A new concept of inner-feedback-style traveling wave tube oscillator, which is based on a traveling-wave tube having a partial reflector located at near the junction between the slow-wave structure and the output coup...A new concept of inner-feedback-style traveling wave tube oscillator, which is based on a traveling-wave tube having a partial reflector located at near the junction between the slow-wave structure and the output coupler and a mechanical tuner connected to the input coupler, is proposed. Simulations by CHIPIC code show that the inner-feedback-style traveling wave tube oscillator having 100W of power, about 10% of electron efficiency and a tunable band of 73.35-73.91 GHz may be achieved. Compared with Backward Wave Oscillators (BWOs), the new devices have similar ability for tuning, and have much higher electron efficiency, suggesting much more potential as a Terahertz source.展开更多
Corresponding to the atmospheric transmission windows of the electromagnetic spectrum in the low terahertz range,the mode coupling and dispersion characteristics of two helically corrugated waveguides(HCW)in the frequ...Corresponding to the atmospheric transmission windows of the electromagnetic spectrum in the low terahertz range,the mode coupling and dispersion characteristics of two helically corrugated waveguides(HCW)in the frequency ranges of 90 GHz-100 GHz and 260 GHz-265 GHz are studied.Through analytic calculations and numerical simulations,dispersion curves and structural parameters of the two frequency ranges waveguides are obtained.A novel method was proposed to obtain the dispersion of the HCW from the eigenwave solution using a periodic boundary condition.The HCW in a frequency range of 90 GHz-100 GHz was fabricated and its dispersion performance was measured.By comparing the measured results with the theoretical and the simulated results,the validity of the analytical and simulation method is verified.Limited to our machining capability,the dispersion of the 260 GHz-265 GHz HCW was only simulated and calculated and it was found that the results agree well with each other.展开更多
The effect of second-harmonic generation (SHG) by primary (fundamental) circumferential guided wave (CGW) propagation is investigated from a numerical standpoint. To enable that the second harmonic of the primar...The effect of second-harmonic generation (SHG) by primary (fundamental) circumferential guided wave (CGW) propagation is investigated from a numerical standpoint. To enable that the second harmonic of the primary CGW mode can accumulate along the circumferential direction, an appropriate mode pair of primary and double frequency CGWs is chosen. Finite element simulations and evaluations of nonlinear CGW propagation are analyzed for the selected CGW mode pair. The numerical simulations performed directly demonstrate that the response of SHG is completely generated by the desired primary CGW mode that satisfies the condition of phase velocity matching at a specific driving frequency, and that the second harmonic of the primary CGW mode does have a cumulative effect with circumferential angles. The numerical perspective obtained yields an insight into the complicated physical process of SHG of primary CGW propagation unavailable previously.展开更多
The experimental observation of cumulative second-harmonic generation of the primary circumferential guided wave propagation is reported. A pair of wedge transducers is used to generate the primary circumferential gui...The experimental observation of cumulative second-harmonic generation of the primary circumferential guided wave propagation is reported. A pair of wedge transducers is used to generate the primary circumferential guided wave desired and to detect its fundamental-frequency and second-harmonic amplitudes on the outside surface of the circular tube. The amplitudes of the fundamental waves and the second harmonics of the circumferential guided wave propagation are measured for different separations between the two wedge transducers. At the driving frequency where the primary and the double-frequency circumferential guided waves have the same linear phase velocities, the clear second-harmonic signals can be observed. The quantitative relationships between the second-harmonic amplitudes and circumferential angle are analyzed. It is experimentally verified that the second harmonics of primary circumferential guided waves do have a cumulative growth effect with the circumferential angle.展开更多
A one-dimensional nonlinear time-dependent theory for helix traveling wave tubes is studied. A generalized electromagnetic field is applied to the expression of the radio frequency field. To simulate the variations of...A one-dimensional nonlinear time-dependent theory for helix traveling wave tubes is studied. A generalized electromagnetic field is applied to the expression of the radio frequency field. To simulate the variations of the high frequency structure, such as the pitch taper and the effect of harmonics, the spatial average over a wavelength is substituted by a time average over a wave period in the equation of the radio frequency field. Under this assumption, the space charge field of the electron beam can be treated by a space charge wave model along with the space charge coefficient. The effects of the radio frequency and the space charge fields on the electrons are presented by the equations of the electron energy and the electron phase. The time-dependent simulation is compared with the frequency-domain simulation for a helix TWT, which validates the availability of this theory.展开更多
