The Experts below are selected from a list of 37275 Experts worldwide ranked by ideXlab platform
Christine Charles - One of the best experts on this subject based on the ideXlab platform.
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collisionless Expansion of pulsed radio frequency Plasmas i front formation
Physics of Plasmas, 2016Co-Authors: T Schroder, Roderick Boswell, O Grulke, T Klinger, Christine CharlesAbstract:The dynamics during Plasma Expansion are studied with the use of a versatile particle-in-cell simulation with a variable neutral gas density profile. The simulation is tailored to a radio frequency Plasma Expansion experiment [Schroder et al., J. Phys. D: Appl. Phys. 47(5), 055207 (2014)]. The experiment has shown the existence of a propagating ion front. The ion front features a strong electric field and features a sharp Plasma potential drop similar to a double layer. However, the presented results of a first principle simulation show that, in general, the ion front does not have to be entangled with an electric field. The propagating electric field reflects the downstream ions, which stream with velocities up to twice as high as that of the ion front propagation. The observed ion density peak forms due to the accumulation of the reflected ions. The simulation shows that the ion front formation strongly depends on the initial ion density profile and is subject to a wave-breaking phenomenon. Virtual diag...
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collisionless Expansion of pulsed radio frequency Plasmas ii parameter study
Physics of Plasmas, 2016Co-Authors: T Schroder, Roderick Boswell, O Grulke, T Klinger, Christine CharlesAbstract:The Plasma parameter dependencies of the dynamics during the Expansion of Plasma are studied with the use of a versatile particle-in-cell simulation tailored to a Plasma Expansion experiment [Schroder et al., J. Phys. D: Appl. Phys. 47, 055207 (2014); Schroder et al., Phys. Plasmas 23, 013511 (2016)]. The Plasma Expansion into a low-density ambient Plasma features a propagating ion front that is preceding a density plateau. It has been shown that the front formation is entangled with a wave-breaking mechanism, i.e., an ion collapse [Sack and Schamel, Plasma Phys. Controlled Fusion 27, 717 (1985); Sack and Schamel, Phys. Lett. A 110, 206 (1985)], and the launch of an ion burst [Schroder et al., Phys. Plasmas 23, 013511 (2016)]. The systematic parameter study presented in this paper focuses on the influence on this mechanism its effect on the maximum velocity of the ion front and burst. It is shown that, apart from the well known dependency of the front propagation on the ion sound velocity, it also depends...
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thermodynamic study on Plasma Expansion along a divergent magnetic field
Physical Review Letters, 2016Co-Authors: Yunchao Zhang, Christine Charles, Rod BoswellAbstract:Thermodynamic properties are revisited for electrons that are governed by nonlocal electron energy probability functions in a Plasma of low collisionality. Measurements in a laboratory helicon double layer experiment have shown that the effective electron temperature and density show a polytropic correlation with an index of γ_{e}=1.17±0.02 along the divergent magnetic field, implying a nearly isothermal Plasma (γ_{e}=1) with heat being brought into the system. However, the evolution of electrons along the divergent magnetic field is essentially an adiabatic process, which should have a γ_{e}=5/3. The reason for this apparent contradiction is that the nearly collisionless Plasma is very far from local thermodynamic equilibrium and the electrons behave nonlocally. The corresponding effective electron enthalpy has a conservation relation with the potential energy, which verifies that there is no heat transferred into the system during the electron evolution. The electrons are shown in nonlocal momentum equilibrium under the electric field and the gradient of the effective electron pressure. The convective momentum of ions, which can be assumed as a cold species, is determined by the effective electron pressure and the effective electron enthalpy is shown to be the source for ion acceleration. For these nearly collisionless Plasmas, the use of traditional thermodynamic concepts can lead to very erroneous conclusions regarding the thermal conductivity.
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Approaching the theoretical limit of diamagnetic-induced momentum in a rapidly diverging magnetic nozzle.
Physical review letters, 2013Co-Authors: Kazunori Takahashi, Christine Charles, Roderick BoswellAbstract:Cross-field diffusion and Plasma Expansion in a rapidly diverging magnetic nozzle are controlled while maintaining constant Plasma production in a contiguously attached radio frequency Plasma source. It is demonstrated that the measured electron-diamagnetic-induced axial momentum increases with increasing magnetic field strength to approach the theoretical limit derived using an ideal nozzle approximation. The measured axial momentum exerted onto the axial and radial Plasma source boundaries validate the prediction from a maximum electron pressure model on the back wall and from a zero net axial momentum model on the radial wall.
S Goldsmith - One of the best experts on this subject based on the ideXlab platform.
