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RSS2013 Vol. 25, No. 02
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2013,
25: 269-275.
doi: 10.3788/HPLPB20132502.0269
Abstract:
The repetitive explosive emission cathode (EEC) is the key component of high power diode for generating repetitive electron beams. The emission mechanisms of the cathodes triggered by whiskers and flashover are introduced in detail. Factors that limit the repetition rate are analyzed. Development and characteristics of some EECs are summarized. LaB6 is proposed as EEC material and a novel configuration of cold cathodes (metal-spoked ceramic compound cathode) is designed.
The repetitive explosive emission cathode (EEC) is the key component of high power diode for generating repetitive electron beams. The emission mechanisms of the cathodes triggered by whiskers and flashover are introduced in detail. Factors that limit the repetition rate are analyzed. Development and characteristics of some EECs are summarized. LaB6 is proposed as EEC material and a novel configuration of cold cathodes (metal-spoked ceramic compound cathode) is designed.
2013,
25: 276-280.
doi: 10.3788/HPLPB20132502.0276
Abstract:
A method for measuring laser intensity distribution based on fiber array is presented. The principle and structural design of the fiber array are introduced. The attenuation characteristic is analyzed theoretically. A demonstration module is built in our lab. And experiments are carried out with a high power fiber laser operating at 1064 nm. The experimental results show that this system can provide laser power density distribution information with a spatial resolution better than 3 mm and with a measurement error less than 3%. Experiments with fiber laser radiation and numerical simulation by the finite element method indicate that the damage threshold of the fiber array is higher than 10 kW/cm2 with a radiation time of 50 s. Therefore, it might be appropriate for the method to measure the high energy laser beam directly.
A method for measuring laser intensity distribution based on fiber array is presented. The principle and structural design of the fiber array are introduced. The attenuation characteristic is analyzed theoretically. A demonstration module is built in our lab. And experiments are carried out with a high power fiber laser operating at 1064 nm. The experimental results show that this system can provide laser power density distribution information with a spatial resolution better than 3 mm and with a measurement error less than 3%. Experiments with fiber laser radiation and numerical simulation by the finite element method indicate that the damage threshold of the fiber array is higher than 10 kW/cm2 with a radiation time of 50 s. Therefore, it might be appropriate for the method to measure the high energy laser beam directly.
2013,
25: 281-286.
doi: 10.3788/HPLPB20132502.0281
Abstract:
The influences on the isolation of the optical isolators in pulsed laser situation are theoretically analyzed, including magneto-optical crystals photoelastic effect caused by temperature gradient on cross section, extinction ratio and Kerr effect, and compared with those in continuous laser situation. The result shows that, in the situation of the same average power, pulsed laser has a lower isolation than continuous laser. When the average power is low, extinction ratio has a larger effect on isolation;when the average power is high, the effect of extinction ratio is limited, and the photoelastic effect is the main effect on isolation. When the peak power density is high, Kerr effect reduces the isolation a lot. And Kerr effect could reduce the isolation more with increasing the peak power density.
The influences on the isolation of the optical isolators in pulsed laser situation are theoretically analyzed, including magneto-optical crystals photoelastic effect caused by temperature gradient on cross section, extinction ratio and Kerr effect, and compared with those in continuous laser situation. The result shows that, in the situation of the same average power, pulsed laser has a lower isolation than continuous laser. When the average power is low, extinction ratio has a larger effect on isolation;when the average power is high, the effect of extinction ratio is limited, and the photoelastic effect is the main effect on isolation. When the peak power density is high, Kerr effect reduces the isolation a lot. And Kerr effect could reduce the isolation more with increasing the peak power density.
2013,
25: 287-291.
doi: 10.3788/HPLPB20132502.0287
Abstract:
In order to measure super-high reflectivity of any sphere optical element at different angles, such as 0, 10, 15, 30 and so on, two optical resonator structures are put forward: one is straight-cavity, and the other is folded-cavity. Physical length of the ring-down cavity is defined based on the concept of light path. These two kinds of measurement methods are analyzed in detail. When spherical surface is put in the ring-down cavity, it brings length misalignment of the ring-down cavity. This varied length is derived based on the beam transmission and transformation law, which can be used as length adjustment guidance of the ring-down cavity for reflectivity measurement. In addition, according to reflectivity measuring principle of cavity ring-down, mathematical expressions of reflectivity measuring for spherical components are deduced at different angles, which are discussed separately. The results expand the super-high reflectivity measurement scope of optical elements for the cavity ring-down method.
In order to measure super-high reflectivity of any sphere optical element at different angles, such as 0, 10, 15, 30 and so on, two optical resonator structures are put forward: one is straight-cavity, and the other is folded-cavity. Physical length of the ring-down cavity is defined based on the concept of light path. These two kinds of measurement methods are analyzed in detail. When spherical surface is put in the ring-down cavity, it brings length misalignment of the ring-down cavity. This varied length is derived based on the beam transmission and transformation law, which can be used as length adjustment guidance of the ring-down cavity for reflectivity measurement. In addition, according to reflectivity measuring principle of cavity ring-down, mathematical expressions of reflectivity measuring for spherical components are deduced at different angles, which are discussed separately. The results expand the super-high reflectivity measurement scope of optical elements for the cavity ring-down method.
2013,
25: 292-296.
doi: 10.3788/HPLPB20132502.0292
Abstract:
In order to determine the imaging quality degradation caused by the laser propagation through atmospheric turbulence in the Fourier telescopy system, the effects of turbulence on beam propagation characteristics are analyzed. We pointed out that the degradation in the quality of imaging is mainly from the beam wander and beam spreading induced by atmospheric turbulence that arises the pointing error. The mechanism of the pointing error affecting imaging process is analyzed. The pointing errors caused by turbulence of the entire uplink are calculated and imaging results are simulated under different atmospheric conditions. It is concluded that in weak and moderate turbulence (the refractive index structure constant of atmospheric turbulence is less than 10-14 m-2/3), the random pointing error is small (the random pointing offset proportion is less than 0.06) while the reconstructed image has good recognizability. However, in strong turbulence, imaging quality suffers severe decline. Thus the Fourier telescopy should be selected to avoid the strong turbulence location and time.
In order to determine the imaging quality degradation caused by the laser propagation through atmospheric turbulence in the Fourier telescopy system, the effects of turbulence on beam propagation characteristics are analyzed. We pointed out that the degradation in the quality of imaging is mainly from the beam wander and beam spreading induced by atmospheric turbulence that arises the pointing error. The mechanism of the pointing error affecting imaging process is analyzed. The pointing errors caused by turbulence of the entire uplink are calculated and imaging results are simulated under different atmospheric conditions. It is concluded that in weak and moderate turbulence (the refractive index structure constant of atmospheric turbulence is less than 10-14 m-2/3), the random pointing error is small (the random pointing offset proportion is less than 0.06) while the reconstructed image has good recognizability. However, in strong turbulence, imaging quality suffers severe decline. Thus the Fourier telescopy should be selected to avoid the strong turbulence location and time.
2013,
25: 297-300.
doi: 10.3788/HPLPB20132502.0297
Abstract:
Based on the discussion of the law of the interaction between optic field and fluid field, we adopted the physical model for high energy laser beams crossing through three-dimensional high speed flow. A two-dimensional Hartmann wavefront sensor was used to measure the aero-optic effects when the high energy laser beam passed through a high speed airflow in the wind tunnel. The density and temperature maps of fluid field and far-field optical path difference map of laser beams were obtained. The disturbance of the fluid field caused by radiation heating and the changing of laser beam optics aberrations after the beam passing through the fluid field were discussed. The results show that the interaction between lasers and the high speed airflow has little influence on the temperature and density of the airflow when the air is not ionized.
Based on the discussion of the law of the interaction between optic field and fluid field, we adopted the physical model for high energy laser beams crossing through three-dimensional high speed flow. A two-dimensional Hartmann wavefront sensor was used to measure the aero-optic effects when the high energy laser beam passed through a high speed airflow in the wind tunnel. The density and temperature maps of fluid field and far-field optical path difference map of laser beams were obtained. The disturbance of the fluid field caused by radiation heating and the changing of laser beam optics aberrations after the beam passing through the fluid field were discussed. The results show that the interaction between lasers and the high speed airflow has little influence on the temperature and density of the airflow when the air is not ionized.
2013,
25: 301-304.
doi: 10.3788/HPLPB20132502.0301
Abstract:
Considering the natural frequency weakening of a high power lasers optical precision mount matching with large aperture, the paper states an optical precision mount with large aperture, with its mechanical model built and its dynamic abilities analyzed. By contrasting theoretical analysis and test data of the optical precision mount with a 420 mm mirror, the reasons for natural frequency weakening have been seeked. The optimized structure of the optical precision mount with large aperture has a first-mode elastomer pitching swing frequency of 157.788 Hz, which could meet the working condition under the intense vibration.
Considering the natural frequency weakening of a high power lasers optical precision mount matching with large aperture, the paper states an optical precision mount with large aperture, with its mechanical model built and its dynamic abilities analyzed. By contrasting theoretical analysis and test data of the optical precision mount with a 420 mm mirror, the reasons for natural frequency weakening have been seeked. The optimized structure of the optical precision mount with large aperture has a first-mode elastomer pitching swing frequency of 157.788 Hz, which could meet the working condition under the intense vibration.
2013,
25: 305-309.
doi: 10.3788/HPLPB20132502.0305
Abstract:
The movement process of bubbles produced by synchronous double-pulse lasers focusing into water and then breaking it down has been recorded by high-speed cameras. The characteristics of four typical laser-induced acoustic signals were analyzed, and opto-acoustic energy transferring efficiency was calculated. Experimental results show that intervals between peak values of laser-induced acoustic signals could be controlled through adjusting the energy difference of pulsed lasers, and that pulse width of laser-induced acoustic signals could be increased. When none dimensional distance between laser-induced bubbles is 1.5, the bubbles begin to fuse in the collapse process, through which the thermodynamic energy of bubbles converts into mechanical energy. The single bubble finally formed has more energy than any single bubble before fusing. The main frequency of laser-induced acoustic signals produced by collapsing of bubbles decreases. The opto-acoustic energy transferring efficiency is 6%-10%.