On the basis of a rigorous field theory, two different physical models of attenuator and sever have been proposed. One is named High attenuation (HATT) model in which both attenuator and sever are considered as a un...On the basis of a rigorous field theory, two different physical models of attenuator and sever have been proposed. One is named High attenuation (HATT) model in which both attenuator and sever are considered as a unified attenuator, but the sever is regarded as an area of very high loss; the other is called Sever and attenuator (SATT) model in which the sever is modelled as a drift area in which the electric and magnetic fields both vanish. A complex function is derived and potential sinking effect is also considered. Thus, a set of more practical self-consistent equations of nonlinear beam-wave interaction is formulated. Simulations are carried out under the conditions of the two different physical models, and the simulation results are compared with the experimental data. The results show that in the case of single signal drive, the unknown second harmonic should be included for predicting the saturated output power. It is also evident that the SATT model and the HATT model predict the same physical nature, whereas the results predicted by the HATT model are much closer to the experimental data than those obtained from the SATT model. Therefore, these results provide a strong theoretical basis for designing broadband and high gain helix travelling wave tubes.展开更多
This paper presents a three-dimensional time-dependent nonlinear theory of helix traveling wave tubes for beam- wave interaction. The radio frequency electromagnetic fields are represented as the superposition of azim...This paper presents a three-dimensional time-dependent nonlinear theory of helix traveling wave tubes for beam- wave interaction. The radio frequency electromagnetic fields are represented as the superposition of azimuthally sym- metric waves in a vacuum sheath helix. Coupling impedance is introduced to the electromagnetic field equations' stimulating sources, which makes the theory easier and more flexible to realize. The space charge fields are calculated by electron beam space-charge waves expressed as the superposition solutions of Helmholtz equations. The focusing forces due to either a solenoidal field or a periodic permanent magnetic field is also included. The dynamical equations of electrons are Lorentz equations associating with electromagnetic fields, focusing fields and space-charge fields. The numerically simulated results of a tube are presented.展开更多
A helix type slow wave structure filled with plasma is immersed in a strong longitudinal magnetic field. Taking into account the effect of the plasma and the dielectric, the system is separated radially into three reg...A helix type slow wave structure filled with plasma is immersed in a strong longitudinal magnetic field. Taking into account the effect of the plasma and the dielectric, the system is separated radially into three regions. By means of the sheath model and Maxwell equation, the distribution of the electromagnetic field is established. Using the boundary conditions of each region, the dispersion relation of the slow wave structure is derived. The trend of change for the radial profile of the axial electric field is analysed respectively in different plasma densities, plasma column radius and dielectric constant by numerical computation. Some useful results are obtained on the basis of the discussion.展开更多
An open-styled dielectric-lined azimuthMly periodic circular waveguide (ODLAP-CW) for a millimeter-wave traveling-wave tube (TWT) is proposed, which is a modified form of a dielectric-lined azimuthally periodic ci...An open-styled dielectric-lined azimuthMly periodic circular waveguide (ODLAP-CW) for a millimeter-wave traveling-wave tube (TWT) is proposed, which is a modified form of a dielectric-lined azimuthally periodic circular waveguide (DLAP-CW). The slow-wave characteristics of the open-styled DLAP-CW are studied by using the spatial harmonics method, which includes normalized phase velocity and interaction impedance. The complicated dispersion equations are numerically solved with MATLAB and the results are in good agreement with the simulation results obtained from HFSS. The influence of structural parameters on the RF properties is investigated based on our theory. The numerical results show that the optimal thickness of the metal rod can increase the interaction impedance, with the dielectric constant held fixed. Finally, the slow-wave characteristics and transmission properties of an open-styled structure are compared with those of the DLAP-CW. The results validate that the mode competition is eliminated in the improved structure with only a slight influence on the dispersion characteristics, which may significantly improve the stability of an open-styled DLAP-CW-based TWT, and the interaction efficiency is also improved.展开更多
