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RSS2015 Vol. 27, No. 04
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2015,
27: 040101.
doi: 10.11884/HPLPB201527.040101
Abstract:
Common Aperture Spectral Beam Combination (SBC) of multiple high power fiber lasers output into a composite beam via a multi-layer dielectric (MLD) gratingis a promising approach for the fiber laser system to scale the output power further while maintaining high efficiency and excellent beam quality simultaneously. A common aperture SBC system with dual-grating dispersion compensation configuration based on five kW-level narrow-linewidth fiber amplifier chains in all-fiber format is set up. A common aperture combing beam is achieved with high efficiency and excellent beam quality in the system by using China-made MLD gratings. The maximum average output power of 5.07 kW of the combined beam and the combination efficiency of 91.2% are obtained. The beam quality factor M2 at a power level of 5 kW is less than 3. The preliminary experimental results have shown that MLD grating, which can maintain high diffraction efficiency in a wide spectrum range under high power level operation, is a perfect element for SBC of high power fiber laser. The results also demonstrate that the beam quality and the linewidth of the individual fiber laser are the key factors affecting the beam quality of the spectral combining beam. Presently, the output power is limited by the amount of the narrow-linewidth fiber amplifier chains and the output power of the individual narrow-linewidth fiber amplifier. So it can be expected that the common aperture SBC system output power can be further scaled.
Common Aperture Spectral Beam Combination (SBC) of multiple high power fiber lasers output into a composite beam via a multi-layer dielectric (MLD) gratingis a promising approach for the fiber laser system to scale the output power further while maintaining high efficiency and excellent beam quality simultaneously. A common aperture SBC system with dual-grating dispersion compensation configuration based on five kW-level narrow-linewidth fiber amplifier chains in all-fiber format is set up. A common aperture combing beam is achieved with high efficiency and excellent beam quality in the system by using China-made MLD gratings. The maximum average output power of 5.07 kW of the combined beam and the combination efficiency of 91.2% are obtained. The beam quality factor M2 at a power level of 5 kW is less than 3. The preliminary experimental results have shown that MLD grating, which can maintain high diffraction efficiency in a wide spectrum range under high power level operation, is a perfect element for SBC of high power fiber laser. The results also demonstrate that the beam quality and the linewidth of the individual fiber laser are the key factors affecting the beam quality of the spectral combining beam. Presently, the output power is limited by the amount of the narrow-linewidth fiber amplifier chains and the output power of the individual narrow-linewidth fiber amplifier. So it can be expected that the common aperture SBC system output power can be further scaled.
2015,
27: 041001.
doi: 10.11884/HPLPB201527.041001
Abstract:
The fast attenuation algorithm of laser intensity is presented in this paper to shorten the time of precisely adjusting attenuation rate. The accurate adjustment of attenuation rate is determined by both the current attenuation rate and the maximal gray level of practically sampled spot image. When the collected spot image was distorted by the saturation of the optoelectronic receiving device, the light spot image could be dealt with by removing the saturated portion of the light intensity information and simulating by tree-dimension Gaussian fitting based on the least squares method. Then the real distribution and amplitude of the laser intensity could be restored. If the attenuation rate is very large, the present amplitude can be obtained directly. The appropriate attenuation adjustment rate can be calculated based on the real distribution and amplitude of the laser intensity. Laser intensity was adjusted fast and accurately. The validity of the fast attenuation algorithm was testified by the experiment of CCD and stepper motor-driven double wheels attenuator.
The fast attenuation algorithm of laser intensity is presented in this paper to shorten the time of precisely adjusting attenuation rate. The accurate adjustment of attenuation rate is determined by both the current attenuation rate and the maximal gray level of practically sampled spot image. When the collected spot image was distorted by the saturation of the optoelectronic receiving device, the light spot image could be dealt with by removing the saturated portion of the light intensity information and simulating by tree-dimension Gaussian fitting based on the least squares method. Then the real distribution and amplitude of the laser intensity could be restored. If the attenuation rate is very large, the present amplitude can be obtained directly. The appropriate attenuation adjustment rate can be calculated based on the real distribution and amplitude of the laser intensity. Laser intensity was adjusted fast and accurately. The validity of the fast attenuation algorithm was testified by the experiment of CCD and stepper motor-driven double wheels attenuator.
2015,
27: 041002.
doi: 10.11884/HPLPB201527.041002
Abstract:
Based on the reduced growth rate equation of electron density, a theoretical model is established to describe the change of the conduction band electron density of fused silica with the laser pulse duration. Using the concept of the critical electron density, a scope of the laser-induced damage of fused silica is calculated with the pulse width from 150 fs to 10 ps. The analysis shows that the avalanche ionization still takes a leading role from 5 ps to 10 ps. Instead of electrons provided by the fused silica itself, the initial electrons produced by the photoionization make a contribution to the impact ionization. It reaches a balance between avalanche ionization and photoionization when the pulse width shrinks to 4 ps. After that, the photoionization plays a main role in the growth of the conduction band electron density. Through the fitting curve, a new pulse width law is obtained to satisfy the laser-induced damage threshold changing from 150 fs to 10 ps. The results demonstrate that the threshold is proportional to tp0.38(tp is the pulse width), and changes to tp0.34 when the temperature dependence is concerned.
Based on the reduced growth rate equation of electron density, a theoretical model is established to describe the change of the conduction band electron density of fused silica with the laser pulse duration. Using the concept of the critical electron density, a scope of the laser-induced damage of fused silica is calculated with the pulse width from 150 fs to 10 ps. The analysis shows that the avalanche ionization still takes a leading role from 5 ps to 10 ps. Instead of electrons provided by the fused silica itself, the initial electrons produced by the photoionization make a contribution to the impact ionization. It reaches a balance between avalanche ionization and photoionization when the pulse width shrinks to 4 ps. After that, the photoionization plays a main role in the growth of the conduction band electron density. Through the fitting curve, a new pulse width law is obtained to satisfy the laser-induced damage threshold changing from 150 fs to 10 ps. The results demonstrate that the threshold is proportional to tp0.38(tp is the pulse width), and changes to tp0.34 when the temperature dependence is concerned.
2015,
27: 041003.
doi: 10.11884/HPLPB201527.041003
Abstract:
A lamp pumped high peak power electro-optical Q-switched Nd:YAG 266 nm UV laser was demonstrated. In combination with the KDP crystal properties, and based on the frequency doubling theory, the influence of KDP crystal length on the conversion efficiency under the condition of existence phase mismatching was analyzed considering the walk-off effect. The compact flat cavity structure was used and the 1064 nm laser generated from lamp pumped electro-optical Q-switched Nd:YAG laser was used as fundamental frequency laser. A type Ⅱ phase-matched KTP crystal and a type Ⅰ phase-matched KDP crystal were used for the extra-cavity second-harmonic generation and fourth-harmonic generation respectively. Using energy meter, oscilloscope and other instruments, the UV laser pulse energy of 35 mJ/pulse at the repetition rate of 1 Hz and the pulse width of 6.0 ns at 266 nm were achieved, the peak power was 5.83 MW. UV laser pulse energy of 28.9 mJ/pulse at 266 nm was achieved at the repetition rate of 10 Hz. A conversion efficiency of 532 nm to 266 nm was up to 31.9%. Laser marking and laser engraving can be achieved with this high peak power, short pulse width 266 nm UV laser.
A lamp pumped high peak power electro-optical Q-switched Nd:YAG 266 nm UV laser was demonstrated. In combination with the KDP crystal properties, and based on the frequency doubling theory, the influence of KDP crystal length on the conversion efficiency under the condition of existence phase mismatching was analyzed considering the walk-off effect. The compact flat cavity structure was used and the 1064 nm laser generated from lamp pumped electro-optical Q-switched Nd:YAG laser was used as fundamental frequency laser. A type Ⅱ phase-matched KTP crystal and a type Ⅰ phase-matched KDP crystal were used for the extra-cavity second-harmonic generation and fourth-harmonic generation respectively. Using energy meter, oscilloscope and other instruments, the UV laser pulse energy of 35 mJ/pulse at the repetition rate of 1 Hz and the pulse width of 6.0 ns at 266 nm were achieved, the peak power was 5.83 MW. UV laser pulse energy of 28.9 mJ/pulse at 266 nm was achieved at the repetition rate of 10 Hz. A conversion efficiency of 532 nm to 266 nm was up to 31.9%. Laser marking and laser engraving can be achieved with this high peak power, short pulse width 266 nm UV laser.
