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RSS2006 Vol. 18, No. 10
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2006,
18.
Abstract:
Coherent beam combination of fiber laser array is an important technology in realizing high power fiber laser system. In this paper, master oscillator-power amplifier scheme is used to realize phase control of three ytterbium fiber amplifiers. In the experiments, the output power of each ytterbium fiber amplifier is not less than 1 W and the total output power of the three amplifiers is not less than 3 W. Phases are controlled by LiNbO3 phase modulator. The heterodyne detection control system works at 40 MHz and the control precision is l/20. The fibers are polarizedly maintained. The experimental results of both two and three fiber amplifiers are given. When the control loop is off, the far field interference pattern is dynamic and blurred. While the control loop is on, the far field
Coherent beam combination of fiber laser array is an important technology in realizing high power fiber laser system. In this paper, master oscillator-power amplifier scheme is used to realize phase control of three ytterbium fiber amplifiers. In the experiments, the output power of each ytterbium fiber amplifier is not less than 1 W and the total output power of the three amplifiers is not less than 3 W. Phases are controlled by LiNbO3 phase modulator. The heterodyne detection control system works at 40 MHz and the control precision is l/20. The fibers are polarizedly maintained. The experimental results of both two and three fiber amplifiers are given. When the control loop is off, the far field interference pattern is dynamic and blurred. While the control loop is on, the far field
2006,
18.
Abstract:
A novel on-line measurement method for continuous wave high energy laser beam is presented. The system based on this method is mainly consisted of a scanning circular reflector and a photoelectric detector array disposed along the circumference of the pan. The laser beam passing through the system except a little sample light is reflected into the detector array. Through the arithmetic of spatial mapping and image restoration with the output signal of detector array, the spatial-temporal distribution of the laser beam parameters is obtained. This method can be used to measure the high energy laser beam on-line with several hundred micrometers in diameter. The spatial resolution is 2 mm and the temporal resolution is 30~50 ms.
A novel on-line measurement method for continuous wave high energy laser beam is presented. The system based on this method is mainly consisted of a scanning circular reflector and a photoelectric detector array disposed along the circumference of the pan. The laser beam passing through the system except a little sample light is reflected into the detector array. Through the arithmetic of spatial mapping and image restoration with the output signal of detector array, the spatial-temporal distribution of the laser beam parameters is obtained. This method can be used to measure the high energy laser beam on-line with several hundred micrometers in diameter. The spatial resolution is 2 mm and the temporal resolution is 30~50 ms.
2006,
18.
Abstract:
By analyzing and comparing their one-dimensional solutions for laser-induced thermoelastic problem, the criterion of model selection between two commonly used laser heating models——surface heating and volumetric heating is presented. It is shown that using the surface heating model for calculating thermal effect of ultra-short laser pulse may lead to highly misleading results, due to the lesser ratio of thermal penetration depth to optical absorption length. Therefore, volumetric heating model should be the only choice for computation relating to picosecond and femtosecond laser heating.
By analyzing and comparing their one-dimensional solutions for laser-induced thermoelastic problem, the criterion of model selection between two commonly used laser heating models——surface heating and volumetric heating is presented. It is shown that using the surface heating model for calculating thermal effect of ultra-short laser pulse may lead to highly misleading results, due to the lesser ratio of thermal penetration depth to optical absorption length. Therefore, volumetric heating model should be the only choice for computation relating to picosecond and femtosecond laser heating.
2006,
18.
Abstract:
Based on the Rytov approximation which is modified with a filter function, expressions are derived for the variance associated with the beam wander in moderate to strong turbulence regimes. The effects of the diameter of the effective scattering region and beam waist on the beam wander are analyzed, and the derived variance expression is compared with experimental data. The results show that the calculated value from the derived displacement variance extending into all regimes is in better agreement with experimental data, compared with the variance based on the exponential model. When the beam waist is larger than the diameter of the effective scattering region, the effects of the saturation don’t occur. When the diameter of the effective scattering region is larger than the beam waist,
Based on the Rytov approximation which is modified with a filter function, expressions are derived for the variance associated with the beam wander in moderate to strong turbulence regimes. The effects of the diameter of the effective scattering region and beam waist on the beam wander are analyzed, and the derived variance expression is compared with experimental data. The results show that the calculated value from the derived displacement variance extending into all regimes is in better agreement with experimental data, compared with the variance based on the exponential model. When the beam waist is larger than the diameter of the effective scattering region, the effects of the saturation don’t occur. When the diameter of the effective scattering region is larger than the beam waist,
2006,
18.
Abstract:
A new system is developed for real-time monitoring of the optical turbulence altitude profile. A laser beam is transmitted and focused on certain height to form an artificial beacon. Its backscattering light propagates through the atmosphere. The lidar receives the signal coming from the scatter light of beacon and, at the same time, obtains the information of the atmosphere turbulence from the beacon to the receiver. When the laser beam is focused on different height, the lidar receives the backscattering light coming from the corresponding beacon in that height, thus an atmosphere turbulence profile could be obtained through algorithms. The profile of the refractive index structure constant is presented using the lidar and this lidar system can be used for turbulence profiles in contrast
A new system is developed for real-time monitoring of the optical turbulence altitude profile. A laser beam is transmitted and focused on certain height to form an artificial beacon. Its backscattering light propagates through the atmosphere. The lidar receives the signal coming from the scatter light of beacon and, at the same time, obtains the information of the atmosphere turbulence from the beacon to the receiver. When the laser beam is focused on different height, the lidar receives the backscattering light coming from the corresponding beacon in that height, thus an atmosphere turbulence profile could be obtained through algorithms. The profile of the refractive index structure constant is presented using the lidar and this lidar system can be used for turbulence profiles in contrast
2006,
18.