Traveling Wave Tubes(TWTs) are widely used in the radar and communications system as RF power amplifiers. A highly sophisticated power supply is required by TWT. In order to meet the severe requirements of Traveling W...Traveling Wave Tubes(TWTs) are widely used in the radar and communications system as RF power amplifiers. A highly sophisticated power supply is required by TWT. In order to meet the severe requirements of Traveling Wave Tube Amplifier(TWTA), a novel two-stage topology high voltage converter for TWTA is proposed.The converter is based on Zero-Voltage Switching and Zero-Current Switching(ZVS/ZCS) resonant techniques. The high voltage converter operation principles are investigated and major features of the converter are discussed. The power switching mode of ZVS/ZCS is obtained. The experimental results show that the converter has good soft switching characteristics. Compared to the conventional hard switched Pulse Width Modulation(PWM) techniques, the high efficiency and low ripple of the converter for TWTA are realized. The efficiency of High Voltage Electronic Power Conditioners(HV-EPC) over 93.5% under the condition of 38~46 V input voltage and 260~300 W input power. The switching frequency of first-stage(preregulator) of HV-EPC is 89 k Hz and the switching frequency of second-stage(postregulator) is 44.5 k Hz. The highest output voltage of the HV-EPC is helix voltage which is about –6.8 kV. It is especially suitable for TWTA utilized in space satellite applications due to its high switching frequency and high power density.展开更多
The folded double-ridged waveguide structure is presented and its properties used for wide-band traveling-wave tube are investigated. Expressions of dispersion characteristics, normalized phase velocity and interactio...The folded double-ridged waveguide structure is presented and its properties used for wide-band traveling-wave tube are investigated. Expressions of dispersion characteristics, normalized phase velocity and interaction impedance of this structure are derived and numerically calculated. The calculated results using our theory agree well with those obtained by using the 3D electromagnetic simulation software HFSS. Influences of the ridge-loaded area and broad-wall dimensions on the high frequency characteristics of the novel slow-wave structure are discussed. It is shown that the folded double-ridged waveguide structure has a much wider relative passband than the folded waveguide slow-wave structure and a relative passband of 67% could be obtained, indicating that this structure can operate in broad-band frequency ranges of beam-wave interaction. The small signal gain property is investigated for ensuring the improvement of bandwidth. Meanwhile, with comparable dispersion characteristics, the transverse section dimension of this novel structure is much smaller than that of conventional one, which indicates an available way to reduce the weight of traveling-wave tube.展开更多
Nolilinarity in thermoacoustics mainly comes from asee-amplitude sound waves)which is necessary for the thermoacoustic phenomena. Exact solutions are found for sound waves in a tube, Mathematical tecniques are develop...Nolilinarity in thermoacoustics mainly comes from asee-amplitude sound waves)which is necessary for the thermoacoustic phenomena. Exact solutions are found for sound waves in a tube, Mathematical tecniques are developed to solve the Riemann equations in cases unsuitable for conventional methods. The tube is characterized by its cross-sectional area and shape, which is reflected in the wave numer in the tube. Exact solutions for different tube configurations are found, includin thermacoustic stacks with temperature gradient. And composite tube containing sections of different characters is sloved, by using the continuity equations of volume velocity and pressure between sections.展开更多
An all-metal slow-wave structure, coaxial-radial line, which is suitable for application in broadband high power traveling wave tube (TWT) and relativistic TWT as a RF system is introduced. Making use of the field mat...An all-metal slow-wave structure, coaxial-radial line, which is suitable for application in broadband high power traveling wave tube (TWT) and relativistic TWT as a RF system is introduced. Making use of the field matching method and variational method together with the orthogonality of the Bessel function and the Floquet Theroem for the periodic system, the dispersion characteristic expression is derived. This equation is more rigorous than that of precious reports.展开更多
This paper presents a theory on accurately analysing the dispersion relation and the interaction impedance of electromagnetic waves propagating through a helical groove waveguide with arbitrary groove shape, in which ...This paper presents a theory on accurately analysing the dispersion relation and the interaction impedance of electromagnetic waves propagating through a helical groove waveguide with arbitrary groove shape, in which the complex groove profile is synthesized by a series of rectangular steps. By introducing the influence of high-order evanescent modes on the connection of any two neighbouring steps by an equivalent susceptance under a modified admittance matching condition, the assumption of the neglecting discontinuity capacitance in previously published analysis is avoided, and the accurate dispersion equation is obtained by means of a combination of field-matching method and admittancematching technique. The validity of this theory is proved by comparison between the measurements and the numerical calculations for two kinds of helical groove waveguides with different groove shapes.展开更多
