The Experts below are selected from a list of 623805 Experts worldwide ranked by ideXlab platform
D Chernin - One of the best experts on this subject based on the ideXlab platform.
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1 d large Signal Model of folded waveguide traveling wave tubes
IEEE Transactions on Electron Devices, 2014Co-Authors: D Chernin, T M Antonsen, K T Nguyen, Alexander N Vlasov, Igor A Chernyavskiy, B LevushAbstract:A recently published hybrid circuit Model for folded-waveguide slow wave structures has been implemented in the 1-D large Signal code CHRISTINE. The resulting code is applied to a design for a G-band (220 GHz) folded-waveguide traveling wave tube. Results of small and large Signal gain are compared with those from TESLA, a 2-D code using the same circuit Model. Conditions for accuracy of the 1-D Model are illustrated and explained. The effects of an offset beam tunnel on circuit dispersion and amplifier stability are illustrated using the CHRISTINE code.
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5 3 a large Signal Model of extended interactions klystrons
International Vacuum Electronics Conference, 2010Co-Authors: D Chernin, T M Antonsen, K T Nguyen, B LevushAbstract:Extended Interaction Klystron (EIK) cavities consist of shorted (resonant) sections of a periodic or bi-periodic structure. The response of such cavities to currents induced by the passage of a bunched beam may be represented by an impedance matrix that relates the voltage in each section to the induced currents. We have implemented this representation in the CHRISTINE large Signal code. Using a modal expansion for the cavity fields we have computed the impedance matrix for a simple ‘ladder’ circuit. Using this matrix in a CHRISTINE simulation, we have found good agreement for the AC current vs. axial location in a 3-cavity circuit, compared with results from the 3D particle-in-cell code MAGIC.
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a three dimensional multifrequency large Signal Model for helix traveling wave tubes
IEEE Transactions on Electron Devices, 2001Co-Authors: D Chernin, T M Antonsen, B Levush, D R WhaleyAbstract:A three-dimensional (3D) multifrequency large Signal Model of the beam wave interaction in a helix TWT is described. The beam is divided into a set of discrete rays, or "beamlets", instead of the disks or rings used in one-dimensional (1-D) or two-dimensional (2-D) Models. The RF fields supported by the helix are represented by a tape helix Model that uses a modal expansion including the full (Bessel function) radial dependence of the fields; both forward and backward synchronous space harmonics are included in the Model. RF space charge fields are obtained from solutions of the Helmholtz equations for the RF electric and RF magnetic fields, using the beam current and charge densities as sources. The dc space charge electric field is similarly obtained from a solution of Poisson's equation. This Model has been implemented in a code called CHRISTINE 3D, a generalization of the one dimensional CHRISTINE code. The full three dimensional treatment permits the accurate computation of large Signal gain and efficiency, taking into account the self-consistent variation of beam radius along the interaction space. The code also computes helix interception current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D Model. Results from the CHRISTINE 3D code are shown to compare very favorably with measurements of output power, efficiency, and interception current vs. drive power. Its predictions for spent beam distributions also compare very well with measurements. Run times for the code are problem dependent, but for a single case of interest are typically 1 to 5 min on a 450 MHz PC, orders of magnitude shorter than that required for a comparable 3D particle-in-cell simulation.
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a three dimensional multifrequency large Signal Model for helix traveling wave tubes
IEEE Transactions on Electron Devices, 2001Co-Authors: D Chernin, T M Antonsen, B Levush, D R WhaleyAbstract:A three-dimensional (3D) multifrequency large Signal Model of the beam wave interaction in a helix TWT is described. The beam is divided into a set of discrete rays, or "beamlets", instead of the disks or rings used in one-dimensional (1-D) or two-dimensional (2-D) Models. The RF fields supported by the helix are represented by a tape helix Model that uses a modal expansion including the full (Bessel function) radial dependence of the fields; both forward and backward synchronous space harmonics are included in the Model. RF space charge fields are obtained from solutions of the Helmholtz equations for the RF electric and RF magnetic fields, using the beam current and charge densities as sources. The dc space charge electric field is similarly obtained from a solution of Poisson's equation. This Model has been implemented in a code called CHRISTINE 3D, a generalization of the one dimensional CHRISTINE code. The full three dimensional treatment permits the accurate computation of large Signal gain and efficiency, taking into account the self-consistent variation of beam radius along the interaction space. The code also computes helix interception current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D Model. Results from the CHRISTINE 3D code are shown to compare very favorably with measurements of output power, efficiency, and interception current vs. drive power. Its predictions for spent beam distributions also compare very well with measurements. Run times for the code are problem dependent, but for a single case of interest are typically 1 to 5 min on a 450 MHz PC, orders of magnitude shorter than that required for a comparable 3D particle-in-cell simulation.