Abstract:
The optical trubulence on the coast has been measured with balloon borne thermosonde developed by ourselves.The thermosonde is lifted up to 20 km by hydrogen inflated balloons at a climbing rate of 4 m·s-1.The microthermal sensor is coupled to a meteorologic radiosonde(59 type),which is able to transmit pressure,temperature, humidity,and refractive index structure constant each 30 m height interval.The outer scale is estimated by Tatarski formula. Comparing with AFGL AMOS model,Hufnagel model,Xinglong fitting model based on balloon measurements from Xinglong station, Beijing observatory, it is shown that refractive index structure constant measured over sea is 2 orders of magnitude higher than those of the models. Profile of refractive index structure constant falls off slowly from the su
The optical trubulence on the coast has been measured with balloon borne thermosonde developed by ourselves.The thermosonde is lifted up to 20 km by hydrogen inflated balloons at a climbing rate of 4 m·s-1.The microthermal sensor is coupled to a meteorologic radiosonde(59 type),which is able to transmit pressure,temperature, humidity,and refractive index structure constant each 30 m height interval.The outer scale is estimated by Tatarski formula. Comparing with AFGL AMOS model,Hufnagel model,Xinglong fitting model based on balloon measurements from Xinglong station, Beijing observatory, it is shown that refractive index structure constant measured over sea is 2 orders of magnitude higher than those of the models. Profile of refractive index structure constant falls off slowly from the su
2006,
18.
Abstract:
In this paper, a theoretical model of the optical transmission was established to study the optical distortion resulted from the dynamic thermal effect. Numerical simulation shows that the optical distortion is mainly caused by the uniformity deformation of the end plane. In order to analyze how the dynamics thermal effect worked on the energy output, numerical calculation on the process of energy conversion in unsteady state was done, and the simulated result matched the experimental result precisely, which also showed that Boltzmann distribution of particle number was not the main reason for the rapid decline of output power when the temperature was under 400 K. The main reason of the rapid decline of output power was the deflection dissipation resulted from dynamic optical distortion.
In this paper, a theoretical model of the optical transmission was established to study the optical distortion resulted from the dynamic thermal effect. Numerical simulation shows that the optical distortion is mainly caused by the uniformity deformation of the end plane. In order to analyze how the dynamics thermal effect worked on the energy output, numerical calculation on the process of energy conversion in unsteady state was done, and the simulated result matched the experimental result precisely, which also showed that Boltzmann distribution of particle number was not the main reason for the rapid decline of output power when the temperature was under 400 K. The main reason of the rapid decline of output power was the deflection dissipation resulted from dynamic optical distortion.
2006,
18.
Abstract:
The thermal effect of the medium in the end-pumped Nd:YAG thin-disk laser on the wavefront distribution was studied, and the calculation expression of the beam distribution in the thin-disk laser was provided. The wavefront distributions of the thin disk pumped by the ideal beam and 4th order super-Gaussian beam were simulated. The relationships between the beam distortion and the laser medium thickness and uniformity of the pumped beam were analyzed. The results show that the thiner the thin-disk is, the more uniform the pumped beam is and the smaller the pump power density is, the smaller the beam distortion is. Compared with the thin-disk thickness and the pump power density, the influence of the intensity distribution of the pumped beam on the wavefront distributioin was greater.
The thermal effect of the medium in the end-pumped Nd:YAG thin-disk laser on the wavefront distribution was studied, and the calculation expression of the beam distribution in the thin-disk laser was provided. The wavefront distributions of the thin disk pumped by the ideal beam and 4th order super-Gaussian beam were simulated. The relationships between the beam distortion and the laser medium thickness and uniformity of the pumped beam were analyzed. The results show that the thiner the thin-disk is, the more uniform the pumped beam is and the smaller the pump power density is, the smaller the beam distortion is. Compared with the thin-disk thickness and the pump power density, the influence of the intensity distribution of the pumped beam on the wavefront distributioin was greater.
2006,
18.
Abstract:
In terms of Fourier optics, the amplitude expression of the output pulse from the misaligned tiled-grating compressor in the far-field is obtained. A theoretical model for the analysis of all the errors is put up, where the idea that the impact of alignment errors on the pulse is the additional phase delay and deflection is summarized. With the criterion that the encircled energy in one times diffraction limit should be kept more than 90% of the ideal case, a design is carried out for a 1 ps pulse with a size of 40 cm and the tolerances of every alignment error are obtained.
In terms of Fourier optics, the amplitude expression of the output pulse from the misaligned tiled-grating compressor in the far-field is obtained. A theoretical model for the analysis of all the errors is put up, where the idea that the impact of alignment errors on the pulse is the additional phase delay and deflection is summarized. With the criterion that the encircled energy in one times diffraction limit should be kept more than 90% of the ideal case, a design is carried out for a 1 ps pulse with a size of 40 cm and the tolerances of every alignment error are obtained.
2006,
18.
Abstract:
A suitable method is proposed for detecting and tracking dim target in IR image sequence with low contrast and moving background. According to the correlation of moving background and position continuity of the moving target, the movement of background is computed with image matching. Complicated background is removed. Target is detected and tracked through adaptive prediction and threshold segmentation. Sequence images of one hundred frames with dim target are processed. The experimental results show that the method can automatically detect the target and track it effectively and steadily.
A suitable method is proposed for detecting and tracking dim target in IR image sequence with low contrast and moving background. According to the correlation of moving background and position continuity of the moving target, the movement of background is computed with image matching. Complicated background is removed. Target is detected and tracked through adaptive prediction and threshold segmentation. Sequence images of one hundred frames with dim target are processed. The experimental results show that the method can automatically detect the target and track it effectively and steadily.
2006,
18.
Abstract:
The development of diamond like carbon(DLC) film coated optical windows with wide spectral transmission is presented in this paper. This DLC coated window can be used as an optical window in the spectral range of 0.53~12.00 μm with the transmission of higher than 70% in most of the spectral band. The uniformity of the film is better than 97% with the area of 60 mm. The optical performance and environment adaptability of the DLC coated window are also tested. It can not only work well in damp, hot or cold environment but also tolerate infrared high power lasers. The windows have been tested by “general specification for optical coatings” (GJB2485—95) and “specification for the coated window with wide spectral transmission”(Q/AF20087—2003).