One of the key factors for solving the problems of re-entry communication interruption is electromagnetic(EM) wave transmission characteristics in a plasma.Theoretical and experimental studies were carried out on sp...One of the key factors for solving the problems of re-entry communication interruption is electromagnetic(EM) wave transmission characteristics in a plasma.Theoretical and experimental studies were carried out on specific transmission characteristics for different plasma sheath characteristic under thin sheath condition in re-entry state.The paper presents systematic studies on the variations of wave attenuation characteristics versus plasma sheath thickness L,collision frequency ν,electron density n e and wave working frequency f in a φ 800 mm high temperature shock tube.In experiments,L is set to 4 cm and 38 cm.ν is 2 GHz and 15 GHz.n e is from 1×10 10 cm(-3) to 1×10 13 cm(-3),and f is set to 2,5,10,14.6 GHz,respectively.Meanwhile,Wentzel-Kramers-Brillouin(WKB) and finite-difference time-domain(FDTD) methods are adopted to carry out theoretical simulation for comparison with experimental results.It is found that when L is much larger than EM wavelength λ(thick sheath) and ν is large,the theoretical result is in good agreement with experimental one,when sheath thickness L is much larger than λ,while ν is relatively small,two theoretical results are obviously different from the experimental ones.It means that the existing theoretical model can not fully describe the contribution of ν.Furthermore,when L and λ are of the same order of magnitude(thin sheath),the experimental result is much smaller than the theoretical values,which indicates that the current model can not properly describe the thin sheath effect on EM attenuation characteristics.展开更多
This paper introduces the refrigeration cycle process of the gas wave oscillation tube(GWOT).Aiming at the problem that the strong reverse compression waves generated during the refrigeration process affect the perfor...This paper introduces the refrigeration cycle process of the gas wave oscillation tube(GWOT).Aiming at the problem that the strong reverse compression waves generated during the refrigeration process affect the performance,this paper proposes a variable-section GWOT that weakens the reverse compression waves and a variable-section structure designed using a numerical method.Results showed that the variable-section structure could reduce the intensity of the incident shock wave by approximately 7%and the total entropy production in the refrigeration cycle by approximately 8%under the design condition.Moreover,the variable-section structure can effectively weaken the strength of the reverse compression waves and improve the refrigeration efficiency by approximately 4%under the same working conditions.The variable-section structure can also widen the highperformance working range of the GWOT.The experimental results reveal that the high-performance working range can be expanded by more than two times under the design condition.The research can guide the subsequent development of gas wave refrigeration technology and a reference for other wave rotor application technologies.展开更多
Although the sonic soot cleaning techniques have been applied in boilers in power plants, petrochemical works and general industries world wide, most of the correlated basic problems have not been well solved yet. By ...Although the sonic soot cleaning techniques have been applied in boilers in power plants, petrochemical works and general industries world wide, most of the correlated basic problems have not been well solved yet. By using Helmholtz integral equation, sound wave scattered by heat-exchanger tubes is numerically calculated. Sound field distribution characteristics on the tube surfaces and around the tube group is obtained. The results can be applied to the development of sonic soot cleaning techniques in boilers.展开更多
The reductive perturbation method of multiple-scales is used to investigate the weak nonlinear modulation of the stress wave on the wall of a fluid-filled elastic circular tube. In the case of a single mode, the nonli...The reductive perturbation method of multiple-scales is used to investigate the weak nonlinear modulation of the stress wave on the wall of a fluid-filled elastic circular tube. In the case of a single mode, the nonlinear Schrodinger equation which the wave amplitude satisfies and its envelope soliton solution of stress wave are obtained.展开更多