2015,
27: 041004.
doi: 10.11884/HPLPB201527.041004
Abstract:
According to the characteristics of infrared dim targets in strong clutter background, this paper presents a method of detecting frared dim signals based on adaptive filtering, which denoises the images first, then eliminates the background based on adaptive filtering enhanced target signals and deletes the false targets based on the determination principles of point target imaging signals characteristics from testing. The algorithm effectively solves the contradiction of the photoelectric detection equipment between high detection probability and low false alarm rate. The test results show that this method can effectively extract the dim signal targets with the small area SNR 4 from the single frame images, and that the detection probability is not less than 0.75, and the false alarm rate is not heigher than 1 time at 100 frames.
According to the characteristics of infrared dim targets in strong clutter background, this paper presents a method of detecting frared dim signals based on adaptive filtering, which denoises the images first, then eliminates the background based on adaptive filtering enhanced target signals and deletes the false targets based on the determination principles of point target imaging signals characteristics from testing. The algorithm effectively solves the contradiction of the photoelectric detection equipment between high detection probability and low false alarm rate. The test results show that this method can effectively extract the dim signal targets with the small area SNR 4 from the single frame images, and that the detection probability is not less than 0.75, and the false alarm rate is not heigher than 1 time at 100 frames.
2015,
27: 041005.
doi: 10.11884/HPLPB201527.041005
Abstract:
A grating and a collimating lens are used to replace the transformer lens in the traditional spectral beam combining structure. As a result, the degradation of the beam quality and the cross-talk are prevented. A spectral beam combining with narrow line-width is achieved. A standard semiconductor laser array is employed in this experiment. An output power of 44.8 W and an electro-optic conversion efficiency of 38.9% are achieved. The spectral line-width is 4.1 nm. A beam quality factor of 1.3711.7 in fast and slow axis directions are obtained. The beam quality of the output is close to that of a single emitter of the array in both directions.
A grating and a collimating lens are used to replace the transformer lens in the traditional spectral beam combining structure. As a result, the degradation of the beam quality and the cross-talk are prevented. A spectral beam combining with narrow line-width is achieved. A standard semiconductor laser array is employed in this experiment. An output power of 44.8 W and an electro-optic conversion efficiency of 38.9% are achieved. The spectral line-width is 4.1 nm. A beam quality factor of 1.3711.7 in fast and slow axis directions are obtained. The beam quality of the output is close to that of a single emitter of the array in both directions.
2015,
27: 041006.
doi: 10.11884/HPLPB201527.041006
Abstract:
Coherent laser communication links of near space are important links of the integrated sky-earth high speed communication networks. This research focused on the heterodyne efficiency which represents coherent index of local laser and signal laser influenced by the atmospheric turbulence. The theoretical heterodyne efficiency expression with the path influenced by non-homogeneous turbulence was derived. The simulations of heterodyne efficiency of near space-earth, near space-near space and near space-low orbit satellite coherent laser communications links were given. The simulation results show that the atmospheric turbulence effect of near space-low orbit satellite links can be neglected. If the link distance between near space-near space is greater than 500 km or the zenith angle of near space to ground link is greater than 600 degrees, the heterodyne efficiency will be less than 50% and it is necessary to compensate the effect of atmospheric turbulence by using of adaptive optics.
Coherent laser communication links of near space are important links of the integrated sky-earth high speed communication networks. This research focused on the heterodyne efficiency which represents coherent index of local laser and signal laser influenced by the atmospheric turbulence. The theoretical heterodyne efficiency expression with the path influenced by non-homogeneous turbulence was derived. The simulations of heterodyne efficiency of near space-earth, near space-near space and near space-low orbit satellite coherent laser communications links were given. The simulation results show that the atmospheric turbulence effect of near space-low orbit satellite links can be neglected. If the link distance between near space-near space is greater than 500 km or the zenith angle of near space to ground link is greater than 600 degrees, the heterodyne efficiency will be less than 50% and it is necessary to compensate the effect of atmospheric turbulence by using of adaptive optics.
2015,
27: 041007.
doi: 10.11884/HPLPB201527.041007
Abstract:
The effects of the nonlinear refraction indexes (n2, n4, n6, n8) on the propagation of the femtosecond high-intensity laser pulse are studied. We consider three models. The first model includes n2, n4, n6, and n8. The second one only includes n2 and n4. The third model includes n2, n4, and n6. Numerical simulations show that the third model cannot properly describe the propagation of the ultra-short high intensity laser pulse, and the index n2 is the most important focusing mechanism at the beginning of the propagation, and n8 and n6 are the most important indexes in the stable propagation stage, and the pulses radius in the first model is almost the same as that in the second model, so does the number of filamentations splitted in the temporal direction. This work is useful in understanding the mechanism of the femtosecond laser pulse propagation in air.
The effects of the nonlinear refraction indexes (n2, n4, n6, n8) on the propagation of the femtosecond high-intensity laser pulse are studied. We consider three models. The first model includes n2, n4, n6, and n8. The second one only includes n2 and n4. The third model includes n2, n4, and n6. Numerical simulations show that the third model cannot properly describe the propagation of the ultra-short high intensity laser pulse, and the index n2 is the most important focusing mechanism at the beginning of the propagation, and n8 and n6 are the most important indexes in the stable propagation stage, and the pulses radius in the first model is almost the same as that in the second model, so does the number of filamentations splitted in the temporal direction. This work is useful in understanding the mechanism of the femtosecond laser pulse propagation in air.
2015,
27: 041008.
doi: 10.11884/HPLPB201527.041008
Abstract:
In the experiment of 532 nm CW laser irradiating linear CCD camera, we found the entirely saturated unilateral smear phenomenon which is different from the smear phenomenon described previously. In order to analyze the characteristics of the entirely saturated unilateral smear, the relationships of the smear length with laser power, integral time and drive frequency were measured in experiment. The smear length was found to increase along with the increase of laser power and integral time, but was independent with the drive frequency. This relationship was consistent with that of electric charge collecting quantity with laser power density and integral time. Through calculating in theory and measuring in experiment, we found that the smear length was related with the product of laser power density and integral time, and the relation expression of smear length and electric charge collecting quantity was educed . These analyses could provide a data basis to the mechanism of the entirely saturated unilateral smear phenomenon.
In the experiment of 532 nm CW laser irradiating linear CCD camera, we found the entirely saturated unilateral smear phenomenon which is different from the smear phenomenon described previously. In order to analyze the characteristics of the entirely saturated unilateral smear, the relationships of the smear length with laser power, integral time and drive frequency were measured in experiment. The smear length was found to increase along with the increase of laser power and integral time, but was independent with the drive frequency. This relationship was consistent with that of electric charge collecting quantity with laser power density and integral time. Through calculating in theory and measuring in experiment, we found that the smear length was related with the product of laser power density and integral time, and the relation expression of smear length and electric charge collecting quantity was educed . These analyses could provide a data basis to the mechanism of the entirely saturated unilateral smear phenomenon.
2015,
27: 041009.
doi: 10.11884/HPLPB201527.041009
Abstract:
This paper reports an end-pumped all-solid-state continuous wave (CW) Cr:LiSAF laser with a tunability of 130 nm. The design of the V-shaped cavity is carefully studied and optimized to improve the efficiency. The slope efficiency of 39.2% and the threshold of 32.8 mW are demonstrated in free running. Tuning range of 783-913 nm and maximum output power of 115 mW are realized when the BF(birefringent filter) is used as the tuning element. However, using the prism for tuning, the tunability decreases to 802-887 nm and the maximum power decreases to 6.5 mW. The BF is more suitable for the tuning of the Cr:LiSAF laser compared to the prism. The results indicate that Cr:LiSAF lasers could be widely tunable, high-efficient and compact laser sources in 800 nm region.