The movement process of bubbles produced by synchronous double-pulse lasers focusing into water and then breaking it down has been recorded by high-speed cameras. The characteristics of four typical laser-induced acoustic signals were analyzed, and opto-acoustic energy transferring efficiency was calculated. Experimental results show that intervals between peak values of laser-induced acoustic signals could be controlled through adjusting the energy difference of pulsed lasers, and that pulse width of laser-induced acoustic signals could be increased. When none dimensional distance between laser-induced bubbles is 1.5, the bubbles begin to fuse in the collapse process, through which the thermodynamic energy of bubbles converts into mechanical energy. The single bubble finally formed has more energy than any single bubble before fusing. The main frequency of laser-induced acoustic signals produced by collapsing of bubbles decreases. The opto-acoustic energy transferring efficiency is 6%-10%.
2013,
25: 310-314.
doi: 10.3788/HPLPB20132502.0310
Abstract:
For high power linewidth-narrowed diode lasers, it's important to study rotation angle tolerance of the volume Bragg grating (VBG) for narrowing the spectral linewidth of two dimensional diode laser stacks. The diode laser with the VBG's external cavity and C-mounted modules is collimated by 200 m and 600 m cylindrical lens separately in the paper. The VBG's angle tolerance is acquired by two stepper motors. According to the research, more accuracy is needed for the VBG's adjustment with higher driving current and better beam collimation. If the laser diode is collimated better in fast axis direction, rotation angle tolerance in slow axis direction will be bigger. When a VBG with a diffraction efficiency of 28% and thickness of 1.4 mm is used to lock the wavelength of a laser diode with a fast axis divergence angle of 7.3 mrad, the grating's rotation angle tolerance is no more than 3.2 mrad in the fast axis direction and that for the slow axis direction is one order of magnitude bigger.
For high power linewidth-narrowed diode lasers, it's important to study rotation angle tolerance of the volume Bragg grating (VBG) for narrowing the spectral linewidth of two dimensional diode laser stacks. The diode laser with the VBG's external cavity and C-mounted modules is collimated by 200 m and 600 m cylindrical lens separately in the paper. The VBG's angle tolerance is acquired by two stepper motors. According to the research, more accuracy is needed for the VBG's adjustment with higher driving current and better beam collimation. If the laser diode is collimated better in fast axis direction, rotation angle tolerance in slow axis direction will be bigger. When a VBG with a diffraction efficiency of 28% and thickness of 1.4 mm is used to lock the wavelength of a laser diode with a fast axis divergence angle of 7.3 mrad, the grating's rotation angle tolerance is no more than 3.2 mrad in the fast axis direction and that for the slow axis direction is one order of magnitude bigger.
2013,
25: 315-318.
doi: 10.3788/HPLPB20132502.0315
Abstract:
In this paper, the GS algorithm used for phase retrieval is elaborated, and the application scope of this algorithm is expanded, no longer confined to the known pupil surface and the focal plane intensity. In the simulation, two vertical axial section of the beam are chosen, where the optical power is detected to retrieve several kinds of common phase aberration based on GS algorithm. An improved GS algorithm is brought forward, which adds two weight coefficients in the circulation. The range of the two weight coefficients is given, too. Results of the simulation show that both the speed and precision of GS algorithm are improved.
In this paper, the GS algorithm used for phase retrieval is elaborated, and the application scope of this algorithm is expanded, no longer confined to the known pupil surface and the focal plane intensity. In the simulation, two vertical axial section of the beam are chosen, where the optical power is detected to retrieve several kinds of common phase aberration based on GS algorithm. An improved GS algorithm is brought forward, which adds two weight coefficients in the circulation. The range of the two weight coefficients is given, too. Results of the simulation show that both the speed and precision of GS algorithm are improved.
2013,
25: 319-324.
doi: 10.3788/HPLPB20132502.0319
Abstract:
In order to control lasing transverse mode, improve laser mode stability, and enhance laser processing quality, the transverse modes of a high power transverse-flow CO2 laser are measured experimentally, and the mechanism of formation of laser transverse modes is analyzed theoretically. The lasing transverse energy distribution of a high power tube-plate transverse-flow CO2 laser is simulated numerically by solving the space-time resolving rate equations derived from the discharging field determined by Maxwells equations. The result shows that the simulated lasing distribution agrees with the experimental observation. Moreover, there is evidence to show that the electrode configuration in the CO2 laser resonator determines the peak value of lasing transverse modes, while the gas flowing rate determines the lasing gain peak and the peak position along the gas flowing direction.
In order to control lasing transverse mode, improve laser mode stability, and enhance laser processing quality, the transverse modes of a high power transverse-flow CO2 laser are measured experimentally, and the mechanism of formation of laser transverse modes is analyzed theoretically. The lasing transverse energy distribution of a high power tube-plate transverse-flow CO2 laser is simulated numerically by solving the space-time resolving rate equations derived from the discharging field determined by Maxwells equations. The result shows that the simulated lasing distribution agrees with the experimental observation. Moreover, there is evidence to show that the electrode configuration in the CO2 laser resonator determines the peak value of lasing transverse modes, while the gas flowing rate determines the lasing gain peak and the peak position along the gas flowing direction.
2013,
25: 325-329.
doi: 10.3788/HPLPB20132502.0325
Abstract:
In the progress of large aspheric mirror manufacturing, computer controlled active lap(CCAL) has been proved to be a useful tool with high precision and efficiency. Before polishing, the deformation measurement of the lap is necessary. The measurement system has 60 high precision displacement sensors. Error analysis and essential data processing of the measurement system are putting forward. The main error contains ball-probe error as the system error, angle error of fitting sensors and error of coordinate offset as the stochastic error. In the mathematic model established based on the characteristic of paraboloid and coordinate transform, the influence of the three kinds of errors is calculated. After some interrelated compensation and data processing, the result gotten shows that the measurement precision improves.
In the progress of large aspheric mirror manufacturing, computer controlled active lap(CCAL) has been proved to be a useful tool with high precision and efficiency. Before polishing, the deformation measurement of the lap is necessary. The measurement system has 60 high precision displacement sensors. Error analysis and essential data processing of the measurement system are putting forward. The main error contains ball-probe error as the system error, angle error of fitting sensors and error of coordinate offset as the stochastic error. In the mathematic model established based on the characteristic of paraboloid and coordinate transform, the influence of the three kinds of errors is calculated. After some interrelated compensation and data processing, the result gotten shows that the measurement precision improves.
2013,
25: 330-334.
doi: 10.3788/HPLPB20132502.0330
Abstract:
High-order harmonics and phase shift miscalibration are the two main systematic error sources that affect the accuracy of fringe analysis. To deal with these problems simultaneously, an iterative phase-shifting algorithm based on frequency filtering is proposed. The proposed method filters the high-order harmonics in spectrum domain by using the Butterworth low-pass filter, and then extracts the phase from three frames of randomly phase-shifting fringes by using the least-squares iterative algorithm. Numerical simulation and experimental results show that the proposed method can effectively reduce the ripple caused by high-order harmonics and randomly phase-shifting error and thus can increase the measurement accuracy. The proposed algorithm is suitable for the high-accuracy interferometry and three-dimensional profilometry measurement.
High-order harmonics and phase shift miscalibration are the two main systematic error sources that affect the accuracy of fringe analysis. To deal with these problems simultaneously, an iterative phase-shifting algorithm based on frequency filtering is proposed. The proposed method filters the high-order harmonics in spectrum domain by using the Butterworth low-pass filter, and then extracts the phase from three frames of randomly phase-shifting fringes by using the least-squares iterative algorithm. Numerical simulation and experimental results show that the proposed method can effectively reduce the ripple caused by high-order harmonics and randomly phase-shifting error and thus can increase the measurement accuracy. The proposed algorithm is suitable for the high-accuracy interferometry and three-dimensional profilometry measurement.
2013,
25: 335-340.
doi: 10.3788/HPLPB20132502.0335
Abstract:
Using deionized-water as working fluid, the large hight-to-width rate micro-fin cooling systems are proposed. The heat transfer characteristics of these micro-fin cooling systems are experimentally studied. It is found that the heat dissipation could reach 2.83106 W/m2 at the flow of 57.225 L/h and the surface temperature of 73.4 ℃, and the heat sink can meet the demand of high power heat dissipation requirements. When the bottom temperature is fixed, the heat dissipation increases with the rise of flow and finally trends to a constant. The Nusselt number increases with the increase of Reynolds number. The heat transfer performance of the present sink is over predicted by the previous correlations. Therefore, new correlation is proposed to evaluate heat transfer performance of micro-fins with consideration of the Nusselt number as a function of the Reyonolds number and Prandtl number. Key words: micro-fin;heat transfer;heat radiator;high heat flux
Using deionized-water as working fluid, the large hight-to-width rate micro-fin cooling systems are proposed. The heat transfer characteristics of these micro-fin cooling systems are experimentally studied. It is found that the heat dissipation could reach 2.83106 W/m2 at the flow of 57.225 L/h and the surface temperature of 73.4 ℃, and the heat sink can meet the demand of high power heat dissipation requirements. When the bottom temperature is fixed, the heat dissipation increases with the rise of flow and finally trends to a constant. The Nusselt number increases with the increase of Reynolds number. The heat transfer performance of the present sink is over predicted by the previous correlations. Therefore, new correlation is proposed to evaluate heat transfer performance of micro-fins with consideration of the Nusselt number as a function of the Reyonolds number and Prandtl number. Key words: micro-fin;heat transfer;heat radiator;high heat flux
2013,
25: 341-344.
doi: 10.3788/HPLPB20132502.0341
Abstract:
A novel zoom design athermalization (ZDA) method was proposed to realize athermalization for airborne CCD camera rapidly and efficiently. The relational model between athermal design and zoom design was built based on optical passive compensation. First a optical system with good performance was designed to satisfy image quality at normal temperature;and then, multiple zooming positions were established to match different temperature statuses, lastly, by means of optimum design, the proper material combination was achieved rapidly and automatically to satisfy the optical system. A athermal design example for complex airborne CCD camera was designed with 650 mm focal length, F/5.6, 5.5 field-of-view in the 0.45-0.70 m waveband by utilizing the ZDA method. The results show that the image quality has a reliable performance with -40-60 ℃ temperature range, and the modulation tranfer function decreases only by 5%. compared with to the previous approaches, the ZDA method has the advantages of convenience, effectiveness, simplification, and no need for external electro-mechanical adjustment. These advantages will allow it to be widely applied in many applications, such as airborne optical system, space optical system.