The development of diamond like carbon(DLC) film coated optical windows with wide spectral transmission is presented in this paper. This DLC coated window can be used as an optical window in the spectral range of 0.53~12.00 μm with the transmission of higher than 70% in most of the spectral band. The uniformity of the film is better than 97% with the area of 60 mm. The optical performance and environment adaptability of the DLC coated window are also tested. It can not only work well in damp, hot or cold environment but also tolerate infrared high power lasers. The windows have been tested by “general specification for optical coatings” (GJB2485—95) and “specification for the coated window with wide spectral transmission”(Q/AF20087—2003).
2006,
18.
Abstract:
Nano-crystalline Cu ribbons were prepared by single-roll method under various technical parameters, and their structures were characterized by XRD. Experimental results show that the crystalline grain of nano-crystalline Cu ribbons is 65.17～121.8 nm. The quicker the speed of copper wheel is, the less the injected gas pressure is, the bigger the protective air pressure is, the colder the protect air is, and the smaller the crystalline grain is. There are distortion and fluctuation of crystalline lattice. All samples possess high preferred orientation crystallographic plane and (200) plane is the most prominent，(311) plane is the second, and other crystallographic planes are not highly preferred. The reason might be related to quick-quenching of single-roller method.
Nano-crystalline Cu ribbons were prepared by single-roll method under various technical parameters, and their structures were characterized by XRD. Experimental results show that the crystalline grain of nano-crystalline Cu ribbons is 65.17～121.8 nm. The quicker the speed of copper wheel is, the less the injected gas pressure is, the bigger the protective air pressure is, the colder the protect air is, and the smaller the crystalline grain is. There are distortion and fluctuation of crystalline lattice. All samples possess high preferred orientation crystallographic plane and (200) plane is the most prominent，(311) plane is the second, and other crystallographic planes are not highly preferred. The reason might be related to quick-quenching of single-roller method.
2006,
18.
Abstract:
Supercontinuum generation and self-focusing effect of ultra-short pulse propagation in Kerr media were investigated according to (3+1) dimensions' nonlinear Schrdinger equation. Results indicate that spectral super-broadening without self-focus can be achieved by adjusting the pump power and the beam diameter. The process of a small diameter ultra-high power pump beam propagating in BK7 glass with or without small scale modulation was simulated. The experimental results indicate that the near-field beam quality improves when the pump power decreases. In this case, the pump beam doesn't collapse by whole beam self-focus and other nonlinear effects are restrained. In order to keep pump intensity in propagating, the best input power used for supercontinuum generation is near the whole beam
Supercontinuum generation and self-focusing effect of ultra-short pulse propagation in Kerr media were investigated according to (3+1) dimensions' nonlinear Schrdinger equation. Results indicate that spectral super-broadening without self-focus can be achieved by adjusting the pump power and the beam diameter. The process of a small diameter ultra-high power pump beam propagating in BK7 glass with or without small scale modulation was simulated. The experimental results indicate that the near-field beam quality improves when the pump power decreases. In this case, the pump beam doesn't collapse by whole beam self-focus and other nonlinear effects are restrained. In order to keep pump intensity in propagating, the best input power used for supercontinuum generation is near the whole beam
2006,
18.
Abstract:
In order to analyze the far-field temperature gradient, a finite element analysis (FEA) of the heat transfer in hollow micro-sphere filled with ICF fuel was made, providing the border adiabatic, meshing the model intellectualizedly, and supposing the parameter as 3, the cell as triangle. When the work temperature of the target was 24 K,in order to maintain the balance of the gas bubble in the micro-sphere, the temperature gradient in the target was 14.02 K/cm, The digital simulation result showed that the external temperature gradient was 7.75 K/cm. The result fits well with the data achieved by experiment. This shows the mathematics model is credible, and can be applied in the manufacture of the cryogenic target.
In order to analyze the far-field temperature gradient, a finite element analysis (FEA) of the heat transfer in hollow micro-sphere filled with ICF fuel was made, providing the border adiabatic, meshing the model intellectualizedly, and supposing the parameter as 3, the cell as triangle. When the work temperature of the target was 24 K,in order to maintain the balance of the gas bubble in the micro-sphere, the temperature gradient in the target was 14.02 K/cm, The digital simulation result showed that the external temperature gradient was 7.75 K/cm. The result fits well with the data achieved by experiment. This shows the mathematics model is credible, and can be applied in the manufacture of the cryogenic target.
2006,
18.
Abstract:
Methyl-situ-modified silica sols were obtained by hydrolysis and co-condensation reactions occurred in base-catalyzed system by carefully controlling the sol-gel process of Methyltriethoxysilane (MTES) and Tetraethoxysilane (TEOS). Hydrophobic- antireflective silica film was then prepared by dipping-coating technique from the modified sols. As a result, the hydrophobicity of antireflective coating was highly improved. The properties of the films were characterized with atomic force microscope (AFM)，ultraviolet-visible spectrum (UV-Vis) and contact angle analyzer measurement. An Nd:YAG laser (1 064 nm,1 ns) was used to irradiate the film by “R on 1” method and the damage thresholds were measured. In addition, comparison was carried out between organically modified coating and pure silica
Methyl-situ-modified silica sols were obtained by hydrolysis and co-condensation reactions occurred in base-catalyzed system by carefully controlling the sol-gel process of Methyltriethoxysilane (MTES) and Tetraethoxysilane (TEOS). Hydrophobic- antireflective silica film was then prepared by dipping-coating technique from the modified sols. As a result, the hydrophobicity of antireflective coating was highly improved. The properties of the films were characterized with atomic force microscope (AFM)，ultraviolet-visible spectrum (UV-Vis) and contact angle analyzer measurement. An Nd:YAG laser (1 064 nm,1 ns) was used to irradiate the film by “R on 1” method and the damage thresholds were measured. In addition, comparison was carried out between organically modified coating and pure silica
2006,
18.