This paper reports an end-pumped all-solid-state continuous wave (CW) Cr:LiSAF laser with a tunability of 130 nm. The design of the V-shaped cavity is carefully studied and optimized to improve the efficiency. The slope efficiency of 39.2% and the threshold of 32.8 mW are demonstrated in free running. Tuning range of 783-913 nm and maximum output power of 115 mW are realized when the BF(birefringent filter) is used as the tuning element. However, using the prism for tuning, the tunability decreases to 802-887 nm and the maximum power decreases to 6.5 mW. The BF is more suitable for the tuning of the Cr:LiSAF laser compared to the prism. The results indicate that Cr:LiSAF lasers could be widely tunable, high-efficient and compact laser sources in 800 nm region.
2015,
27: 041010.
doi: 10.11884/HPLPB201527.041010
Abstract:
For the characteristics of wavelength and output power, discharge initiated repetitively pulsed HF/DF laser has become the hotspot in mid-infrared laser research field. The design and performance of a closed cycle, repetitively pulsed HF/DF laser is described. The homogeneous glow discharge is formed with UV pre-ionization and a transverse discharge structure. With the discharge characteristics in SF6/C2H6 gas mixture and the output characteristics of laser pulse are investigated and the repetitively discharge stability and gas circulation of laser device are researched. The energy depositing and extracting is achieved efficiently. A maximal running frequency of 50 Hz is obtained and it works stably. Under these conditions, the laser average power is 28 W and the peak power is 5.6 MW with a 100 ns pulse duration.
For the characteristics of wavelength and output power, discharge initiated repetitively pulsed HF/DF laser has become the hotspot in mid-infrared laser research field. The design and performance of a closed cycle, repetitively pulsed HF/DF laser is described. The homogeneous glow discharge is formed with UV pre-ionization and a transverse discharge structure. With the discharge characteristics in SF6/C2H6 gas mixture and the output characteristics of laser pulse are investigated and the repetitively discharge stability and gas circulation of laser device are researched. The energy depositing and extracting is achieved efficiently. A maximal running frequency of 50 Hz is obtained and it works stably. Under these conditions, the laser average power is 28 W and the peak power is 5.6 MW with a 100 ns pulse duration.
2015,
27: 041011.
doi: 10.11884/HPLPB201527.041011
Abstract:
Experimental measurement was employed to study the effects of the DF high-power laser irradiation on 45# steel in different gas flow. The surface picture was analyzed and the temperature histories were measured. The effect of steel ablation was obvious and the temperature on the rear center of the coupon was highest in the tangential air flow. The experimental results showed that some melt was removed by the tangential gas flow, especially in the air flow where combustion played an important role in heating the material. The target was cooled after laser irradiation. According to the experimental results, a numerical model was established to simulate the irradiation effects of high power density laser on steel targets in different gas flow. The method of Element birth and death was employed to simulate the ablation effects of laser on steel targets in the air flow, where the effects of heat releasing by oxidation were included. The results of the numerical simulation agreed well with the experimental results. It explained the effects of the gas flow in the laser irradiation.
Experimental measurement was employed to study the effects of the DF high-power laser irradiation on 45# steel in different gas flow. The surface picture was analyzed and the temperature histories were measured. The effect of steel ablation was obvious and the temperature on the rear center of the coupon was highest in the tangential air flow. The experimental results showed that some melt was removed by the tangential gas flow, especially in the air flow where combustion played an important role in heating the material. The target was cooled after laser irradiation. According to the experimental results, a numerical model was established to simulate the irradiation effects of high power density laser on steel targets in different gas flow. The method of Element birth and death was employed to simulate the ablation effects of laser on steel targets in the air flow, where the effects of heat releasing by oxidation were included. The results of the numerical simulation agreed well with the experimental results. It explained the effects of the gas flow in the laser irradiation.
2015,
27: 041012.
doi: 10.11884/HPLPB201527.041012
Abstract:
To obtain high energy ultraviolet laser pulse, the XeCl excimer laser pumped by electron-beam was studied. This paper describes the construction and the principle of the XeCl excimer laser with electron-beam pump source in detail. Experimental study on laser output characteristic of the XeCl excimer laser was carried out, and effects on pressure of mix gas in laser chamber on output energy were shown. The energy of the laser pulse of 200 ns duration at half-amplitude exceeded 100 J under conditions of 81 kV charge voltage of laser and a befitting composition of gas mixture at a total pressure of 200 kPa, and the laser efficiency, calculated relative to all the energy deposited in the active volume, was 3.2%. The experimental research on impulse coupling produced by XeCl excimer laser (308 nm) interaction with the coating layer was performed. Impulse coupling was measured by the subminiature impulse detector, and impulse coupling coefficient was calculated for different air pressure. The impulse coupling coefficient under ambient air, which was 8.3210-5 NW-1, was about twice that under vacuum condition.
To obtain high energy ultraviolet laser pulse, the XeCl excimer laser pumped by electron-beam was studied. This paper describes the construction and the principle of the XeCl excimer laser with electron-beam pump source in detail. Experimental study on laser output characteristic of the XeCl excimer laser was carried out, and effects on pressure of mix gas in laser chamber on output energy were shown. The energy of the laser pulse of 200 ns duration at half-amplitude exceeded 100 J under conditions of 81 kV charge voltage of laser and a befitting composition of gas mixture at a total pressure of 200 kPa, and the laser efficiency, calculated relative to all the energy deposited in the active volume, was 3.2%. The experimental research on impulse coupling produced by XeCl excimer laser (308 nm) interaction with the coating layer was performed. Impulse coupling was measured by the subminiature impulse detector, and impulse coupling coefficient was calculated for different air pressure. The impulse coupling coefficient under ambient air, which was 8.3210-5 NW-1, was about twice that under vacuum condition.
2015,
27: 041013.
doi: 10.11884/HPLPB201527.041013
Abstract:
The multi-path effect can cause undesirable phase error in regions with dramatically varied albedo. This paper proposes an effective method to correct such an error. The difference map of modulation is generated to precisely detect regions affected by the multi-path effect, and the phase error in the detected regions is corrected according to neighbor phase. Experimental results demonstrate the validity of the proposed method and show a reduction by 57.3% in the root mean square of phase errors.
The multi-path effect can cause undesirable phase error in regions with dramatically varied albedo. This paper proposes an effective method to correct such an error. The difference map of modulation is generated to precisely detect regions affected by the multi-path effect, and the phase error in the detected regions is corrected according to neighbor phase. Experimental results demonstrate the validity of the proposed method and show a reduction by 57.3% in the root mean square of phase errors.
2015,
27: 041014.
doi: 10.11884/HPLPB201527.041014
Abstract:
Reflective volume Bragg grating (VBG) is the first choice to improve the output characteristics of the diode laser (DL). The non-sphere equation of fast axis collimation (FAC) lens is simulated. In this paper, based on the ray-trace method, calculation principles and approaches of feedback efficiency for diode laser wavelength stabilization system are investigated, and the tolerance of FAC lens and reflection VBG are presented. The results show the feedback efficiency is not sensitive to VBG spatial location error, but the FAC spatial location error and tilt angle error and the VBG tilt angle error will cause an acute decline of the feedback efficiency.
Reflective volume Bragg grating (VBG) is the first choice to improve the output characteristics of the diode laser (DL). The non-sphere equation of fast axis collimation (FAC) lens is simulated. In this paper, based on the ray-trace method, calculation principles and approaches of feedback efficiency for diode laser wavelength stabilization system are investigated, and the tolerance of FAC lens and reflection VBG are presented. The results show the feedback efficiency is not sensitive to VBG spatial location error, but the FAC spatial location error and tilt angle error and the VBG tilt angle error will cause an acute decline of the feedback efficiency.