This paper presents the model cavity tune and cold test of an S-band 2MeV on-axis coupling SW accelerator. The measurement of the model cavity's frequency,degree of coupling,Q value and on-axis field distribution ...This paper presents the model cavity tune and cold test of an S-band 2MeV on-axis coupling SW accelerator. The measurement of the model cavity's frequency,degree of coupling,Q value and on-axis field distribution are described in detail.In addition,the results of cavity tune and cold test of the accelerating tube are given.The frequency consistency of the accelerator is within±0.3MHz,the coupling degree in the supersaturation state 1.14,the quality factor of the accelerator 12000±200,and the field distribution ratio 1:2.2:2.All the results observed show that the accelerator satisfies the physics design with microwave debugging.展开更多
基金Supported by the National Natural Science Foundation of China (No. 61172016)
文摘A new concept of inner-feedback-style traveling wave tube oscillator, which is based on a traveling-wave tube having a partial reflector located at near the junction between the slow-wave structure and the output coupler and a mechanical tuner connected to the input coupler, is proposed. Simulations by CHIPIC code show that the inner-feedback-style traveling wave tube oscillator having 100W of power, about 10% of electron efficiency and a tunable band of 73.35-73.91 GHz may be achieved. Compared with Backward Wave Oscillators (BWOs), the new devices have similar ability for tuning, and have much higher electron efficiency, suggesting much more potential as a Terahertz source.
文摘Corresponding to the atmospheric transmission windows of the electromagnetic spectrum in the low terahertz range,the mode coupling and dispersion characteristics of two helically corrugated waveguides(HCW)in the frequency ranges of 90 GHz-100 GHz and 260 GHz-265 GHz are studied.Through analytic calculations and numerical simulations,dispersion curves and structural parameters of the two frequency ranges waveguides are obtained.A novel method was proposed to obtain the dispersion of the HCW from the eigenwave solution using a periodic boundary condition.The HCW in a frequency range of 90 GHz-100 GHz was fabricated and its dispersion performance was measured.By comparing the measured results with the theoretical and the simulated results,the validity of the analytical and simulation method is verified.Limited to our machining capability,the dispersion of the 260 GHz-265 GHz HCW was only simulated and calculated and it was found that the results agree well with each other.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11474361,11474093 and 11274388
文摘The effect of second-harmonic generation (SHG) by primary (fundamental) circumferential guided wave (CGW) propagation is investigated from a numerical standpoint. To enable that the second harmonic of the primary CGW mode can accumulate along the circumferential direction, an appropriate mode pair of primary and double frequency CGWs is chosen. Finite element simulations and evaluations of nonlinear CGW propagation are analyzed for the selected CGW mode pair. The numerical simulations performed directly demonstrate that the response of SHG is completely generated by the desired primary CGW mode that satisfies the condition of phase velocity matching at a specific driving frequency, and that the second harmonic of the primary CGW mode does have a cumulative effect with circumferential angles. The numerical perspective obtained yields an insight into the complicated physical process of SHG of primary CGW propagation unavailable previously.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11474361 and 11274388
文摘The experimental observation of cumulative second-harmonic generation of the primary circumferential guided wave propagation is reported. A pair of wedge transducers is used to generate the primary circumferential guided wave desired and to detect its fundamental-frequency and second-harmonic amplitudes on the outside surface of the circular tube. The amplitudes of the fundamental waves and the second harmonics of the circumferential guided wave propagation are measured for different separations between the two wedge transducers. At the driving frequency where the primary and the double-frequency circumferential guided waves have the same linear phase velocities, the clear second-harmonic signals can be observed. The quantitative relationships between the second-harmonic amplitudes and circumferential angle are analyzed. It is experimentally verified that the second harmonics of primary circumferential guided waves do have a cumulative growth effect with the circumferential angle.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60601004, 60801029, 10876005, and 60931001)
文摘A one-dimensional nonlinear time-dependent theory for helix traveling wave tubes is studied. A generalized electromagnetic field is applied to the expression of the radio frequency field. To simulate the variations of the high frequency structure, such as the pitch taper and the effect of harmonics, the spatial average over a wavelength is substituted by a time average over a wave period in the equation of the radio frequency field. Under this assumption, the space charge field of the electron beam can be treated by a space charge wave model along with the space charge coefficient. The effects of the radio frequency and the space charge fields on the electrons are presented by the equations of the electron energy and the electron phase. The time-dependent simulation is compared with the frequency-domain simulation for a helix TWT, which validates the availability of this theory.