Abstract:
The effects of the environmental condition and the beam quality of the third harmonic UV laser with a pulse width of about 1 ns and a wavelength of 351 nm on the self-focusing intensity and self-focusing distance in fused silica were analyzed. The threshold of the nonlinear self-focusing of the UV laser was studied. The results show that, for the given beam quality of UV laser, the value of B integral remains almost the same, which can be defined as the threshold of the nonlinear self-focusing effect. The worse the beam quality is, the lower the threshold is. Furthermore, the dusts in the air can induce self-focusing in fused silica even for the input UV laser with uniform intensity and phase distributions. Moreover, when the dust particle is larger, the self-focusing effect is more obviou
The effects of the environmental condition and the beam quality of the third harmonic UV laser with a pulse width of about 1 ns and a wavelength of 351 nm on the self-focusing intensity and self-focusing distance in fused silica were analyzed. The threshold of the nonlinear self-focusing of the UV laser was studied. The results show that, for the given beam quality of UV laser, the value of B integral remains almost the same, which can be defined as the threshold of the nonlinear self-focusing effect. The worse the beam quality is, the lower the threshold is. Furthermore, the dusts in the air can induce self-focusing in fused silica even for the input UV laser with uniform intensity and phase distributions. Moreover, when the dust particle is larger, the self-focusing effect is more obviou
2006,
18.
Abstract:
By employing the method of the separation of variables in the circular-cylindrical system, a recursive formula for the electromagnetic fields in the metal coaxial line filled with multi-layer reciprocal chiral media is derived. The general mode eigenequation is given. In the same way the eigenequation for the metal circular waveguide filled with multi-layer reciprocal chiral media can also be obtained. From the general eigenequations of the metal coaxial line and the metal circular waveguide filled with multi-layer reciprocal chiral media, the mode eigenequations of the coaxial line and the circular waveguide filled with one-layer reciprocal chiral medium can be obtained. When the chiral parameter equals zero, the mode eigenequation of the metal coaxial line filled with ordinary one-layer
By employing the method of the separation of variables in the circular-cylindrical system, a recursive formula for the electromagnetic fields in the metal coaxial line filled with multi-layer reciprocal chiral media is derived. The general mode eigenequation is given. In the same way the eigenequation for the metal circular waveguide filled with multi-layer reciprocal chiral media can also be obtained. From the general eigenequations of the metal coaxial line and the metal circular waveguide filled with multi-layer reciprocal chiral media, the mode eigenequations of the coaxial line and the circular waveguide filled with one-layer reciprocal chiral medium can be obtained. When the chiral parameter equals zero, the mode eigenequation of the metal coaxial line filled with ordinary one-layer
2006,
18.
Abstract:
Through placing a thin hollow electron beam in the electronic tunnel of the tunneladder TNT, this article derived the linear theory of the tunneladder traveling wave tubes(TWT). A dispersion equation of the tunneladder TWT was derived, and the small signal gain and the working phase velocity were computed. The results manifest that the gain of the Tunneladder TWT is high, and the bandwidth is narrow. When the width of the channel varies from zero to the double of the ring radius, the linear gain decreases within 1%. When the ring radius augment 10%, the linear gain decreases 57%, and the ridge height augment 10%, the linear gain increases 62%. Thus, the width of the channel plays a small role on small signal gain, but the height of the ridge and the radius of the ring affect small signal g
Through placing a thin hollow electron beam in the electronic tunnel of the tunneladder TNT, this article derived the linear theory of the tunneladder traveling wave tubes(TWT). A dispersion equation of the tunneladder TWT was derived, and the small signal gain and the working phase velocity were computed. The results manifest that the gain of the Tunneladder TWT is high, and the bandwidth is narrow. When the width of the channel varies from zero to the double of the ring radius, the linear gain decreases within 1%. When the ring radius augment 10%, the linear gain decreases 57%, and the ridge height augment 10%, the linear gain increases 62%. Thus, the width of the channel plays a small role on small signal gain, but the height of the ridge and the radius of the ring affect small signal g
2006,
18.
Abstract:
An asymmetrical flat-plate guided-wave EMP simulator (MDES-60) with distributed terminators, which is mainly used for short-line test, has been designed and constructed. The volume between two parallel plates is 5 m long, 2 m wide and 1 m high. The whole simulator positioned above a concrete support is 1.5 m high. The design has been optimized by means of reducing the obliquity, widening the bottom plate and tuning the distributed terminator. The improvements allow a good E-field shape and uniformity inside the working volume. This simulator can simulate several kinds of EMP waveforms as defined by IEC61000-2-9, Bell laboratory and standard in 1976 publication, with the peak E-field strengths of 15~60 kV/m available, when being energized by corresponding transient pulse source.
An asymmetrical flat-plate guided-wave EMP simulator (MDES-60) with distributed terminators, which is mainly used for short-line test, has been designed and constructed. The volume between two parallel plates is 5 m long, 2 m wide and 1 m high. The whole simulator positioned above a concrete support is 1.5 m high. The design has been optimized by means of reducing the obliquity, widening the bottom plate and tuning the distributed terminator. The improvements allow a good E-field shape and uniformity inside the working volume. This simulator can simulate several kinds of EMP waveforms as defined by IEC61000-2-9, Bell laboratory and standard in 1976 publication, with the peak E-field strengths of 15~60 kV/m available, when being energized by corresponding transient pulse source.
2006,
18.
