Claudio Costa Motta - Academia.edu (original) (raw)

Papers by Claudio Costa Motta

Anais do 2002 International Telecommunications Symposium

  A numerical code based on the Finite Element Method (FEM) was developed to solve the ridged w... more   A numerical code based on the Finite Element Method (FEM) was developed to solve the ridged waveguide eigenvalue problem. In order to apply the FEM, the Galerkin Weak Formulation was used. The solution is obtained by using the Finite Element Method with quadratic triangular shape functions. The eigenvalue spectrum of the single and double rectangular ridged waveguide is shown and it is compared with other numerical approaches and the electrical field distribution of lower modes is also presented. The code was developed using C language.

Materials Research, 2022

A metallurgical process using a very high temperature Mo-Ru brazing filler alloy to join a contro... more A metallurgical process using a very high temperature Mo-Ru brazing filler alloy to join a controlled porous tungsten cathode button and a single-crystalline molybdenum cathode body for microwave tubes manufacture was developed †. The Mo-Ru brazing alloy was obtained by mixing and milling powders in the eutectic composition with a binder, and a braze paste was applied on the surface cathode parts. Brazing was performed in two temperatures by using a resistive dry hydrogen cold wall furnace for 10 minutes: at 1890 °C and 1967 °C. It was observed a fillability by the Mo-Ru system only in the tests performed in temperatures above 1967°C. The brazed samples were analyzed by Scanning Electron Microscopy coupled to Energy Dispersive Spectroscopy. It was observed absence of microstructural defects in the interface between the tungsten porous and dense molybdenum joint. Stress-strain tests, followed by SEM analysis were performed to determine the mechanical behavior of the brazing joining. The results indicate the origin region of the cracking and show an intergranular propagation; some evidence as grain cleavage indicates a brittle failure behavior.

2022 SBFoton International Optics and Photonics Conference (SBFoton IOPC)

2022 SBFoton International Optics and Photonics Conference (SBFoton IOPC)

Proceedings of the 2003 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference - IMOC 2003. (Cat. No.03TH8678)

An experimental set-up to investigate the life-time of traveling-wave tube thermionic cathodes ha... more An experimental set-up to investigate the life-time of traveling-wave tube thermionic cathodes has been developed and is reported in this paper. The cathode developed is one of the aluminate emitter type. The experimental apparatus to measure the cathode life-time consists of a high voltage power supply, auxiliary circuitries to feed the cathode heater, a grid modulator, a magnetic focusing, and an ultra-high vacuum chamber. For a typical traveling-wave tube operation, with 30 kV of acceleration potential and 3.68 A beam current pulse, a 0.73 /spl mu/ perveance was found for the electron gun. Up to the present moment 400 h of cathode life-time has been recorded.

SBMO/IEEE MTT-S International Conference on Microwave and Optoelectronics, 2005.

ABSTRACT This paper reported an investigation about the interaction impedance behavior for slow-w... more ABSTRACT This paper reported an investigation about the interaction impedance behavior for slow-wave structures (SWS) in order to provide some guidelines to aid on traveling-wave tubes (TWT) and backward-wave oscillators (BWO) design. The analysis is made rigorous by removing the usual approximation of considering the radial propagation constant to be the same in the different structure regions. Furthermore, a tape-helix model instead of a simpler sheath-helix model has been used to consider the space-harmonic effects on the interaction impedance. Functional variations are given of interaction impedance with frequency and with the effective relative dielectric constant of support rods. Additionally, the dispersion equation is solved for the first backward-mode and its interaction impedance curve is shown.