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theoretical study of Plasma Expansion in a magnetic field in a disk anode vacuum arc
Journal of Applied Physics, 1998Co-Authors: I I Beilis, Michael Keidar, R L Boxman, S GoldsmithAbstract:The low-density Plasma flow in an axial magnetic field to a disk-shaped anode in a vacuum arc was studied theoretically using a two-dimensional model. The Plasma Expansion was modeled using the sourceless steady-state hydrodynamic equations, where the free boundary of the Plasma was determined by a self-consistent solution of the gas-dynamic and electrical current equations. The anode was modeled as a current and Plasma collector, which does not influence the Plasma flow field. Magnetic forces from both the azimuthal self-magnetic field, and the imposed axial magnetic field were taken into account. It was found that the self-magnetic field does not substantially influence either the Plasma jet shape, density, velocity, or the current density distribution for arc currents I⩽200 A. On the other hand, the Plasma jet angle (α0) at the starting plane and the radial Plasma density gradient force in the Expansion region do have a strong influence on the Plasma and current flow. The mass and current flow in a 500...
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theoretical study of Plasma Expansion in a magnetic field in a disk anode vacuum arc
Journal of Applied Physics, 1998Co-Authors: I I Beilis, Michael Keidar, R L Boxman, S GoldsmithAbstract:The low-density Plasma flow in an axial magnetic field to a disk-shaped anode in a vacuum arc was studied theoretically using a two-dimensional model. The Plasma Expansion was modeled using the sourceless steady-state hydrodynamic equations, where the free boundary of the Plasma was determined by a self-consistent solution of the gas-dynamic and electrical current equations. The anode was modeled as a current and Plasma collector, which does not influence the Plasma flow field. Magnetic forces from both the azimuthal self-magnetic field, and the imposed axial magnetic field were taken into account. It was found that the self-magnetic field does not substantially influence either the Plasma jet shape, density, velocity, or the current density distribution for arc currents I⩽200 A. On the other hand, the Plasma jet angle (α0) at the starting plane and the radial Plasma density gradient force in the Expansion region do have a strong influence on the Plasma and current flow. The mass and current flow in a 500 A arc are compressed in the near axis region, leading to an increase in the Plasma and axial current density by a factor of 1.5 at a distance of about two Plasma jet radii from the starting plane. The calculated arc current–voltage characteristics agree qualitatively with experiments on arc behavior in an axial magnetic field.
Roderick Boswell - One of the best experts on this subject based on the ideXlab platform.
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collisionless Expansion of pulsed radio frequency Plasmas ii parameter study
Physics of Plasmas, 2016Co-Authors: T Schroder, Roderick Boswell, O Grulke, T Klinger, Christine CharlesAbstract:The Plasma parameter dependencies of the dynamics during the Expansion of Plasma are studied with the use of a versatile particle-in-cell simulation tailored to a Plasma Expansion experiment [Schroder et al., J. Phys. D: Appl. Phys. 47, 055207 (2014); Schroder et al., Phys. Plasmas 23, 013511 (2016)]. The Plasma Expansion into a low-density ambient Plasma features a propagating ion front that is preceding a density plateau. It has been shown that the front formation is entangled with a wave-breaking mechanism, i.e., an ion collapse [Sack and Schamel, Plasma Phys. Controlled Fusion 27, 717 (1985); Sack and Schamel, Phys. Lett. A 110, 206 (1985)], and the launch of an ion burst [Schroder et al., Phys. Plasmas 23, 013511 (2016)]. The systematic parameter study presented in this paper focuses on the influence on this mechanism its effect on the maximum velocity of the ion front and burst. It is shown that, apart from the well known dependency of the front propagation on the ion sound velocity, it also depends...
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collisionless Expansion of pulsed radio frequency Plasmas i front formation
Physics of Plasmas, 2016Co-Authors: T Schroder, Roderick Boswell, O Grulke, T Klinger, Christine CharlesAbstract:The dynamics during Plasma Expansion are studied with the use of a versatile particle-in-cell simulation with a variable neutral gas density profile. The simulation is tailored to a radio frequency Plasma Expansion experiment [Schroder et al., J. Phys. D: Appl. Phys. 47(5), 055207 (2014)]. The experiment has shown the existence of a propagating ion front. The ion front features a strong electric field and features a sharp Plasma potential drop similar to a double layer. However, the presented results of a first principle simulation show that, in general, the ion front does not have to be entangled with an electric field. The propagating electric field reflects the downstream ions, which stream with velocities up to twice as high as that of the ion front propagation. The observed ion density peak forms due to the accumulation of the reflected ions. The simulation shows that the ion front formation strongly depends on the initial ion density profile and is subject to a wave-breaking phenomenon. Virtual diag...
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Approaching the theoretical limit of diamagnetic-induced momentum in a rapidly diverging magnetic nozzle.
Physical review letters, 2013Co-Authors: Kazunori Takahashi, Christine Charles, Roderick BoswellAbstract:Cross-field diffusion and Plasma Expansion in a rapidly diverging magnetic nozzle are controlled while maintaining constant Plasma production in a contiguously attached radio frequency Plasma source. It is demonstrated that the measured electron-diamagnetic-induced axial momentum increases with increasing magnetic field strength to approach the theoretical limit derived using an ideal nozzle approximation. The measured axial momentum exerted onto the axial and radial Plasma source boundaries validate the prediction from a maximum electron pressure model on the back wall and from a zero net axial momentum model on the radial wall.