2015,
27: 041015.
doi: 10.11884/HPLPB201527.041015
Abstract:
To improve angular amplification of optical phased array and the signal-to-noise ratio of every grating, multiplexing volume holographic gratings (MVHGs) are studied. Coupled wave theory of MVHGs for angular amplifier is derived and compared with Kogelnik coupled-wave theory. To reduce the crosstalk in MVHGs, the law of adjusting grating parameters and crosstalk optimization are discussed, validated and analyzed experimentally. The results indicate that when the Bragg angle interval between two adjacent VHGs is less than the sum of angular selectivity, crosstalk is serious and multiple coupled-wave theory is needed to describe the interaction between different VHGs. Adjusting vector slant angle, reducing the grating period and increasing the thickness of the media will all reduce the crosstalk MVHGs. Increasing vector slant angle interval and reducing grating period of adjacent VHG can reduce crosstalk significantly, but they will reduce the angular magnification. Medium thickness has to increase several times to weaken crosstalk, but this will not affect the angular magnification.
To improve angular amplification of optical phased array and the signal-to-noise ratio of every grating, multiplexing volume holographic gratings (MVHGs) are studied. Coupled wave theory of MVHGs for angular amplifier is derived and compared with Kogelnik coupled-wave theory. To reduce the crosstalk in MVHGs, the law of adjusting grating parameters and crosstalk optimization are discussed, validated and analyzed experimentally. The results indicate that when the Bragg angle interval between two adjacent VHGs is less than the sum of angular selectivity, crosstalk is serious and multiple coupled-wave theory is needed to describe the interaction between different VHGs. Adjusting vector slant angle, reducing the grating period and increasing the thickness of the media will all reduce the crosstalk MVHGs. Increasing vector slant angle interval and reducing grating period of adjacent VHG can reduce crosstalk significantly, but they will reduce the angular magnification. Medium thickness has to increase several times to weaken crosstalk, but this will not affect the angular magnification.
2015,
27: 041017.
doi: 10.11884/HPLPB201527.041017
Abstract:
The experiments and analysis about thermodynamics and kinetics have been conducted to improve the stability of chemical iodine generator for COIL. The change of conversion rate and reaction velocity with reaction temperature and time was researched. The results show that the ash layer diffuseness of the solid production is the control procedure of reaction and the suitable temperature is about 410 K. They also indicate CuI should be excessive in experiments, and the iodine flow rate should be controlled by chlorine flow rate. The change of iodine flow rate is less than 15% in nearly 15 s after optimizing the generator structure and experimental condition. And the CuI conversion rate is 23%.
The experiments and analysis about thermodynamics and kinetics have been conducted to improve the stability of chemical iodine generator for COIL. The change of conversion rate and reaction velocity with reaction temperature and time was researched. The results show that the ash layer diffuseness of the solid production is the control procedure of reaction and the suitable temperature is about 410 K. They also indicate CuI should be excessive in experiments, and the iodine flow rate should be controlled by chlorine flow rate. The change of iodine flow rate is less than 15% in nearly 15 s after optimizing the generator structure and experimental condition. And the CuI conversion rate is 23%.
2015,
27: 041018.
doi: 10.11884/HPLPB201527.041018
Abstract:
In order to study the extinction effect of ablating soot produced by carbon fiber reinforced composite materials, which are located in an air flow field and are irradiated by laser, Laser induced incandescence (LII) and laser extinction methods are employed. Experiment is set up to diagnose the soot extinction characteristics combining these two methods. In the experiment, a laser light is set in the excitation plane of LII, then laser transmittance and LII signals are recorded synchronously to obtain the laser extinction ratio and soot concentration field. From these data, the mean mass extinction coefficients of soot are derived at a series of air flow velocities. The normalized mean mass extinction coefficient values of soot for 1064 nm laser are 2.51, 1.08, 1.00 at air flow velocities 7 m/s, 10 m/s, 20 m/s, respectively. When the air flow velocity is low, the amplitude of N curve fluctuation is big, and the mean value is big too. When the air flow velocity is high, the N curve fluctuation is slight, and the mean value is small.
In order to study the extinction effect of ablating soot produced by carbon fiber reinforced composite materials, which are located in an air flow field and are irradiated by laser, Laser induced incandescence (LII) and laser extinction methods are employed. Experiment is set up to diagnose the soot extinction characteristics combining these two methods. In the experiment, a laser light is set in the excitation plane of LII, then laser transmittance and LII signals are recorded synchronously to obtain the laser extinction ratio and soot concentration field. From these data, the mean mass extinction coefficients of soot are derived at a series of air flow velocities. The normalized mean mass extinction coefficient values of soot for 1064 nm laser are 2.51, 1.08, 1.00 at air flow velocities 7 m/s, 10 m/s, 20 m/s, respectively. When the air flow velocity is low, the amplitude of N curve fluctuation is big, and the mean value is big too. When the air flow velocity is high, the N curve fluctuation is slight, and the mean value is small.
2015,
27: 041019.
doi: 10.11884/HPLPB201527.041019
Abstract:
A miniaturized, eye-safe laser with wide adaptive temperature is reported. Er3+, Yb3+ co-doped phosphate glass is used as the gain medium. A Co2+: MgAl2O4 crystal is used as the saturable absorber. The miniaturized laser structure suitable for wide temperature range and the output characteristics of the passively Q-switched laser are investigated. The pump energy of 9 mJ, repetition frequency of 10 Hz, pump duration of 5 ms, pulse energy of 130 J, pulse duration of 5.5 ns, peak power of 20 kW, and beam quality M2 of 1.3 were obtained. The laser structure uses vacuum packaging and can run stably in the temperature range of －40 ℃ to 50 ℃. The output instability is less than 5% by natural cooling. The laser can also be driven by lithium batteries for further application.
A miniaturized, eye-safe laser with wide adaptive temperature is reported. Er3+, Yb3+ co-doped phosphate glass is used as the gain medium. A Co2+: MgAl2O4 crystal is used as the saturable absorber. The miniaturized laser structure suitable for wide temperature range and the output characteristics of the passively Q-switched laser are investigated. The pump energy of 9 mJ, repetition frequency of 10 Hz, pump duration of 5 ms, pulse energy of 130 J, pulse duration of 5.5 ns, peak power of 20 kW, and beam quality M2 of 1.3 were obtained. The laser structure uses vacuum packaging and can run stably in the temperature range of －40 ℃ to 50 ℃. The output instability is less than 5% by natural cooling. The laser can also be driven by lithium batteries for further application.
2015,
27: 041020.
doi: 10.11884/HPLPB201527.041020
Abstract:
A gain-switched high repetition rate pulse all fiber laser pumped by pulsed laser diode is developed. The linear cavity laser with fiber Bragg grating was designed in which directly modulated laser diode was used as the pump source, the double cladding fiber was the gain medium. Stable laser pulse trains were obtained by testing different peak pump power and the cavity length. Under peak pump power of 21 W and pulse duration of 2.5 s at repetition rate of 100 kHz, stable laser pulse trains were obtained at 1.06 m with pulse duration of 247 ns. The values of laser pulse peak power have good consistency, and the long term average power stability is proved to be less than 2%. The sub-pulses on top of the envelope caused by longitudinal mode beating were observed and analyzed. The output power of single stage amplifier is 89.6 W.
A gain-switched high repetition rate pulse all fiber laser pumped by pulsed laser diode is developed. The linear cavity laser with fiber Bragg grating was designed in which directly modulated laser diode was used as the pump source, the double cladding fiber was the gain medium. Stable laser pulse trains were obtained by testing different peak pump power and the cavity length. Under peak pump power of 21 W and pulse duration of 2.5 s at repetition rate of 100 kHz, stable laser pulse trains were obtained at 1.06 m with pulse duration of 247 ns. The values of laser pulse peak power have good consistency, and the long term average power stability is proved to be less than 2%. The sub-pulses on top of the envelope caused by longitudinal mode beating were observed and analyzed. The output power of single stage amplifier is 89.6 W.