2009 IEEE Pulsed Power Conference, 2009

ABSTRACT This work deals with an investigation of possibilities of using ring-bar slow-wave struc... more ABSTRACT This work deals with an investigation of possibilities of using ring-bar slow-wave structures in medium-high power traveling-wave tubes in the Ku-band (13.75-14.50 GHz). Ring-bar SWSs are often used in high (pulsed) power TWTs and narrow band purposes. Its main advantages over the single helix are the higher interaction impedance (roughly twice) and the good rejection factor to the backward mode. The main drawback of this kind of SWS is a more dispersive phase-velocity profile that limits its bandwidth. The investigation here verified that this slow-wave structure, under some dispersion profile linearization techniques, can result in an interaction circuit with satisfactory gain profile over the Ku-band. An encouraging output power level around 60 dBm was theoretically achieved with variation of a few more than 0.5 dBm. The large signal analysis (hot model) was performed by an in house large signal lagrangian code under development and the cold tests with a 3D eigensolver.

2007 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference, 2007

Page 1. An analysis of the Sloped-Ring Slow-Wave Structure for High-Power Traveling-Wave Tubes Da... more Page 1. An analysis of the Sloped-Ring Slow-Wave Structure for High-Power Traveling-Wave Tubes Daniel T. Lopes1 and Cláudio C. Motta2 Microwave Lab, Technology Center of the Brazilian Navy in São Paulo, São Paulo ...

2007 IEEE Pulsed Power Plasma Science Conference, 2007

Summary form only given. A large-signal analysis was used to model nonlinear effects of a multica... more Summary form only given. A large-signal analysis was used to model nonlinear effects of a multicavity klystron amplifier associated with the growth of the signal wave such as intermodulation distortion. The analysis was developed using 1D nonlinear Eulerian electron beam equations as well a Lagrangian model. The plasma frequency reduction factor was calculated using Rowe approach where the beam is considered as a pencil beam. The cavities are modeled as RLC circuit with a single resonance frequency. From this analysis it was possible to describe the intermodulation distortion generation and suppression.

2007 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference, 2007

In this paper the large-signal or the nonlinear behavior of a helix traveling-wave tube (TWT) is ... more In this paper the large-signal or the nonlinear behavior of a helix traveling-wave tube (TWT) is investigated by numerical integrating of a set of electron equations of motion, including the space-charge repulsion forces between the electrons, and the coupling between the slow-wave structure and the electron beam. The simulations were conducted for typical parameters of a power TWT. The Pierce

2011 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC 2011), 2011

In this paper a methodology to determine the suitable magnetic focusing properties that minimizes... more In this paper a methodology to determine the suitable magnetic focusing properties that minimizes the electron beam ripple, propagating in a drift region, is presented. The methodology is applied in a typical C-band, power traveling-wave tube (TWT) which needs a 9.0 keV and 0.4 A electron beam with 0.8 mm of beam waist for a right operation. Using numerical simulation

2009 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC), 2009

Abstract In this paper we present results obtained while testing the 3D electromagnetic solver CS... more Abstract In this paper we present results obtained while testing the 3D electromagnetic solver CST Microwave Studio as a CAD tool in the design of some parts of the beam-wave interaction circuit of an X-band traveling-wave tube. A pair of impedance transformers, ...

IVEC 2012, 2012

In this work the design of multiple-beam reentrant cavities with 4, 6, and 8 beam tunnels for a 3... more In this work the design of multiple-beam reentrant cavities with 4, 6, and 8 beam tunnels for a 350 MHz is presented. These cavities can be useful in a multiple-beam klystron development for proton linac including spallation neutron source applications. The study was carried out using the electromagnetic tool CST Microwave Studio.

Materials Research, 2007

Pr 16 Fe 76 B 8 magnets have been produced using the hydrogen decrepitation (HD) process and high... more Pr 16 Fe 76 B 8 magnets have been produced using the hydrogen decrepitation (HD) process and highenergy planetary ball milling. Investigations have been carried out to evaluate the influence of the milling speed and time. The best magnetic properties obtained were B r = (1020 ± 20) mT, µ 0i H c = (1420 ± 30) mT and (BH) max = (200 ± 4) kJm-3 , for a magnet prepared with the alloy milled at 200 rpm for 4.5 ks. Magnets prepared from this powder exhibited a superior intrinsic coercivity compared to that of magnets produced using low-energy ball milling. However, the remanence and energy product of the latter were somewhat lower. An important feature was the dramatic reduction in the processing time (about 90%). Microstructural observation have shown that increasing the milling time and keeping constant the rotational mill speed caused an exponential grain size reduction in the sintered magnet. Increasing the milling speed also reduced the grain size and influenced both remanence and intrinsic coercivity.

