163 results on '"SPACE-CHARGE"'
Search Results
2. Simulation as a Tool for Understanding Experimental Observations—Ion Beam Extraction from an ECRIS
- Author
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Peter Spädtke
- Subjects
ECRIS ,ion beam ,extraction ,ion beam transport ,space-charge ,simulation ,Physics ,QC1-999 ,Plasma physics. Ionized gases ,QC717.6-718.8 - Abstract
A model for the simulation of ion beam extraction from an electron-cyclotron resonance ion source is proposed. It is based on the simple fact that charged particles follow magnetic field lines. Therefore, magnetic field lines are used to generate initial conditions for ray-tracing. This model reproduces in simulation experimentally obtained results. The importance of correlations in phase-space caused by the magnetic field is shown in the simulation. This model also describes the physics of space-charge and its compensation in the extracted (fast) ion beam by low-energy electrons. Simulation provides the possibility to test theoretical assumptions, as well as to optimize technical designs.
- Published
- 2022
- Full Text
- View/download PDF
3. Poisson's equation in semiconductors: impact of charge depletion on Hall effect measurements.
- Author
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Masut, Remo A.
- Abstract
Space-charge effects are familiar to students of solid state physics, semiconductor devices, and surface science. They are usually estimated under the strong depletion or space-charge layer approximation (SCLA), whose limitations are rarely fully discussed. A formal description of these effects is presented, followed by numerical solutions to a one-dimensional Poisson's equation. This equation is valid in cases of charge depletion and of mild accumulation near surfaces and interfaces. Poisson's equation as it applies to a film/substrate interface is analyzed to obtain the boundary condition for the potential at the metallurgical junction. A practical applied example discusses the impact of depletion effects on the determination of the charge carrier concentration by Hall effect measurement in homoepitaxial semiconductor thin films. Examples are highlighted where the SCLA is not an accurate approximation. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
4. Recommended Practice for Use of Emissive Probes in Electric Propulsion Testing
- Author
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McDonald, Michael [Naval Research Laboratory, Washington, D.C. (Unietd States)]
- Published
- 2016
- Full Text
- View/download PDF
5. Benchmark testing of DIII-D neutral beam modeling with water flow calorimetry
- Author
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Murphy, C. [General Atomics, San Diego, CA (United States). DIII-D National Fusion Facility]
- Published
- 2016
- Full Text
- View/download PDF
6. Half-wavelength velocity bunching: non-adiabatic temporal focusing of charged particle beams
- Author
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Anatoliy Opanasenko, Giovanni Perosa, Johan Ribbing, and Vitaliy Goryashko
- Subjects
femtosecond high-brightness electron beams ,space-charge ,bunch compression ,Science ,Physics ,QC1-999 - Abstract
X-ray free-electron lasers (XFELs) and megaelectronvolt ultrafast electron diffractometers (MeV UEDs) are revolutionary scientific instruments that allow visualizing the dynamics of elementary excitations in a wide range of systems from atoms and molecules to phonons, magnons and plasmons. Femtosecond (fs) electron beams are at the heart of XFELs and MeV UEDs, and the formation of fs electron beams with ultrahigh brightness is the subject of active research. We report an interesting regime of non-adiabatic temporal compression of electron beams by two orders of magnitude. Via analytical calculations and numerical simulations, we show that few MeV electron bunches can be trapped and compressed by a strong electromagnetic field within a half of the field wavelength. Furthermore, in a multi-cell accelerating cavity, the bunch is first compressed and then accelerated, thus allowing one to preserve very short bunch duration. For example, a 3 ps 16 pC 1 MeV electron bunch is compressed to 21 fs rms and accelerated to 12 MeV in a TESLA superconducting cavity. Another example is the production of 1.2 fs 16 fC 3.3 MeV bunches with a coherence length of 20 nm and and an energy spread less than 3 keV. The discovered mechanism of compression, which is another mode of velocity bunching, opens the door for obtaining very high electron brightness.
- Published
- 2023
- Full Text
- View/download PDF
7. Coherent Emission: Linear Theory
- Author
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Freund, H. P., Antonsen, T. M., Jr., Freund, H. P., and Antonsen, Jr., T. M.
- Published
- 2018
- Full Text
- View/download PDF
8. Dynamics of a Field Emitted Beam From a Microscopic Inhomogeneous Cathode.
- Author
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Torfason, Kristinn, Sitek, Anna, Manolescu, Andrei, and Valfells, Agust
- Subjects
- *
FIELD emission , *CATHODES , *ELECTRON beams , *MOLECULAR dynamics , *ELECTRON work function , *GRID cells - Abstract
We investigate by molecular dynamics simulations (Torfason et al., 2015; 2016) a beam of electrons released via field emission from a planar cathode surface of 1 μm2 with an inhomogeneous two-level work function, φlow and φhigh. A rectangular grid, where each cell can have one out of two values of the work function, is used as a model. The number of cells in the grid ranges from 6 × 6 to 96 × 96. We compare a periodic checkerboard arrangement with disordered distributions of patches. We perform multiple simulations and randomize the pattern each time. We study the beam behavior by calculating the position and velocity of each electron, r.m.s. emittance, and the brightness of the electron beam. The emittance increases while brightness decreases, with the mean distance between patches with φlow when they are in minority, and they switch the behavior versus the mean distance between patches with φhigh when these patches are in minority, respectively. The Coulomb interaction between all particles is fully included in our simulations. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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- View/download PDF
9. Molecular Dynamics Simulations of Mutual Space-Charge Effect Between Planar Field Emitters.
- Author
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Haraldsson, Hakon Valur, Torfason, Kristinn, Manolescu, Andrei, and Valfells, Agust
- Subjects
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FIELD emission , *ELECTRON sources , *SPACE charge , *MOLECULAR dynamics , *DIODES - Abstract
Molecular dynamics simulations, with full Coulomb interaction and self-consistent field emission, are used to examine mutual space–charge interactions between beams originating from several emitter areas, in a planar infinite diode. The simulations allow observation of the trajectory of each individual electron through the diode gap. Results show that when the center-to-center spacing between emitters is greater than half of the gap spacing the emitters are essentially independent. For smaller spacing the mutual space–charge effect increases rapidly and should not be discounted. A simple qualitative explanation for this effect is given. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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10. Paving the way to nanoionics: atomic origin of barriers for ionic transport through interfaces
- Author
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Frechero, M. A., Rocci, Mirko, Sánchez Santolino, Gabriel, Salafranca, Juan, Schmidt, Rainer, Díaz Guillén, M. R., Durá, O. J., Rivera Calzada, Alberto Carlos, Varela del Arco, María, Santamaría Sánchez-Barriga, Jacobo, León Yebra, Carlos, Frechero, M. A., Rocci, Mirko, Sánchez Santolino, Gabriel, Salafranca, Juan, Schmidt, Rainer, Díaz Guillén, M. R., Durá, O. J., Rivera Calzada, Alberto Carlos, Varela del Arco, María, Santamaría Sánchez-Barriga, Jacobo, and León Yebra, Carlos
- Abstract
We acknowledge financial support by Spanish MICINN through grants MAT2011-27470-C01 and Consolider Ingenio 2010 - CSD2009-00013 (Imagine), by CAM through grant S2009/MAT-1756 (Phama) and by the ERC starting Investigator Award, grant #239739 STEMOX. RS wishes to acknowledge the MICINN (Spain) for granting a Ramon y Cajal fellowship. MAF is Research Fellow of CONICET (Argentine). Financial support of CONICET is gratefully acknowledged. OJD acknowledges a postdoctoral fellowship from JCCM. JS acknowledges a Juan de la Cierva fellowship from MICINN (Spain). The authors thank Dr. Hugo Schlich from Mateck GmbH for providing information about the process of bicrystals production, Masashi Watanabe for the Digital Micrograph PCA plug-in and J. Luck for help with specimen preparation, and A. de Andrés for helpful discussion and assistance on experimental matters. Electron microscopy observations at ORNL (SJP, MV) were sponsored by the Materials Sciences and Engineering Division of the U.S. Department of Energy (DOE) and and through the Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, DOE-BES. ESM measurements (SVK, SJ, AK) were performed at the Center for Nanophase Materials Sciences and supported by the Division of Scientific User Facilities of the U.S. Department of Energy (DOE)., The blocking of ion transport at interfaces strongly limits the performance of electrochemical nanodevices for energy applications. The barrier is believed to arise from space-charge regions generated by mobile ions by analogy to semiconductor junctions. Here we show that something different is at play by studying ion transport in a bicrystal of yttria (9% mol) stabilized zirconia (YSZ), an emblematic oxide ion conductor. Aberration-corrected scanning transmission electron microscopy (STEM) provides structure and composition at atomic resolution, with the sensitivity to directly reveal the oxygen ion profile. We find that Y segregates to the grain boundary at Zr sites, together with a depletion of oxygen that is confined to a small length scale of around 0.5nm. Contrary to the main thesis of the space-charge model, there exists no evidence of a long-range O vacancy depletion layer. Combining ion transport measurements across a single grain boundary by nanoscale electrochemical strain microscopy (ESM), broadband dielectric spectroscopy measurements, and density functional calculations, we show that grain-boundary-induced electronic states act as acceptors, resulting in a negatively charged core. Besides the possible effect of the modified chemical bonding, this negative charge gives rise to an additional barrier for ion transport at the grain boundary., Ministerio de Ciencia e Innovación (MICINN), Comunidad de Madrid, Consolider Ingenio 2010, ERC starting Investigator Award, CONICET, JCCM, Materials Sciences and Engineering Division of the U.S. Department of Energy (DOE), Center for Nanophase Materials Sciences (CNMS), Scientific User Facilities Division, DOE-BES, Division of Scientific User Facilities of the U.S. Department of Energy (DOE), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub
- Published
- 2023
11. Half-wavelength velocity bunching : non-adiabatic temporal focusing of charged particle beams
- Author
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Opanasenko, Anatoliy, Perosa, Giovanni, Ribbing, Johan, Goryashko, Vitaliy, Opanasenko, Anatoliy, Perosa, Giovanni, Ribbing, Johan, and Goryashko, Vitaliy
- Abstract
X-ray free-electron lasers (XFELs) and megaelectronvolt ultrafast electron diffractometers (MeV UEDs) are revolutionary scientific instruments that allow visualizing the dynamics of elementary excitations in a wide range of systems from atoms and molecules to phonons, magnons and plasmons. Femtosecond (fs) electron beams are at the heart of XFELs and MeV UEDs, and the formation of fs electron beams with ultrahigh brightness is the subject of active research. We report an interesting regime of non-adiabatic temporal compression of electron beams by two orders of magnitude. Via analytical calculations and numerical simulations, we show that few MeV electron bunches can be trapped and compressed by a strong electromagnetic field within a half of the field wavelength. Furthermore, in a multi-cell accelerating cavity, the bunch is first compressed and then accelerated, thus allowing one to preserve very short bunch duration. For example, a 3 ps 16 pC 1 MeV electron bunch is compressed to 21 fs rms and accelerated to 12 MeV in a TESLA superconducting cavity. Another example is the production of 1.2 fs 16 fC 3.3 MeV bunches with a coherence length of 20 nm and and an energy spread less than 3 keV. The discovered mechanism of compression, which is another mode of velocity bunching, opens the door for obtaining very high electron brightness.
- Published
- 2023
- Full Text
- View/download PDF
12. Grain growth in strontium titanate in electric fields: The impact of space‐charge on the grain‐boundary mobility.
- Author
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Rheinheimer, Wolfgang, Parras, Jana P., Preusker, Jan‐Helmut, De Souza, Roger A., and Hoffmann, Michael J.
- Subjects
- *
STRONTIUM titanate , *GRAIN growth , *SPACE charge , *ELECTRIC fields , *NEGATIVE electrode , *CRYSTAL grain boundaries , *STRONTIUM oxide - Abstract
This study investigates grain growth in the perovskite oxide strontium titanate in an electric field. The seeded polycrystal technique was chosen as it provides a sensitive and controlled setup to evaluate the impact of different parameters on grain growth due to the well‐defined driving force for grain growth. Current blocking electrodes were used to prevent Joule heating. The results show faster grain growth, and thus, higher grain‐boundary mobility at the negative electrode. It is argued that the electric field causes point‐defect redistribution, resulting in a higher oxygen vacancy concentration at the negative electrode. The local oxygen vacancy concentration is suggested to affect the space‐charge potential at the grain boundaries. A thermodynamic treatment of the grain‐boundary potential at a grain boundary without field shows that for a high oxygen vacancy concentration less space‐charge and less accumulation of cationic defects to the boundary occurs. Therefore, at the negative electrode, a higher oxygen vacancy concentration results in less space‐charge and less accumulation of cationic defects. The lower degree of defect accumulation requires less diffusion of segregated defects during grain‐boundary migration, so that at the negative electrode faster grain growth is expected, as found in the experiments. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
13. First Beam Matching and Transmission Studies on the ESS RFQ
- Author
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Noll, Daniel, Baron, Rafael, Chauveau, Anne-Catherine, Derrez, Clement, Donegani, Elena, Eshraqi, Mohammad, Grespan, Francesco, Hassanzadegan, Hooman, Jones, Bryan, Levinsen, Yngve, Milas, Natalia, Miyamoto, Ryoichi, Piquet, Olivier, Plostinar, Ciprian, Sosa, Alejandro, Zeng, Rihua, Institut de Recherches sur les lois Fondamentales de l'Univers (IRFU), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay
- Subjects
rfq ,LEBT ,emittance ,MMI ,[PHYS.PHYS.PHYS-ACC-PH]Physics [physics]/Physics [physics]/Accelerator Physics [physics.acc-ph] ,space-charge ,Proton and Ion Accelerators and Applications ,Accelerator Physics - Abstract
The European Spallation Source will be driven by a 5 MW linear accelerator, producing 2.86 ms long proton beam pulses with a peak current of 62.5 mA at 14 Hz. Following the source commissioning in 2018 and 2019, the RFQ was successfully conditioned and subsequently commissioned with beam in 2021. In this paper, we will present results of studies on beam matching to the RFQ, both for low and high current beam modes, and will compare these results to model predictions., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK
- Published
- 2022
14. Blocking effect in promising proton conductors based on Ba3Ca1.18Nb1.82-xRxO9-δ (R = Y3+, Gd3+, Sm3+, Nd3+) ordered perovskites for PC-SOFCs.
- Author
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Francisco, L.H., Rodrigues, J.E., Correr, W.R., and Hernandes, A.C.
- Subjects
- *
SOLID state proton conductors , *PEROVSKITE , *STOICHIOMETRY , *POLYCRYSTALS , *ELECTRIC conductivity - Abstract
High proton conductivity and good chemical stability are keys to development of new electrolytes for PC-SOFCs as the next-future energy generation systems. However, the extensive use of new polycrystalline materials as solid electrolytes is still avoided, since the grain boundary response usually leads to a decrease in total conductivity due to electrical blocking effect. Here, we present our results on the space-charge modeling of impedance spectroscopy data obtained for Ba 3 Ca 1.18 Nb 1.82- x R x O 9-δ proton conducting ceramics, where x = 0, 0.30 and R = Y 3+ , Gd 3+ , Sm 3+ , Nd 3+ are doping agents. Non-stoichiometric barium calcium niobate perovskites have received much attention as potential solid electrolytes for proton conducting solid oxide fuel cells. We show that despite their increased grain conductivity, the doped ceramics possess Schottky barriers that are higher than those observed for undoped Ba 3 Ca 1.18 Nb 1.82 O 9-δ . In view of the space-charge model, proton depletion at the space-charge layer is the reason for the reduction of grain boundary conductivity in the doped compositions. Our findings are important for the understanding of proton conduction mechanisms in polycrystalline materials, which may allow future optimization of new doped electrolytes based on barium calcium niobate perovskites. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
15. On the (Apparent) Paradox between Space-Charge Forces and Space-Charge Effects
- Author
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Nghiem, Phu Anh Phi, Institut de Recherches sur les lois Fondamentales de l'Univers (IRFU), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay
- Subjects
focusing ,rfq ,emittance ,[PHYS.PHYS.PHYS-ACC-PH]Physics [physics]/Physics [physics]/Accelerator Physics [physics.acc-ph] ,MC5: Beam Dynamics and EM Fields ,Physics::Accelerator Physics ,space-charge ,linac ,Accelerator Physics - Abstract
With the advent of high-intensity linacs, space charge forces are now well known as a major issue causing undesirable effects on particle beam qualities like emittance growth or sudden losses. They should be stronger when there are more particles or when the latter are contained in a smaller volume. But a detailed examination of the beam along an accelerator show that space charge effects are weaker where the beam size is smaller. This article clarifies this paradox and revisits the recommendations on beam sizes in view of mitigating space charge effects., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand
- Published
- 2022
16. FT-ICR Mass Spectrometry Imaging at Extreme Mass Resolving Power Using a Dynamically Harmonized ICR Cell with 1ω or 2ω Detection
- Author
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Mathieu Tiquet, Raphaël La Rocca, Stefan Kirnbauer, Samuele Zoratto, Daan Van Kruining, Loïc Quinton, Gauthier Eppe, Pilar Martinez-Martinez, Martina Marchetti-Deschmann, Edwin De Pauw, Johann Far, RS: MHeNs - R3 - Neuroscience, and Basic Neuroscience 3
- Subjects
CALIBRATION ,Diagnostic Imaging ,Ions ,SPACE-CHARGE ,MOTION ,Fourier Analysis ,ACCURACY ,Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization ,SAMPLE PREPARATION ,Cyclotrons ,ELECTRIC-FIELD ,Analytical Chemistry - Abstract
MALDI mass spectrometry imaging (MALDI MSI) is a powerful analytical method for achieving 2D localization of compounds from thin sections of typically but not exclusively biological samples. The dynamically harmonized ICR cell (ParaCell) was recently introduced to achieve extreme spectral resolution capable of providing the isotopic fine structure of ions detected in complex samples. The latest improvement in the ICR technology also includes 2 omega detection, which significantly reduces the transient time while preserving the nominal mass resolving power of the ICR cell. High-resolution MS images acquired on FT-ICR instruments equipped with 7T and 9.4T superconducting magnets and the dynamically harmonized ICR cell operating at suboptimal parameters suffered severely from the pixel-to-pixel shifting of m/z peaks due to space-charge effects. The resulting profile average mass spectra have depreciated mass measurement accuracy and mass resolving power under the instrument specifications that affect the confidence level of the identified ions. Here, we propose an analytical workflow based on the monitoring of the total ion current to restrain the pixel-to-pixel m/z shift. Adjustment of the laser parameters is proposed to maintain high spectral resolution and mass accuracy measurement within the instrument specifications during MSI analyses. The optimized method has been successfully employed in replicates to perform high-quality MALDI MS images at resolving power (FWHM) above 1,000,000 in the lipid mass range across the whole image for superconducting magnets of 7T and 9.4T using 1 and 2 omega detection. Our data also compare favorably with MALDI MSI experiments performed on higher-magnetic-field superconducting magnets, including the 21T MALDI FT-ICR prototype instrument of the NHMFL group at Tallahassee, Florida.
