Ralf Schneider - Academia.edu (original) (raw)
Papers by Ralf Schneider
AIP Conference Proceedings, 2007
AIP Conference Proceedings, 2008
A 3-dimensional Particle-Particle Particle-Mesh (P3M) code is applied to study the charging proce... more A 3-dimensional Particle-Particle Particle-Mesh (P3M) code is applied to study the charging process of micrometer size dust grains confined in a capacitive RF discharge. In our model, particles (electrons and ions) are treated kinetically (Particle-in-Cell with Monte Carlo Collisions (PIC-MCC)). In order to accurately resolve the plasma particles' motion close to the dust grain, the PIC technique is supplemented with
ABSTRACT The Particle-in-Cell (PIC) method was used to study two different ion thruster concepts ... more ABSTRACT The Particle-in-Cell (PIC) method was used to study two different ion thruster concepts –Stationary Plasma Thrusters (SPT) and High Efficiency Multistage Plasma Thrusters (HEMP-T), in particular the plasma properties in the discharge chamber due to the different magnetic field configurations. Special attention was paid to the simulation of plasma particle fluxes on the thrusters' channel surfaces. In both cases, PIC proved itself as a powerful tool, delivering important insight into the basic physics of the different thruster concepts. The simulations demonstrated that the new HEMP thruster concept allows for a high thermal efficiency due to both minimal energy dissipation and high acceleration efficiency. In the HEMP thruster the plasma contact to the wall is limited only to very small areas of the magnetic field cusps, which results in much smaller ion energy flux to the thruster channel surface as compared to SPT. The erosion yields for dielectric discharge channel walls of SPT and HEMP thrusters were calculated with the binary collision code SDTrimSP. For SPT, an erosion rate on the level of 1 mm of sputtered material per hour was observed. For HEMP, thruster simulations have shown that there is no erosion inside the dielectric discharge channel.
2010 18th Euromicro Conference on Parallel, Distributed and Network-based Processing, 2010
In this work we describe an optimization technique for PIC/MC modeling of the plasma edge using H... more In this work we describe an optimization technique for PIC/MC modeling of the plasma edge using High Performance Computing. The developed code BIT1 can be used for 1D3V plasma and 2D3V neutral particle modeling with a reasonable scaling up to 1000 and more processors.
ABSTRACT The spectral emission of argon atoms in a dusty radio frequence (RF) discharge has been ... more ABSTRACT The spectral emission of argon atoms in a dusty radio frequence (RF) discharge has been investigated experimentally and in simulations. It was observed that the spatially and temporally resolved emission of the argon atoms in the dusty discharge was increased compared to the dust‐free case during sheath expansion. The corresponding simulations have revealed that the dust trapped in the sheath of the discharge leads to a small, but important, increase of the amount of high‐energy electrons that in turn leads to an increased argon emission.
Two-dimensional fluid codes have become standard modeling tools for scrape-off layer and divertor... more Two-dimensional fluid codes have become standard modeling tools for scrape-off layer and divertor in tokamaks. Such 2D codes (UEDGE, B2, EDGE2D) solve a reduced set of plasma fluid equations with the assumption of toroidal symmetry. However perfect toroidal symmetry in tokamak edge never holds due to details of plasma facing components. Moreover, with the renewed interest in stellarators with several major experiments under way or planned (W7AS, W7X, LHD, NCSX) there is a demand for 3D modeling tools for the edge plasma. One such tool under development is the 3D fluid edge code BoRiS. (M.Borchardt et al., J. Nucl. Mater., 290-293 (2001) 546-550.) A focus of the present investigation is development and testing robust numerical schemes for edge plasma fluid equations in 3D. This analysis includes benchmarking of BoRiS on sample problems where an exact solution can be found, and benchmarking against a 2D code such as UEDGE for the toroidally symmetric case. We will discuss the options ...
Plasma Sources Science and Technology, 2011
ABSTRACT In this paper we present results of different particle-based models of expansion and ext... more ABSTRACT In this paper we present results of different particle-based models of expansion and extraction regions for the ITER negative ion source. Results show the important role of electron-induced processes (eV excitation and dissociation) and gas-surface and plasma-surface interactions (atom recombinative desorption and ion neutralization) for the production of negative ion precursors. The spatial distribution of neutral and ionized caesium as well as the drag due to the deuterium flow and its re-evaporation from the plasma grid is calculated. The self-consistent two-dimensional electric field distribution in the extraction region allows a better understanding of the transport of surface-produced negative ions towards the orifice. The model delivers an extraction probability of less than 25%.
Plasma Physics and Controlled Fusion, 2010
... A 7 2758 [4] Bouchoule A 1999 Dusty Plasmas: Physics, Chemistry and Technological Impacts in ... more ... A 7 2758 [4] Bouchoule A 1999 Dusty Plasmas: Physics, Chemistry and Technological Impacts in Plasma Processing (New York: Wiley) [5] Swinkels GHPM ... 266269 22833 [10] Rubel M, Cecconello M, Malmberg JA, Sergienko G, Biel W, Drake JR, Hedqvist A, Huber A and ...