Materials Research, 2005

Sintered Pr-based magnets were produced using a new laboratory technique for powder handling. Unl... more Sintered Pr-based magnets were produced using a new laboratory technique for powder handling. Unlike the conventional procedure for preparing sintered permanent magnets in the laboratory, the powder technique used in this investigation does not require a glove box. The effects of processing parameters on the magnetic properties of Pr-based sintered magnets prepared using the hydrogen decrepitation process have been studied. Specifically, the effects of sintering temperature and milling time for processing Pr 16 Fe 76 B 8 magnets have been investigated. Pr 16 Fe 76 B 8 magnets with the best magnetic properties were sintered between 1015 °C to 1075 °C.

Journal of Magnetism and Magnetic Materials, 2008

ABSTRACT

IEEE Transactions on Magnetics, 2010

This work reports some initial results of a 2-D electron gun design code (XMGUN) based on the fin... more This work reports some initial results of a 2-D electron gun design code (XMGUN) based on the finite-element method (FEM). Using the Galerkin weak formulation, the nodal analysis, and the first-order elements, the Poisson equation was solved for the electron gun electrostatic potential. The nonrelativistic particle paths were numerically calculated by a fourth-order Runge-Kutta method. An iterative scheme was repeated until the electron paths convergence was achieved under full space-charge limited condition. In order to validate the algorithm, the focusing properties of a 2-D Pierce electron gun with planar symmetry were studied. The quality of the beam was evaluated based on the particle's final position, the transit time, and the particle energy evaluations. Using these three parameters, a good agreement was found between the theoretical and calculated results. Absolute current density errors of less than 1% were found, even with a coarse discretization of the domain. The XMGUN tool was used to design a 30-kV, 7.1-A, and 1.37-Perv axis-symmetric high-power electron gun for use in vacuum microwave devices. The figure of merit used as reference to measure the quality of the electron beam was the normalized transverse velocity.

IEEE Transactions on Magnetics, 2009

The magnetic stability of RE-FeB (RE = Nd or Pr) sintered magnets above room temperature was inve... more The magnetic stability of RE-FeB (RE = Nd or Pr) sintered magnets above room temperature was investigated by monitoring the squareness factor (SF). At 293 423 K, commercial anisotropic NdFeB-based sintered magnets with a Curie temperature () of around 585 K showed no appreciable change in their squareness factors. This indicates that the SF is controlled mainly by the samples' microstructural features. Magnets with 593 K showed a tendency for improved squareness factor at higher temperatures due to the methodology employed to characterize the SF. On the other hand, PrFeCoBCuNb sintered magnets with 593 K presented a reduction in the SF with temperature rising from 298 to 373 K.

IEEE Transactions on Electron Devices, 2008

In this paper, we present results from an extensive study concerning the phase velocity and the i... more In this paper, we present results from an extensive study concerning the phase velocity and the interaction impedance characteristics of slow-wave structures (SWSs) for high-power traveling-wave tubes (TWTs). The SWS under analysis is the ring-bar one, which has been very suitable when high-power levels are needed in TWTs. We develop an analytical model based on the contrawound helix theory, which allows us to characterize the electromagnetic behavior of an equivalent ring-bar SWS. The theoretical model presented in this paper is able to reproduce all previously published results for the contrawound helix, and we also present new results. Additionally, we compare analytical results from the model to experimental results and to 3-D simulation results obtained using CST Microwave Studio. Index Terms-Contrawound helix, interaction impedance, phase velocity, power traveling-wave tube (TWT), ring bar, slow-wave structure (SWS). Daniel Teixeira Lopes was born in São Paulo, SP, Brazil, in 1981. He received the B.S. degree in materials, processes, and electronic components (with honors) from the Faculdade de Tecnologia de São Paulo in 2005 and the M.S. degree in nuclear technology from the Nuclear and