- Published
- 2022
17. Space-Charge Effects with REXTRAP
- Author
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the REX ISOLDE Collaboration, Ames, F., Schmidt, P., Forstner, O., Bollen, G., Engels, O., Habs, D., Huber, G., Lunney, David, editor, Audi, Georges, editor, and Kluge, H.-Jürgen, editor
- Published
- 2001
- Full Text
- View/download PDF
18. Proton segregation and space-charge at the BaZrO3 (0 0 1)/MgO (0 0 1) heterointerface.
- Author
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Polfus, Jonathan M., Norby, Truls, and Bredesen, Rune
- Subjects
- *
SEGREGATION , *SPACE-charge limited devices , *ELECTRICAL conductors , *MAGNESIUM oxide , *THERMODYNAMICS - Abstract
Y-doped BaZrO 3 (BZY) can be deposited epitaxially on MgO (0 0 1) and the considered interface serves as a model system for studying heterointerface properties of protonic conductors. In this study, the defect chemistry of the interface between ZrO 2 -terminated BaZrO 3 (0 0 1) and MgO (0 0 1) was investigated by first-principles calculations and space-charge theory. Segregation energies from the BZY bulk to the interface ZrO 2 and MgO layers were calculated for effectively charged protons, oxygen vacancies, Y-acceptors as well as cation vacancies. Protons were found to exhibit a strong tendency for segregating to the interface, particularly to an oxide ion in the MgO layer, rendering a net positive charge of the interface. According to the applied thermodynamic space-charge models, the interface potential could reach more than 1 V under the Mott-Schottky approximation, with depletion regions extending up to 2 nm into BZY. With fully equilibrated Y-segregation profiles, the interface potential was significantly diminished to about 0.2 V at 573 K and 0.025 bar H 2 O. While the interface was found to be close to saturated by protons under most condition, it was concluded that proton conduction along the interface could not contribute significantly to the in-plane conductivity of BZY films deposited on MgO substrate. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
19. Excitation of the σ_{l}_{l} = 90° Resonance by the Cavity RF Accelerating Fields
- Author
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Lagniel, Jean-Michel, Grand Accélérateur National d'Ions Lourds (GANIL), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
focusing ,resonance ,[PHYS.PHYS.PHYS-ACC-PH]Physics [physics]/Physics [physics]/Accelerator Physics [physics.acc-ph] ,MC5: Beam Dynamics and EM Fields ,Physics::Accelerator Physics ,cavity ,space-charge ,linac ,Accelerator Physics - Abstract
In RF linacs the longitudinal focusing is done by nonlinear forces and at high accelerating fields the zero-current longitudinal phase advance per longitudinal focusing period σ₀l_{l} can be high. The nonlinear components of the RF field (sextupolar, octupolar and higher order components) can then excite parametric resonances, including the 4th-order resonance (σ_{l}_{l} = 90°) when σ₀l_{l} is higher than 90°, inducing strong longitudinal emittance growths and acceptance reductions. The longitudinal beam dynamics is therefore complex, even when the nonlinear space-charge forces are ignored. The parametric resonance excitation by the RF field is analyzed before discussing the additional effect of the nonlinear space-charge forces, in particular to explain why the zero-current longitudinal phase advance per transverse focusing period σ₀l_{t} is not a relevant parameter. Examples are given in the SPIRAL2 linac case., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand
- Published
- 2022
- Full Text
- View/download PDF
20. Accelerating Linear Beam Dynamics Simulations for Machine Learning Applications
- Author
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Stein, Oliver, Agapov, Ilya, Eichler, Annika, and Kaiser, Jan
- Subjects
experiment ,GPU ,MC5: Beam Dynamics and EM Fields ,Beam Dynamics and EM Fields [MC5] ,controls ,space-charge ,simulation ,Accelerator Physics - Abstract
[Ebook] 13th International Particle Accelerator Conference : June 12-17, 2022, Impact Forum, Muangthong Thani, Bangkok, Thailand : conference proceedings / Chanwattana, Thakonwat , [Geneva] : JACoW Publishing, July 2022, 13th International Particle Accelerator Conference, IPAC'22, Bangkok, Thailand, 12 Jun 2022 - 17 Jun 2022; [Geneva] : JACoW Publishing, Geneva, Switzerland 2330-2333 (2022). doi:10.18429/JACoW-IPAC2022-WEPOMS036, Machine learning has proven to be a powerful tool with many applications in the field of accelerator physics. Training machine learning models is a highly iterative process that requires large numbers of samples. However, beam time is often limited and many of the available simulation frameworks are not optimized for fast computation. As a result, training complex models can be infeasible. In this contribution, we introduce Cheetah, a linear beam dynamics framework optimized for fast computations. We show that Cheetah outperforms existing simulation codes in terms of speed and furthermore demonstrate the application of Cheetah to a reinforcement-learning problem as well as the successful transfer of the Cheetah-trained model to the real world. We anticipate that Cheetah will allow for faster development of more capable machine learning solutions in the field, one day enabling the development of autonomous accelerators., Published by JACoW Publishing, Geneva, Switzerland, [Geneva]
- Published
- 2022
- Full Text
- View/download PDF
21. Improvements in Longitudinal Phase Space Tomography at PITZ
- Author
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Aftab, Namra, Aboulbanine, Zakaria, Boonpornprasert, Prach, Georgiev, Georgi, Good, James, Groß, Matthias, Hillert, Wolfgang, Hoffmann, Andreas, Krasilnikov, Mikhail, Li, Xiangkun, Lueangaramwong, Anusorn, Niemczyk, Raffael, Oppelt, Anne, Qian, Houjun, Reader, Andrew, Richard, Christopher, Stephan, Frank, and Vashchenko, Grygorii
- Subjects
effect: space charge ,electron ,phase space: longitudinal ,bunching: length ,data analysis method ,05 Longitudinal Diagnostics and Synchronization ,beam monitoring ,experiment ,space charge [effect] ,measurement methods ,longitudinal [phase space] ,beam [electron] ,Accelerator Physics ,beta function ,gun ,booster ,length [bunching] ,DESY Lab ,electron: beam ,space-charge ,numerical calculations ,activity report - Abstract
[Ebook] IBIC 2022, International Beam Instrumentation Conference : 11-15 September 2022, Krakow, Poland : IBIC2022 - proceedings / Organizers: GSI [Helmholtzzentrum für Schwerionenforschung]; SOLARIS, National Synchrotron Radiation Centre, Jagiellonian University in Krakow , [Geneva, Switzerland] : JACoW Publishing, [2022], 11th International Beam Instrumentation Conference, IBIC 2022, Cracow, Poland, 11 Sep 2022 - 15 Sep 2022; Geneva, Switzerland : JACoW Publishing 105-108 (2022). doi:10.18429/JACoW-IBIC2022-MOP28, Methodical studies to improve the longitudinal phase space (LPS) tomography of space-charge dominated electron beams were carried out at the Photo Injector Test facility at DESY in Zeuthen (PITZ). An analytical model was developed to quantify mean momentum, RMS energy spread, bunch length and phase advance. Phase advance analysis determined the booster phase scan range and step size to be used for obtaining momentum projections. A slit was introduced before the booster to truncate the beam in transverse plane to strongly reduce the space charge effects. The signal resolution of this truncated beam was improved by careful beta function control at the reference screen of the momentum measurements. The reconstruction algorithm was changed from Algebraic Reconstruction Technique (ART) to Image Space Reconstruction Algorithm (ISRA) owing to its assurance of non-negative solutions. In addition, the initial physically justified assumption of LPS, based on low-energy section measurements, was established to clear out noise-like artefacts. This paper will highlight the improvements made in the LPS tomography and compare the simulated and experimental results., Published by JACoW Publishing, Geneva, Switzerland