A novel zoom design athermalization (ZDA) method was proposed to realize athermalization for airborne CCD camera rapidly and efficiently. The relational model between athermal design and zoom design was built based on optical passive compensation. First a optical system with good performance was designed to satisfy image quality at normal temperature;and then, multiple zooming positions were established to match different temperature statuses, lastly, by means of optimum design, the proper material combination was achieved rapidly and automatically to satisfy the optical system. A athermal design example for complex airborne CCD camera was designed with 650 mm focal length, F/5.6, 5.5 field-of-view in the 0.45-0.70 m waveband by utilizing the ZDA method. The results show that the image quality has a reliable performance with -40-60 ℃ temperature range, and the modulation tranfer function decreases only by 5%. compared with to the previous approaches, the ZDA method has the advantages of convenience, effectiveness, simplification, and no need for external electro-mechanical adjustment. These advantages will allow it to be widely applied in many applications, such as airborne optical system, space optical system.
2013,
25: 345-349.
doi: 10.3788/HPLPB20132502.0345
Abstract:
In order to improve the resolution of digital holographic imaging system, the recording and reconstruction processes of a pre-magnification digital holographic system with a spherical reference wave are theoretically deduced. Then the point spread function is obtained and the factors to determine the imaging resolution of this system are analyzed. In the case of the CCD imaging resolution higher than that of the microscope objective, the relationship between the resolution and the recording distance of the system is discussed through the experiment of resolution target USAF. The result show that the resolution of reconstructed images is not sensitive to the recording distance. But as the recording distance is zero, which is named digital image-plane holography, the resolution of reconstructed images is highest. The experimental results are consistent with the theoretical analysis.
In order to improve the resolution of digital holographic imaging system, the recording and reconstruction processes of a pre-magnification digital holographic system with a spherical reference wave are theoretically deduced. Then the point spread function is obtained and the factors to determine the imaging resolution of this system are analyzed. In the case of the CCD imaging resolution higher than that of the microscope objective, the relationship between the resolution and the recording distance of the system is discussed through the experiment of resolution target USAF. The result show that the resolution of reconstructed images is not sensitive to the recording distance. But as the recording distance is zero, which is named digital image-plane holography, the resolution of reconstructed images is highest. The experimental results are consistent with the theoretical analysis.
2013,
25: 350-354.
doi: 10.3788/HPLPB20132502.0350
Abstract:
The two-photon absorption of water soluble CdTe quantum dots and Mn2+-doped CdTe quantum dots in four different sizes has been studied, by using the open Z-scan technique, with a Ti: sapphire laser at 800 nm wavelength, 50 fs pulsewidth, 1 kHz repetition frequency. The results show that, the two-photon absorption coefficient of CdTe: Mn quantum dots is 1.1 times that of CdTe quantum dots for the same growth time, and the relationship between the two-photon absorption coefficient of quantum dots and the particle size is inverse proportion, because the nonlinear absorption of CdTe: Mn quantum dots belongs to the saturated absorption. It is shown that Mn2+-doped quantum dots exhibit good two-photon absorption phenomenon, and have broad application prospects in optical switches and optical limiting devices.
The two-photon absorption of water soluble CdTe quantum dots and Mn2+-doped CdTe quantum dots in four different sizes has been studied, by using the open Z-scan technique, with a Ti: sapphire laser at 800 nm wavelength, 50 fs pulsewidth, 1 kHz repetition frequency. The results show that, the two-photon absorption coefficient of CdTe: Mn quantum dots is 1.1 times that of CdTe quantum dots for the same growth time, and the relationship between the two-photon absorption coefficient of quantum dots and the particle size is inverse proportion, because the nonlinear absorption of CdTe: Mn quantum dots belongs to the saturated absorption. It is shown that Mn2+-doped quantum dots exhibit good two-photon absorption phenomenon, and have broad application prospects in optical switches and optical limiting devices.
2013,
25: 355-357.
doi: 10.3788/HPLPB20132502.0355
Abstract:
The existing tuning methods of fiber lasers are researched, and they usually cannot take into account the requirements of the tuning range and tuning rate. To solve this problem, a new tuning method based on the photo-thermal effect is proposed, the experimental phenomenon shows that the output wavelength of fiber lasers varies with the pumps power. The static and dynamic tuning characteristics of fiber lasers reveal that the tuning range is about 392 MHz/100 mA and the tuning rate is more than 2 kHz in 980 nm pump source self-tuning. The feasibility of this tuning method has been verified.
The existing tuning methods of fiber lasers are researched, and they usually cannot take into account the requirements of the tuning range and tuning rate. To solve this problem, a new tuning method based on the photo-thermal effect is proposed, the experimental phenomenon shows that the output wavelength of fiber lasers varies with the pumps power. The static and dynamic tuning characteristics of fiber lasers reveal that the tuning range is about 392 MHz/100 mA and the tuning rate is more than 2 kHz in 980 nm pump source self-tuning. The feasibility of this tuning method has been verified.
2013,
25: 358-362.
doi: 10.3788/HPLPB20132502.0358
Abstract:
This paper introduces the beam characteristics of the MOPA slab laser system, including near-field intensity distribution, spatial character and temporal frequency of wavefront distortion. The deformable mirror with large dynamic range and high spatial resolution was developed. The adaptive optics closed-loop correction system was designed to complete the closed-loop control of the whole propagation process of high power beams. The value of of beam quality has been improved from 7.4 to 4.06. According to the residual error of the closed-loop wavefront correction, the beam quality of the MOPA might be further improved.
This paper introduces the beam characteristics of the MOPA slab laser system, including near-field intensity distribution, spatial character and temporal frequency of wavefront distortion. The deformable mirror with large dynamic range and high spatial resolution was developed. The adaptive optics closed-loop correction system was designed to complete the closed-loop control of the whole propagation process of high power beams. The value of of beam quality has been improved from 7.4 to 4.06. According to the residual error of the closed-loop wavefront correction, the beam quality of the MOPA might be further improved.
2013,
25: 363-366.
doi: 10.3788/HPLPB20132502.0363
Abstract:
By selecting appropriate optical materials and placing them in reasonable arrangements, an optical engine for the laser-LCOS projector has been designed, with its light sources comprising three LCOS panels and three primary-color lasers. The software ZEMAX is used in the design simulation. Furthermore, it is demonstrated that the optical specimen of laser-LCOS display has high efficiency and uniformity, which meets the design requirement of laser-LCOS display.
By selecting appropriate optical materials and placing them in reasonable arrangements, an optical engine for the laser-LCOS projector has been designed, with its light sources comprising three LCOS panels and three primary-color lasers. The software ZEMAX is used in the design simulation. Furthermore, it is demonstrated that the optical specimen of laser-LCOS display has high efficiency and uniformity, which meets the design requirement of laser-LCOS display.
2013,
25: 367-370.
doi: 10.3788/HPLPB20132502.0367
Abstract:
In order to better evaluate the beam combination and the character of combined beams, all the existing evaluating standards for beam quality are analyzed, and their disadvantages are also discussed. A new conception named generalized beam quality (GBQ) is advanced to measure the beam quality of combined beams. Compared with other beam quality parameters, GBQ has many advantages on physical concept, feasibility and measurement in the project.
In order to better evaluate the beam combination and the character of combined beams, all the existing evaluating standards for beam quality are analyzed, and their disadvantages are also discussed. A new conception named generalized beam quality (GBQ) is advanced to measure the beam quality of combined beams. Compared with other beam quality parameters, GBQ has many advantages on physical concept, feasibility and measurement in the project.
2013,
25: 371-374.
doi: 10.3788/HPLPB20132502.0371
Abstract:
The object and the image of the KBA X-ray microscope are not in the same horizontal plane. To overcome the difficulty of installing the KBA X-ray microscope in the target chamber，a double-aiming mode is adopted. Unlike general optical systems, the angle of the KBA X-ray microscope between the pseudo-axis and the real axis is 8.748 6，thus an observing system is designed to satisfy the demand of the grazing incident angle. As the object angle is small, the focus depth is too big if the visual light is used to install the microscope, so an auxiliary optical system is designed, and the focus depth is within 5 mm.
The object and the image of the KBA X-ray microscope are not in the same horizontal plane. To overcome the difficulty of installing the KBA X-ray microscope in the target chamber，a double-aiming mode is adopted. Unlike general optical systems, the angle of the KBA X-ray microscope between the pseudo-axis and the real axis is 8.748 6，thus an observing system is designed to satisfy the demand of the grazing incident angle. As the object angle is small, the focus depth is too big if the visual light is used to install the microscope, so an auxiliary optical system is designed, and the focus depth is within 5 mm.