Anais do 2002 International Telecommunications Symposium

  A numerical code based on the Finite Element Method (FEM) was developed to solve the ridged w... more   A numerical code based on the Finite Element Method (FEM) was developed to solve the ridged waveguide eigenvalue problem. In order to apply the FEM, the Galerkin Weak Formulation was used. The solution is obtained by using the Finite Element Method with quadratic triangular shape functions. The eigenvalue spectrum of the single and double rectangular ridged waveguide is shown and it is compared with other numerical approaches and the electrical field distribution of lower modes is also presented. The code was developed using C language.

Materials Research, 2022

A metallurgical process using a very high temperature Mo-Ru brazing filler alloy to join a contro... more A metallurgical process using a very high temperature Mo-Ru brazing filler alloy to join a controlled porous tungsten cathode button and a single-crystalline molybdenum cathode body for microwave tubes manufacture was developed †. The Mo-Ru brazing alloy was obtained by mixing and milling powders in the eutectic composition with a binder, and a braze paste was applied on the surface cathode parts. Brazing was performed in two temperatures by using a resistive dry hydrogen cold wall furnace for 10 minutes: at 1890 °C and 1967 °C. It was observed a fillability by the Mo-Ru system only in the tests performed in temperatures above 1967°C. The brazed samples were analyzed by Scanning Electron Microscopy coupled to Energy Dispersive Spectroscopy. It was observed absence of microstructural defects in the interface between the tungsten porous and dense molybdenum joint. Stress-strain tests, followed by SEM analysis were performed to determine the mechanical behavior of the brazing joining. The results indicate the origin region of the cracking and show an intergranular propagation; some evidence as grain cleavage indicates a brittle failure behavior.

2022 SBFoton International Optics and Photonics Conference (SBFoton IOPC)

2022 SBFoton International Optics and Photonics Conference (SBFoton IOPC)

Proceedings of the 2003 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference - IMOC 2003. (Cat. No.03TH8678)

An experimental set-up to investigate the life-time of traveling-wave tube thermionic cathodes ha... more An experimental set-up to investigate the life-time of traveling-wave tube thermionic cathodes has been developed and is reported in this paper. The cathode developed is one of the aluminate emitter type. The experimental apparatus to measure the cathode life-time consists of a high voltage power supply, auxiliary circuitries to feed the cathode heater, a grid modulator, a magnetic focusing, and an ultra-high vacuum chamber. For a typical traveling-wave tube operation, with 30 kV of acceleration potential and 3.68 A beam current pulse, a 0.73 /spl mu/ perveance was found for the electron gun. Up to the present moment 400 h of cathode life-time has been recorded.

SBMO/IEEE MTT-S International Conference on Microwave and Optoelectronics, 2005.

ABSTRACT This paper reported an investigation about the interaction impedance behavior for slow-w... more ABSTRACT This paper reported an investigation about the interaction impedance behavior for slow-wave structures (SWS) in order to provide some guidelines to aid on traveling-wave tubes (TWT) and backward-wave oscillators (BWO) design. The analysis is made rigorous by removing the usual approximation of considering the radial propagation constant to be the same in the different structure regions. Furthermore, a tape-helix model instead of a simpler sheath-helix model has been used to consider the space-harmonic effects on the interaction impedance. Functional variations are given of interaction impedance with frequency and with the effective relative dielectric constant of support rods. Additionally, the dispersion equation is solved for the first backward-mode and its interaction impedance curve is shown.

2009 IEEE Pulsed Power Conference, 2009

ABSTRACT This work deals with an investigation of possibilities of using ring-bar slow-wave struc... more ABSTRACT This work deals with an investigation of possibilities of using ring-bar slow-wave structures in medium-high power traveling-wave tubes in the Ku-band (13.75-14.50 GHz). Ring-bar SWSs are often used in high (pulsed) power TWTs and narrow band purposes. Its main advantages over the single helix are the higher interaction impedance (roughly twice) and the good rejection factor to the backward mode. The main drawback of this kind of SWS is a more dispersive phase-velocity profile that limits its bandwidth. The investigation here verified that this slow-wave structure, under some dispersion profile linearization techniques, can result in an interaction circuit with satisfactory gain profile over the Ku-band. An encouraging output power level around 60 dBm was theoretically achieved with variation of a few more than 0.5 dBm. The large signal analysis (hot model) was performed by an in house large signal lagrangian code under development and the cold tests with a 3D eigensolver.