Abstract:
The characteristic of high power microwave(HPM) propagation through ionosphere is mainly determined by the diversification of the atmospheric refractive index, while the refractive index has positive correlation with the electron concentration at corresponding propagation layer. The critical frequency of ionosphere in linearity condition and the atmospheric refractive index formula are derived. The electron concentration and the atmospheric refractive index are numerically simulated based on ionospheric electron concentration distributing model. The diversification of the refractive index and the refractive index gradient relating to the altitude are also analyzed, and experiment has been taken under low power microwave condition which validates that the corrected value is closer to the pr
The characteristic of high power microwave(HPM) propagation through ionosphere is mainly determined by the diversification of the atmospheric refractive index, while the refractive index has positive correlation with the electron concentration at corresponding propagation layer. The critical frequency of ionosphere in linearity condition and the atmospheric refractive index formula are derived. The electron concentration and the atmospheric refractive index are numerically simulated based on ionospheric electron concentration distributing model. The diversification of the refractive index and the refractive index gradient relating to the altitude are also analyzed, and experiment has been taken under low power microwave condition which validates that the corrected value is closer to the pr
2006,
18.
Abstract:
The calculation of coaxial output cavities, simulation of microwave extraction from a modulated intense relativistic electron beams, optimization on beams and output cavity geometry parameters, as well as the experiments of microwave extraction for an S-band long-pulse-intense-current relativistic klystron amplifier are described in this paper. Applying a three dimensional code, an output power of 500 MW is obtained. The efficiency is about 21.5%. In experiments, a hollow electron beam of 550 kV, 4 kA generates an electron beam with modulated current of 3.2 kA after idler cavity gap. About 500 MW RF power is obtained. The efficiency is about 22.7%.The results of simulation agree well with the experimental results.
The calculation of coaxial output cavities, simulation of microwave extraction from a modulated intense relativistic electron beams, optimization on beams and output cavity geometry parameters, as well as the experiments of microwave extraction for an S-band long-pulse-intense-current relativistic klystron amplifier are described in this paper. Applying a three dimensional code, an output power of 500 MW is obtained. The efficiency is about 21.5%. In experiments, a hollow electron beam of 550 kV, 4 kA generates an electron beam with modulated current of 3.2 kA after idler cavity gap. About 500 MW RF power is obtained. The efficiency is about 22.7%.The results of simulation agree well with the experimental results.
2006,
18.
Abstract:
BEPCII upgrading project needs a new high current electron gun. The design stage such as physical design, mechanical design and control system design of this new electron gun is described. The emission current is designed to be higher than 10 A for the pulse width of 1 ns with repetition rate of 50 Hz. The gun will operate with a pulsed high voltage power supply which can provide up to 200 kV high voltage. Computer simulations and optimizations have been carried out in the design stage, including the gun geometry and beam transport. EGUN and DGUN codes are used to simulate the gun geometry, and the results show that the perveance is about 0.22 mA·V-3/2, and the emittance at gun exit is about 16 p·mm·mrad. PARMELA code shows that the electron beam can be easily transported to
BEPCII upgrading project needs a new high current electron gun. The design stage such as physical design, mechanical design and control system design of this new electron gun is described. The emission current is designed to be higher than 10 A for the pulse width of 1 ns with repetition rate of 50 Hz. The gun will operate with a pulsed high voltage power supply which can provide up to 200 kV high voltage. Computer simulations and optimizations have been carried out in the design stage, including the gun geometry and beam transport. EGUN and DGUN codes are used to simulate the gun geometry, and the results show that the perveance is about 0.22 mA·V-3/2, and the emittance at gun exit is about 16 p·mm·mrad. PARMELA code shows that the electron beam can be easily transported to
2006,
18.
Abstract:
To abstract linear optics of storage ring, response matrix fitting technique was developed as an advanced diagnostic tool of storage ring. The Matlab-based LOCO(Linear Optics of Closed Orbit) was a representative of response matrix fitting codes. Recently, in order to get accurate lattice model of storage ring, LOCO was applied to Hefei light source. In this paper, firstly the principle of response matrix fitting was briefly reviewed and the numerical simulation of application of LOCO to HLS storage ring and the simulation results were introduced. Through numerical simulation, the effect of BPM noise level on accuracy of fitting results was demonstrated. Finally, experimental results made at Hefei light source to calibrate focusing strength of quadrupoles and edge focusing strength of dipo
To abstract linear optics of storage ring, response matrix fitting technique was developed as an advanced diagnostic tool of storage ring. The Matlab-based LOCO(Linear Optics of Closed Orbit) was a representative of response matrix fitting codes. Recently, in order to get accurate lattice model of storage ring, LOCO was applied to Hefei light source. In this paper, firstly the principle of response matrix fitting was briefly reviewed and the numerical simulation of application of LOCO to HLS storage ring and the simulation results were introduced. Through numerical simulation, the effect of BPM noise level on accuracy of fitting results was demonstrated. Finally, experimental results made at Hefei light source to calibrate focusing strength of quadrupoles and edge focusing strength of dipo
2006,
18.
Abstract:
The high intense electron beam interacts with a high Z target, producing the X-rays for flash radiography. The focal spot size of the X-ray source is a critical parameter which degrades resolution in the flash radiography. This paper describes a slit which is used to measure the focal spot size. The X-ray spot image is obtained through the slit. The line spread function(LSF) and modulation transfer function(MTF) of X-ray spot are obtained from the slit image data, and the X-ray spot size is determined by the MTF. The measured X-ray spot size of the 12 MeV linear induction accelerator(LIA) is 3.2 mm. Different focal lengths are used, and the relevant X-ray spots size is measured for tuning the accelerator.
The high intense electron beam interacts with a high Z target, producing the X-rays for flash radiography. The focal spot size of the X-ray source is a critical parameter which degrades resolution in the flash radiography. This paper describes a slit which is used to measure the focal spot size. The X-ray spot image is obtained through the slit. The line spread function(LSF) and modulation transfer function(MTF) of X-ray spot are obtained from the slit image data, and the X-ray spot size is determined by the MTF. The measured X-ray spot size of the 12 MeV linear induction accelerator(LIA) is 3.2 mm. Different focal lengths are used, and the relevant X-ray spots size is measured for tuning the accelerator.
2006,
18.