2013,
25: 375-380.
doi: 10.3788/HPLPB20132502.0375
Abstract:
The passive diagnostic for radiation driven shock velocity is of critical importance in the research of radiation driven fusion and extreme high-pressure equation of state. Such diagnostic has been set up on SG-Ⅱ and the laser prototype facility. The control technique of signal-to-noise of shock breakout images has been developed based on the theoretical analysis and experimental study which shows that the stray light such as stimulated scattering light is 4 order stronger than the shock light. The precise temporal-resolved technique has also been developed based on the successful application of the faster sweep rate of the streak camera with aids of high-quality light triggering instead of traditional electronic triggering. The developed passive diagnostic has been validated successfully by an experiment whose results show the shock image is clear and the deduced shock velocity is consistent with the calculated one.
The passive diagnostic for radiation driven shock velocity is of critical importance in the research of radiation driven fusion and extreme high-pressure equation of state. Such diagnostic has been set up on SG-Ⅱ and the laser prototype facility. The control technique of signal-to-noise of shock breakout images has been developed based on the theoretical analysis and experimental study which shows that the stray light such as stimulated scattering light is 4 order stronger than the shock light. The precise temporal-resolved technique has also been developed based on the successful application of the faster sweep rate of the streak camera with aids of high-quality light triggering instead of traditional electronic triggering. The developed passive diagnostic has been validated successfully by an experiment whose results show the shock image is clear and the deduced shock velocity is consistent with the calculated one.
2013,
25: 381-384.
doi: 10.3788/HPLPB20132502.0381
Abstract:
In laser proton acceleration experiments, identifying different ions in the ion products is a basic and important issue. In this paper, we accomplished a calibration experiment, in which the CR39 detector is irradiated by monoenergetic proton and carbon ion beams. With standard etching conditions we developed, their track diameter vs energy response curves were obtained. These curves were further applied to determining the energy of ions and distinguishing protons from carbon ions in our laser proton acceleration experiment. In this experiment, the diameter and relative gray of ion tracks were measured, proton tracks were picked out and proton spectra were obtained finally.
In laser proton acceleration experiments, identifying different ions in the ion products is a basic and important issue. In this paper, we accomplished a calibration experiment, in which the CR39 detector is irradiated by monoenergetic proton and carbon ion beams. With standard etching conditions we developed, their track diameter vs energy response curves were obtained. These curves were further applied to determining the energy of ions and distinguishing protons from carbon ions in our laser proton acceleration experiment. In this experiment, the diameter and relative gray of ion tracks were measured, proton tracks were picked out and proton spectra were obtained finally.
2013,
25: 385-388.
doi: 10.3788/HPLPB20132502.0385
Abstract:
Indirectly driven capsule implosions are driven by four shock waves whose strength and relative timing must be controlled to high precision to keep the fuel on a low adiabat. The symmetry during the first 2 ns should be tuned carefully. The mainline tuning targets chosen are the high Z re-emission spheres. For record of instantaneous asymmetry during the first 2 ns, multiple images in the time of the soft X-ray re-emission from a non-imploding Bi ball on SGⅡ facility were taken in 2011. The re-emitted images with hohlraum lengths of 1350 m and 1500 m were obtained and the experimental P2/P0 and P4/P0 time histories were deduced. A simple analytical view-factor model is established, and the simulation result of P2/P0 is in agreement with the measured P2/P0.
Indirectly driven capsule implosions are driven by four shock waves whose strength and relative timing must be controlled to high precision to keep the fuel on a low adiabat. The symmetry during the first 2 ns should be tuned carefully. The mainline tuning targets chosen are the high Z re-emission spheres. For record of instantaneous asymmetry during the first 2 ns, multiple images in the time of the soft X-ray re-emission from a non-imploding Bi ball on SGⅡ facility were taken in 2011. The re-emitted images with hohlraum lengths of 1350 m and 1500 m were obtained and the experimental P2/P0 and P4/P0 time histories were deduced. A simple analytical view-factor model is established, and the simulation result of P2/P0 is in agreement with the measured P2/P0.
2013,
25: 389-393.
doi: 10.3788/HPLPB20132502.0389
Abstract:
The low-density foam of Z-pinch dynamic hohlraum has special requirements to the adhesive because of its porous structure and low mechanical intensity. The present paper reports the preparation of ultraviolet curable adhesives applicable for low-density foam using polyurethane acrylate as prepolymer and isobornyl acrylate as activator diluent. The adhesives were compounded by mixing the prepolymer, diluent with photoinitiator and coupling agent. The test results indicate that the volume shrinkage of a prepared adhesive is only 2.25%, the adhesives have quick curing speed and adequate shear strength to meet the requirements of assemblage. According to the interface observation, there are few adhesives entering the diagnose hole, and the diffuse thickness of adhesives in foam is small and uniform.
The low-density foam of Z-pinch dynamic hohlraum has special requirements to the adhesive because of its porous structure and low mechanical intensity. The present paper reports the preparation of ultraviolet curable adhesives applicable for low-density foam using polyurethane acrylate as prepolymer and isobornyl acrylate as activator diluent. The adhesives were compounded by mixing the prepolymer, diluent with photoinitiator and coupling agent. The test results indicate that the volume shrinkage of a prepared adhesive is only 2.25%, the adhesives have quick curing speed and adequate shear strength to meet the requirements of assemblage. According to the interface observation, there are few adhesives entering the diagnose hole, and the diffuse thickness of adhesives in foam is small and uniform.
2013,
25: 394-398.
doi: 10.3788/HPLPB20132502.0394
Abstract:
High power microwave(HPM) sources usually employ overmoded output waveguide to obtain higher power capacity. In designing feeder of beam waveguide and reflect antenna, TE11 mode needs to be convert to HE11 mode to radiate a quasiGaussian beam with quite low side lobe. RF breakdown will occur in corrugate gap when traditional corrugated TE11 HE11 mode converter is used in HPM field. In order to solve this problem, a method to design overmoded smoothwall TE11HE11 converter was investigated. Using an iterative synthesis method based on coupledmode theory, a 9.4 GHz, 70 mm overmoded smoothwall TE11 HE11 converter was designed, and contrast to electromagnetic simulation result, the scalar Gauss ratio of the output beam is higher than 99.5% from 9.1 GHz to 9.7 GHz, the power capacity is as high as 4.9 GW.
High power microwave(HPM) sources usually employ overmoded output waveguide to obtain higher power capacity. In designing feeder of beam waveguide and reflect antenna, TE11 mode needs to be convert to HE11 mode to radiate a quasiGaussian beam with quite low side lobe. RF breakdown will occur in corrugate gap when traditional corrugated TE11 HE11 mode converter is used in HPM field. In order to solve this problem, a method to design overmoded smoothwall TE11HE11 converter was investigated. Using an iterative synthesis method based on coupledmode theory, a 9.4 GHz, 70 mm overmoded smoothwall TE11 HE11 converter was designed, and contrast to electromagnetic simulation result, the scalar Gauss ratio of the output beam is higher than 99.5% from 9.1 GHz to 9.7 GHz, the power capacity is as high as 4.9 GW.
2013,
25: 399-406.
doi: 10.3788/HPLPB20132502.0399
Abstract:
The phenomenon of multipactor discharge suppressing on the grooved dielectric surfaceadopted in experiment is simulated with the Monte Carlo method. Dynamic equations, grooved surface boundary, initial energy and angular distribution of secondary electrons, and the secondary electron emission ratio are introduced. The suppressing effect of multipactor discharge depending on the depth and width of the groove is discussed. In addition, the suppressing ability of multipactor discharge on a fixed grooved surface depending on electric field and frequency of microwave is studied. Finally, the avoidance of two-sided multipactor discharge on the grooved surface is put forward. The numerical results are as follows: increasing groove depth and decreasing groove width could improve suppressing ability of multipactor discharge;it could be easy to suppress high frequency and weak or high electric field of microwave for a fixed grooved surface structure;it is necessary for avoiding the region of two-sided multipactor discharge. The numerical results agree with relevant experimental phenomena.
The phenomenon of multipactor discharge suppressing on the grooved dielectric surfaceadopted in experiment is simulated with the Monte Carlo method. Dynamic equations, grooved surface boundary, initial energy and angular distribution of secondary electrons, and the secondary electron emission ratio are introduced. The suppressing effect of multipactor discharge depending on the depth and width of the groove is discussed. In addition, the suppressing ability of multipactor discharge on a fixed grooved surface depending on electric field and frequency of microwave is studied. Finally, the avoidance of two-sided multipactor discharge on the grooved surface is put forward. The numerical results are as follows: increasing groove depth and decreasing groove width could improve suppressing ability of multipactor discharge;it could be easy to suppress high frequency and weak or high electric field of microwave for a fixed grooved surface structure;it is necessary for avoiding the region of two-sided multipactor discharge. The numerical results agree with relevant experimental phenomena.
2013,
25: 407-410.
doi: 10.3788/HPLPB20132502.0407
Abstract:
A scheme for designing the double-gap output cavity with two coupling apertures, as well as a method for calculating the external quality factor of the output cavity were proposed in this paper based on the equivalent-circuit theory. A double-gap output structure with single coupling aperture that satisfied the needs of the impedance-frequency characteristics was designed by using the CST-MWS code, and then a double-gap output structure with double coupling apertures was obtained, with the same geometrical size of the front-cavity and output-cavity. The impedance-frequency characteristic curve of the output cavity with double coupling apertures can be consistent with that of the cavity with single coupling aperture, by properly adjusting the geometrical size of the cavity and the coupling slot. The novel method used in this paper can provide a simple and effective way of designing the double-gap output cavity with two coupling apertures.