2015,
27: 042001.
doi: 10.11884/HPLPB201527.042001
Abstract:
Based on the relative motion of the workpiece and polishing dish, using the material removal model of fused silica optics, the influence of speed ratio and eccentricity on material removal function was analyzed, and the influence of polishing process parameters on the low frequency surface accuracy was studied by theoretical analysis and polishing experiments. Low frequency surface errors were detected using high-resolution detection equipment, preferred polishing process parameters were obtained, and the corresponding experiment was done for verification, an appropriate method was proposed to improve the low-frequency surface accuracy of fused silica optics in the polishing process.
Based on the relative motion of the workpiece and polishing dish, using the material removal model of fused silica optics, the influence of speed ratio and eccentricity on material removal function was analyzed, and the influence of polishing process parameters on the low frequency surface accuracy was studied by theoretical analysis and polishing experiments. Low frequency surface errors were detected using high-resolution detection equipment, preferred polishing process parameters were obtained, and the corresponding experiment was done for verification, an appropriate method was proposed to improve the low-frequency surface accuracy of fused silica optics in the polishing process.
2015,
27: 043001.
doi: 10.11884/HPLPB201527.043001
Abstract:
A high power wideband patch antenna array driven by two switched oscillators with synchronism output was designed, so as to increase the radiation factor of the mesoband high power microwave radiator. A single layer patch and an air substrate were employed to reduce the weight of the array, each patch is E-shaped for broadening the bandwidth. Optimization of the arrays geometric parameters was performed to get the highest radiation factor. As a result, the radiation factor is 3.4 times of the magnitude of the feed in mesoband pulse, the percentage of bandwidth is 47%, and the gain of the array is 11.8 dB at frequency of 300 MHz. Filling SF6 gas with a pressure of 1 atm in the nylon-case, the power capability of the array is as high as 7.45 GW. A novel mesoband pulse generator with the two-port synchronous output was provided. The generator has a dual-path sync output wideband resonator structure, in which two resonators share a shorting switch to achieve synchronous output. The design of the generator is optimized, and the coupler has a couple ratio of 0.644 at the frequency of 300 MHz. The simulation comparison between the generators with and without T-shaped charging structure was performed, which shows that the output pulse amplitude of the generator with the charging structure is only 4%, lower than that without the charging structure.
A high power wideband patch antenna array driven by two switched oscillators with synchronism output was designed, so as to increase the radiation factor of the mesoband high power microwave radiator. A single layer patch and an air substrate were employed to reduce the weight of the array, each patch is E-shaped for broadening the bandwidth. Optimization of the arrays geometric parameters was performed to get the highest radiation factor. As a result, the radiation factor is 3.4 times of the magnitude of the feed in mesoband pulse, the percentage of bandwidth is 47%, and the gain of the array is 11.8 dB at frequency of 300 MHz. Filling SF6 gas with a pressure of 1 atm in the nylon-case, the power capability of the array is as high as 7.45 GW. A novel mesoband pulse generator with the two-port synchronous output was provided. The generator has a dual-path sync output wideband resonator structure, in which two resonators share a shorting switch to achieve synchronous output. The design of the generator is optimized, and the coupler has a couple ratio of 0.644 at the frequency of 300 MHz. The simulation comparison between the generators with and without T-shaped charging structure was performed, which shows that the output pulse amplitude of the generator with the charging structure is only 4%, lower than that without the charging structure.
2015,
27: 043002.
doi: 10.11884/HPLPB201527.043002
Abstract:
In order to meet the requirement of miniaturization on high power microwave (HPM) measuring system at L-band, an miniaturized HPM measuring antenna with coaxial feeding is designed. On the basics of the structure of TEM horn, the electric-magnetic vibrator structure is used to improve the performance of radiation pattern. The relationship between electric-magnetic vibrator structure and the character of the gain, the radiation pattern and VSWR is investigated by theoretical analysis and numerical calculation. The structure size is 100 mm100 mm100 mm. It shows that with the frequency varying from 1.2 to 1.8 GHz, the gain increases from 2.8 to 6.1 dB linearly, and the width of the radiation beam is smooth and larger than 70. In the meanwhile, the VSWR is less than 1.5.
In order to meet the requirement of miniaturization on high power microwave (HPM) measuring system at L-band, an miniaturized HPM measuring antenna with coaxial feeding is designed. On the basics of the structure of TEM horn, the electric-magnetic vibrator structure is used to improve the performance of radiation pattern. The relationship between electric-magnetic vibrator structure and the character of the gain, the radiation pattern and VSWR is investigated by theoretical analysis and numerical calculation. The structure size is 100 mm100 mm100 mm. It shows that with the frequency varying from 1.2 to 1.8 GHz, the gain increases from 2.8 to 6.1 dB linearly, and the width of the radiation beam is smooth and larger than 70. In the meanwhile, the VSWR is less than 1.5.
2015,
27: 043003.
doi: 10.11884/HPLPB201527.043003
Abstract:
In order to explore more elements of triangle-grid subarray radial-line feed network, research is carried out on the 92-element subarray feed network, and a new coupling probe is designed, which can satisfy the required coupling amount and amplitude-frequency characteristics of feed network. The problem that the equal amplitude outputs of coupling amount is difficult to achieve, which is caused by the non-uniform energy in the feed network, is analyzed and solved. Experiment result indicates that: At the central frequency of 2.856, the VSWR is 1.1, the amplitude-frequency characteristics consistency of feed network output ports is good; In the frequency range of 2.76-2.92 GHz subarray, the VSWR is less than 1.5, and the amplitude-frequency characteristics of each output port is basically consistent. The experimental results are basically consistent with those of the simulation.
In order to explore more elements of triangle-grid subarray radial-line feed network, research is carried out on the 92-element subarray feed network, and a new coupling probe is designed, which can satisfy the required coupling amount and amplitude-frequency characteristics of feed network. The problem that the equal amplitude outputs of coupling amount is difficult to achieve, which is caused by the non-uniform energy in the feed network, is analyzed and solved. Experiment result indicates that: At the central frequency of 2.856, the VSWR is 1.1, the amplitude-frequency characteristics consistency of feed network output ports is good; In the frequency range of 2.76-2.92 GHz subarray, the VSWR is less than 1.5, and the amplitude-frequency characteristics of each output port is basically consistent. The experimental results are basically consistent with those of the simulation.
2015,
27: 043101.
doi: 10.11884/HPLPB201527.043101
Abstract:
In this paper, the design process and experimental results of a beam optical system (BOS) for a 220 GHz folded waveguide (FW) backward wave oscillator (BWO) are demonstrated. The BOS is comprised of three parts: the Pierce convergent electron gun, the magnetic focusing transmission section and the single-stage depressed collector. For a vacuum electronics device operating in terahertz frequency (THz) regime, the ultra-small and long beam tunnel makes it tough for electron beam to pass through at a high rate. The space charge effect, the machining and assembly precision, the thermal velocity spread and thermal expansion will all make things worse. Therefore, to develop a practical BOS with sufficient passing rate is an urgent but difficult task for the development of the 220 GHz FW BWO. Using theoretical method and numerical tool, the three parts were designed one by one, to satisfy the requirement proposed by earlier analysis on beam-wave interaction. Based on the design results and error analysis, the sample tube of BOS was preliminarily developed and tested. The experiment data show that the BOS can generate an electron beam with a beam voltage of 15.4 kV, a beam current of 22 mA to pass a beam tunnel with a diameter of 0.19 mm, a length of 30 mm, where the passing rate is over 80%.
In this paper, the design process and experimental results of a beam optical system (BOS) for a 220 GHz folded waveguide (FW) backward wave oscillator (BWO) are demonstrated. The BOS is comprised of three parts: the Pierce convergent electron gun, the magnetic focusing transmission section and the single-stage depressed collector. For a vacuum electronics device operating in terahertz frequency (THz) regime, the ultra-small and long beam tunnel makes it tough for electron beam to pass through at a high rate. The space charge effect, the machining and assembly precision, the thermal velocity spread and thermal expansion will all make things worse. Therefore, to develop a practical BOS with sufficient passing rate is an urgent but difficult task for the development of the 220 GHz FW BWO. Using theoretical method and numerical tool, the three parts were designed one by one, to satisfy the requirement proposed by earlier analysis on beam-wave interaction. Based on the design results and error analysis, the sample tube of BOS was preliminarily developed and tested. The experiment data show that the BOS can generate an electron beam with a beam voltage of 15.4 kV, a beam current of 22 mA to pass a beam tunnel with a diameter of 0.19 mm, a length of 30 mm, where the passing rate is over 80%.