2007 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference, 2007

Page 1. An analysis of the Sloped-Ring Slow-Wave Structure for High-Power Traveling-Wave Tubes Da... more Page 1. An analysis of the Sloped-Ring Slow-Wave Structure for High-Power Traveling-Wave Tubes Daniel T. Lopes1 and Cláudio C. Motta2 Microwave Lab, Technology Center of the Brazilian Navy in São Paulo, São Paulo ...

2007 IEEE Pulsed Power Plasma Science Conference, 2007

Summary form only given. A large-signal analysis was used to model nonlinear effects of a multica... more Summary form only given. A large-signal analysis was used to model nonlinear effects of a multicavity klystron amplifier associated with the growth of the signal wave such as intermodulation distortion. The analysis was developed using 1D nonlinear Eulerian electron beam equations as well a Lagrangian model. The plasma frequency reduction factor was calculated using Rowe approach where the beam is considered as a pencil beam. The cavities are modeled as RLC circuit with a single resonance frequency. From this analysis it was possible to describe the intermodulation distortion generation and suppression.

2007 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference, 2007

In this paper the large-signal or the nonlinear behavior of a helix traveling-wave tube (TWT) is ... more In this paper the large-signal or the nonlinear behavior of a helix traveling-wave tube (TWT) is investigated by numerical integrating of a set of electron equations of motion, including the space-charge repulsion forces between the electrons, and the coupling between the slow-wave structure and the electron beam. The simulations were conducted for typical parameters of a power TWT. The Pierce

2011 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC 2011), 2011

In this paper a methodology to determine the suitable magnetic focusing properties that minimizes... more In this paper a methodology to determine the suitable magnetic focusing properties that minimizes the electron beam ripple, propagating in a drift region, is presented. The methodology is applied in a typical C-band, power traveling-wave tube (TWT) which needs a 9.0 keV and 0.4 A electron beam with 0.8 mm of beam waist for a right operation. Using numerical simulation

2009 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC), 2009

Abstract In this paper we present results obtained while testing the 3D electromagnetic solver CS... more Abstract In this paper we present results obtained while testing the 3D electromagnetic solver CST Microwave Studio as a CAD tool in the design of some parts of the beam-wave interaction circuit of an X-band traveling-wave tube. A pair of impedance transformers, ...

IVEC 2012, 2012

In this work the design of multiple-beam reentrant cavities with 4, 6, and 8 beam tunnels for a 3... more In this work the design of multiple-beam reentrant cavities with 4, 6, and 8 beam tunnels for a 350 MHz is presented. These cavities can be useful in a multiple-beam klystron development for proton linac including spallation neutron source applications. The study was carried out using the electromagnetic tool CST Microwave Studio.

Materials Research, 2007

Pr 16 Fe 76 B 8 magnets have been produced using the hydrogen decrepitation (HD) process and high... more Pr 16 Fe 76 B 8 magnets have been produced using the hydrogen decrepitation (HD) process and highenergy planetary ball milling. Investigations have been carried out to evaluate the influence of the milling speed and time. The best magnetic properties obtained were B r = (1020 ± 20) mT, µ 0i H c = (1420 ± 30) mT and (BH) max = (200 ± 4) kJm-3 , for a magnet prepared with the alloy milled at 200 rpm for 4.5 ks. Magnets prepared from this powder exhibited a superior intrinsic coercivity compared to that of magnets produced using low-energy ball milling. However, the remanence and energy product of the latter were somewhat lower. An important feature was the dramatic reduction in the processing time (about 90%). Microstructural observation have shown that increasing the milling time and keeping constant the rotational mill speed caused an exponential grain size reduction in the sintered magnet. Increasing the milling speed also reduced the grain size and influenced both remanence and intrinsic coercivity.