- Published
- 2022
22. Numerical analysis of space charge effects in electron bunches at laser-driven plasma accelerators
- Author
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Ashmore Anthony, Bartolini Riccardo, and Delerue Nicolas
- Subjects
emittance ,space-charge ,laser-driven plasma acceleration ,Physics ,QC1-999 - Published
- 2011
- Full Text
- View/download PDF
23. Photovoltage Reversal in Organic Optoelectronic Devices with Insulator-Semiconductor Interfaces
- Author
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Laigui Hu, Wei Jin, Rui Feng, Muhammad Zaheer, Qingmiao Nie, Guoping Chen, Zhi-Jun Qiu, Chunxiao Cong, and Ran Liu
- Subjects
organic semiconductor ,organic photodiodes ,organic optoelectronic devices ,space-charge ,insulator layer ,Technology ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Microscopy ,QH201-278.5 ,Descriptive and experimental mechanics ,QC120-168.85 - Abstract
Photoinduced space-charges in organic optoelectronic devices, which are usually caused by poor mobility and charge injection imbalance, always limit the device performance. Here we demonstrate that photoinduced space-charge layers, accumulated at organic semiconductor-insulator interfaces, can also play a role for photocurrent generation. Photocurrent transients from organic devices, with insulator-semiconductor interfaces, were systematically studied by using the double-layer model with an equivalent circuit. Results indicated that the electric fields in photoinduced space-charge layers can be utilized for charge generation and can even induce a photovoltage reversal. Such an operational process of light harvesting would be promising for photoelectric conversion in organic devices.
- Published
- 2018
- Full Text
- View/download PDF
24. Space-Charge Control of Magnetism in Ferromagnetic Metals: Coupling Giant Magnitude and Robust Endurance.
- Author
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Li Z, Liu H, Zhao Z, Zhang Q, Fu X, Li X, Gu F, Zhong H, Pan Y, Chen G, Li Q, Li H, Chen Y, Gu L, Jin K, Yan S, Miao GX, Ge C, and Li Q
- Abstract
Ferromagnetic metals show great prospects in ultralow-power-consumption spintronic devices, due to their high Curie temperature and robust magnetization. However, there is still a lack of reliable solutions for giant and reversible voltage control of magnetism in ferromagnetic metal films. Here, a novel space-charge approach is proposed which allows for achieving a modulation of 30.3 emu/g under 1.3 V in Co/TiO
2 multilayer granular films. The robust endurance with more than 5000 cycles is demonstrated. Similar phenomena exist in Ni/TiO2 and Fe/TiO2 multilayer granular films, which shows its universality. The magnetic change of 107% in Ni/TiO2 underlines its potential in a voltage-driven ON-OFF magnetism. Such giant and reversible voltage control of magnetism can be ascribed to space-charge effect at the ferromagnetic metals/TiO2 interfaces, in which spin-polarized electrons are injected into the ferromagnetic metal layer with the adsorption of lithium-ions on the TiO2 surface. These results open the door for a promising method to modulate the magnetization in ferromagnetic metals, paving the way toward the development of ionic-magnetic-electric coupled applications., (© 2022 Wiley-VCH GmbH.)- Published
- 2023
- Full Text
- View/download PDF
25. Local dipole enhancement of space-charge piezophototronic catalysts of core-shell polytetrafluoroethylene@TiO2 nanospheres.
- Author
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Jhang, Sheng-Ruei, Lin, Hsun-Yen, Liao, Yin-Song, Chou, Jyh-Pin, and Wu, Jyh Ming
- Abstract
This study demonstrates the hydrothermal treatment of core-shell polytetrafluoroethylene (PTFE) nanoparticles decorated with TiO 2 (h -PTFE@TiO 2); this material exhibits strain-induced local dipole enhancement of the space-charge piezopotential that improves the photocatalytic effect. Under acoustic cavitation, dielectric barrier discharge and electric dipole formation are initiated in voids within the PTFE nanoparticles and at the TiO 2 –PTFE interface. The h -PTFE@TiO 2 nanoparticles (NPs) have exceptionally high catalytic activity in organic dye degradation because of the local dipole enhancement of photoinduced charge separation with a carrier lifetime of 3.14 ns. The observed rate constant of the h- PTFE@TiO 2 NPs in the piezophototronic reaction reaches 0.1388 min
−1 , which is 17 times that of the photocatalytic reaction (0.0084 min−1 ) and 66 times that of the piezocatalytic reaction (0.0021 min−1 ). Computational simulation reveals that large strain-induced space charge piezoelectric polarization induces an internal electric field between the unsaturated PTFE (fluorine vacancies) and TiO 2 surface. The piezopotential has a critical role in band bending at PTFE-TiO 2 interfaces to enhance the electron-hole separation when PTFE is constrained in TiO 2 shells. Results of piezoresponse force microscopy reveal that the piezoelectric coefficient d 33 of PTFE is approximately 79.77 pCN−1 . The findings provide insights into catalytic activity for environmental remediation. This study demonstrates the hydrothermal treatment of core-shell polytetrafluoroethylene (PTFE) nanoparticles decorated with TiO2; this material exhibits strain-induced local dipole enhancement of the space-charge piezopotential improves the photocatalytic effect. Computational simulation reveals that large strain-induced space charge piezoelectric polarization induces an internal electric field between the unsaturated PTFE (fluorine vacancies) and TiO2 surface. Considerable local dipole enhancement was observed in the fluorine vacancies of the PTFE, further enhancing the space-charge piezophototronic effect that benefits the performance of the material when used as a photocatalyst. [Display omitted] • Space charge piezoelectric polarization occurs between the fluorine vacancies of PTFE and TiO 2 surface. • The piezoelectric coefficient d 33 of PTFE is approximately 79.77 pCN−1 . • A local dipole enhancement of PTFE@TiO 2 photoinduced charge separation with a carrier lifetime of 3.14ns. • Piezopotential modulates the band bending at PTFE-TiO 2 interfaces to enhance electron-hole separation. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
26. Matching sub-fs electron bunches for laser-driven plasma acceleration at SINBAD.
- Author
-
Zhu, J., Assmann, R.W., Dorda, U., and Marchetti, B.
- Subjects
- *
PARTICLE beam bunching , *PLASMA acceleration , *FEMTOSECOND lasers , *LASER-plasma interactions , *NUCLEAR energy , *PHASE space - Abstract
We present theoretical and numerical studies of matching sub-femtosecond space-charge-dominated electron bunch into the Laser-plasma Wake Field Accelerator (LWFA) foreseen at the SINBAD facility. The longitudinal space-charge (SC) effect induced growths of the energy spread and longitudinal phase-space chirp are major issues in the matching section, which will result in bunch elongation, emittance growth and spot size dilution. In addition, the transverse SC effect would lead to a mismatch of the beam optics if it were not compensated for. Start-to-end simulations and preliminary optimizations were carried out in order to understand the achievable beam parameters at the entrance of the plasma accelerator. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
27. Review of ferroelectric hydroxyapatite and its application to biomedicine.
- Author
-
Lang, Sidney B.