2015,
27: 043102.
doi: 10.11884/HPLPB201527.043102
Abstract:
This research presents the calculation method of transmittance, reflectance and loss for hybrid output coupler (HOC). We introduce Q factor for loss analyses to evaluate the quality of HOC. We simulate the suppression of F-P etalon effect and distortion of output THz beam pattern with a wedged substrate. A 0.3 wedge angle makes transmittance not sensitive to small change of wavelength and substrate thickness. The distortion introduced by the 0.3 wedge angle will not dramatically change the Gaussian beam pattern.
This research presents the calculation method of transmittance, reflectance and loss for hybrid output coupler (HOC). We introduce Q factor for loss analyses to evaluate the quality of HOC. We simulate the suppression of F-P etalon effect and distortion of output THz beam pattern with a wedged substrate. A 0.3 wedge angle makes transmittance not sensitive to small change of wavelength and substrate thickness. The distortion introduced by the 0.3 wedge angle will not dramatically change the Gaussian beam pattern.
2015,
27: 043103.
doi: 10.11884/HPLPB201527.043103
Abstract:
A submillimeter wave large-power pulse detector for 300-400 GHz frequency band is fabricated and tested. Based on the hot electron effect under high electric field, the overmoded detecting segment of the detector is composed of a waveguide WR10 and an n-type silicon detecting chip placed on the wide waveguide wall. By using lithography and electroplating techniques, the detecting chips are manufactured well with excellent ohmic contact and high dimensional precision. Submillimeter wave large-power pulses is tested and measurement of voltage standing wave ratio (VSWR) is carried out for the detector prototype. Results show that the developed detector has a response time of picoseconds-level, a relative sensitivity of about 0.46 kW-1, VSWR less than 2.4, and the maximum enduring power no less than tens of watts, agreeing well with the improved simulation results. So it satisfies the demand of the direct detect of large power pulses at submillimeter wavelength.
A submillimeter wave large-power pulse detector for 300-400 GHz frequency band is fabricated and tested. Based on the hot electron effect under high electric field, the overmoded detecting segment of the detector is composed of a waveguide WR10 and an n-type silicon detecting chip placed on the wide waveguide wall. By using lithography and electroplating techniques, the detecting chips are manufactured well with excellent ohmic contact and high dimensional precision. Submillimeter wave large-power pulses is tested and measurement of voltage standing wave ratio (VSWR) is carried out for the detector prototype. Results show that the developed detector has a response time of picoseconds-level, a relative sensitivity of about 0.46 kW-1, VSWR less than 2.4, and the maximum enduring power no less than tens of watts, agreeing well with the improved simulation results. So it satisfies the demand of the direct detect of large power pulses at submillimeter wavelength.
2015,
27: 043201.
doi: 10.11884/HPLPB201527.043201
Abstract:
In order to measure the electric field of electromagnetic pulse(EMP) with nanosecond rise time, a kind of broadband E-field sensor based on asymptotic conical antenna is proposed. The performance of the antenna is verified by modeling and simulation. An optical transmitter is designed to realize the electro-optical conversion and a fiber is used to transmit the signal. The output voltage of the sensor is integrated by Matlab. The performance of the sensor is tested by experiment. Research results show that this kind of measurement system has the characteristic of small size, good linearity, high noise immunity and wide-band response and it can be used to measure the E-field of EMP with nanosecond rise time. The development of the E-field sensor is of great significance for the measurement of EMP and further research on the characteristics and protection of EMP.
In order to measure the electric field of electromagnetic pulse(EMP) with nanosecond rise time, a kind of broadband E-field sensor based on asymptotic conical antenna is proposed. The performance of the antenna is verified by modeling and simulation. An optical transmitter is designed to realize the electro-optical conversion and a fiber is used to transmit the signal. The output voltage of the sensor is integrated by Matlab. The performance of the sensor is tested by experiment. Research results show that this kind of measurement system has the characteristic of small size, good linearity, high noise immunity and wide-band response and it can be used to measure the E-field of EMP with nanosecond rise time. The development of the E-field sensor is of great significance for the measurement of EMP and further research on the characteristics and protection of EMP.
2015,
27: 043202.
doi: 10.11884/HPLPB201527.043202
Abstract:
We studied the reflection and transmission performance by controlling the thickness of the concrete slabs and the mixing amount of reduced iron powder and introducing wire netting into the concrete slabs. We used a bow-frame for the test of reflectivity and a two-port method for the test of transmission attenuation. The frequency band of the reflectivity ranges from 2 to 18 GHz. The frequency band of the transmissions measurement ranges from 12 to 18 GHz. The reflectivity of different concrete slabs is around -5 dB. When the mixing amount of reduced iron power in concrete slabs is above 200 kg/m3, the transmission attenuation can reach －50 dB. By analyzing experimental results, we can find that the concrete slabs thickness, the mixing amount of reduced iron powder and the wire netting have heavy effect on transmission attenuation, but little effect on reflectivity.
We studied the reflection and transmission performance by controlling the thickness of the concrete slabs and the mixing amount of reduced iron powder and introducing wire netting into the concrete slabs. We used a bow-frame for the test of reflectivity and a two-port method for the test of transmission attenuation. The frequency band of the reflectivity ranges from 2 to 18 GHz. The frequency band of the transmissions measurement ranges from 12 to 18 GHz. The reflectivity of different concrete slabs is around -5 dB. When the mixing amount of reduced iron power in concrete slabs is above 200 kg/m3, the transmission attenuation can reach －50 dB. By analyzing experimental results, we can find that the concrete slabs thickness, the mixing amount of reduced iron powder and the wire netting have heavy effect on transmission attenuation, but little effect on reflectivity.
2015,
27: 043203.
doi: 10.11884/HPLPB201527.043208
Abstract:
In order to study the security effect on a certain radio fuze of lightning electromagnetic pulse (LEMP), and confirm the energy coupling channel and the effect rules, an experiment system is constructed and LEMP irradiation experiments are done. Experiment results show that the best coupling pose is that the fuze is vertically upward, and the bomb body axis and the antenna plane are perpendicular to the radiation field propagation direction. The bomb body is the main energy coupling channel. Different irradiation wave has different threshold interference field. Under the 152 mm bomb body, the threshold interference fields of the irradiation waves of 1.2/50, 5.4/70, 0.25/100 and 10/350 s, are about 74, 60, 65 and 75 kV/m. The effect mechanism of LEMP is that the irradiation energy couples to the input of the executive circuit. The pulse width of the coupling signal satisfies the requirement of the startup pulse width, leading to the miss-action of the executive circuit.
In order to study the security effect on a certain radio fuze of lightning electromagnetic pulse (LEMP), and confirm the energy coupling channel and the effect rules, an experiment system is constructed and LEMP irradiation experiments are done. Experiment results show that the best coupling pose is that the fuze is vertically upward, and the bomb body axis and the antenna plane are perpendicular to the radiation field propagation direction. The bomb body is the main energy coupling channel. Different irradiation wave has different threshold interference field. Under the 152 mm bomb body, the threshold interference fields of the irradiation waves of 1.2/50, 5.4/70, 0.25/100 and 10/350 s, are about 74, 60, 65 and 75 kV/m. The effect mechanism of LEMP is that the irradiation energy couples to the input of the executive circuit. The pulse width of the coupling signal satisfies the requirement of the startup pulse width, leading to the miss-action of the executive circuit.