基金supported by the National Natural Science Foundation of China (Grant Nos 60601007 and 60532010)the Youth Science and Technology Foundation of University of Electronic Science and Technology of China (Grant No JX05018)
文摘On the basis of a rigorous field theory, two different physical models of attenuator and sever have been proposed. One is named High attenuation (HATT) model in which both attenuator and sever are considered as a unified attenuator, but the sever is regarded as an area of very high loss; the other is called Sever and attenuator (SATT) model in which the sever is modelled as a drift area in which the electric and magnetic fields both vanish. A complex function is derived and potential sinking effect is also considered. Thus, a set of more practical self-consistent equations of nonlinear beam-wave interaction is formulated. Simulations are carried out under the conditions of the two different physical models, and the simulation results are compared with the experimental data. The results show that in the case of single signal drive, the unknown second harmonic should be included for predicting the saturated output power. It is also evident that the SATT model and the HATT model predict the same physical nature, whereas the results predicted by the HATT model are much closer to the experimental data than those obtained from the SATT model. Therefore, these results provide a strong theoretical basis for designing broadband and high gain helix travelling wave tubes.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60601004,60801029,10876005,and60931001)
文摘This paper presents a three-dimensional time-dependent nonlinear theory of helix traveling wave tubes for beam- wave interaction. The radio frequency electromagnetic fields are represented as the superposition of azimuthally sym- metric waves in a vacuum sheath helix. Coupling impedance is introduced to the electromagnetic field equations' stimulating sources, which makes the theory easier and more flexible to realize. The space charge fields are calculated by electron beam space-charge waves expressed as the superposition solutions of Helmholtz equations. The focusing forces due to either a solenoidal field or a periodic permanent magnetic field is also included. The dynamical equations of electrons are Lorentz equations associating with electromagnetic fields, focusing fields and space-charge fields. The numerically simulated results of a tube are presented.
基金Project supported by the National Natural Science Foundation of China (Grant No 10347009) and the Science Foundation of Education Bureau of Sichuan Province, China (Grant No 2003B019).
文摘A helix type slow wave structure filled with plasma is immersed in a strong longitudinal magnetic field. Taking into account the effect of the plasma and the dielectric, the system is separated radially into three regions. By means of the sheath model and Maxwell equation, the distribution of the electromagnetic field is established. Using the boundary conditions of each region, the dispersion relation of the slow wave structure is derived. The trend of change for the radial profile of the axial electric field is analysed respectively in different plasma densities, plasma column radius and dielectric constant by numerical computation. Some useful results are obtained on the basis of the discussion.
基金supported by the National Natural Science Foundation of China (Grant No. 60971038)the Fundamental Research Funds for the Central Universities, China (Grant Nos. ZYGX2009Z003 and ZYGX2010J054)
文摘An open-styled dielectric-lined azimuthMly periodic circular waveguide (ODLAP-CW) for a millimeter-wave traveling-wave tube (TWT) is proposed, which is a modified form of a dielectric-lined azimuthally periodic circular waveguide (DLAP-CW). The slow-wave characteristics of the open-styled DLAP-CW are studied by using the spatial harmonics method, which includes normalized phase velocity and interaction impedance. The complicated dispersion equations are numerically solved with MATLAB and the results are in good agreement with the simulation results obtained from HFSS. The influence of structural parameters on the RF properties is investigated based on our theory. The numerical results show that the optimal thickness of the metal rod can increase the interaction impedance, with the dielectric constant held fixed. Finally, the slow-wave characteristics and transmission properties of an open-styled structure are compared with those of the DLAP-CW. The results validate that the mode competition is eliminated in the improved structure with only a slight influence on the dispersion characteristics, which may significantly improve the stability of an open-styled DLAP-CW-based TWT, and the interaction efficiency is also improved.
