The Experts below are selected from a list of 20673 Experts worldwide ranked by ideXlab platform
Julian Schulze - One of the best experts on this subject based on the ideXlab platform.
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heavy particle induced Secondary Electrons in capacitive radio frequency discharges driven by tailored voltage waveforms
Journal of Applied Physics, 2019Co-Authors: Z Donko, Julian Schulze, A Derzsi, Benedek Horvath, I KorolovAbstract:Particle-in-Cell/Monte Carlo Collision simulations are performed to investigate the effects of heavy-particle induced Secondary Electrons (SEs) on the ionization dynamics and on the control of ion properties at the electrodes in geometrically symmetric capacitively coupled argon discharges driven by tailored voltage waveforms. The driving voltage waveform is composed of a maximum of four ( 1≤N≤4) consecutive harmonics of the fundamental frequency of 13.56 MHz and is tailored by adjusting the identical phases of the even harmonics, θ. The simulations are carried out at neutral gas pressures of 3 Pa (nearly collisionless low-pressure regime) and 100 Pa (collisional high-pressure regime). Different approaches are used in the simulations to describe the Secondary electron emission (SEE) at the electrodes: we adopt (i) constant ion-induced Secondary electron emission coefficients (SEECs), γ, and (ii) realistic, energy-dependent SE yields for ions and fast neutrals. The mean ion energy at the electrodes, ⟨Ei⟩, ...
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Secondary Electrons in dual frequency capacitive radio frequency discharges
Plasma Sources Science and Technology, 2011Co-Authors: Z Donko, Julian Schulze, Edmund Schungel, Uwe CzarnetzkiAbstract:Two fundamentally different types of dual-frequency (DF) capacitively coupled radio frequency discharges can be used for plasma processing applications to realize separate control of the ion mean energy, Ei, and the ion flux, Γi, at the substrate surface: (i) classical discharges operated at substantially different frequencies, where the low- and high-frequency voltage amplitudes, lf and hf, are used to control Ei and Γi, respectively; (ii) electrically asymmetric (EA) discharges operated at a fundamental frequency and its second harmonic with fixed, but adjustable phase shift between the driving frequencies, θ. In EA discharges the voltage amplitudes are used to control Γi and θ is used to control Ei. Here, we report our systematic simulation studies of the effect of Secondary Electrons on the ionization dynamics and the quality of this separate control in both discharge types in argon at different gas pressures. We focus on the effect of the control parameter for Ei on Γi for different Secondary yields, γ. We find a dramatic effect of tuning lf in classical DF discharges, which is caused by a transition from α- to γ-mode induced by changing lf. In EA discharges we find that no such mode transition is induced by changing θ within the parameter range studied here and, consequently, Γi remains nearly constant as a function of θ. Thus, despite some limitations at high values of γ the quality of the separate control of ion energy and flux is generally better in EA discharges compared with classical DF discharges.
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the effect of Secondary Electrons on the separate control of ion energy and flux in dual frequency capacitively coupled radio frequency discharges
Applied Physics Letters, 2010Co-Authors: Z Donko, Julian Schulze, Peter Hartmann, Ihor Korolov, Uwe Czarnetzki, Edmund SchungelAbstract:Dual-frequency capacitive discharges are used to separately control the mean ion energy, e¯ion, and flux, Γion, at the electrodes. We study the effect of Secondary Electrons on this separate control in argon discharges driven at 2+27 MHz at different pressures using Particle in Cell simulations. For Secondary yield γ≈0, Γion decreases as a function of the low frequency voltage amplitude due to the frequency coupling, while it increases at high γ due to the effective multiplication of Secondary Electrons inside the sheaths. Therefore, separate control is strongly limited. e¯ion increases with γ, which might allow an in situ determination of γ-coefficients.
David A Jaffray - One of the best experts on this subject based on the ideXlab platform.
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su e t 668 comparison of the physical characteristics of Secondary Electrons and dose enhancement from x ray irradiation of gold nanoparticles using monte carlo simulation
Medical Physics, 2011Co-Authors: Michael K K Leung, James C L Chow, Devika B Chithrani, M J G Lee, David A JaffrayAbstract:Purpose: To investigate Secondary electron production in gold nanoparticle (GNP) aided radiotherapy through Monte Carlo simulations, thereby advance the understanding of dose enhancements and their role in improving cell kill. Methods: Using the Geant4 toolkit, simulations were performed with four polyenergetic sources, namely 50 kVp, 250 kVp, Cobalt‐60, and 6 MV, to irradiate a gold sphere of diameters 2, 50, or 100 nm in water. The energy of the Secondary Electrons and the frequency and type of physics interaction that created them were tracked. This allowed calculation of the absorbed dose and energy deposition inside and outside of the nanoparticle. Results: The presence of a GNP can enhance the production of Electrons by approximately 3 orders of magnitude at kV beam energies. For MV beams, the increase in electron production was approximately 10 folds. Considerable dose enhancement occurred when gold was present, at approximately 1000 folds for kV beams, and between 2 to 7 folds for MV beams. The energy deposited was calculated to compare how many additional Electrons were generated and take into account their energies. In the kV beams, the addition of a GNP caused significantly greater deposited energy surrounding the nanoparticle by 2 to 3 orders of magnitude. For the MV beams, the increase was approximately 5 folds. The proportion of energy deposition inside the GNP versus the outside was also analyzed. At greater nanoparticle diameters, a larger portion of the overall deposited energy resided within the nanoparticle. Conclusions: We present simulation results that show the presence of GNP's can considerably increase the dose and energy deposition outside the nanoparticle, especially at kV energies. This enhancement is also present for MV beams, although to a lesser degree.