2015,
27: 044001.
doi: 10.11884/HPLPB201527.044001
Abstract:
In order to make reasonable proposals on the magnetic design of 30 cm diameter ion thruster, the effects of magnet diameter and the spacing on the magnet strength and the confinement length of the discharge electron have been studied. By utilizing Maxwell-3D software, the magnetic field distribution was obtained with the permanent magnet on the cylindrical section oriented at 30, 60 and 90 to that on the conical section. According to different field calculated, several discharge parameters, such as electron temperature, ion density and ionization efficiency were calculated. The results indicate that when discharge voltage of 30 V，magnet pole length of 0.008 m and magnet spacing of 0.12 m are set, the confinement length of the primary is in the order of 50 m. When the angles between the permanent magnet on the cylindrical section and that on the conical section are 30, 60 and 90, the magnetic field contour inside the discharge chamber is in the range of 0.002-0.005 T. With the angle being 60, the magnetic field and filed free region are more reasonable compared to the cases of 30 and 90, when the electron temperature is about 2-6 eV, the plasma density is about (4-8)1017/m3and the collisional frequency rate of electron is in the range of 0.2-1.8.
In order to make reasonable proposals on the magnetic design of 30 cm diameter ion thruster, the effects of magnet diameter and the spacing on the magnet strength and the confinement length of the discharge electron have been studied. By utilizing Maxwell-3D software, the magnetic field distribution was obtained with the permanent magnet on the cylindrical section oriented at 30, 60 and 90 to that on the conical section. According to different field calculated, several discharge parameters, such as electron temperature, ion density and ionization efficiency were calculated. The results indicate that when discharge voltage of 30 V，magnet pole length of 0.008 m and magnet spacing of 0.12 m are set, the confinement length of the primary is in the order of 50 m. When the angles between the permanent magnet on the cylindrical section and that on the conical section are 30, 60 and 90, the magnetic field contour inside the discharge chamber is in the range of 0.002-0.005 T. With the angle being 60, the magnetic field and filed free region are more reasonable compared to the cases of 30 and 90, when the electron temperature is about 2-6 eV, the plasma density is about (4-8)1017/m3and the collisional frequency rate of electron is in the range of 0.2-1.8.
2015,
27: 044002.
doi: 10.11884/HPLPB201527.044002
Abstract:
The dual energy CT method can be used in nondestructive test for large size multilayer spherical shell with high density difference materials. Low Z materials basically have no barrier to high energy X-ray scanning, while low energy scanning will be truncated by high Z materials, hence image reconstruction methods need to be studied according to the dual energy X-ray projection features. The simulation model is designed according to the structure characteristics of the multilayer spherical shell, and projection sonograms for both high and low energy X-rays are simulated respectively, on this basis, images are reconstructed with Filtered Back Projection(FBP) or Algebraic Reconstruction Technique(ART) algorithm. Through a mass of simulation and comparative analysis, the conclusion is drawn that the F-R(fuse first and then reconstruct) method is better than the R-F(reconstruct first and then fuse) method for image reconstruction of the dual energy CT. It is pointed out that in order to ensure the image reconstruction quality, for the scanning X-ray energy choice, it is necessary not only to improve local projection quality, but also to minimize the total amount of the truncated projection.
The dual energy CT method can be used in nondestructive test for large size multilayer spherical shell with high density difference materials. Low Z materials basically have no barrier to high energy X-ray scanning, while low energy scanning will be truncated by high Z materials, hence image reconstruction methods need to be studied according to the dual energy X-ray projection features. The simulation model is designed according to the structure characteristics of the multilayer spherical shell, and projection sonograms for both high and low energy X-rays are simulated respectively, on this basis, images are reconstructed with Filtered Back Projection(FBP) or Algebraic Reconstruction Technique(ART) algorithm. Through a mass of simulation and comparative analysis, the conclusion is drawn that the F-R(fuse first and then reconstruct) method is better than the R-F(reconstruct first and then fuse) method for image reconstruction of the dual energy CT. It is pointed out that in order to ensure the image reconstruction quality, for the scanning X-ray energy choice, it is necessary not only to improve local projection quality, but also to minimize the total amount of the truncated projection.
2015,
27: 044003.
doi: 10.11884/HPLPB201527.044003
Abstract:
Forward imaging technique is the base of the combined method for density reconstruction with forward calculation and inverse problem solution. This paper proposes the idea of girding the areal source as many point sources. Using the blurring window as the affecting factor of the detector blur, the projecting matrix from any point source to any detector pixel with X-ray trace technique is obtained, the projection equation for the radiographic system with areal source blur and detector blur is introduced. The projection equation is used to gain the same deviation information about the object edge as the experimental image. The forward projection equation is combined with the constrained conjugate gradient method to form a full procedure of density reconstruction, which is applied on a simulated image of French Test Object and an experimental image. The results show that using the projection equation, the affecting range of the blur is decreased and can be controlled in one or two pixels.
Forward imaging technique is the base of the combined method for density reconstruction with forward calculation and inverse problem solution. This paper proposes the idea of girding the areal source as many point sources. Using the blurring window as the affecting factor of the detector blur, the projecting matrix from any point source to any detector pixel with X-ray trace technique is obtained, the projection equation for the radiographic system with areal source blur and detector blur is introduced. The projection equation is used to gain the same deviation information about the object edge as the experimental image. The forward projection equation is combined with the constrained conjugate gradient method to form a full procedure of density reconstruction, which is applied on a simulated image of French Test Object and an experimental image. The results show that using the projection equation, the affecting range of the blur is decreased and can be controlled in one or two pixels.
2015,
27: 044101.
doi: 10.11884/HPLPB201527.044101
Abstract:
Nanowelding configuration under thermal effects is investigated with molecular dynamics method. The influence of single walled carbon nanotube (SWNT) diameter and time on the interface structure is analyzed, and the detailed process is illustrated at 1530 K. Nanowires are observed in SWNT (6,6), (7,7), (9,9) as well as (11,11) at 13.8, 14.6, 17.5 and 19.6 ps respectively except for SWNT (5,5). These nanowires are composed of one or several Ni atom chains. The numbers of Ni atom chains for SWNT (6,6), (7,7), (9,9), (11,11) are 1, 3, 7 and 16 respectively. The interface structures of both inside nanowelding and outside nanowelding are also revealed. The critical diameter of inside nanowelding can be determined by SWNT (6,6) with a diameter of 0.814nm. As for outside nanowelding, a longer outside contact length can be obtained with a larger diameter of SWNT. The growth rate of the outside contact length increases with the diameter of SWNT. The maximal growth rate of the outside contact length is up to 0.013 nm/ps. The critical temperature of the interface structure is provided, which indicates the critical temperature of outside nanowelding is higher than that of inside nanowelding for the same diameter of SWNT, and the critical temperature is irrelevant to the diameter of SWNT.
Nanowelding configuration under thermal effects is investigated with molecular dynamics method. The influence of single walled carbon nanotube (SWNT) diameter and time on the interface structure is analyzed, and the detailed process is illustrated at 1530 K. Nanowires are observed in SWNT (6,6), (7,7), (9,9) as well as (11,11) at 13.8, 14.6, 17.5 and 19.6 ps respectively except for SWNT (5,5). These nanowires are composed of one or several Ni atom chains. The numbers of Ni atom chains for SWNT (6,6), (7,7), (9,9), (11,11) are 1, 3, 7 and 16 respectively. The interface structures of both inside nanowelding and outside nanowelding are also revealed. The critical diameter of inside nanowelding can be determined by SWNT (6,6) with a diameter of 0.814nm. As for outside nanowelding, a longer outside contact length can be obtained with a larger diameter of SWNT. The growth rate of the outside contact length increases with the diameter of SWNT. The maximal growth rate of the outside contact length is up to 0.013 nm/ps. The critical temperature of the interface structure is provided, which indicates the critical temperature of outside nanowelding is higher than that of inside nanowelding for the same diameter of SWNT, and the critical temperature is irrelevant to the diameter of SWNT.