Abstract:
The paper describes the equipment of integral measurement of dipole magnetic field for HIRFL-CSRe and introduces integral field measurement method and content. In order to adjust the effective length of magnet and to improve the dispersivity of the 16 dipole magnets, dispersivity is ceaselessly measured after adding or taking out silicon steel slice or changing current of rectifiable coil. After magnetic padding and measurement, the dispersivity of dipole magnets satisfies the requirement of CSR project. The final measurement result of integral magnetic field distribution and transfer function is given. The magnet design and manufacture are also emended with measurement data.
The paper describes the equipment of integral measurement of dipole magnetic field for HIRFL-CSRe and introduces integral field measurement method and content. In order to adjust the effective length of magnet and to improve the dispersivity of the 16 dipole magnets, dispersivity is ceaselessly measured after adding or taking out silicon steel slice or changing current of rectifiable coil. After magnetic padding and measurement, the dispersivity of dipole magnets satisfies the requirement of CSR project. The final measurement result of integral magnetic field distribution and transfer function is given. The magnet design and manufacture are also emended with measurement data.
2006,
18.
Abstract:
The principle and technical advantages of a linear transformer driver are introduced and the critical points in designing the fast LTD stage are presented. A fast LTD stage with current rising time less than 100 ns was designed and primary experiments were conducted on this stage. According to the experiment results, the stage can provide a current of 23.7 kA with a quarter period of 69.6 ns to a shorted load when charged to ±16 kV. When charged to ±50 kV, the stage can provide a current of 41.4 kA in 36.8 ns (10%~90% peak value of current) to a matched load of 0.85 Ω.
The principle and technical advantages of a linear transformer driver are introduced and the critical points in designing the fast LTD stage are presented. A fast LTD stage with current rising time less than 100 ns was designed and primary experiments were conducted on this stage. According to the experiment results, the stage can provide a current of 23.7 kA with a quarter period of 69.6 ns to a shorted load when charged to ±16 kV. When charged to ±50 kV, the stage can provide a current of 41.4 kA in 36.8 ns (10%~90% peak value of current) to a matched load of 0.85 Ω.
2006,
18.
Abstract:
The ultra-wide band(UWB) impulse radar system is developed and studied, which includes a solid state pulser based on power synthesis technology, an UWB planar TEM horn antenna array for transmitting, an UWB slot array for receiving, a quadrature demodulation receiver and a computer. By heightening the distances between the ground and the target, and the transmitting and receiving arrays, and adding the time window, the radar system can detect the target which is 2 km away and the RCS of optics area is 0.01 m2, which shows that the system is feasible. The echo signal is stronger when 16 transmitting cells are adopted than that when 8 transmitting cells are adopted, which shows that the technology of power synthesis is effective.
The ultra-wide band(UWB) impulse radar system is developed and studied, which includes a solid state pulser based on power synthesis technology, an UWB planar TEM horn antenna array for transmitting, an UWB slot array for receiving, a quadrature demodulation receiver and a computer. By heightening the distances between the ground and the target, and the transmitting and receiving arrays, and adding the time window, the radar system can detect the target which is 2 km away and the RCS of optics area is 0.01 m2, which shows that the system is feasible. The echo signal is stronger when 16 transmitting cells are adopted than that when 8 transmitting cells are adopted, which shows that the technology of power synthesis is effective.
2006,
18.
Abstract:
This paper mainly discusses the life characteristic and failure mechanism of the multilayer ceramic capacitor (MLC) under various working conditions such as charge-discharge frequency, charge voltage, charge-discharge duty radio and discharge inverse peak factor. Experiments discover that the breakdown of MLC is the result of continuous extending of partial discharge. Exothermicity and alternating internal stress are the key factors which make partial discharge channels keep on growing. The increase of charge-discharge frequency shortens the life of MLC by accelerating the heat production. The increase of charge voltage and discharge inverse peak factor make the life of MLC over 90％ shorter by enhancing both heat production and internal stress of the dielectric. An effective method to inc
This paper mainly discusses the life characteristic and failure mechanism of the multilayer ceramic capacitor (MLC) under various working conditions such as charge-discharge frequency, charge voltage, charge-discharge duty radio and discharge inverse peak factor. Experiments discover that the breakdown of MLC is the result of continuous extending of partial discharge. Exothermicity and alternating internal stress are the key factors which make partial discharge channels keep on growing. The increase of charge-discharge frequency shortens the life of MLC by accelerating the heat production. The increase of charge voltage and discharge inverse peak factor make the life of MLC over 90％ shorter by enhancing both heat production and internal stress of the dielectric. An effective method to inc
2006,
18.
Abstract:
The paper discusses the magnetic-core structure of high power pulse transformer and its magnetic-core material selection. The effect of magnetic core on the distribution of transformer electric and magnetic field and the coupling coefficient is theoretically simulated and analyzed. The experimental and theoretic results indicate that the coupling coefficient is increased and the distribution field is improved by using magnetic core. In this case, the coupling coefficient of the transformer with magnetic core is up to 0.88. Compared with air-core transformer of the same size, its coupling coefficient increases 10%.
The paper discusses the magnetic-core structure of high power pulse transformer and its magnetic-core material selection. The effect of magnetic core on the distribution of transformer electric and magnetic field and the coupling coefficient is theoretically simulated and analyzed. The experimental and theoretic results indicate that the coupling coefficient is increased and the distribution field is improved by using magnetic core. In this case, the coupling coefficient of the transformer with magnetic core is up to 0.88. Compared with air-core transformer of the same size, its coupling coefficient increases 10%.
2006,
18.
