0e 2 me /mi , where β0e is the ratio of Electron thermal pressure to magnetic pressure), the Electron energy gain is controlled by the magnitude of the E-cross-B velocity induced by the ion cyclotron waves. This term is independent of the Initial Electron temperature, so it provides a solid energy floor even for Electrons starting with extremely low temperatures. On the other hand, the Electron energy gain for β0e 2 me /mi —governed by the conservation of the particle magnetic moment in the growing fields of the instability—is proportional to the Initial Electron temperature, and it scales with the magnetic energy of ion cyclotron waves. Our results have implications for two-temperature accretion flows as well as for solar wind and intracluster plasmas.