I I Beilis - One of the best experts on this subject based on the ideXlab platform.
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theoretical study of Plasma Expansion in a magnetic field in a disk anode vacuum arc
Journal of Applied Physics, 1998Co-Authors: I I Beilis, Michael Keidar, R L Boxman, S GoldsmithAbstract:The low-density Plasma flow in an axial magnetic field to a disk-shaped anode in a vacuum arc was studied theoretically using a two-dimensional model. The Plasma Expansion was modeled using the sourceless steady-state hydrodynamic equations, where the free boundary of the Plasma was determined by a self-consistent solution of the gas-dynamic and electrical current equations. The anode was modeled as a current and Plasma collector, which does not influence the Plasma flow field. Magnetic forces from both the azimuthal self-magnetic field, and the imposed axial magnetic field were taken into account. It was found that the self-magnetic field does not substantially influence either the Plasma jet shape, density, velocity, or the current density distribution for arc currents I⩽200 A. On the other hand, the Plasma jet angle (α0) at the starting plane and the radial Plasma density gradient force in the Expansion region do have a strong influence on the Plasma and current flow. The mass and current flow in a 500...
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theoretical study of Plasma Expansion in a magnetic field in a disk anode vacuum arc
Journal of Applied Physics, 1998Co-Authors: I I Beilis, Michael Keidar, R L Boxman, S GoldsmithAbstract:The low-density Plasma flow in an axial magnetic field to a disk-shaped anode in a vacuum arc was studied theoretically using a two-dimensional model. The Plasma Expansion was modeled using the sourceless steady-state hydrodynamic equations, where the free boundary of the Plasma was determined by a self-consistent solution of the gas-dynamic and electrical current equations. The anode was modeled as a current and Plasma collector, which does not influence the Plasma flow field. Magnetic forces from both the azimuthal self-magnetic field, and the imposed axial magnetic field were taken into account. It was found that the self-magnetic field does not substantially influence either the Plasma jet shape, density, velocity, or the current density distribution for arc currents I⩽200 A. On the other hand, the Plasma jet angle (α0) at the starting plane and the radial Plasma density gradient force in the Expansion region do have a strong influence on the Plasma and current flow. The mass and current flow in a 500 A arc are compressed in the near axis region, leading to an increase in the Plasma and axial current density by a factor of 1.5 at a distance of about two Plasma jet radii from the starting plane. The calculated arc current–voltage characteristics agree qualitatively with experiments on arc behavior in an axial magnetic field.
Mark E Dieckmann - One of the best experts on this subject based on the ideXlab platform.
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weibel induced filamentation during an ultrafast laser driven Plasma Expansion
Physical Review Letters, 2012Co-Authors: K Quinn, L Romagnani, B Ramakrishna, G Sarri, Mark E Dieckmann, P A Wilson, J Fuchs, L Lancia, A Pipahl, T ToncianAbstract:The development of current instabilities behind the front of a cylindrically expanding Plasma has been investigated experimentally via proton probing techniques. A multitude of tubelike filamentary structures is observed to form behind the front of a Plasma created by irradiating solid-density wire targets with a high-intensity (I ~ 10(19) W/cm(2)), picosecond-duration laser pulse. These filaments exhibit a remarkable degree of stability, persisting for several tens of picoseconds, and appear to be magnetized over a filament length corresponding to several filament radii. Particle-in-cell simulations indicate that their formation can be attributed to a Weibel instability driven by a thermal anisotropy of the electron population. We suggest that these results may have implications in astrophysical scenarios, particularly concerning the problem of the generation of strong, spatially extended and sustained magnetic fields in astrophysical jets.
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simulation of a collisionless planar electrostatic shock in a proton electron Plasma with a strong initial thermal pressure change
Plasma Physics and Controlled Fusion, 2010Co-Authors: L Romagnani, G Sarri, Mark E Dieckmann, Ioannis Kourakis, M BorghesiAbstract:The localized deposition of the energy of a laser pulse, as it ablates a solid target, introduces high thermal pressure gradients in the Plasma. The thermal Expansion of this laser-heated Plasma into the ambient medium (ionized residual gas) triggers the formation of non-linear structures in the collisionless Plasma. Here an electron–proton Plasma is modelled with a particle-in-cell simulation to reproduce aspects of this Plasma Expansion. A jump is introduced in the thermal pressure of the Plasma, across which the otherwise spatially uniform temperature and density change by a factor of 100. The electrons from the hot Plasma expand into the cold one and the charge imbalance drags a beam of cold electrons into the hot Plasma. This double layer reduces the electron temperature gradient. The presence of the low-pressure Plasma modifies the proton dynamics compared with the Plasma Expansion into a vacuum. The jump in the thermal pressure develops into a primary shock. The fast protons, which move from the hot into the cold Plasma in the form of a beam, give rise to the formation of phase space holes in the electron and proton distributions. The proton phase space holes develop into a secondary shock that thermalizes the beam.