- Subjects
- *
HYDROXYAPATITE , *FERROELECTRICITY , *CRYSTAL structure , *PIEZOELECTRICITY , *THICK films - Abstract
Hydroxyapatite (HA) is a major component of bone in humans and animals. Until about 10 years ago, it was considered to have a centrosymmetric crystal structure and could not contribute to the well-known piezoelectric effect in bone. This review describes the theoretical and experimental studies that showed that HA does have a non-centrosymmetric structure. Recent experiments have shown that HA exhibits piezoelectricity, pyroelectricity, and ferroelectricity. It has been made in the form of thick films and as space-charge electrets. It has an important biomedical application as an implant for bone cell attachment and growth. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
28. Analysis of the grain boundary conductivity of singly and doubly doped CeO2 thin films at elevated temperature.
- Author
-
Kwak, No Woo and Jung, WooChul
- Subjects
- *
CRYSTAL grain boundaries , *THERMAL conductivity , *DOPED semiconductors , *CERIUM oxides , *HIGH temperatures - Abstract
Acceptor-doped cerium oxides are a promising solid electrolyte material for solid oxide fuel cells (SOFCs) due to their exceptionally high oxygen ion conductivity. Typical solid electrolytes are polycrystalline with a number of grain boundaries, and it is common for grain boundaries to block the motion of mobile oxygen ions as they migrate from one grain to the next. Accordingly, it is important precisely to measure the grain boundary conductivities of doped cerium oxides, particularly at the temperature of relevance (>500 °C). Here, we undertake a quantitative analysis of the transport properties of singly and doubly doped cerium oxides. So that we may precisely extract the grain boundary contribution out of the total conductivity at an elevated temperature (>500 °C), both epitaxial and polycrystalline thin films of the oxides are grown via pulsed layer deposition (PLD) on two different insulating, single-crystal substrates: Al 2 O 3 (0001) and SiO 2 (001), and these are then characterized by a range of analysis tools, in this case TEM, SEM, XRD, ICP-MS and AFM. These samples with controlled microstructures, in combination with in-plane ionic conductivity measurements by impedance spectroscopy as a function of the thickness, temperature and p O 2 , enable us precisely to measure the grain boundary conductivity of the doped ceria at temperatures ranging from 620 to 700 °C. The impact of the number and type of dopants on the transport properties are also explored. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
29. Dynamics of energy level alignment at ITO/organic semiconductor interfaces.
- Author
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Coutinho, Douglas J., Faria, Gregório C., Faria, Roberto M., and von Seggern, Heinz
- Subjects
- *
ENERGY levels (Quantum mechanics) , *ORGANIC semiconductors , *SPACE charge , *DIFFUSION , *CHARGE transfer - Abstract
Time-dependence of space-charge built-up at the ITO/organic semiconductor interface has been investigated for the first time using the charge extraction by linearly increasing voltage (CELIV) technique in the dark. It will be demonstrated that space-charge next to an ITO/P3HT interface is extracted during the initial CELIV ramp establishing a non-equilibrium situation whose temporal recovery can be probed by utilizing sequentially prolonged delay times for successive voltage ramps. It will be reported that the build-up time constant for space charge at the ITO/P3HT interface amounts to 230 μs. The dynamics of the relatively slow charge transfer at the interface of the transparent conducting oxide and the organic semiconductor as well as time-limiting processes will be discussed by considering tunneling, thermal detrapping and diffusion of the involved electrons and holes. It will be shown that thermal detrapping of electrons from molecules with their ground state close the center of the HOMO-DOS to vibronic states within the same molecule followed by tunneling to neighboring molecules with their not occupied ground state within the tail states of the DOS is the time limiting process and responsible for the long build-up time. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
30. Effect of oxygen defects blocking barriers on gadolinium doped ceria (GDC) electro-chemo-mechanical properties
- Author
-
Ngo Van Nong, Robin Nigon, Simone Santucci, Paul Muralt, Ahsanul Kabir, Igor Lubomirsky, Maxim Varenik, and Vincenzo Esposito
- Subjects
Materials science ,Polymers and Plastics ,FOS: Physical sciences ,Spark plasma sintering ,Sintering ,chemistry.chemical_element ,Electrostriction ,gadolinium-doped ceria ,02 engineering and technology ,ionic-conductivity ,size ,01 natural sciences ,Oxygen ,Physics - Chemical Physics ,0103 physical sciences ,Gadolinium-doped ceria ,Vacancies ,Chemical Physics (physics.chem-ph) ,010302 applied physics ,Condensed Matter - Materials Science ,sintering ,Dopant ,sm ,Metals and Alloys ,Materials Science (cond-mat.mtrl-sci) ,vacancies ,021001 nanoscience & nanotechnology ,electrostriction ,Grain size ,Electronic, Optical and Magnetic Materials ,Chemical engineering ,chemistry ,oxides ,Ceramics and Composites ,Crystallite ,space-charge ,0210 nano-technology ,zirconia ,grain-boundaries - Abstract
Some oxygen defective metal oxides, such as cerium and bismuth oxides, have recently shown exceptional electrostrictive properties that are even superior to the best performing lead-based electrostrictors, e.g. lead-magnesium-niobates (PMN). Compared to piezoelectric ceramics, electromechanical mechanisms of such materials do not depend on crystalline symmetry but on the concentration of oxygen vacancy (V-(O) over dot ) in the lattice. In this work, we investigate for the first time the role of oxygen defects configuration on the electro-chemo-mechanical properties. This is achieved by tuning the oxygen defects blocking barrier density in polycrystalline gadolinium doped ceria with known oxygen vacancy concentration, Ce0.9Gd0.1O2-delta, delta = 0.05. Nanometric starting powders of ca. similar to 12 nm are sintered in different conditions, including field assisted spark plasma sintering (SPS), fast firing and conventional method at high temperatures. These approaches allow controlling grain size and Gd-dopant diffusion, i.e. via thermally driven solute drag mechanism. By correlating the electro-chemo-mechanical properties, we show that oxygen vacancy distribution in the materials plays a key role in ceria electrostriction, overcoming the expected contributions from grain size and dopant concentration. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
- Published
- 2019
31. Improved Model for Increased Surface Recombination Current in Irradiated Bipolar Junction Transistors.
- Author
-
Barnaby, H. J., Vermeire, B., and Campola, M. J.
- Subjects
- *
SURFACE recombination , *JUNCTION transistors , *SPACE charge , *ELECTRON traps , *RADIATION damage , *BIPOLAR integrated circuits - Abstract
Current gain degradation in irradiated bipolar junction transistors is primarily due to excess base current caused by enhanced carrier recombination in the emitter-base space-charge region (SCR). Radiation-induced traps at the interface between silicon and the bipolar base oxide facilitate the recombination process primarily above the sensitive emitter-base junction. This leads to an increase in surface recombination current in the SCR, which is a non-ideal component of the BJT’s base current characteristic under active bias conditions. In this paper, we derive a precise analytical model for surface recombination current that captures bias dependencies typically omitted from traditional models. This improved model is validated by comparisons to these traditional approaches. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
32. Space-charge effects in Penning ion traps.
- Author
-
Porobić, T., Beck, M., Breitenfeldt, M., Couratin, C., Finlay, P., Knecht, A., Fabian, X., Friedag, P., Fléchard, X., Liénard, E., Ban, G., Zákoucký, D., Soti, G., Van Gorp, S., Weinheimer, Ch., Wursten, E., and Severijns, N.
- Subjects
- *
SPACE charge , *ION traps , *CYCLOTRON resonance , *MAGNETRONS , *HELIUM - Abstract
The influence of space-charge on ion cyclotron resonances and magnetron eigenfrequency in a gas-filled Penning ion trap has been investigated. Off-line measurements with K + 39 using the cooling trap of the WITCH retardation spectrometer-based setup at ISOLDE/CERN were performed. Experimental ion cyclotron resonances were compared with ab initio Coulomb simulations and found to be in agreement. As an important systematic effect of the WITCH experiment, the magnetron eigenfrequency of the ion cloud was studied under increasing space-charge conditions. Finally, the helium buffer gas pressure in the Penning trap was determined by comparing experimental cooling rates with simulations. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
33. Envelope dynamics and stability with non-linear space-charge forces
- Author
-
Holz, Michael, Ziemann, Volker, Holz, Michael, and Ziemann, Volker
- Abstract
We developed a model to calculate the stability of Gaussian beam distributionswith non-linear space-charge forces in the presence of random and skewquadrupoleerrors. The eect of the space-charge force on the beam matrix iscalculated analytically including full cross-plane coupling in 4D phase space,which allows us to perform fast parameter studies. For stability analysis, wend the xed points of the beam including the space-charge forces and constructa Jacobi-matrix by slightly perturbing the periodic solution. The stability ofenvelope oscillations is inferred by eigenvalue analysis. Furthermore, we employenvelope tracking as a complementary method and compare the results ofthe eigenvalue analysis with FFT data from the tracked envelope. The nonlinearityof the space-charge force in combination with lattice errors and beamcoupling opens up for envelope-lattice resonances and envelope coupling resonances.Hitting these resonances leads to envelope blow-up, causing an eectivebeam mismatch. Therefore, we nally examine the eect of beam mismatch onthe envelope tune-shift and its stability.