D R Whaley - One of the best experts on this subject based on the ideXlab platform.
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a three dimensional multifrequency large Signal Model for helix traveling wave tubes
IEEE Transactions on Electron Devices, 2001Co-Authors: D Chernin, T M Antonsen, B Levush, D R WhaleyAbstract:A three-dimensional (3D) multifrequency large Signal Model of the beam wave interaction in a helix TWT is described. The beam is divided into a set of discrete rays, or "beamlets", instead of the disks or rings used in one-dimensional (1-D) or two-dimensional (2-D) Models. The RF fields supported by the helix are represented by a tape helix Model that uses a modal expansion including the full (Bessel function) radial dependence of the fields; both forward and backward synchronous space harmonics are included in the Model. RF space charge fields are obtained from solutions of the Helmholtz equations for the RF electric and RF magnetic fields, using the beam current and charge densities as sources. The dc space charge electric field is similarly obtained from a solution of Poisson's equation. This Model has been implemented in a code called CHRISTINE 3D, a generalization of the one dimensional CHRISTINE code. The full three dimensional treatment permits the accurate computation of large Signal gain and efficiency, taking into account the self-consistent variation of beam radius along the interaction space. The code also computes helix interception current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D Model. Results from the CHRISTINE 3D code are shown to compare very favorably with measurements of output power, efficiency, and interception current vs. drive power. Its predictions for spent beam distributions also compare very well with measurements. Run times for the code are problem dependent, but for a single case of interest are typically 1 to 5 min on a 450 MHz PC, orders of magnitude shorter than that required for a comparable 3D particle-in-cell simulation.
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a three dimensional multifrequency large Signal Model for helix traveling wave tubes
IEEE Transactions on Electron Devices, 2001Co-Authors: D Chernin, T M Antonsen, B Levush, D R WhaleyAbstract:A three-dimensional (3D) multifrequency large Signal Model of the beam wave interaction in a helix TWT is described. The beam is divided into a set of discrete rays, or "beamlets", instead of the disks or rings used in one-dimensional (1-D) or two-dimensional (2-D) Models. The RF fields supported by the helix are represented by a tape helix Model that uses a modal expansion including the full (Bessel function) radial dependence of the fields; both forward and backward synchronous space harmonics are included in the Model. RF space charge fields are obtained from solutions of the Helmholtz equations for the RF electric and RF magnetic fields, using the beam current and charge densities as sources. The dc space charge electric field is similarly obtained from a solution of Poisson's equation. This Model has been implemented in a code called CHRISTINE 3D, a generalization of the one dimensional CHRISTINE code. The full three dimensional treatment permits the accurate computation of large Signal gain and efficiency, taking into account the self-consistent variation of beam radius along the interaction space. The code also computes helix interception current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D Model. Results from the CHRISTINE 3D code are shown to compare very favorably with measurements of output power, efficiency, and interception current vs. drive power. Its predictions for spent beam distributions also compare very well with measurements. Run times for the code are problem dependent, but for a single case of interest are typically 1 to 5 min on a 450 MHz PC, orders of magnitude shorter than that required for a comparable 3D particle-in-cell simulation.
B Levush - One of the best experts on this subject based on the ideXlab platform.