A scheme for designing the double-gap output cavity with two coupling apertures, as well as a method for calculating the external quality factor of the output cavity were proposed in this paper based on the equivalent-circuit theory. A double-gap output structure with single coupling aperture that satisfied the needs of the impedance-frequency characteristics was designed by using the CST-MWS code, and then a double-gap output structure with double coupling apertures was obtained, with the same geometrical size of the front-cavity and output-cavity. The impedance-frequency characteristic curve of the output cavity with double coupling apertures can be consistent with that of the cavity with single coupling aperture, by properly adjusting the geometrical size of the cavity and the coupling slot. The novel method used in this paper can provide a simple and effective way of designing the double-gap output cavity with two coupling apertures.
2013,
25: 411-414.
doi: 10.3788/HPLPB20132502.0411
Abstract:
A sequential test method based on Bayesian posterior probability was proposed to perform tests of hypotheses about probability of success of binomial distribution in complicated hypothesis conditions. The decision rules were constructed and the method for calculating the criterion value was given. For a given maximal sample size, the truncated method of judge criteria for hypothesis test was discussed. An experimental program was given to test the hypotheses about the probability of failure of device affected by microwave using the proposed method. At last, an example was presented to illustrate the proposed method and the result is compared with that of the existing methods.
A sequential test method based on Bayesian posterior probability was proposed to perform tests of hypotheses about probability of success of binomial distribution in complicated hypothesis conditions. The decision rules were constructed and the method for calculating the criterion value was given. For a given maximal sample size, the truncated method of judge criteria for hypothesis test was discussed. An experimental program was given to test the hypotheses about the probability of failure of device affected by microwave using the proposed method. At last, an example was presented to illustrate the proposed method and the result is compared with that of the existing methods.
2013,
25: 415-418.
doi: 10.3788/HPLPB20132502.0415
Abstract:
This paper presents a process of designing compact TE01-TE02 mode converters with broadband. Mode conversion condition are approximately derived while propagation constants vary along axis and initial structure of the mode converters is calculated. The initial structure is optimized utilizing iterative method. Two period TE01-TE02 mode converter in Ka band and one period mode converter in W band are designed, and the bandwidths (above 95% conversion efficiency) reach 2.47 GHz and 8 GHz respectively. CST simulation data agree well with those calculated by coupled mode algorithm for both converters.
This paper presents a process of designing compact TE01-TE02 mode converters with broadband. Mode conversion condition are approximately derived while propagation constants vary along axis and initial structure of the mode converters is calculated. The initial structure is optimized utilizing iterative method. Two period TE01-TE02 mode converter in Ka band and one period mode converter in W band are designed, and the bandwidths (above 95% conversion efficiency) reach 2.47 GHz and 8 GHz respectively. CST simulation data agree well with those calculated by coupled mode algorithm for both converters.
2013,
25: 419-422.
doi: 10.3788/HPLPB20132502.0419
Abstract:
Propagation characteristic of plane waves passing through infinite dielectric boards is studied using optical methods, and the effect of dielectric windows on microwave propagation is analyzed in the paper. The microwave discharge experiments of polytetrafluoroethylene (PTFE) were performed in vacuum under S-band high-power microwave with a frequency of 2.86 GHz. After a long time of surface flashover, tracks and electrical trees appear on the PTFE material surface. In the 100 ns pulse condition, partial discharge on the dielectric surface has been observed by optical photography, and the partial discharge can still cause electrical trees appear on the material surface. As a comparison, an electrical aging experiment of the polystyrene material was conducted. The experimental results show that the polystyrene material has good resistance to tracking and electrical treeing.
Propagation characteristic of plane waves passing through infinite dielectric boards is studied using optical methods, and the effect of dielectric windows on microwave propagation is analyzed in the paper. The microwave discharge experiments of polytetrafluoroethylene (PTFE) were performed in vacuum under S-band high-power microwave with a frequency of 2.86 GHz. After a long time of surface flashover, tracks and electrical trees appear on the PTFE material surface. In the 100 ns pulse condition, partial discharge on the dielectric surface has been observed by optical photography, and the partial discharge can still cause electrical trees appear on the material surface. As a comparison, an electrical aging experiment of the polystyrene material was conducted. The experimental results show that the polystyrene material has good resistance to tracking and electrical treeing.
2013,
25: 423-426.
doi: 10.3788/HPLPB20132502.0423
Abstract:
The thermal deformation of gridded electron gun in traveling wave tube has much influence on the performance of its electronic optics system and the problem has been investigated by means of the coupling of the thermal field and the mechanics field based on FEM (infinite element method). The results show that the total deformation of the anode is maximum and reaches 0.28 mm and the deformation of control grid, shadow grid, cathode and some supporting structure is toward the anode. Besides, contact or cross of control grid and shadow grid doesnt occur due to their deformation caused by temperature rise, while the cathode will contact the shadow grid when the deformation of the cathode is larger. The above contact will affect the performance of the gun, even cause the damage to shadow grid. The deformation of the components can be lessened by means of lowering probability of electron interception, thickening control grid and shadow grid properly as well as adopting the material with higher thermal conductivity and lower coefficient of linear expansion.
The thermal deformation of gridded electron gun in traveling wave tube has much influence on the performance of its electronic optics system and the problem has been investigated by means of the coupling of the thermal field and the mechanics field based on FEM (infinite element method). The results show that the total deformation of the anode is maximum and reaches 0.28 mm and the deformation of control grid, shadow grid, cathode and some supporting structure is toward the anode. Besides, contact or cross of control grid and shadow grid doesnt occur due to their deformation caused by temperature rise, while the cathode will contact the shadow grid when the deformation of the cathode is larger. The above contact will affect the performance of the gun, even cause the damage to shadow grid. The deformation of the components can be lessened by means of lowering probability of electron interception, thickening control grid and shadow grid properly as well as adopting the material with higher thermal conductivity and lower coefficient of linear expansion.
2013,
25: 427-430.
doi: 10.3788/HPLPB20132502.0427
Abstract:
On the basis of numerical calculation methods, thepropagation characteristics of the high-order mode TE31,12 in the conventional open cavity with weakly tapered cross-section and improved cavity are simulated by numerical computation. Diffractive quality factors of open cavities with weakly tapered cross-section are also numerically computed. Then the influence of the curvature radius of the connection segment on the diffractive quality factor is investigated . The results show that the curvature radius of the connection segment is another factor that affects the diffractive quality factor and the larger the curvature radius of the connection segment is, the smaller the diffractive quality factor becomes. In order to prove the correctness of this conclusion, another improved cavity operating in the low-order mode TE0,1 is simulated by the simulation software HFSS, and the same conclusion is attained.
On the basis of numerical calculation methods, thepropagation characteristics of the high-order mode TE31,12 in the conventional open cavity with weakly tapered cross-section and improved cavity are simulated by numerical computation. Diffractive quality factors of open cavities with weakly tapered cross-section are also numerically computed. Then the influence of the curvature radius of the connection segment on the diffractive quality factor is investigated . The results show that the curvature radius of the connection segment is another factor that affects the diffractive quality factor and the larger the curvature radius of the connection segment is, the smaller the diffractive quality factor becomes. In order to prove the correctness of this conclusion, another improved cavity operating in the low-order mode TE0,1 is simulated by the simulation software HFSS, and the same conclusion is attained.
Transmission characteristics of microwave rectangular waveguide with transverse inductive diaphragms
2013,
25: 431-435.
doi: 10.3788/HPLPB20132502.0431
Abstract:
The structure of the rectangular waveguide with transverse inductive diaphragms is approximately analyzed with the equivalent circuit theory of microwave transmission line two-port network. Calculation result shows that the widths of a pair of diaphragms can affect the phase and amplitude of the scattering parameter, but the diaphragm positions have no effect on the magnitude of the scatting parameter and the bandwidth. Microwave equivalent circuit transfer matrix of the rectangular waveguide with two pairs of symmetrical inductive diaphragms is studied with Matlab according to the counteracting of incidence and reflection, i.e. no reflection requirement. Longitudinal optimum spacing between two pairs of diaphragms is calculated on the basis of least insert attenuation. The bandwidth obtained with microwave equivalent circuit theory and the result of the high-frequency electromagnetic field software CST are nearly consistent, the difference between them is only 0.59%. The results have some significance for design of rectangular waveguide filters applied to high-frequency power vacuum device.
The structure of the rectangular waveguide with transverse inductive diaphragms is approximately analyzed with the equivalent circuit theory of microwave transmission line two-port network. Calculation result shows that the widths of a pair of diaphragms can affect the phase and amplitude of the scattering parameter, but the diaphragm positions have no effect on the magnitude of the scatting parameter and the bandwidth. Microwave equivalent circuit transfer matrix of the rectangular waveguide with two pairs of symmetrical inductive diaphragms is studied with Matlab according to the counteracting of incidence and reflection, i.e. no reflection requirement. Longitudinal optimum spacing between two pairs of diaphragms is calculated on the basis of least insert attenuation. The bandwidth obtained with microwave equivalent circuit theory and the result of the high-frequency electromagnetic field software CST are nearly consistent, the difference between them is only 0.59%. The results have some significance for design of rectangular waveguide filters applied to high-frequency power vacuum device.
2013,
25: 436-440.
doi: 10.3788/HPLPB20132502.0436
Abstract:
The rectangular close-packed antenna array is studied in the paper. The far-field directional diagram of the array is emulated, which indicates it is possible to get highly active combination based on the close-packed antenna array and the main beam can be got. Then the impact of element separation and initial phase of the element on spatial power combining of the antenna array is analysed, and the results show that the smaller the element separation is, the less the grating lobes becomes, and the wider the main beam is, the shorter the critical distance becomes when the main beam can be obtained. When the distance between the target and the arrays exceeds the critical distance, the synthesis efficiency increases with the decrease of the phase difference of the arrays. But the arrays cant obtain certain main beam when the distribution range of initial phase of the arrays exceeds /2. So the above factors should be considered in array design.