文摘Traveling Wave Tubes(TWTs) are widely used in the radar and communications system as RF power amplifiers. A highly sophisticated power supply is required by TWT. In order to meet the severe requirements of Traveling Wave Tube Amplifier(TWTA), a novel two-stage topology high voltage converter for TWTA is proposed.The converter is based on Zero-Voltage Switching and Zero-Current Switching(ZVS/ZCS) resonant techniques. The high voltage converter operation principles are investigated and major features of the converter are discussed. The power switching mode of ZVS/ZCS is obtained. The experimental results show that the converter has good soft switching characteristics. Compared to the conventional hard switched Pulse Width Modulation(PWM) techniques, the high efficiency and low ripple of the converter for TWTA are realized. The efficiency of High Voltage Electronic Power Conditioners(HV-EPC) over 93.5% under the condition of 38~46 V input voltage and 260~300 W input power. The switching frequency of first-stage(preregulator) of HV-EPC is 89 k Hz and the switching frequency of second-stage(postregulator) is 44.5 k Hz. The highest output voltage of the HV-EPC is helix voltage which is about –6.8 kV. It is especially suitable for TWTA utilized in space satellite applications due to its high switching frequency and high power density.
基金Project supported in part by the National Natural Science Foundation of China (Grant No. 60971038)in part by the Fundamental Research Funds for Central Universities,China (Grant No. ZYGX2009Z003)
文摘The folded double-ridged waveguide structure is presented and its properties used for wide-band traveling-wave tube are investigated. Expressions of dispersion characteristics, normalized phase velocity and interaction impedance of this structure are derived and numerically calculated. The calculated results using our theory agree well with those obtained by using the 3D electromagnetic simulation software HFSS. Influences of the ridge-loaded area and broad-wall dimensions on the high frequency characteristics of the novel slow-wave structure are discussed. It is shown that the folded double-ridged waveguide structure has a much wider relative passband than the folded waveguide slow-wave structure and a relative passband of 67% could be obtained, indicating that this structure can operate in broad-band frequency ranges of beam-wave interaction. The small signal gain property is investigated for ensuring the improvement of bandwidth. Meanwhile, with comparable dispersion characteristics, the transverse section dimension of this novel structure is much smaller than that of conventional one, which indicates an available way to reduce the weight of traveling-wave tube.
文摘Nolilinarity in thermoacoustics mainly comes from asee-amplitude sound waves)which is necessary for the thermoacoustic phenomena. Exact solutions are found for sound waves in a tube, Mathematical tecniques are developed to solve the Riemann equations in cases unsuitable for conventional methods. The tube is characterized by its cross-sectional area and shape, which is reflected in the wave numer in the tube. Exact solutions for different tube configurations are found, includin thermacoustic stacks with temperature gradient. And composite tube containing sections of different characters is sloved, by using the continuity equations of volume velocity and pressure between sections.
基金Supported by the Fund of National Key Laboratory (No.51440020101DZ7604)
文摘An all-metal slow-wave structure, coaxial-radial line, which is suitable for application in broadband high power traveling wave tube (TWT) and relativistic TWT as a RF system is introduced. Making use of the field matching method and variational method together with the orthogonality of the Bessel function and the Floquet Theroem for the periodic system, the dispersion characteristic expression is derived. This equation is more rigorous than that of precious reports.
基金Project supported in part by the National Natural Science Foundation of China (Grant Nos 60401005 and 60532010) and the Fok Ying Tung Education Foundation(Grant No 91063).