- Published
- 2020
- Full Text
- View/download PDF
34. Beam Dynamics in a Hybrid Standing Wave-Traveling Wave Photoinjector.
- Author
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Rosenzweig, J. B., Alesini, D., Boni, A., Ferrario, M., Ficcadenti, L., Fukusawa, A., Mostacci, A., O’Shea, B., Palumbo, L., Spataro, B., and Fusco, V.
- Subjects
- *
BEAM dynamics , *TRAVELING-wave tubes , *STANDING waves , *ELECTROMAGNETIC measurements , *OSCILLATIONS , *ACCELERATION (Mechanics) , *SPACE charge - Abstract
We discuss the dynamics of a photoinjector beam in a hybrid traveling wave-standing wave photoinjector. With the field profile deduced from electromagnetic simulations, it is seen that the acceleration program induces strong velocity bunching. The beam dynamics in this scenario are explored using UCLA PARMELA. With a solenoid field overlaid on the TW section one may control emittance oscillations during bunching and acceleration. It is seen that the S-band device currently under development at UCLA may produce a 1 nC, 21 MeV, 100 micron rms pulse length beam, with emittance of 3 mm-mrad. Applications of this beam for creating coherent radiation are discussed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
35. Experimental Testing of Dynamically Optimized Photoelectron Beams.
- Author
-
Rosenzweig, J. B., Cook, A. M., Dunning, M., England, R. J., Musumeci, P., Bellaveglia, M., Boscolo, M., Catani, L., Cianchi, A., Di Pirro, G., Ferrario, M., Fillipetto, D., Gatti, G., Palumbo, L., Serafini, L., Vicario, C., and Jones, S.
- Subjects
- *
ELECTRON beams , *BEAM dynamics , *STREAK cameras , *SPACE charge , *CHERENKOV radiation , *PHOTOELECTRONS , *BEAM emittance (Nuclear physics) , *IMAGING systems in chemistry - Abstract
We discuss the design of and initial results from an experiment in space-charge dominated beam dynamics which explores a new regime of high-brightness electron beam generation at the SPARC photoinjector. The scheme under study employs the tendency of intense electron beams to rearrange to produce uniform density, giving a nearly ideal beam from the viewpoint of space charge-induced emittance. The experiments are aimed at testing the marriage of this idea with a related concept, emittance compensation. We show that this new regime of operating photoinjector may be the preferred method of obtaining highest brightness beams with lower energy spread. We discuss the design of the experiment, including developing of a novel time-dependent, aerogel-based imaging system. This system has been installed at SPARC, and first evidence for nearly uniformly filled ellipsoidal charge distributions recorded. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
36. Advanced Modeling Techniques for Analysis of High Current Ribbon Beam Transport and Control.
- Author
-
Kellerman, Peter and Sinclair, Frank
- Subjects
- *
FOCUSED ion beams , *PARTICLE range (Nuclear physics) , *ION implantation , *ELECTROSTATIC lenses , *FIRST-order logic , *SPACE charge - Abstract
A computer model capable of analyzing electrostatic lenses, including the effects of space charge, yet simple enough to run an entire beamline system calculation in seconds, has been developed and applied to VSEA’s latest high current beamline. Such a code is a useful tool in exploring tuning possibilities when running in various modes of drift and decel, and can be used to find solutions that optimize transport, as well as providing a basis for beam tuning. This paper details the basis of the model and compares results with more rigorous models. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
37. Design of low energy beam transport for new LANSCE H+ injector.
- Author
-
Batygin, Y.K., Draganic, I.N., Fortgang, C.M., Garnett, R.W., Kurennoy, S.S., McCrady, R.C., O’Hara, J.F., and Rybarcyk, L.J.
- Subjects
- *
ENERGY transfer , *HYDROGEN ions , *INJECTORS , *PARTICLE accelerators , *RADIO frequency , *QUADRUPOLES , *SPACE charge - Abstract
Abstract: The present LANSCE injector utilizes two 750-keV Cockcroft–Walton (CW) based injectors for simultaneous injection of H+ and H− beams into 800-MeV accelerator. To reduce long-term operational risks, the new project to replace the existing H+ CW injector with a Radio-Frequency Quadrupole (RFQ) accelerator is underway [1]. The new injector requires a Low-Energy Beam Transport (LEBT). An ion source and 2-solenoid magnetic LEBT have been designed and optimized to transport beams over a wide range of space-charge neutralization and transverse emittance, while allowing sufficient space for diagnostics and a beam deflector. The design layout minimizes the beam size in the LEBT and potential emittance growth due to solenoid aberrations and nonlinear space-charge forces. This paper describes the details of the LEBT design activity. [Copyright &y& Elsevier]
- Published
- 2014
- Full Text
- View/download PDF
38. Multidimensional aspects of nonlinear electromagnetic solitary pulses.
- Author
-
Bonatto, A., Nunes, R.P., Bonatto, C., Pakter, R., Lopes, S.R., and Rizzato, F.B.
- Subjects
- *
NONLINEAR theories , *ELECTROMAGNETIC pulses , *ELECTROMAGNETIC radiation , *SPACE charge waves , *LASER-plasma interactions , *SOLITONS - Abstract
Abstract: This work is devoted to the study of the interaction between pulses of electromagnetic radiation and space-charge waves in laser-plasmas settings. We analyse modes depending only on the co-moving coordinate of the beam frame, but make no a priori assumption on the longitudinal-to-transverse aspect ratio of the pulses. The model thus constructed allows us to investigate regimes where transverse and longitudinal length scales of the pulses are comparable. Resonant and nonresonant excitations of space-charge modes are analyzed and the endurance of trains of solitons against transverse effects is clarified. [Copyright &y& Elsevier]
- Published
- 2014
- Full Text
- View/download PDF
39. Modeling HIF relevant longitudinal dynamics in UMER.
- Author
-
Beaudoin, B.L., Bernal, S., Blanco, C., Haber, I., Kishek, R.A., Koeth, T., and Mo, Y.
- Subjects
- *
HEAVY ion fusion reactions , *DYNAMICAL systems , *SPACE charge , *ELECTRON ring accelerators , *SOLITONS , *LONGITUDINAL method - Abstract
Abstract: The foremost challenge for Heavy-Ion Fusion (HIF) is achieving sufficiently low emittances and small energy spreads in the presence of intense space-charge, to achieve the high deposition densities necessary for pellet ignition. The University of Maryland Electron Ring (UMER) uses intense low-energy electron beams to access the scaled physics of HIF drivers. In particular, the long path-length propagation in UMER presents an opportunity to study, at realistic scales, the longitudinal beam dynamics and manipulations required for such a driver. With the use of induction modules, as in the ion machines such as NDCX-II, the resulting bunch dynamics show evidence of space-charge waves excited by an initial mismatch between the detailed initial beam distribution at the bunch ends and the applied focusing waveforms, persisting with multiple damped reflections propagating along the bunch flat-top. Using the induction module we are able to suppress space-charge waves with great accuracy, at amplitudes that include wave steepening prior to the formation of solitary wave trains. The longitudinal dynamics largely dominates when no containment fields are applied, coupling through the natural chromaticity of the ring even within the first turn. After subsequent turns, the bunch elongates and wraps the circumference of the machine multiple times; eventually reaching a point of instability that has also been shown through simulation, obtaining excellent agreement when the detailed longitudinal dynamics of the experiment are carefully incorporated into the model. [Copyright &y& Elsevier]
- Published
- 2014
- Full Text
- View/download PDF
40. Simulations of ion beams for NDCX-II.
- Author
-
Grote, D.P., Friedman, A., and Sharp, W.M.