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1 d large Signal Model of folded waveguide traveling wave tubes
IEEE Transactions on Electron Devices, 2014Co-Authors: D Chernin, T M Antonsen, K T Nguyen, Alexander N Vlasov, Igor A Chernyavskiy, B LevushAbstract:A recently published hybrid circuit Model for folded-waveguide slow wave structures has been implemented in the 1-D large Signal code CHRISTINE. The resulting code is applied to a design for a G-band (220 GHz) folded-waveguide traveling wave tube. Results of small and large Signal gain are compared with those from TESLA, a 2-D code using the same circuit Model. Conditions for accuracy of the 1-D Model are illustrated and explained. The effects of an offset beam tunnel on circuit dispersion and amplifier stability are illustrated using the CHRISTINE code.
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5 3 a large Signal Model of extended interactions klystrons
International Vacuum Electronics Conference, 2010Co-Authors: D Chernin, T M Antonsen, K T Nguyen, B LevushAbstract:Extended Interaction Klystron (EIK) cavities consist of shorted (resonant) sections of a periodic or bi-periodic structure. The response of such cavities to currents induced by the passage of a bunched beam may be represented by an impedance matrix that relates the voltage in each section to the induced currents. We have implemented this representation in the CHRISTINE large Signal code. Using a modal expansion for the cavity fields we have computed the impedance matrix for a simple ‘ladder’ circuit. Using this matrix in a CHRISTINE simulation, we have found good agreement for the AC current vs. axial location in a 3-cavity circuit, compared with results from the 3D particle-in-cell code MAGIC.
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a three dimensional multifrequency large Signal Model for helix traveling wave tubes
IEEE Transactions on Electron Devices, 2001Co-Authors: D Chernin, T M Antonsen, B Levush, D R WhaleyAbstract:A three-dimensional (3D) multifrequency large Signal Model of the beam wave interaction in a helix TWT is described. The beam is divided into a set of discrete rays, or "beamlets", instead of the disks or rings used in one-dimensional (1-D) or two-dimensional (2-D) Models. The RF fields supported by the helix are represented by a tape helix Model that uses a modal expansion including the full (Bessel function) radial dependence of the fields; both forward and backward synchronous space harmonics are included in the Model. RF space charge fields are obtained from solutions of the Helmholtz equations for the RF electric and RF magnetic fields, using the beam current and charge densities as sources. The dc space charge electric field is similarly obtained from a solution of Poisson's equation. This Model has been implemented in a code called CHRISTINE 3D, a generalization of the one dimensional CHRISTINE code. The full three dimensional treatment permits the accurate computation of large Signal gain and efficiency, taking into account the self-consistent variation of beam radius along the interaction space. The code also computes helix interception current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D Model. Results from the CHRISTINE 3D code are shown to compare very favorably with measurements of output power, efficiency, and interception current vs. drive power. Its predictions for spent beam distributions also compare very well with measurements. Run times for the code are problem dependent, but for a single case of interest are typically 1 to 5 min on a 450 MHz PC, orders of magnitude shorter than that required for a comparable 3D particle-in-cell simulation.
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a three dimensional multifrequency large Signal Model for helix traveling wave tubes
IEEE Transactions on Electron Devices, 2001Co-Authors: D Chernin, T M Antonsen, B Levush, D R WhaleyAbstract:A three-dimensional (3D) multifrequency large Signal Model of the beam wave interaction in a helix TWT is described. The beam is divided into a set of discrete rays, or "beamlets", instead of the disks or rings used in one-dimensional (1-D) or two-dimensional (2-D) Models. The RF fields supported by the helix are represented by a tape helix Model that uses a modal expansion including the full (Bessel function) radial dependence of the fields; both forward and backward synchronous space harmonics are included in the Model. RF space charge fields are obtained from solutions of the Helmholtz equations for the RF electric and RF magnetic fields, using the beam current and charge densities as sources. The dc space charge electric field is similarly obtained from a solution of Poisson's equation. This Model has been implemented in a code called CHRISTINE 3D, a generalization of the one dimensional CHRISTINE code. The full three dimensional treatment permits the accurate computation of large Signal gain and efficiency, taking into account the self-consistent variation of beam radius along the interaction space. The code also computes helix interception current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D Model. Results from the CHRISTINE 3D code are shown to compare very favorably with measurements of output power, efficiency, and interception current vs. drive power. Its predictions for spent beam distributions also compare very well with measurements. Run times for the code are problem dependent, but for a single case of interest are typically 1 to 5 min on a 450 MHz PC, orders of magnitude shorter than that required for a comparable 3D particle-in-cell simulation.