文摘This paper presents a theory on accurately analysing the dispersion relation and the interaction impedance of electromagnetic waves propagating through a helical groove waveguide with arbitrary groove shape, in which the complex groove profile is synthesized by a series of rectangular steps. By introducing the influence of high-order evanescent modes on the connection of any two neighbouring steps by an equivalent susceptance under a modified admittance matching condition, the assumption of the neglecting discontinuity capacitance in previously published analysis is avoided, and the accurate dispersion equation is obtained by means of a combination of field-matching method and admittancematching technique. The validity of this theory is proved by comparison between the measurements and the numerical calculations for two kinds of helical groove waveguides with different groove shapes.
文摘One of the key factors for solving the problems of re-entry communication interruption is electromagnetic(EM) wave transmission characteristics in a plasma.Theoretical and experimental studies were carried out on specific transmission characteristics for different plasma sheath characteristic under thin sheath condition in re-entry state.The paper presents systematic studies on the variations of wave attenuation characteristics versus plasma sheath thickness L,collision frequency ν,electron density n e and wave working frequency f in a φ 800 mm high temperature shock tube.In experiments,L is set to 4 cm and 38 cm.ν is 2 GHz and 15 GHz.n e is from 1×10 10 cm(-3) to 1×10 13 cm(-3),and f is set to 2,5,10,14.6 GHz,respectively.Meanwhile,Wentzel-Kramers-Brillouin(WKB) and finite-difference time-domain(FDTD) methods are adopted to carry out theoretical simulation for comparison with experimental results.It is found that when L is much larger than EM wavelength λ(thick sheath) and ν is large,the theoretical result is in good agreement with experimental one,when sheath thickness L is much larger than λ,while ν is relatively small,two theoretical results are obviously different from the experimental ones.It means that the existing theoretical model can not fully describe the contribution of ν.Furthermore,when L and λ are of the same order of magnitude(thin sheath),the experimental result is much smaller than the theoretical values,which indicates that the current model can not properly describe the thin sheath effect on EM attenuation characteristics.
基金supported by the National Key Research and Development Program of China (Grant No.2018YFA0704601)the National Natural Science Foundation of China (Grant No.22078040)the Fundamental Research Funds for the Central Universities (Grant No.DUT22LAB604)。
文摘This paper introduces the refrigeration cycle process of the gas wave oscillation tube(GWOT).Aiming at the problem that the strong reverse compression waves generated during the refrigeration process affect the performance,this paper proposes a variable-section GWOT that weakens the reverse compression waves and a variable-section structure designed using a numerical method.Results showed that the variable-section structure could reduce the intensity of the incident shock wave by approximately 7%and the total entropy production in the refrigeration cycle by approximately 8%under the design condition.Moreover,the variable-section structure can effectively weaken the strength of the reverse compression waves and improve the refrigeration efficiency by approximately 4%under the same working conditions.The variable-section structure can also widen the highperformance working range of the GWOT.The experimental results reveal that the high-performance working range can be expanded by more than two times under the design condition.The research can guide the subsequent development of gas wave refrigeration technology and a reference for other wave rotor application technologies.
文摘Although the sonic soot cleaning techniques have been applied in boilers in power plants, petrochemical works and general industries world wide, most of the correlated basic problems have not been well solved yet. By using Helmholtz integral equation, sound wave scattered by heat-exchanger tubes is numerically calculated. Sound field distribution characteristics on the tube surfaces and around the tube group is obtained. The results can be applied to the development of sonic soot cleaning techniques in boilers.
基金The Project Supported by National Science Foundation of China
文摘The reductive perturbation method of multiple-scales is used to investigate the weak nonlinear modulation of the stress wave on the wall of a fluid-filled elastic circular tube. In the case of a single mode, the nonlinear Schrodinger equation which the wave amplitude satisfies and its envelope soliton solution of stress wave are obtained.
文摘This paper presents the model cavity tune and cold test of an S-band 2MeV on-axis coupling SW accelerator. The measurement of the model cavity's frequency,degree of coupling,Q value and on-axis field distribution are described in detail.In addition,the results of cavity tune and cold test of the accelerating tube are given.The frequency consistency of the accelerator is within±0.3MHz,the coupling degree in the supersaturation state 1.14,the quality factor of the accelerator 12000±200,and the field distribution ratio 1:2.2:2.All the results observed show that the accelerator satisfies the physics design with microwave debugging.