The rectangular close-packed antenna array is studied in the paper. The far-field directional diagram of the array is emulated, which indicates it is possible to get highly active combination based on the close-packed antenna array and the main beam can be got. Then the impact of element separation and initial phase of the element on spatial power combining of the antenna array is analysed, and the results show that the smaller the element separation is, the less the grating lobes becomes, and the wider the main beam is, the shorter the critical distance becomes when the main beam can be obtained. When the distance between the target and the arrays exceeds the critical distance, the synthesis efficiency increases with the decrease of the phase difference of the arrays. But the arrays cant obtain certain main beam when the distribution range of initial phase of the arrays exceeds /2. So the above factors should be considered in array design.
2013,
25: 441-445.
doi: 10.3788/HPLPB20132502.0441
Abstract:
Based on conformal construction of the physical model in the three-dimensional orthogonal mesh system, an integral-based conformal convolutional perfectly matched layer(CPML) algorithm is given for solving the open port truncation problem when the enlarged cell technique combining with conformal finite-difference time-domain (ECT-CFDTD) method is used to simulate the wave propagation inside a hollow waveguide, and the algorithm has the same numerical stability as the ECT-CFDTD method. For the evanescent wave long-time propagation problems in a waveguide, several numerical simulations are done to analyse the reflection error by conducting sweeps of constitutive parameters of the integral-based conformal CPML. Numerical results show that the integral-based conformal CPML can be used for efficiently truncating the open port of the waveguide.
Based on conformal construction of the physical model in the three-dimensional orthogonal mesh system, an integral-based conformal convolutional perfectly matched layer(CPML) algorithm is given for solving the open port truncation problem when the enlarged cell technique combining with conformal finite-difference time-domain (ECT-CFDTD) method is used to simulate the wave propagation inside a hollow waveguide, and the algorithm has the same numerical stability as the ECT-CFDTD method. For the evanescent wave long-time propagation problems in a waveguide, several numerical simulations are done to analyse the reflection error by conducting sweeps of constitutive parameters of the integral-based conformal CPML. Numerical results show that the integral-based conformal CPML can be used for efficiently truncating the open port of the waveguide.
2013,
25: 446-450.
doi: 10.3788/HPLPB20132502.0446
Abstract:
The paper presents the thermal and deformation analysis of electron gun cathode for Gyro-TWT using the finite element analysis software ANSYS, which obtains the temperature distribution and thermal deformation of the cathode model. In order to maintain the uniformity of surface temperature of the cathode emitter, the contact area of the thermal conductive medium with the emitter bottom is extended and the amount of the heater coil near the top of the emitter is reduced, the temperature difference decreases from 18 ℃ to 0.9 ℃. On the basis of the thermal analysis, thermal deformation analysis is demonstrated and the velocity ratio, longitudinal and transverse velocity spread, guide center radius all increase in EGUN code simulation.
The paper presents the thermal and deformation analysis of electron gun cathode for Gyro-TWT using the finite element analysis software ANSYS, which obtains the temperature distribution and thermal deformation of the cathode model. In order to maintain the uniformity of surface temperature of the cathode emitter, the contact area of the thermal conductive medium with the emitter bottom is extended and the amount of the heater coil near the top of the emitter is reduced, the temperature difference decreases from 18 ℃ to 0.9 ℃. On the basis of the thermal analysis, thermal deformation analysis is demonstrated and the velocity ratio, longitudinal and transverse velocity spread, guide center radius all increase in EGUN code simulation.
2013,
25: 451-454.
doi: 10.3788/HPLPB20132502.0451
Abstract:
Preliminary experimental research on a relativistic terahertz source with 0.14 THz based on the surface wave oscillator was carried out. The device adopts an overmoded rectangular slow wave structure for the sake of large power capacity and easy fabrication. The experiment was performed on the CKP1000 generator according to theoretical analysis and numerical simulation results. Power measurement uses the radiation power density integral method and frequency measurement employs the cut-off waveguide method. A terahertz wave with a frequency more than 0.136 THz, a pulse duration of 1.5 ns and output power more than 2 MW is obtained, under the condition of the electron beam voltage of 320 kV, the beam current of 2.1 kA, and the guiding magnetic field of 5 T.
Preliminary experimental research on a relativistic terahertz source with 0.14 THz based on the surface wave oscillator was carried out. The device adopts an overmoded rectangular slow wave structure for the sake of large power capacity and easy fabrication. The experiment was performed on the CKP1000 generator according to theoretical analysis and numerical simulation results. Power measurement uses the radiation power density integral method and frequency measurement employs the cut-off waveguide method. A terahertz wave with a frequency more than 0.136 THz, a pulse duration of 1.5 ns and output power more than 2 MW is obtained, under the condition of the electron beam voltage of 320 kV, the beam current of 2.1 kA, and the guiding magnetic field of 5 T.
2013,
25: 455-460.
doi: 10.3788/HPLPB20132502.0455
Abstract:
Researches on responses of an n-type silicon bar fixed in a rectangular waveguide to high power terahertz pulse have been carried out for the 0.3~0.4 THz band. The distribution of electromagnetic field components, voltage standing-wave ratio(VSWR) in the waveguide, and the average electric field in the n-type silicon bar is determined by means of a three-dimensional finite-difference time-domain method. By adjusting several factors, such as the length, width, height and the specific resistance of the silicon bar, a novel project of a sensor that can be used as measurement device for high power terahertz pulse directly is presented. The relative sensitivity of the sensor is about 0.509 kW-1, its fluctuation is in the range of 14%, and its VSWR is no more than 1.34.
Researches on responses of an n-type silicon bar fixed in a rectangular waveguide to high power terahertz pulse have been carried out for the 0.3~0.4 THz band. The distribution of electromagnetic field components, voltage standing-wave ratio(VSWR) in the waveguide, and the average electric field in the n-type silicon bar is determined by means of a three-dimensional finite-difference time-domain method. By adjusting several factors, such as the length, width, height and the specific resistance of the silicon bar, a novel project of a sensor that can be used as measurement device for high power terahertz pulse directly is presented. The relative sensitivity of the sensor is about 0.509 kW-1, its fluctuation is in the range of 14%, and its VSWR is no more than 1.34.
2013,
25: 461-464.
doi: 10.3788/HPLPB20132502.0461
Abstract:
The electron beam of high average power Free Electron Laser Terahertz scientific research device in Chinese Academy of Engineering Physics (CAEP) has the characteristic of high average current. Non-destructive measurement technique is required for the measurement of the beam parameters. The beam position monitor (BPM) is one of the basic measurement instruments. The method of extracting the signal spectrum of the BPM to obtain the bunch length is simple and can be used as a supplement or replacement of other bunch length measurement methods. This paper analyzes the frequency domain characteristics of the driving electron beam bunches, and analyzes the theoretical basement of the bunch length measurement based on the BPM. 3D simulation program was used for the numerical simulation of BPM transfer impedance modeling, the bunches of different length were measured and calculated, and the impact of the bunchs off-center position in the vacuum pipe on the bunch length measurements was also analyzed. The study results show that when the bunch length varies from 10 ps to 100 ps, all the measurement error is less than 2%, which meets the requirements of CAEP-THz-FEL operation.
The electron beam of high average power Free Electron Laser Terahertz scientific research device in Chinese Academy of Engineering Physics (CAEP) has the characteristic of high average current. Non-destructive measurement technique is required for the measurement of the beam parameters. The beam position monitor (BPM) is one of the basic measurement instruments. The method of extracting the signal spectrum of the BPM to obtain the bunch length is simple and can be used as a supplement or replacement of other bunch length measurement methods. This paper analyzes the frequency domain characteristics of the driving electron beam bunches, and analyzes the theoretical basement of the bunch length measurement based on the BPM. 3D simulation program was used for the numerical simulation of BPM transfer impedance modeling, the bunches of different length were measured and calculated, and the impact of the bunchs off-center position in the vacuum pipe on the bunch length measurements was also analyzed. The study results show that when the bunch length varies from 10 ps to 100 ps, all the measurement error is less than 2%, which meets the requirements of CAEP-THz-FEL operation.
2013,
25: 465-470.
doi: 10.3788/HPLPB20132502.0465
Abstract:
The rapid cycling synchrotron of the China Spallation Neutron Source is a high intensity proton accelerator, with an average beam power of 100 kW. The collective effects caused by the coupling impedances from the vacuum components may be the limit to beam power. The impedances from various kinds of components were investigated and the impedance budgets were summarized. According to the summarized impedances, the thresholds for instability were estimated. Because of the serious instability from the resistive wall impedance, a simple resistive-wall wake-field model was used to track the bunch oscillation, and the growth rate was derived from simulation which was consistent with analysis. When the natural chromaticity which helps to stabilize the beam is considered in the simulation, the instability of resistive wall will disappear.
The rapid cycling synchrotron of the China Spallation Neutron Source is a high intensity proton accelerator, with an average beam power of 100 kW. The collective effects caused by the coupling impedances from the vacuum components may be the limit to beam power. The impedances from various kinds of components were investigated and the impedance budgets were summarized. According to the summarized impedances, the thresholds for instability were estimated. Because of the serious instability from the resistive wall impedance, a simple resistive-wall wake-field model was used to track the bunch oscillation, and the growth rate was derived from simulation which was consistent with analysis. When the natural chromaticity which helps to stabilize the beam is considered in the simulation, the instability of resistive wall will disappear.
2013,
25: 471-476.
doi: 10.3788/HPLPB20132502.0471
Abstract:
With the computer program TRANSOPTR including space charge effect calculations, a axial injection line for the CYCIAE-100 cyclotron is designed. The focusing structure is confirmed after considering space, focusing elements, vacuum, space charge effect, axial magnetic field and cost. The transfer matrix for the inflector under the real varying axial magnetic field is obtained by numerical tracking and it is built into TRANSOPTR for the beam line optics calculations from the downstream of the ion source to the exit of the inflector. The layout and the optical results of the injection line of CYCIAE-100, and the designs of the main elements in the injection line are given. After the electrode structure of the central region and the centering orbit are obtained, the beam matching is studied using the multi-particle tracing. The matching matrix is achieved by ellipses fitting for the tracking results and the analytic formula, which is useful in injection line design.