Abstract:
The explosively-driven flux compression generators(FCGs) are always used to drive pulse modulators, and high power pulses can be generated on the diodes. In this paper, two dynamically cascaded FCGs were ignited one after another to drive a modulator made up of a pulsed transformer and a pulse forming line(PFL). The two FCGs were controlled by a selftimer with 20 ms interval and the electrical isolation between them was achieved by two fuses. Two pulses with peak power more than 20 GW and pulse interval 20 ms were generated on the diode. The experiment shows that multiple pulses could be obtained by a single modulator if more driving FCGs are used. This method could test the pulsed power apparatus' electricity recovery characteristics, which are necessary to build high power and high repet
The explosively-driven flux compression generators(FCGs) are always used to drive pulse modulators, and high power pulses can be generated on the diodes. In this paper, two dynamically cascaded FCGs were ignited one after another to drive a modulator made up of a pulsed transformer and a pulse forming line(PFL). The two FCGs were controlled by a selftimer with 20 ms interval and the electrical isolation between them was achieved by two fuses. Two pulses with peak power more than 20 GW and pulse interval 20 ms were generated on the diode. The experiment shows that multiple pulses could be obtained by a single modulator if more driving FCGs are used. This method could test the pulsed power apparatus' electricity recovery characteristics, which are necessary to build high power and high repet
2006,
18.
Abstract:
Gas discharge performance of LaB6 in helium and nitrogen is reported. The results show that as the voltage rises, the discharge mechanism changes from glow discharge into arc discharge, the helium discharge tube can work long time and steadily under impulses. The peak value of discharge current is more than 120 A when the pulse voltage is 2.2 kV, the pulse width is 10 ms, frequency is 13.3 Hz. In the discharging process, the ions can clean and activate the surfaces of the cathodes, which can reduce the work function of the cathodes, improve the discharge tubes’ emission capability and stability. As electrode, LaB6 has the advantages of long lifetime, short breakdown time delay, great current, etc., so it is suitable to be applied in repetitive pulsed gas discharge components with large cu
Gas discharge performance of LaB6 in helium and nitrogen is reported. The results show that as the voltage rises, the discharge mechanism changes from glow discharge into arc discharge, the helium discharge tube can work long time and steadily under impulses. The peak value of discharge current is more than 120 A when the pulse voltage is 2.2 kV, the pulse width is 10 ms, frequency is 13.3 Hz. In the discharging process, the ions can clean and activate the surfaces of the cathodes, which can reduce the work function of the cathodes, improve the discharge tubes’ emission capability and stability. As electrode, LaB6 has the advantages of long lifetime, short breakdown time delay, great current, etc., so it is suitable to be applied in repetitive pulsed gas discharge components with large cu
2006,
18.
Abstract:
Due to the high density of the prebreakdown current of explosive electron emission, the space charge effect should be considered in the simulation of the initial thermal instability of explosive electron emission. Based on the metallic microprtrusion model of explosive electron emission, a model dealing with the space charge effect is presented. The simulation results show that the space charge effect could greatly lengthen the delay time of explosive electron emission. According to the simulation, the thermal instability process is strongly affected by the space charge effect of prebreakdown current. The space charge effect of prebreakdown current should not be neglected in the analysis of microprotrusion model of explosive electron emission.
Due to the high density of the prebreakdown current of explosive electron emission, the space charge effect should be considered in the simulation of the initial thermal instability of explosive electron emission. Based on the metallic microprtrusion model of explosive electron emission, a model dealing with the space charge effect is presented. The simulation results show that the space charge effect could greatly lengthen the delay time of explosive electron emission. According to the simulation, the thermal instability process is strongly affected by the space charge effect of prebreakdown current. The space charge effect of prebreakdown current should not be neglected in the analysis of microprotrusion model of explosive electron emission.
2006,
18.
Abstract:
A new coupled-mode theory based on scalar modes is presented for the anisotropic waveguide with random disturbance via Helmholtz equation and a modified dielectric tensor. The polarization coupling term and birefringence coupling term are included in the coupling coefficient expression. In addition, the numerical modeling of the propagation is made constant for the Ti: LiNbO3 with the Marcatili's approximation and the first-order perturbation. It is found that the change of the propagation constant due to birefringence coupling is about as three percent as that due to the main perturbation term, which shows that the birefringence can not be neglected for the Ti: LiNbO3 rectangle waveguide. The work has a guidance to the study of the optical waveguide devices with the Ti: LiNbO3 waveguide.
A new coupled-mode theory based on scalar modes is presented for the anisotropic waveguide with random disturbance via Helmholtz equation and a modified dielectric tensor. The polarization coupling term and birefringence coupling term are included in the coupling coefficient expression. In addition, the numerical modeling of the propagation is made constant for the Ti: LiNbO3 with the Marcatili's approximation and the first-order perturbation. It is found that the change of the propagation constant due to birefringence coupling is about as three percent as that due to the main perturbation term, which shows that the birefringence can not be neglected for the Ti: LiNbO3 rectangle waveguide. The work has a guidance to the study of the optical waveguide devices with the Ti: LiNbO3 waveguide.
2006,
18.
Abstract:
Contrastive experiment of hydrogen gas discharge source bombarding targets has been done. The result of contrast between hydrogen gas discharge source bombarding new and used targets ensures that a kind of anomalous particles have been produced through hydrogen gas discharge and it is proved that new spectral lines have been eradiated when X-ray or particle beam bombarding the anomalous particles. It is concluded that the new spectral lines are energy level lines of anomalous particles and domonstrate the anomalous particle’s energy level characteristics. The new spectral lines are the sign of anomalous particles.
Contrastive experiment of hydrogen gas discharge source bombarding targets has been done. The result of contrast between hydrogen gas discharge source bombarding new and used targets ensures that a kind of anomalous particles have been produced through hydrogen gas discharge and it is proved that new spectral lines have been eradiated when X-ray or particle beam bombarding the anomalous particles. It is concluded that the new spectral lines are energy level lines of anomalous particles and domonstrate the anomalous particle’s energy level characteristics. The new spectral lines are the sign of anomalous particles.
2006,
18.