Materials Research, 2005

Sintered Pr-based magnets were produced using a new laboratory technique for powder handling. Unl... more Sintered Pr-based magnets were produced using a new laboratory technique for powder handling. Unlike the conventional procedure for preparing sintered permanent magnets in the laboratory, the powder technique used in this investigation does not require a glove box. The effects of processing parameters on the magnetic properties of Pr-based sintered magnets prepared using the hydrogen decrepitation process have been studied. Specifically, the effects of sintering temperature and milling time for processing Pr 16 Fe 76 B 8 magnets have been investigated. Pr 16 Fe 76 B 8 magnets with the best magnetic properties were sintered between 1015 °C to 1075 °C.

Journal of Magnetism and Magnetic Materials, 2008

ABSTRACT

IEEE Transactions on Magnetics, 2010

This work reports some initial results of a 2-D electron gun design code (XMGUN) based on the fin... more This work reports some initial results of a 2-D electron gun design code (XMGUN) based on the finite-element method (FEM). Using the Galerkin weak formulation, the nodal analysis, and the first-order elements, the Poisson equation was solved for the electron gun electrostatic potential. The nonrelativistic particle paths were numerically calculated by a fourth-order Runge-Kutta method. An iterative scheme was repeated until the electron paths convergence was achieved under full space-charge limited condition. In order to validate the algorithm, the focusing properties of a 2-D Pierce electron gun with planar symmetry were studied. The quality of the beam was evaluated based on the particle's final position, the transit time, and the particle energy evaluations. Using these three parameters, a good agreement was found between the theoretical and calculated results. Absolute current density errors of less than 1% were found, even with a coarse discretization of the domain. The XMGUN tool was used to design a 30-kV, 7.1-A, and 1.37-Perv axis-symmetric high-power electron gun for use in vacuum microwave devices. The figure of merit used as reference to measure the quality of the electron beam was the normalized transverse velocity.

IEEE Transactions on Magnetics, 2009

The magnetic stability of RE-FeB (RE = Nd or Pr) sintered magnets above room temperature was inve... more The magnetic stability of RE-FeB (RE = Nd or Pr) sintered magnets above room temperature was investigated by monitoring the squareness factor (SF). At 293 423 K, commercial anisotropic NdFeB-based sintered magnets with a Curie temperature () of around 585 K showed no appreciable change in their squareness factors. This indicates that the SF is controlled mainly by the samples' microstructural features. Magnets with 593 K showed a tendency for improved squareness factor at higher temperatures due to the methodology employed to characterize the SF. On the other hand, PrFeCoBCuNb sintered magnets with 593 K presented a reduction in the SF with temperature rising from 298 to 373 K.

IEEE Transactions on Electron Devices, 2008

In this paper, we present results from an extensive study concerning the phase velocity and the i... more In this paper, we present results from an extensive study concerning the phase velocity and the interaction impedance characteristics of slow-wave structures (SWSs) for high-power traveling-wave tubes (TWTs). The SWS under analysis is the ring-bar one, which has been very suitable when high-power levels are needed in TWTs. We develop an analytical model based on the contrawound helix theory, which allows us to characterize the electromagnetic behavior of an equivalent ring-bar SWS. The theoretical model presented in this paper is able to reproduce all previously published results for the contrawound helix, and we also present new results. Additionally, we compare analytical results from the model to experimental results and to 3-D simulation results obtained using CST Microwave Studio. Index Terms-Contrawound helix, interaction impedance, phase velocity, power traveling-wave tube (TWT), ring bar, slow-wave structure (SWS). Daniel Teixeira Lopes was born in São Paulo, SP, Brazil, in 1981. He received the B.S. degree in materials, processes, and electronic components (with honors) from the Faculdade de Tecnologia de São Paulo in 2005 and the M.S. degree in nuclear technology from the Nuclear and