Plasma Physics and Controlled Fusion, 2003
ABSTRACT
Physics of Plasmas, 2005
This work represents a two-dimensional axisymmetric fully kinetic particle-in-cell/Monte Carlo co... more This work represents a two-dimensional axisymmetric fully kinetic particle-in-cell/Monte Carlo collision model of the plasmadynamics in the acceleration channel of a stationary plasma thruster. The model includes the process of secondary electron emission from the ...
Journal of Nuclear Materials, 2005
The 3D fluid transport code BoRiS is applied to a hydrogen plasma and a neutral fluid in a stella... more The 3D fluid transport code BoRiS is applied to a hydrogen plasma and a neutral fluid in a stellarator-like geometry equipped with a poloidal ring limiter. The results demonstrate the capability of dealing with 3D effects which can be related to both the influence of the geometry and the plasma-neutral interaction as well. The setup used has similarities with a poloidal gas target in a fusion device.
International Journal for Multiscale Computational Engineering, 2006
ABSTRACT Non-Maxwellian behavior and plasma-wall interaction are key processes in the physics of ... more ABSTRACT Non-Maxwellian behavior and plasma-wall interaction are key processes in the physics of Hall thrusters. For this purpose, a 2D {r, z}-3V axisymmetric fully kinetic particle-in-cell/Monte Carlo collision (PIC-MCC) model of the acceleration channel including the ...
Contributions to Plasma Physics, 2008
It has been shown experimentally that the channel wall material has a substantial effect on the b... more It has been shown experimentally that the channel wall material has a substantial effect on the behaviour of Hall discharges. For this reason, the radial profile inside the Hall thruster SPT-100 is investigated in detail. This is done by a one-dimensional fully kinetic self-consistent Particle-in-Cell model between the two walls in the acceleration region of the channel. A detailed Monte Carlo probabilistic model for secondary electron emission is implemented as boundary module. Using the local field approximation, two different operative conditions (axial electric field Ez=100 V/cm and 300 V/cm) have been simulated. For high discharge voltage case, a strong radial asymmetry and a stream instability propagating all along the radial domain are detected, while in the low voltage case a stable classical situation is recovered. The critical parameters for triggering this unstable regime are the electron azimuthal drift energy and the induced secondary electron emission, while the saturation mechanism is the increasing of the temperature of the initially cold secondary-electrons.
Contributions to Plasma Physics, 1992
AIP Conference Proceedings, 2007
AIP Conference Proceedings, 2008
A 3-dimensional Particle-Particle Particle-Mesh (P3M) code is applied to study the charging proce... more A 3-dimensional Particle-Particle Particle-Mesh (P3M) code is applied to study the charging process of micrometer size dust grains confined in a capacitive RF discharge. In our model, particles (electrons and ions) are treated kinetically (Particle-in-Cell with Monte Carlo Collisions (PIC-MCC)). In order to accurately resolve the plasma particles' motion close to the dust grain, the PIC technique is supplemented with
ABSTRACT The Particle-in-Cell (PIC) method was used to study two different ion thruster concepts ... more ABSTRACT The Particle-in-Cell (PIC) method was used to study two different ion thruster concepts –Stationary Plasma Thrusters (SPT) and High Efficiency Multistage Plasma Thrusters (HEMP-T), in particular the plasma properties in the discharge chamber due to the different magnetic field configurations. Special attention was paid to the simulation of plasma particle fluxes on the thrusters' channel surfaces. In both cases, PIC proved itself as a powerful tool, delivering important insight into the basic physics of the different thruster concepts. The simulations demonstrated that the new HEMP thruster concept allows for a high thermal efficiency due to both minimal energy dissipation and high acceleration efficiency. In the HEMP thruster the plasma contact to the wall is limited only to very small areas of the magnetic field cusps, which results in much smaller ion energy flux to the thruster channel surface as compared to SPT. The erosion yields for dielectric discharge channel walls of SPT and HEMP thrusters were calculated with the binary collision code SDTrimSP. For SPT, an erosion rate on the level of 1 mm of sputtered material per hour was observed. For HEMP, thruster simulations have shown that there is no erosion inside the dielectric discharge channel.
2010 18th Euromicro Conference on Parallel, Distributed and Network-based Processing, 2010
In this work we describe an optimization technique for PIC/MC modeling of the plasma edge using H... more In this work we describe an optimization technique for PIC/MC modeling of the plasma edge using High Performance Computing. The developed code BIT1 can be used for 1D3V plasma and 2D3V neutral particle modeling with a reasonable scaling up to 1000 and more processors.