Abstract:
Effects of ultrasonic cleaning and laser conditioning of antireflective coatings on laser damage behaviors were investigated. The antireflective coatings at 1 064 nm were prepared by electron beam evaporation, and the samples were post-treated by ultrasonic cleaning and laser conditioning respectively. Laser induced damage threshold(LIDT) was measured and the damage morphologies were plotted by optical profiler. It was found that both ultrasonic cleaning and laser conditioning could improve the LIDT of coatings, but laser conditioning gained much higher enhancement. The damage depth had no obvious change before and after ultrasonic cleaning, while the depth became very shallow after laser conditioning compared with that before laser conditioning. The reason is that the ultrasonic cleaning
Effects of ultrasonic cleaning and laser conditioning of antireflective coatings on laser damage behaviors were investigated. The antireflective coatings at 1 064 nm were prepared by electron beam evaporation, and the samples were post-treated by ultrasonic cleaning and laser conditioning respectively. Laser induced damage threshold(LIDT) was measured and the damage morphologies were plotted by optical profiler. It was found that both ultrasonic cleaning and laser conditioning could improve the LIDT of coatings, but laser conditioning gained much higher enhancement. The damage depth had no obvious change before and after ultrasonic cleaning, while the depth became very shallow after laser conditioning compared with that before laser conditioning. The reason is that the ultrasonic cleaning
2006,
18.
Abstract:
It is pointed out that the depth of focus, diffraction from aperture and radiation scattering are three main sources for image blurring of CCD receiving system. The radiation scattering is studied by MCNP simulation. The distributions of energy deposition in CsI:Tl crystal under different energy spectrum and depth of screen are given. It is shown that energy deposition increases linearly with the depth of screen increasing. The blurring from radiation scattering is related with the spectrum of photons. Furthermore, the blurring caused by the hardened spectrum changing with the depth of screen is less than that by non-hardened spectrum. It can be seen that the radiation scattering is the main source for image blurring, and the blurring from radiation scattering is different from the Gaussia
It is pointed out that the depth of focus, diffraction from aperture and radiation scattering are three main sources for image blurring of CCD receiving system. The radiation scattering is studied by MCNP simulation. The distributions of energy deposition in CsI:Tl crystal under different energy spectrum and depth of screen are given. It is shown that energy deposition increases linearly with the depth of screen increasing. The blurring from radiation scattering is related with the spectrum of photons. Furthermore, the blurring caused by the hardened spectrum changing with the depth of screen is less than that by non-hardened spectrum. It can be seen that the radiation scattering is the main source for image blurring, and the blurring from radiation scattering is different from the Gaussia
2006,
18.
Abstract:
Penetrating depth and dose distribution of electron beam in flue gas can influence efficiency of desulfurization and denitration. Beam energy loss during passing through the metal foil window has been calculated by theory and Monte Carlo simulation. Electron beam penetrating depth and dose distribution in the flue gas irradiation vessel have been obtained as well. Some conclusions have been gotten: the optimal electron beam energy is 700 keV. Cross sectional dimensions of the reaction chamber is selected about 1.0 m×3.5 m. The work mode is face to face irradiation with two electron accelerators.
Penetrating depth and dose distribution of electron beam in flue gas can influence efficiency of desulfurization and denitration. Beam energy loss during passing through the metal foil window has been calculated by theory and Monte Carlo simulation. Electron beam penetrating depth and dose distribution in the flue gas irradiation vessel have been obtained as well. Some conclusions have been gotten: the optimal electron beam energy is 700 keV. Cross sectional dimensions of the reaction chamber is selected about 1.0 m×3.5 m. The work mode is face to face irradiation with two electron accelerators.
2006,
18.
Abstract:
The profile and its detail information of the center projecting line of the radiographic image is interpreted with the results of the Monte Carlo simulation. It is found that the scatter, the source spot size and the shape of H-D characteristic curve all affect the experimental gray curve and its detail information of the center projecting line. The more the scatter exposure is, the lower the amplitude of the center signal is. The severer the non-linearity on the toe of H-D curve is, the lower the amplitude of the center signal is. It is pointed out that comparing the experimental gray curve with the Monte Carlo simulation results can ensure the scatter level and the source spot size half-quantitatively. When the exposure is being measured, the scatter interference should be removed. It is
The profile and its detail information of the center projecting line of the radiographic image is interpreted with the results of the Monte Carlo simulation. It is found that the scatter, the source spot size and the shape of H-D characteristic curve all affect the experimental gray curve and its detail information of the center projecting line. The more the scatter exposure is, the lower the amplitude of the center signal is. The severer the non-linearity on the toe of H-D curve is, the lower the amplitude of the center signal is. It is pointed out that comparing the experimental gray curve with the Monte Carlo simulation results can ensure the scatter level and the source spot size half-quantitatively. When the exposure is being measured, the scatter interference should be removed. It is
2006,
18.
Abstract:
The Nd3+ doped 2% 40B2O3-(15-χ)Nb2O5-45BaO-χLa2O3(χ=10, 7.5, 5, 2.5, molar percent) glass was prepared by melting method. The absorption, emission spectra and DTA curves of the glass were measured. The Judd-Ofelt parameters were calculated from their emission spectra. Various spectroscopic parameters, such as the radiative transition probabilities, total radiative transition probability, radiative lifetime, branching ratios and the stimulated emission cross-sections between the metastable 4F3/2 and terminal 4I11/2 were obtained with the help of J-O parameters. The result showed that with the increase of Nb2O5 and decrease of La2O3 content, the intensity parameters Ω2 and the thermal stability increased, while the intensity parameters Ω6 and the stimulated emission cross-sections decre
The Nd3+ doped 2% 40B2O3-(15-χ)Nb2O5-45BaO-χLa2O3(χ=10, 7.5, 5, 2.5, molar percent) glass was prepared by melting method. The absorption, emission spectra and DTA curves of the glass were measured. The Judd-Ofelt parameters were calculated from their emission spectra. Various spectroscopic parameters, such as the radiative transition probabilities, total radiative transition probability, radiative lifetime, branching ratios and the stimulated emission cross-sections between the metastable 4F3/2 and terminal 4I11/2 were obtained with the help of J-O parameters. The result showed that with the increase of Nb2O5 and decrease of La2O3 content, the intensity parameters Ω2 and the thermal stability increased, while the intensity parameters Ω6 and the stimulated emission cross-sections decre