With the computer program TRANSOPTR including space charge effect calculations, a axial injection line for the CYCIAE-100 cyclotron is designed. The focusing structure is confirmed after considering space, focusing elements, vacuum, space charge effect, axial magnetic field and cost. The transfer matrix for the inflector under the real varying axial magnetic field is obtained by numerical tracking and it is built into TRANSOPTR for the beam line optics calculations from the downstream of the ion source to the exit of the inflector. The layout and the optical results of the injection line of CYCIAE-100, and the designs of the main elements in the injection line are given. After the electrode structure of the central region and the centering orbit are obtained, the beam matching is studied using the multi-particle tracing. The matching matrix is achieved by ellipses fitting for the tracking results and the analytic formula, which is useful in injection line design.
2013,
25: 477-480.
doi: 10.3788/HPLPB20132502.0477
Abstract:
Some models of the space charge in magnetrons are reviewed. PIC simulations are taken on X band magnetrons to compare with the theory analysis. The Brilliouns theory is effective in getting the height and density of the hub, but it is difficult to explain charge density at the edge of the hub for the Brillouins theory uses single-particle motion theory. There is discrepancy in spoke density with all these theories. The difference of the charge density at the edge of the hub is assumed to be the reason for the discrepancy. Approaches to maintain spoke density in magnetrons are proposed according to the guiding center fluid theory in S.Riyopoulos work.
Some models of the space charge in magnetrons are reviewed. PIC simulations are taken on X band magnetrons to compare with the theory analysis. The Brilliouns theory is effective in getting the height and density of the hub, but it is difficult to explain charge density at the edge of the hub for the Brillouins theory uses single-particle motion theory. There is discrepancy in spoke density with all these theories. The difference of the charge density at the edge of the hub is assumed to be the reason for the discrepancy. Approaches to maintain spoke density in magnetrons are proposed according to the guiding center fluid theory in S.Riyopoulos work.
2013,
25: 481-484.
doi: 10.3788/HPLPB20132502.0481
Abstract:
To improve the scanning uniformity and beam extraction efficiency, and to solve the problem of beam central deviation of DG-type electron accelerators, a scanning system has been developed, whose scanning coil and self-correcting coil are set in the same magnetic core. The system can scan along the X and Y axes and adjust the beam to the centre of the extraction window automatically. This paper introduces the parameter-selection basis of scanning magnet and scanning power-supply. We expound the design principle of the shaping circuit of the triangle wave current based square wave voltage. Moreover, the interlock signal from the scanning system is used to ensure the accelerators operation safety and stabilization. It is proved that the scanning system completely achieves the industrialization demand and the scanning uniformity meets the industrial irradiation requirements by the fact that the accelerator with the steady self-correcting scanning system is successfully used in practice.
To improve the scanning uniformity and beam extraction efficiency, and to solve the problem of beam central deviation of DG-type electron accelerators, a scanning system has been developed, whose scanning coil and self-correcting coil are set in the same magnetic core. The system can scan along the X and Y axes and adjust the beam to the centre of the extraction window automatically. This paper introduces the parameter-selection basis of scanning magnet and scanning power-supply. We expound the design principle of the shaping circuit of the triangle wave current based square wave voltage. Moreover, the interlock signal from the scanning system is used to ensure the accelerators operation safety and stabilization. It is proved that the scanning system completely achieves the industrialization demand and the scanning uniformity meets the industrial irradiation requirements by the fact that the accelerator with the steady self-correcting scanning system is successfully used in practice.
2013,
25: 485-489.
doi: 10.3788/HPLPB20132502.0485
Abstract:
The space radiation environment could induce radiation damage on the electronic devices. As the performance of commercial devices is generally superior to that of radiation hardened devices, it is necessary to screen out the devices with good radiation hardened performance from the commercial devices and applying these devices to space systems could improve the reliability of the systems. Combining the mathematical regression analysis with the different physical stressing experiments, we investigated the non-destructive screening method for radiation hardened performance of the integrated circuit. The relationship between the change of typical parameters and the radiation performance of the circuit was discussed. The irradiation-sensitive parameters were confirmed. The pluralistic linear regression equation toward the prediction of the radiation performance was established. Finally, the regression equations under stress conditions were verified by practical irradiation. The results show that the reliability and accuracy of the non-destructive screening method can be elevated by combining the mathematical regression analysis with the practical stressing experiment.
The space radiation environment could induce radiation damage on the electronic devices. As the performance of commercial devices is generally superior to that of radiation hardened devices, it is necessary to screen out the devices with good radiation hardened performance from the commercial devices and applying these devices to space systems could improve the reliability of the systems. Combining the mathematical regression analysis with the different physical stressing experiments, we investigated the non-destructive screening method for radiation hardened performance of the integrated circuit. The relationship between the change of typical parameters and the radiation performance of the circuit was discussed. The irradiation-sensitive parameters were confirmed. The pluralistic linear regression equation toward the prediction of the radiation performance was established. Finally, the regression equations under stress conditions were verified by practical irradiation. The results show that the reliability and accuracy of the non-destructive screening method can be elevated by combining the mathematical regression analysis with the practical stressing experiment.
2013,
25: 490-494.
doi: 10.3788/HPLPB20132502.0490
Abstract:
This paper introduces the transmission line method which is used to calculate the coaxial response to X-ray and the drift-diffusion method which is used to calculate the parameters of semiconductor devices. Combining the transmission line method with the drift-diffusion method, we calculated the X-ray transient response of coaxial line with PIN diode. The coupled model shows the relation of coaxial lines response to pulsed X-ray and the diodes status. An example was calculated using the coupled model, the implications of the data were discussed in detail. The coupled model can be used in calculating the responses of coaxial lines with other semiconductor devices to pulsed X-ray.
This paper introduces the transmission line method which is used to calculate the coaxial response to X-ray and the drift-diffusion method which is used to calculate the parameters of semiconductor devices. Combining the transmission line method with the drift-diffusion method, we calculated the X-ray transient response of coaxial line with PIN diode. The coupled model shows the relation of coaxial lines response to pulsed X-ray and the diodes status. An example was calculated using the coupled model, the implications of the data were discussed in detail. The coupled model can be used in calculating the responses of coaxial lines with other semiconductor devices to pulsed X-ray.
2013,
25: 495-499.
doi: 10.3788/HPLPB20132502.0495
Abstract:
The excited-state nonlinearities of the C70/toluene solution are studied using a time-resolved non-degenerate pump-probe system. The 532 nm laser beam with 21 ps duration is used as the excitation and the laser beam of 600 nm with 10 ps duration is used for probing. The parameters associated with the five-energy-level model are evaluated by numerically simulation based on the non-degenerate pump-probe theory. The experimental results demonstrate that the lifetime of the excited state remains unchanged under non-degenerate condition, but the absorption cross section of the first excited state decreases with probe beam wavelength increase.
The excited-state nonlinearities of the C70/toluene solution are studied using a time-resolved non-degenerate pump-probe system. The 532 nm laser beam with 21 ps duration is used as the excitation and the laser beam of 600 nm with 10 ps duration is used for probing. The parameters associated with the five-energy-level model are evaluated by numerically simulation based on the non-degenerate pump-probe theory. The experimental results demonstrate that the lifetime of the excited state remains unchanged under non-degenerate condition, but the absorption cross section of the first excited state decreases with probe beam wavelength increase.
2013,
25: 500-504.
doi: 10.3788/HPLPB20132502.0500
Abstract:
The relations of the mass fraction and temperature of mixtures of water and dimethyl sulphoxide (DMSO) to refractive index are theoretically and experimentally studied. The empirical formula fit for calculating the refractive index of the mixture is chosen by comparing the simulation results of several classical models. Then the effects of mass fraction and temperature of the mixture of aqueous gold colloids and DMSO on localized surface plasmon resonance are studied. The theoretical and experimental results show that the mass fraction of the mixture of aqueous gold colloids and DSMO has linear relationship with the resonance wavelength of localized surface plasmon in a large range. The resonance wavelength of the mixed gold colloids increases by 1367 pm when the temperature increases from 20 ℃ to 60 ℃, and its temperature sensitivity is 34 pm/K. The increase of resonance wavelength with mass fraction is 8.5103 pm in a 0-100% mass fraction range.
The relations of the mass fraction and temperature of mixtures of water and dimethyl sulphoxide (DMSO) to refractive index are theoretically and experimentally studied. The empirical formula fit for calculating the refractive index of the mixture is chosen by comparing the simulation results of several classical models. Then the effects of mass fraction and temperature of the mixture of aqueous gold colloids and DMSO on localized surface plasmon resonance are studied. The theoretical and experimental results show that the mass fraction of the mixture of aqueous gold colloids and DSMO has linear relationship with the resonance wavelength of localized surface plasmon in a large range. The resonance wavelength of the mixed gold colloids increases by 1367 pm when the temperature increases from 20 ℃ to 60 ℃, and its temperature sensitivity is 34 pm/K. The increase of resonance wavelength with mass fraction is 8.5103 pm in a 0-100% mass fraction range.
2013,
25: 505-507.
doi: 10.3788/HPLPB20132502.0505
Abstract:
This paper studies parameters of InGaAsSb/AlGaAsSb multi-quantum-well (MQW) materials grown by molecular beam epitaxy (MBE), including the growth rate, growth temperature and flux for high quality MQW materials, respectively. As well, characterization of the epi-layers by X-ray diffraction (XRD) indicates high uniformity and excellent crystalline quality with satellite peaks. Emitting wavelength is about 2.0 m measured by photoluminescence(PL) at room temperature (RT). The excellent crystalline quality and optical characteristic are obtained through optimization of growth conditions and structure parameters. The threshold current of the fabricated device is about 300 mA, the output power is 22 mW at room temperature.