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irradiation of gold nanoparticles by x rays monte carlo simulation of dose enhancements and the spatial properties of the Secondary Electrons production
Medical Physics, 2011Co-Authors: Michael K K Leung, James C L Chow, Devika B Chithrani, M J G Lee, Barbara Oms, David A JaffrayAbstract:Purpose: The aim of this study is to understand the characteristics of Secondary Electrons generated from the interaction of gold nanoparticles (GNPs) with x-rays as a function of nanoparticle size and beam energy and thereby further the understanding of GNP-enhanced radiotherapy. Methods: The effective range, deflection angle, dose deposition, energy, and interaction processes of Electrons produced from the interaction of x-rays with a GNP were calculated by Monte Carlo simulations. The GEANT4 code was used to simulate and track Electrons generated from a 2, 50, and 100 nm diameter GNP when it is irradiated with a 50 kVp, 250 kVp, cobalt-60, and 6 MV photon beam in water. Results: When a GNP was present, depending on the beam energies used, Secondary electron production was increased by 10- to 2000-fold compared to an absence of a GNP. Low-energy photon beams were much more efficient at interacting with the GNP by two to three orders of magnitude compared to MV energies and increased the deflection angle. GNPs with larger diameters also contributed more dose. The majority of the energy deposition was outside the GNP, rather than self-absorbed by the nanoparticle. The mean effective range of electron tracks for the beams tested rangedmore » from approximately 3 {mu}m to 1 mm. Conclusions: These simulated results yield important insights concerning the spatial distributions and elevated dose in GNP-enhanced radiotherapy. The authors conclude that the irradiation of GNP at lower photon energies will be more efficient for cell killing. This conclusion is consistent with published studies.« less
V A Dogiel - One of the best experts on this subject based on the ideXlab platform.
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multi wavelength emission from the fermi bubble ii Secondary Electrons and the hadronic model of the bubble
The Astrophysical Journal, 2015Co-Authors: K S Cheng, D O Chernyshov, V A DogielAbstract:We analyze the origin of the gamma-ray flux from the Fermi Bubbles (FBs) in the framework of the hadronic model in which gamma-rays are produced by collisions of relativistic protons with the protons of the background plasma in the Galactic halo. It is assumed in this model that the observed radio emission from the FBs is due to synchrotron radiation of Secondary Electrons produced by pp collisions. However, if these Electrons lose their energy through synchrotron and inverse-Compton emission, the spectrum of Secondary Electrons will be too soft, and an additional arbitrary component of the primary Electrons will be necessary in order to reproduce the radio data. Thus, a mixture of the hadronic and leptonic models is required for the observed radio flux. It was shown that if the spectrum of primary Electrons is , the permitted range of the magnetic field strength is within the 2-7 μG region. The fraction of gamma-rays produced by pp collisions can reach about 80% of the total gamma-ray flux from the FBs. If the magnetic field is 7 μG the model is unable to reproduce the data. Alternatively, the Electrons in the FBs may lose their energy through adiabatic energy losses if there is a strong plasma outflow in the GC. Then, the pure hadronic model is able to reproduce characteristics of the radio and gamma-ray flux from the FBs. However, in this case the required magnetic field strength in the FBs and the power of CR sources are much higher than those following from observations.
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multi wavelength emission from the fermi bubble ii Secondary Electrons and the hadronic model of the bubble
arXiv: Astrophysics of Galaxies, 2014Co-Authors: K S Cheng, D O Chernyshov, V A DogielAbstract:We analyse the origin of the gamma-ray flux from the Fermi Bubbles (FBs) in the framework of the hadronic model in which gamma-rays are produced by collisions of relativistic protons with the protons of background plasma in the Galactic halo. It is assumed in this model that the observed radio emission from the FBs is due to synchrotron radiation of Secondary Electrons produced by $pp$ collisions. However, if these Electrons loose their energy by the synchrotron and inverse-Compton, the spectrum of Secondary Electrons is too soft, and an additional arbitrary component of primary Electrons is necessary in order to reproduce the radio data. Thus, a mixture of the hadronic and leptonic models is required for the observed radio flux. It was shown that if the spectrum of primary Electrons is $\propto E_e^{-2}$, the permitted range of the magnetic field strength is within 2 - 7 $\mu$G region. The fraction of gamma-rays produced by $pp$ collisions can reach about 80% of the total gamma-ray flux from the FBs. If magnetic field is 7 $\mu$G the model is unable to reproduce the data. Alternatively, the Electrons in the FBs may lose their energy by adiabatic energy losses if there is a strong plasma outflow in the GC. Then, the pure hadronic model is able to reproduce characteristics of the radio and gamma-ray flux from the FBs. However, in this case the required magnetic field strength in the FBs and the power of CR sources are much higher than those followed from observations.