T M Antonsen - One of the best experts on this subject based on the ideXlab platform.
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1 d large Signal Model of folded waveguide traveling wave tubes
IEEE Transactions on Electron Devices, 2014Co-Authors: D Chernin, T M Antonsen, K T Nguyen, Alexander N Vlasov, Igor A Chernyavskiy, B LevushAbstract:A recently published hybrid circuit Model for folded-waveguide slow wave structures has been implemented in the 1-D large Signal code CHRISTINE. The resulting code is applied to a design for a G-band (220 GHz) folded-waveguide traveling wave tube. Results of small and large Signal gain are compared with those from TESLA, a 2-D code using the same circuit Model. Conditions for accuracy of the 1-D Model are illustrated and explained. The effects of an offset beam tunnel on circuit dispersion and amplifier stability are illustrated using the CHRISTINE code.
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5 3 a large Signal Model of extended interactions klystrons
International Vacuum Electronics Conference, 2010Co-Authors: D Chernin, T M Antonsen, K T Nguyen, B LevushAbstract:Extended Interaction Klystron (EIK) cavities consist of shorted (resonant) sections of a periodic or bi-periodic structure. The response of such cavities to currents induced by the passage of a bunched beam may be represented by an impedance matrix that relates the voltage in each section to the induced currents. We have implemented this representation in the CHRISTINE large Signal code. Using a modal expansion for the cavity fields we have computed the impedance matrix for a simple ‘ladder’ circuit. Using this matrix in a CHRISTINE simulation, we have found good agreement for the AC current vs. axial location in a 3-cavity circuit, compared with results from the 3D particle-in-cell code MAGIC.
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a three dimensional multifrequency large Signal Model for helix traveling wave tubes
IEEE Transactions on Electron Devices, 2001Co-Authors: D Chernin, T M Antonsen, B Levush, D R WhaleyAbstract:A three-dimensional (3D) multifrequency large Signal Model of the beam wave interaction in a helix TWT is described. The beam is divided into a set of discrete rays, or "beamlets", instead of the disks or rings used in one-dimensional (1-D) or two-dimensional (2-D) Models. The RF fields supported by the helix are represented by a tape helix Model that uses a modal expansion including the full (Bessel function) radial dependence of the fields; both forward and backward synchronous space harmonics are included in the Model. RF space charge fields are obtained from solutions of the Helmholtz equations for the RF electric and RF magnetic fields, using the beam current and charge densities as sources. The dc space charge electric field is similarly obtained from a solution of Poisson's equation. This Model has been implemented in a code called CHRISTINE 3D, a generalization of the one dimensional CHRISTINE code. The full three dimensional treatment permits the accurate computation of large Signal gain and efficiency, taking into account the self-consistent variation of beam radius along the interaction space. The code also computes helix interception current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D Model. Results from the CHRISTINE 3D code are shown to compare very favorably with measurements of output power, efficiency, and interception current vs. drive power. Its predictions for spent beam distributions also compare very well with measurements. Run times for the code are problem dependent, but for a single case of interest are typically 1 to 5 min on a 450 MHz PC, orders of magnitude shorter than that required for a comparable 3D particle-in-cell simulation.