This paper studies parameters of InGaAsSb/AlGaAsSb multi-quantum-well (MQW) materials grown by molecular beam epitaxy (MBE), including the growth rate, growth temperature and flux for high quality MQW materials, respectively. As well, characterization of the epi-layers by X-ray diffraction (XRD) indicates high uniformity and excellent crystalline quality with satellite peaks. Emitting wavelength is about 2.0 m measured by photoluminescence(PL) at room temperature (RT). The excellent crystalline quality and optical characteristic are obtained through optimization of growth conditions and structure parameters. The threshold current of the fabricated device is about 300 mA, the output power is 22 mW at room temperature.
2013,
25: 508-512.
doi: 10.3788/HPLPB20132502.0508
Abstract:
The properties of ultrashort pulse propagation in metamaterials (MMs) are investigated, and special attention is paid to the anomalous phenomena of pulse splitting inaccessible in ordinary materials. It is found that the interaction of anomalous group velocity dispersion(GVD) and self-defocus effect will lead to the symmetric pulse splitting due to negative index in MMs. In addition, we have investigated the influence of controllable self-steepening(SS) induced by dispersive magnetic permeability on the pulse splitting. It is shown that both positive and negative SS lead to the asymmetric pulse splitting in MMs. Analysis shows that negative SS effect gives rise to the trailing pulse being higher than the leading pulse, same as the corresponding case in ordinary material;positive SS in MMs causes the opposite of the previous case, namely, the trailing pulse being lower than the leading pulse.
The properties of ultrashort pulse propagation in metamaterials (MMs) are investigated, and special attention is paid to the anomalous phenomena of pulse splitting inaccessible in ordinary materials. It is found that the interaction of anomalous group velocity dispersion(GVD) and self-defocus effect will lead to the symmetric pulse splitting due to negative index in MMs. In addition, we have investigated the influence of controllable self-steepening(SS) induced by dispersive magnetic permeability on the pulse splitting. It is shown that both positive and negative SS lead to the asymmetric pulse splitting in MMs. Analysis shows that negative SS effect gives rise to the trailing pulse being higher than the leading pulse, same as the corresponding case in ordinary material;positive SS in MMs causes the opposite of the previous case, namely, the trailing pulse being lower than the leading pulse.
2013,
25: 513-516.
doi: 10.3788/HPLPB20132502.0513
Abstract:
C-Ti granular films with different thickness were prepared, acting as the cathode emission film, to study the influence of granular film thickness on electron emission characteristics. When symmetric triangular wave voltages of different magnitudes are applied to the prepared cathode device, electrical formation is then carried out to the devices. It is shown that the turn-on voltage of the 69 nm-thick-film equipped device is 32 V, with the emission efficiency reaching its maximum at 33 V, while the turn-on voltage of the 855 nm-thick-film equipped device was 23 V, with the maximum emission efficiency appearing at 23 V. It is also illustrated that the 855 nm-thick-film device has a much wider voltage range and a much higher electron emission efficiency than the 69 nm-thick-film one.
C-Ti granular films with different thickness were prepared, acting as the cathode emission film, to study the influence of granular film thickness on electron emission characteristics. When symmetric triangular wave voltages of different magnitudes are applied to the prepared cathode device, electrical formation is then carried out to the devices. It is shown that the turn-on voltage of the 69 nm-thick-film equipped device is 32 V, with the emission efficiency reaching its maximum at 33 V, while the turn-on voltage of the 855 nm-thick-film equipped device was 23 V, with the maximum emission efficiency appearing at 23 V. It is also illustrated that the 855 nm-thick-film device has a much wider voltage range and a much higher electron emission efficiency than the 69 nm-thick-film one.
2013,
25: 517-521.
Abstract:
The transmission characteristics of ultra-short electron beams of the ultra-fast electron guns in scanning state were analysed, and the deflection distance of the ultra-short electron beams passing the deflection-scan system was calculated. The results indicate that the initial voltage must be within the range of 700-1400 V to counterbalance the effect of the negative scan slope voltage, ensuring that the electron beams will pass the deflection-scan system and finally hit the phosphor screen of 30 mm in diameter, and the cooperative function of the initial voltage and the negative scan slope voltage is one of the two premises of the scan experiment. The other premise is the synchronization of the electrical and the optical signals. Following the discussion of the great difficulty caused by the first promise, an experimental system that can adjust the optical delay more effectively in the scan experiment was designed, which can facilitate the synchronization of the negative scan slope voltage and the ultra-fast electron pulse.
The transmission characteristics of ultra-short electron beams of the ultra-fast electron guns in scanning state were analysed, and the deflection distance of the ultra-short electron beams passing the deflection-scan system was calculated. The results indicate that the initial voltage must be within the range of 700-1400 V to counterbalance the effect of the negative scan slope voltage, ensuring that the electron beams will pass the deflection-scan system and finally hit the phosphor screen of 30 mm in diameter, and the cooperative function of the initial voltage and the negative scan slope voltage is one of the two premises of the scan experiment. The other premise is the synchronization of the electrical and the optical signals. Following the discussion of the great difficulty caused by the first promise, an experimental system that can adjust the optical delay more effectively in the scan experiment was designed, which can facilitate the synchronization of the negative scan slope voltage and the ultra-fast electron pulse.
2013,
25: 522-526.
Abstract:
In this paper, the Hilbert spectrum is used to analyze the nuclear explosion and lightning electromagnetic pulse for NEMP and LEMP signals based on their non-stationary and non-linear characters. The region features of Hilbert spectrum of NEMP and LEMP signals are calculated to discriminate them, and the discrimination result is analyzed based on different mechanisms of the nuclear explosion and lightning. The experiment results indicate that, using the nearest neighbor pattern classification method, the average discrimination rate of NEMP and LEMP signals is over 90% based on area, the center of gravity and six dimension image region features of Hilbert spectrum. Finally, we get a conclusion that the image region features of the Hilbert spectrum are effective features to discriminate NEMP and LEMP.
In this paper, the Hilbert spectrum is used to analyze the nuclear explosion and lightning electromagnetic pulse for NEMP and LEMP signals based on their non-stationary and non-linear characters. The region features of Hilbert spectrum of NEMP and LEMP signals are calculated to discriminate them, and the discrimination result is analyzed based on different mechanisms of the nuclear explosion and lightning. The experiment results indicate that, using the nearest neighbor pattern classification method, the average discrimination rate of NEMP and LEMP signals is over 90% based on area, the center of gravity and six dimension image region features of Hilbert spectrum. Finally, we get a conclusion that the image region features of the Hilbert spectrum are effective features to discriminate NEMP and LEMP.
2013,
25: 527-530.
doi: 10.3788/HPLPB20132502.0527
Abstract:
An optical fiber array is designed for testing initial discharge time of coaxial multi-gap gas switch, it has less than 1 ns time consistency and consists of two parts: optical fiber probe array and multi-channel photoelectric convertor. Based on a 100 kA-LTD module which has 10 parallel discharge branches, discharge time jitter of all switches has been tested. Experimental results show that: As the ratio of charge voltage and operating voltage is 85%, the time jitter is less than 6.9 ns, load current waveform has well consistency;while the ratio falls to 53%, time jitter dramatically increases to 117.7 ns and load current waveform consistency is deteriorated significantly. Experimental data from optic fiber array are put into the PSpice circuit model for simulation, the results show that the simulation results and experimental ones have better consistency. Itproves the accuracy of the diagnosis system and the correctness of the analysis.
An optical fiber array is designed for testing initial discharge time of coaxial multi-gap gas switch, it has less than 1 ns time consistency and consists of two parts: optical fiber probe array and multi-channel photoelectric convertor. Based on a 100 kA-LTD module which has 10 parallel discharge branches, discharge time jitter of all switches has been tested. Experimental results show that: As the ratio of charge voltage and operating voltage is 85%, the time jitter is less than 6.9 ns, load current waveform has well consistency;while the ratio falls to 53%, time jitter dramatically increases to 117.7 ns and load current waveform consistency is deteriorated significantly. Experimental data from optic fiber array are put into the PSpice circuit model for simulation, the results show that the simulation results and experimental ones have better consistency. Itproves the accuracy of the diagnosis system and the correctness of the analysis.
2013,
25: 531-536.
doi: 10.3788/HPLPB20132502.0531
Abstract:
This paper presents a SPICE modeling method which combines the equivalent cable bundle method (ECBM) with the time-domain transmission line method. The parameters of the cable bundles are obtained by the finite element method. And the completed model and the reduced model are analyzed in SPICE. The computational efficiency of the models analyzing in time domain is enhanced by above 50%, compared with that for the traditional methods of frequency domain. The computation time and the memory required are greatly saved. Two numerical examples are adopted to validate the proposed model, and the results are in good agreement. The computational error is limited in 5%.The proposed method is suit for the analysis of the conducted coupling, crosstalk and radiated coupling of the cable bundles.
This paper presents a SPICE modeling method which combines the equivalent cable bundle method (ECBM) with the time-domain transmission line method. The parameters of the cable bundles are obtained by the finite element method. And the completed model and the reduced model are analyzed in SPICE. The computational efficiency of the models analyzing in time domain is enhanced by above 50%, compared with that for the traditional methods of frequency domain. The computation time and the memory required are greatly saved. Two numerical examples are adopted to validate the proposed model, and the results are in good agreement. The computational error is limited in 5%.The proposed method is suit for the analysis of the conducted coupling, crosstalk and radiated coupling of the cable bundles.