- Subjects
- *
ION beams , *PHYSICS experiments , *HEAVY ion accelerators , *SYSTEMS design , *SOLENOIDS , *COMPRESSION loads , *SIMULATION methods & models - Abstract
Abstract: NDCX-II, the second neutralized drift compression experiment, is a moderate energy, high current accelerator designed to drive targets for warm dense matter and IFE-relevant energy coupling studies, and to serve as a testbed for high current accelerator physics. As part of the design process, studies were carried out to assess the sensitivities of the accelerator to errors, and to further optimize the design in concert with the evolving pulsed power engineering. The Warp code was used to carry out detailed simulations in both axisymmetric and full 3-D geometry. Ensembles of simulations were carried out to characterize the effects of errors, such as timing jitter and noise on the accelerator waveforms, noise on the source waveform, and solenoid and source offsets. In some cases, the ensemble studies resulted in better designs, revealing operating points with improved performance and showing possible means for further improvement. These studies also revealed a new non-paraxial effect of the final focus solenoid on the beam, which must be taken into account in designing an optimal final focusing system. [Copyright &y& Elsevier]
- Published
- 2014
- Full Text
- View/download PDF
41. Dynamic coupling between particle-in-cell and atomistic simulations
- Author
-
Flyura Djurabekova, Kyrre Sjobak, Alvo Aabloo, Vahur Zadin, Andreas Kyritsakis, Mihkel Veske, Helsinki Institute of Physics, and Department of Physics
- Subjects
CURRENTS ,FOS: Computer and information sciences ,SPACE-CHARGE ,Materials science ,SURFACE ,Field (physics) ,Thermal runaway ,Evaporation ,COPPER ,ECTONS ,114 Physical sciences ,7. Clean energy ,01 natural sciences ,010305 fluids & plasmas ,SECONDARY-ELECTRON EMISSION ,Computational Engineering, Finance, and Science (cs.CE) ,Physics::Plasma Physics ,Electric field ,0103 physical sciences ,Computer Science - Computational Engineering, Finance, and Science ,010306 general physics ,cs.CE ,VACUUM-ARC ,Vacuum arc ,Mechanics ,Finite element method ,Computing and Computers ,Plasma arc welding ,MOLECULAR-DYNAMICS ,Particle-in-cell ,FIELD-EMISSION ,RESISTIVITY - Abstract
We propose a method to directly couple molecular dynamics, finite element method and particle-in-cell techniques to simulate metal surface response to high electric fields. We use this method to simulate the evolution of a field emitting tip under thermal runaway by fully including the 3D space-charge effects. We also present a comparison of the runaway process between the two tip geometries of different widths. The results show with high statistical significance that in case of sufficiently narrow field emitters, the thermal runaway occurs in cycles where intensive neutral evaporation alternates with the cooling periods. The comparison with previous works shows, that the evaporation rate in the regime of intensive evaporation is sufficient to ignite a plasma arc above the simulated field emitters., Comment: 15 pages, 12 figures
- Published
- 2020
42. Explorations of Space-Charge Limits in Parallel-Plate Diodes and Associated Techniques for Automation
- Author
-
Ragan-Kelley, Benjamin
- Subjects
Plasma physics ,child-langmuir ,simulation ,space-charge - Abstract
Space-charge limited flow is a topic of much interest and varied application.We extend existing understanding of space-charge limits by simulations,and develop new tools and techniques for doing these simulations along the way.The Child-Langmuir limit is a simple analytic solution for space-charge limitedcurrent density in a one-dimensional diode. It has been previously extended to two dimensionsby numerical calculation in planar geometries. By considering an axisymmetric cylindrical system with axial emission from a circular cathode of finite radius $r$ and outer drift tube $R > r$and gap length $L$, we further examine the space charge limit in two dimensions.We simulate a two-dimensional axisymmetric parallel plate diode of various aspect ratios ($r/L$),and develop a scaling law for the measured two-dimensional space-charge limit (2DSCL)relative to the Child-Langmuir limit as a function of the aspect ratio of the diode.These simulations are done with a large ($100 T$) longitudinal magnetic field to restrict electronmotion to 1D, with the two-dimensional particle-in-cell simulation code OOPIC.We find a scaling law that is a monotonically decreasing function of this aspect ratio,and the one-dimensional result is recovered in the limit as $r >> L$.The result is in good agreement with prior results in planar geometry,where the emission area is proportional to the cathode width.We find a weak contribution from the effects of the drift tube for current at the beam edge,and a strong contribution of high current-density ``wings'' at the outer-edge of the beam,with a very large relative contribution when the beam is narrow.Mechanisms for enhancing current beyond the Child-Langmuir limit remain a matter of great importance.We analyze the enhancement effects of upstream ion injection on the transmitted current in a one-dimensional parallel plate diode.Electrons are field-emitted at the cathode,and ions are injected at a controlled current from the anode.An analytic solution is derived for maximizing the electron current throughput in terms of the ion current.This analysis accounts for various energy regimes, from classical to fully relativistic.The analytical result is then confirmed by simulation of the diode in each energy regime.The simulation approach involved iteratively testing injected ion current,and treating the measured transmitted electron current as a feedback mechanism.The feedback loop was automated, allowing for a single simulation to locate the optimized current.By tuning the injected ion current, we are able to optimize the transmitted electron current.This tuning of the ion current is automated by the integration of a high-level Python interface,wrapping the C++ particle-in-cell simulation code OOPD1.In this particular system, analysis showed that simulation runtime would be a function of transit time, and thus ion mass.By experimenting with reduced ion mass, we were able to significantly reduce simulation times,while recovering the same physical results.Field-limited emission is an approach for using Gauss's law to to satisfy the space charge limit for emitting current in particle-in-cell simulations.We find that simple field-limited emission models make several assumptions,which introduce small, systematic errors in the system.We make a thorough analysis of each assumption,and ultimately develop and test a new emission scheme that accounts for each.The first correction we make is to allow for a non-zero surface field at the boundary.Since traditional field-emission schemes only aim to balance Gauss's law at the surface,a zero surface field is an assumed condition.But for many systems, this is not appropriate,so the addition of a \emph{target} surface field is made.The next correction is to account for nonzero initial velocity,which, if neglected, results in a systematic underestimation of the current,due to assuming that all emitted charge will be weighted to the boundary,when in fact it will be weighted as a fraction strictly less than unity,depending on the distance across the initial cell the particle travels in its initial fractional timestep.A correction is made to the scheme, to use the actual particle weight to adjust the target emission.The final analyses involve geometric terms,analyzing the effects of cylindrical coordinates,and taking particular care to analyze the center of a cylindrical beam,as well as the outer edge of the beam, in Cartesian coordinates.We find that balancing Gauss's law at the edge of the beam is not the correct behavior,and that it is important to resolve the profile of the emitted current,in order to avoid systematic errors.A thorough analysis is done of the assumptions made in prior implementations,and corrections are introduced for cylindrical geometry,non-zero injection velocity, and non-zero surface field.Particular care is taken to determine special conditions for the outermost node,where we find that forcing a balance of Gauss's law would be incorrect.The new emission scheme is tested in a two-dimensional periodic simulation,to demonstrate that the Jaffe limit for a one-dimensional diode with finite initial velocity is recovered.We also extend the iterative scheme developed earlier,and apply it to determine a scaling law for the Child-Langmuir limitin an axisymmetric planar diode, with finite initial velocity.We find that the new scheme reproduces prior results,and in significantly less computation time due to no longer needing to overinject,and leads to rapid convergence of the surface field,using our new algorithmic optimization wrapper to seek the local limiting current along an emitter.
- Published
- 2013
43. Numerical analysis of space charge effects in electron bunches at laser-driven plasma accelerators.
- Author
-
Ashmore, Anthony, Bartolini, Riccardo, and Delerue, Nicolas
- Abstract
Laser-driven Plasma Accelerators (LPA) have successfully generated high energy, high charge electron bunches which can reach many kA peak current, over short distances. Space charge issues, even in transport lines as simple as a drift section, have to be carefully taken into account since they can degrade the beam quality, preventing any further application of such electron beams. We analyse the space charge effects within an electron bunch with numerical simulations in order to assess their effect on the beam. We use LPA beam parameters published in previous experimental studies. These studies can give an indication of the working point where space charge can dominate the beam dynamics and has to be taken into account in the application of such beams. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
44. Mass-selective operation with REXTRAP
- Author
-
Gustafsson, A., Herlert, A., and Wenander, F.