Tomoya Yamauchi - One of the best experts on this subject based on the ideXlab platform.
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elucidation of the two step damage formation process of latent tracks in poly allyl diglycol carbonate padc role of Secondary low energy Electrons
Journal of Physical Chemistry C, 2018Co-Authors: Tamon Kusumoto, Pierre Cloutier, M Fromm, A D Bass, Leon Sanche, Remi Barillon, Tomoya YamauchiAbstract:The aim of the present study is to evaluate the mechanisms by which Secondary Electrons of low energy degrade poly(allyl diglycol carbonate) (PADC) when it is used as a Solid State Nuclear Track De...
Michael K K Leung - One of the best experts on this subject based on the ideXlab platform.
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su e t 668 comparison of the physical characteristics of Secondary Electrons and dose enhancement from x ray irradiation of gold nanoparticles using monte carlo simulation
Medical Physics, 2011Co-Authors: Michael K K Leung, James C L Chow, Devika B Chithrani, M J G Lee, David A JaffrayAbstract:Purpose: To investigate Secondary electron production in gold nanoparticle (GNP) aided radiotherapy through Monte Carlo simulations, thereby advance the understanding of dose enhancements and their role in improving cell kill. Methods: Using the Geant4 toolkit, simulations were performed with four polyenergetic sources, namely 50 kVp, 250 kVp, Cobalt‐60, and 6 MV, to irradiate a gold sphere of diameters 2, 50, or 100 nm in water. The energy of the Secondary Electrons and the frequency and type of physics interaction that created them were tracked. This allowed calculation of the absorbed dose and energy deposition inside and outside of the nanoparticle. Results: The presence of a GNP can enhance the production of Electrons by approximately 3 orders of magnitude at kV beam energies. For MV beams, the increase in electron production was approximately 10 folds. Considerable dose enhancement occurred when gold was present, at approximately 1000 folds for kV beams, and between 2 to 7 folds for MV beams. The energy deposited was calculated to compare how many additional Electrons were generated and take into account their energies. In the kV beams, the addition of a GNP caused significantly greater deposited energy surrounding the nanoparticle by 2 to 3 orders of magnitude. For the MV beams, the increase was approximately 5 folds. The proportion of energy deposition inside the GNP versus the outside was also analyzed. At greater nanoparticle diameters, a larger portion of the overall deposited energy resided within the nanoparticle. Conclusions: We present simulation results that show the presence of GNP's can considerably increase the dose and energy deposition outside the nanoparticle, especially at kV energies. This enhancement is also present for MV beams, although to a lesser degree.
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irradiation of gold nanoparticles by x rays monte carlo simulation of dose enhancements and the spatial properties of the Secondary Electrons production
Medical Physics, 2011Co-Authors: Michael K K Leung, James C L Chow, Devika B Chithrani, M J G Lee, Barbara Oms, David A JaffrayAbstract:Purpose: The aim of this study is to understand the characteristics of Secondary Electrons generated from the interaction of gold nanoparticles (GNPs) with x-rays as a function of nanoparticle size and beam energy and thereby further the understanding of GNP-enhanced radiotherapy. Methods: The effective range, deflection angle, dose deposition, energy, and interaction processes of Electrons produced from the interaction of x-rays with a GNP were calculated by Monte Carlo simulations. The GEANT4 code was used to simulate and track Electrons generated from a 2, 50, and 100 nm diameter GNP when it is irradiated with a 50 kVp, 250 kVp, cobalt-60, and 6 MV photon beam in water. Results: When a GNP was present, depending on the beam energies used, Secondary electron production was increased by 10- to 2000-fold compared to an absence of a GNP. Low-energy photon beams were much more efficient at interacting with the GNP by two to three orders of magnitude compared to MV energies and increased the deflection angle. GNPs with larger diameters also contributed more dose. The majority of the energy deposition was outside the GNP, rather than self-absorbed by the nanoparticle. The mean effective range of electron tracks for the beams tested rangedmore » from approximately 3 {mu}m to 1 mm. Conclusions: These simulated results yield important insights concerning the spatial distributions and elevated dose in GNP-enhanced radiotherapy. The authors conclude that the irradiation of GNP at lower photon energies will be more efficient for cell killing. This conclusion is consistent with published studies.« less