ABSTRACT The spectral emission of argon atoms in a dusty radio frequence (RF) discharge has been ... more ABSTRACT The spectral emission of argon atoms in a dusty radio frequence (RF) discharge has been investigated experimentally and in simulations. It was observed that the spatially and temporally resolved emission of the argon atoms in the dusty discharge was increased compared to the dust‐free case during sheath expansion. The corresponding simulations have revealed that the dust trapped in the sheath of the discharge leads to a small, but important, increase of the amount of high‐energy electrons that in turn leads to an increased argon emission.
Two-dimensional fluid codes have become standard modeling tools for scrape-off layer and divertor... more Two-dimensional fluid codes have become standard modeling tools for scrape-off layer and divertor in tokamaks. Such 2D codes (UEDGE, B2, EDGE2D) solve a reduced set of plasma fluid equations with the assumption of toroidal symmetry. However perfect toroidal symmetry in tokamak edge never holds due to details of plasma facing components. Moreover, with the renewed interest in stellarators with several major experiments under way or planned (W7AS, W7X, LHD, NCSX) there is a demand for 3D modeling tools for the edge plasma. One such tool under development is the 3D fluid edge code BoRiS. (M.Borchardt et al., J. Nucl. Mater., 290-293 (2001) 546-550.) A focus of the present investigation is development and testing robust numerical schemes for edge plasma fluid equations in 3D. This analysis includes benchmarking of BoRiS on sample problems where an exact solution can be found, and benchmarking against a 2D code such as UEDGE for the toroidally symmetric case. We will discuss the options ...
Plasma Sources Science and Technology, 2011
ABSTRACT In this paper we present results of different particle-based models of expansion and ext... more ABSTRACT In this paper we present results of different particle-based models of expansion and extraction regions for the ITER negative ion source. Results show the important role of electron-induced processes (eV excitation and dissociation) and gas-surface and plasma-surface interactions (atom recombinative desorption and ion neutralization) for the production of negative ion precursors. The spatial distribution of neutral and ionized caesium as well as the drag due to the deuterium flow and its re-evaporation from the plasma grid is calculated. The self-consistent two-dimensional electric field distribution in the extraction region allows a better understanding of the transport of surface-produced negative ions towards the orifice. The model delivers an extraction probability of less than 25%.
Plasma Physics and Controlled Fusion, 2010
... A 7 2758 [4] Bouchoule A 1999 Dusty Plasmas: Physics, Chemistry and Technological Impacts in ... more ... A 7 2758 [4] Bouchoule A 1999 Dusty Plasmas: Physics, Chemistry and Technological Impacts in Plasma Processing (New York: Wiley) [5] Swinkels GHPM ... 266269 22833 [10] Rubel M, Cecconello M, Malmberg JA, Sergienko G, Biel W, Drake JR, Hedqvist A, Huber A and ...
Plasma Physics and Controlled Fusion, 2003
ABSTRACT
Physics of Plasmas, 2005
This work represents a two-dimensional axisymmetric fully kinetic particle-in-cell/Monte Carlo co... more This work represents a two-dimensional axisymmetric fully kinetic particle-in-cell/Monte Carlo collision model of the plasmadynamics in the acceleration channel of a stationary plasma thruster. The model includes the process of secondary electron emission from the ...
Journal of Nuclear Materials, 2005
The 3D fluid transport code BoRiS is applied to a hydrogen plasma and a neutral fluid in a stella... more The 3D fluid transport code BoRiS is applied to a hydrogen plasma and a neutral fluid in a stellarator-like geometry equipped with a poloidal ring limiter. The results demonstrate the capability of dealing with 3D effects which can be related to both the influence of the geometry and the plasma-neutral interaction as well. The setup used has similarities with a poloidal gas target in a fusion device.
International Journal for Multiscale Computational Engineering, 2006
ABSTRACT Non-Maxwellian behavior and plasma-wall interaction are key processes in the physics of ... more ABSTRACT Non-Maxwellian behavior and plasma-wall interaction are key processes in the physics of Hall thrusters. For this purpose, a 2D {r, z}-3V axisymmetric fully kinetic particle-in-cell/Monte Carlo collision (PIC-MCC) model of the acceleration channel including the ...
Contributions to Plasma Physics, 2008
It has been shown experimentally that the channel wall material has a substantial effect on the b... more It has been shown experimentally that the channel wall material has a substantial effect on the behaviour of Hall discharges. For this reason, the radial profile inside the Hall thruster SPT-100 is investigated in detail. This is done by a one-dimensional fully kinetic self-consistent Particle-in-Cell model between the two walls in the acceleration region of the channel. A detailed Monte Carlo probabilistic model for secondary electron emission is implemented as boundary module. Using the local field approximation, two different operative conditions (axial electric field Ez=100 V/cm and 300 V/cm) have been simulated. For high discharge voltage case, a strong radial asymmetry and a stream instability propagating all along the radial domain are detected, while in the low voltage case a stable classical situation is recovered. The critical parameters for triggering this unstable regime are the electron azimuthal drift energy and the induced secondary electron emission, while the saturation mechanism is the increasing of the temperature of the initially cold secondary-electrons.
Contributions to Plasma Physics, 1992