- Subjects
- *
RADIATION trapping , *ION bombardment , *NUCLEAR facilities , *SPACE charge , *PARTICLE acceleration , *NUCLEAR isobars , *ATOMIC mass , *RADIOISOTOPES - Abstract
Abstract: At the radioactive ion-beam facility REX-ISOLDE more than 60 different types of radionuclide ions have been post-accelerated to energies up to 3.15MeV/u within the last years. The transmission efficiency of the system has continually increased with gained operation experience. Apart from striving for the highest possible intensity, the beam purity is also of crucial importance for many experiments. For this reason isobaric contaminant suppression in the low energy stage of REX-ISOLDE has been investigated. Until now the Penning trap system REXTRAP was used solely as a device for bunching the incoming quasi-continuous radioactive ion-beam from ISOLDE and reducing the emittance for efficient injection into the REXEBIS charge breeder. The possibility of operating REXTRAP in a mass-resolving mode and injecting bunched beams from the recently installed radiofrequency quadrupole cooler and buncher ISCOOL has been studied in detail. Results related to transmission efficiency,achieved mass-resolving power, and limitations due to space-charge effects are presented. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
45. Simulation study of sub-femtosecond electron bunch generation using photocathode RF gun linac
- Author
-
Kan, K., Yang, J., Kondoh, T., Norizawa, K., Ogata, A., Kozawa, T., and Yoshida, Y.
- Subjects
- *
SIMULATION methods & models , *PHOTOCATHODES , *RADIO frequency , *STROBOSCOPES , *LINEAR accelerators , *NUCLEAR reactions , *FEASIBILITY studies , *SPACE charge - Abstract
Abstract: Pulse radiolysis, a stroboscopic method involving the use of an ultrashort electron bunch and ultrashort light, is essential for the observation of ultrafast reactions. The time resolution of pulse radiolysis depends on the electron bunch length. At Osaka University, a 98-fs electron bunch was generated using a photocathode RF gun linac for the development of femtosecond pulse radiolysis. In order to improve the time resolution of pulse radiolysis, the feasibility of sub-femtosecond electron bunch generation using a photocathode RF gun linac and a magnetic bunch compressor was studied in a simulation. Increase in bunch length due to higher-order effects and bunch charge was investigated using the simulation codes PARMELA and ELEGANT. [Copyright &y& Elsevier]
- Published
- 2010
- Full Text
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46. Influence of antioxidants on heterocharge generation in polymeric dielectrics.
- Author
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Suzuki, Hirokazu, Sekii, Yasuo, Noguchi, Kazuo, Shimura, Koichi, and Maeno, Takashi
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ANTIOXIDANTS , *DIELECTRICS , *CHEMICAL inhibitors , *ACETOPHENONE , *KETONES - Abstract
The generation of space charges in polymeric dielectric materials is known to be affected by such inclusions as cross-linking by-products, antioxidants, and moisture. We reported previously that negative heterocharges in XLPE are generated in the presence of acetophenone and sulfur-containing antioxidants. In this paper we describe further experiments using samples containing DCP and three different antioxidants in order to examine the mechanism of this phenomenon. Negative heterocharges near the positive electrode were detected in samples containing both DCP and antioxidants when those samples were soaked in acetophenone. Negative heterocharges were not detected in samples containing either DCP or the antioxidant, even when the sample was soaked in acetophenone. These results demonstrate that a heterocharge is generated by the combined effect of acetophenone and the substance produced by interaction between DCP and the antioxidant. Based on the results of experiments measuring the amount of heterocharge in samples that had been heatpressed at different temperatures, the mechanism of negative heterocharge generation in polymeric dielectric material is inferred. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 172(2): 1–9, 2010; Published online in Wiley InterScience (
www.interscience.wiley.com ). DOI 10.1002/eej.20941 [ABSTRACT FROM AUTHOR]- Published
- 2010
- Full Text
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47. A fast parallel Poisson solver on irregular domains applied to beam dynamics simulations
- Author
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Adelmann, A., Arbenz, P., and Ineichen, Y.
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NUMERICAL solutions to Poisson's equation , *BEAM dynamics , *ELECTRON beams , *PARTICLE accelerators , *FINITE differences , *NUMERICAL solutions to the Dirichlet problem , *ALGORITHMS - Abstract
Abstract: We discuss the scalable parallel solution of the Poisson equation within a Particle-In-Cell (PIC) code for the simulation of electron beams in particle accelerators of irregular shape. The problem is discretized by Finite Differences. Depending on the treatment of the Dirichlet boundary the resulting system of equations is symmetric or ‘mildly’ nonsymmetric positive definite. In all cases, the system is solved by the preconditioned conjugate gradient algorithm with smoothed aggregation (SA) based algebraic multigrid (AMG) preconditioning. We investigate variants of the implementation of SA-AMG that lead to considerable improvements in the execution times. We demonstrate good scalability of the solver on distributed memory parallel processor with up to 2048 processors. We also compare our iterative solver with an FFT-based solver that is more commonly used for applications in beam dynamics. [Copyright &y& Elsevier]
- Published
- 2010
- Full Text
- View/download PDF
48. Influence of an applied dc electric field on the plastic deformation kinetics of oxide ceramics.
- Author
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Conrad, Hans and Yang, Di
- Subjects
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PLASTIC deterioration , *ELECTROMAGNETIC fields , *PROPERTIES of matter , *CRYSTAL growth , *SEMICONDUCTOR doping , *MICROMECHANICS - Abstract
A modest dc electric field markedly reduced the tensile flow stress at high temperatures in three polycrystalline oxides, i.e. MgO, Al2O3 and yttria-stabilized tetragonal ZrO2 (Y-TZP). The reduction in flow stress ΔσE in Y-TZP consisted of three components: (i) ΔσT due to Joule heating, (ii) [image omitted] a rapid, reversible component obtained in on-off and electric field step tests and (iii) [image omitted] the cumulative effect of the field on microstructure. Only ΔσT and [image omitted] occurred in MgO and Al2O3. It is concluded that [image omitted] results from a reduction in the electrochemical potential for the formation of vacancies corresponding to the diffusion of the rate-controlling ion in the space-charge at the grain boundary. The calculated magnitude of the space-charge zone width and its temperature and solute composition dependence are in accord with theory and experiment; [image omitted] is attributed mainly to the retardation of grain growth by the field. The retardation could be due to one or more of the following effects of the field on the space-charge zone: (i) an increase in the segregated solute ions, (ii) a decrease in grain boundary energy and (iii) a decrease in solute ion mobility. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
49. Theoretical treatment and numerical simulation of potential and concentration profiles in extremely thin non-electroneutral membranes used for ion-selective electrodes
- Author
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Morf, W.E., Pretsch, E., and Rooij, N.F. de
- Subjects
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NUMERICAL analysis , *SIMULATION methods & models , *ELECTROCHEMISTRY , *ARTIFICIAL membranes , *ION selective electrodes , *SPACE charge , *CONSERVATION laws (Physics) , *CHEMICAL equilibrium - Abstract
Abstract: The applicability of extremely thin non-electroneutral membranes for ion-selective electrodes (ISEs) is investigated. A theoretical treatment of potential and concentration profiles in space-charge membranes of ≪1μm thickness is presented. The theory is based on the Nernst–Planck equation for ion fluxes, which reduces to Boltzmann’s formula at equilibrium, and on the Poisson relationship between space-charge density and electric field gradient. A general solution in integral form is obtained for the potential function and the corresponding ion profiles at equilibrium. A series of explicit sub-solutions is derived for particular cases. Membrane systems with up to three different ion species are discussed, including trapped ionic sites and co-extracted ions. Solid-contacted thin membranes (without formation of aqueous films at the inner interface) are shown to exhibit a sub-Nernstian response. The theoretical results are confirmed by numerical simulations using a simplified finite-difference procedure based on the Nernst–Planck–Poisson model, which are shown to be in excellent agreement. [Copyright &y& Elsevier]
- Published
- 2010
- Full Text
- View/download PDF
50. Recombination at the interface between a metallic precipitate and a semiconductor matrix: Application to the electron-beam-induced-current contrast
- Author
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Debez, M., Tarento, R.-J., and Mekki, D.E.
- Subjects
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RECOMBINATION in semiconductors , *ELECTRON beams , *SEMICONDUCTOR junctions , *SILICON , *GALLIUM arsenide , *CONTRAST effect , *SPACE charge - Abstract
Abstract: A self-consistent calculation of the barrier height and of the effective recombination velocity at the interface between a metallic precipitate and a semiconductor matrix has been performed within the Read–Hall–Schockley framework. The recombination has been investigated for Si, Ge and GaAs. The precipitate size has a dramatic effect on recombination due to the enhancement of the surface charge density on the metallic precipitate when the size decreases. The electron beam induced current (EBIC) contrast of metallic precipitate has been investigated. [Copyright &y& Elsevier]
- Published
- 2009
- Full Text
- View/download PDF
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