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a three dimensional multifrequency large Signal Model for helix traveling wave tubes
IEEE Transactions on Electron Devices, 2001Co-Authors: D Chernin, T M Antonsen, B Levush, D R WhaleyAbstract:A three-dimensional (3D) multifrequency large Signal Model of the beam wave interaction in a helix TWT is described. The beam is divided into a set of discrete rays, or "beamlets", instead of the disks or rings used in one-dimensional (1-D) or two-dimensional (2-D) Models. The RF fields supported by the helix are represented by a tape helix Model that uses a modal expansion including the full (Bessel function) radial dependence of the fields; both forward and backward synchronous space harmonics are included in the Model. RF space charge fields are obtained from solutions of the Helmholtz equations for the RF electric and RF magnetic fields, using the beam current and charge densities as sources. The dc space charge electric field is similarly obtained from a solution of Poisson's equation. This Model has been implemented in a code called CHRISTINE 3D, a generalization of the one dimensional CHRISTINE code. The full three dimensional treatment permits the accurate computation of large Signal gain and efficiency, taking into account the self-consistent variation of beam radius along the interaction space. The code also computes helix interception current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D Model. Results from the CHRISTINE 3D code are shown to compare very favorably with measurements of output power, efficiency, and interception current vs. drive power. Its predictions for spent beam distributions also compare very well with measurements. Run times for the code are problem dependent, but for a single case of interest are typically 1 to 5 min on a 450 MHz PC, orders of magnitude shorter than that required for a comparable 3D particle-in-cell simulation.
Yi Wang - One of the best experts on this subject based on the ideXlab platform.
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bone quantitative susceptibility mapping using a chemical species specific r2 Signal Model with ultrashort and conventional echo data
Magnetic Resonance in Medicine, 2018Co-Authors: Alexey Dimov, Pascal Spincemaille, Martin R Prince, Jiang Du, Yi WangAbstract:To develop quantitative susceptibility mapping (QSM) of bone using an ultrashort echo time (UTE) gradient echo (GRE) sequence for Signal acquisition and a bone-specific effective transverse relaxation rate ( R2*) to Model water-fat MR Signals for field mapping.Three-dimensional radial UTE data (echo times ≥ 40 μs) was acquired on a 3 Tesla scanner and fitted with a bone-specific Signal Model to map the chemical species and susceptibility field. Experiments were performed ex vivo on a porcine hoof and in vivo on healthy human subjects (n = 7). For water-fat separation, a bone-specific Model assigning R2* decay mostly to water was compared with the standard Models that assigned the same decay for both fat and water. In the ex vivo experiment, bone QSM was correlated with CT.Compared with standard Models, the bone-specific R2* method significantly reduced errors in the fat fraction within the cortical bone in all tested data sets, leading to reduced artifacts in QSM. Good correlation was found between bone CT and QSM values in the porcine hoof (R2 = 0.77). Bone QSM was successfully generated in all subjects.The QSM of bone is feasible using UTE with a conventional echo time GRE acquisition and a bone-specific R2* Signal Model. Magn Reson Med 79:121-128, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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bone quantitative susceptibility mapping using a chemical species specific r2 Signal Model with ultrashort and conventional echo data
Magnetic Resonance in Medicine, 2018Co-Authors: Alexey Dimov, Pascal Spincemaille, Martin R Prince, Zhe Liu, Yi WangAbstract:Author(s): Dimov, Alexey V; Liu, Zhe; Spincemaille, Pascal; Prince, Martin R; Du, Jiang; Wang, Yi | Abstract: PurposeTo develop quantitative susceptibility mapping (QSM) of bone using an ultrashort echo time (UTE) gradient echo (GRE) sequence for Signal acquisition and a bone-specific effective transverse relaxation rate ( R2*) to Model water-fat MR Signals for field mapping.MethodsThree-dimensional radial UTE data (echo times ≥ 40 μs) was acquired on a 3 Tesla scanner and fitted with a bone-specific Signal Model to map the chemical species and susceptibility field. Experiments were performed ex vivo on a porcine hoof and in vivo on healthy human subjects (n = 7). For water-fat separation, a bone-specific Model assigning R2* decay mostly to water was compared with the standard Models that assigned the same decay for both fat and water. In the ex vivo experiment, bone QSM was correlated with CT.ResultsCompared with standard Models, the bone-specific R2* method significantly reduced errors in the fat fraction within the cortical bone in all tested data sets, leading to reduced artifacts in QSM. Good correlation was found between bone CT and QSM values in the porcine hoof (R2 = 0.77). Bone QSM was successfully generated in all subjects.ConclusionsThe QSM of bone is feasible using UTE with a conventional echo time GRE acquisition and a bone-specific R2* Signal Model. Magn Reson Med 79:121-128, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