2015,
27: 044102.
doi: 10.11884/HPLPB201527.044102
Abstract:
The cup-wheel is adopted in arc grinding wheel truing and the non-contact displacement sensor is used for arc grinding wheel measurement. The radial run-out error and arc radius error after meshed are proposed to evaluate the quality of the truing. The matching truing measurement parameters are calculated based on the principle of aspheric grinding, by which truing error compensation grinding is carried out. The results of truing experiment show that the cup-wheel truing is an ideal truing method. Compared to tradition grinding, the effect of truing error compensation is obvious. The surface form errors after two compensation grinding decrease by 36.5% and 28.1%, respectively, which means the truing error compensation grinding can effectively improve accuracy.
The cup-wheel is adopted in arc grinding wheel truing and the non-contact displacement sensor is used for arc grinding wheel measurement. The radial run-out error and arc radius error after meshed are proposed to evaluate the quality of the truing. The matching truing measurement parameters are calculated based on the principle of aspheric grinding, by which truing error compensation grinding is carried out. The results of truing experiment show that the cup-wheel truing is an ideal truing method. Compared to tradition grinding, the effect of truing error compensation is obvious. The surface form errors after two compensation grinding decrease by 36.5% and 28.1%, respectively, which means the truing error compensation grinding can effectively improve accuracy.
2015,
27: 045001.
doi: 10.11884/HPLPB201527.045001
Abstract:
A Marx generator for triggering used in pulsed power system has been researched. The principle and main parameters are introduced. A Marx generator is designed based on single polarity charge and coaxial structure. The Marx generator meets the following design specifications on the 75 load matching with the coaxial cable: more than 170 kV output voltage, more than 200 ns pulse width, 3 ns risetime and less than 1.5 ns jitter from 140 kV to 160 kV. The Marx generator can work stably and reliably at large range voltage. The demand for triggering is satisfied commendably.
A Marx generator for triggering used in pulsed power system has been researched. The principle and main parameters are introduced. A Marx generator is designed based on single polarity charge and coaxial structure. The Marx generator meets the following design specifications on the 75 load matching with the coaxial cable: more than 170 kV output voltage, more than 200 ns pulse width, 3 ns risetime and less than 1.5 ns jitter from 140 kV to 160 kV. The Marx generator can work stably and reliably at large range voltage. The demand for triggering is satisfied commendably.
2015,
27: 045002.
doi: 10.11884/HPLPB201527.045002
Abstract:
In order to reveal the developing progress of flashover in dodecylbenzene and study the effective methods to improve the creepage discharge of pulsed power devices,fashover voltag of polymethyl methacrylate and nylon6 were measured under negative pulse voltage through experiments at different pulse risetime and different electric form. Form the results of the experiments, it is found that the flashover voltage increases as impulse steepness increases. With the flashover distance increasing, the flashover voltage increases, but the flashover field strength decreases. The more nonuniform the electric field is, the more the flashover occurs, and if there is a large distance, flashover voltage has a slowing trend with flashover distance increasing in a very nonuniform field, and there is a clear inflection point. It is believed that they have similar flashover mechanism in vacuum and insulation oil and the flashover is completed in a gasifying path.
In order to reveal the developing progress of flashover in dodecylbenzene and study the effective methods to improve the creepage discharge of pulsed power devices,fashover voltag of polymethyl methacrylate and nylon6 were measured under negative pulse voltage through experiments at different pulse risetime and different electric form. Form the results of the experiments, it is found that the flashover voltage increases as impulse steepness increases. With the flashover distance increasing, the flashover voltage increases, but the flashover field strength decreases. The more nonuniform the electric field is, the more the flashover occurs, and if there is a large distance, flashover voltage has a slowing trend with flashover distance increasing in a very nonuniform field, and there is a clear inflection point. It is believed that they have similar flashover mechanism in vacuum and insulation oil and the flashover is completed in a gasifying path.
2015,
27: 045003.
doi: 10.11884/HPLPB201527.045003
Abstract:
The Z-pinch Primary Test Stand (PTS) which has been completed is composed of 24 modules, adopting capacitive storage scheme. It has a large number of control and monitoring nodes. For enhancing transplant and maintainability of server program and debasing exploitation difficulty of client, a control system based upon CORBA Controls Middle Ware is built to realize irrespective characteristic of platform and field of network communication. The application of CORBA technology and the control framework and the structure of PTS control system which has worked stably for one year are studied in this paper. It is a very important reference for building national high power laser equipment, X-ray free electron laser (XFEL) and designing large experimental physics control systems.
The Z-pinch Primary Test Stand (PTS) which has been completed is composed of 24 modules, adopting capacitive storage scheme. It has a large number of control and monitoring nodes. For enhancing transplant and maintainability of server program and debasing exploitation difficulty of client, a control system based upon CORBA Controls Middle Ware is built to realize irrespective characteristic of platform and field of network communication. The application of CORBA technology and the control framework and the structure of PTS control system which has worked stably for one year are studied in this paper. It is a very important reference for building national high power laser equipment, X-ray free electron laser (XFEL) and designing large experimental physics control systems.
2015,
27: 045004.
doi: 10.11884/HPLPB201527.045004
Abstract:
A 21-way high-voltage nanosecond rectangle wave pulsed power generator was developed for pulsed power experiments that require multi-way high-voltage nanosecond rectangle wave as excitation. This generator was composed of a 1-way high-voltage nanosecond rectangle wave pulsed power generator and a 1-way to 21-way convertor. The output voltage wave of the 1-way high-voltage nanosecond rectangle wave pulsed power generator was a rectangle wave whose amplitude was about 1070 V, full width at half maximum about 10.10 ns and rise time about 1.45 ns. This rectangle wave could be converted to 21-way rectangle wave using the 21-way convertor. Each way output rectangle wave of the 21-way convertor had an amplitude of 50.98 V, a full width at half maximum of about 10.15 ns and a rise time of about 2.25 ns.
A 21-way high-voltage nanosecond rectangle wave pulsed power generator was developed for pulsed power experiments that require multi-way high-voltage nanosecond rectangle wave as excitation. This generator was composed of a 1-way high-voltage nanosecond rectangle wave pulsed power generator and a 1-way to 21-way convertor. The output voltage wave of the 1-way high-voltage nanosecond rectangle wave pulsed power generator was a rectangle wave whose amplitude was about 1070 V, full width at half maximum about 10.10 ns and rise time about 1.45 ns. This rectangle wave could be converted to 21-way rectangle wave using the 21-way convertor. Each way output rectangle wave of the 21-way convertor had an amplitude of 50.98 V, a full width at half maximum of about 10.15 ns and a rise time of about 2.25 ns.
2015,
27: 045005.
doi: 10.11884/HPLPB201527.045005
Abstract:
Large electromagnetic force is put on rails of the Rail-Launcher, and the encapsulation of the launcher is always preloaded for caliber control and ablation avoidance. For one launch instrument, the caliber change under different pre-compression with bolt was calculated in 3-D coupling field, based on which some experiments were carried out. The result shows that the launch without ablation could be realized if the caliber change percentage is limited within 0.61%.
Large electromagnetic force is put on rails of the Rail-Launcher, and the encapsulation of the launcher is always preloaded for caliber control and ablation avoidance. For one launch instrument, the caliber change under different pre-compression with bolt was calculated in 3-D coupling field, based on which some experiments were carried out. The result shows that the launch without ablation could be realized if the caliber change percentage is limited within 0.61%.
2015,
27: 045006.
doi: 10.11884/HPLPB201527.045006
Abstract:
Magnetized target fusion is an alternative approach to fusion, which lies between the conventional inertial confinement fusion and magnetic confinement fusion. In this paper, a two-dimensional magneto-hydrodynamic code MPF-2D is used to study the formation process of field reversed configuration on Ying-Guang 1 device, which is constructed by the Institute of Fluid Physics, China Academy of Engineering Physics. The influence of experimental parameters is studied in details, and three groups of experimental input parameters are suggested for the incoming experiment, of which the bias fields are 0.3 T, the initial densities are 71015 cm-3, the cusp fields are from -1.0 T to -2.0 T and the main fields are from -3.0 T to -4.0 T.
Magnetized target fusion is an alternative approach to fusion, which lies between the conventional inertial confinement fusion and magnetic confinement fusion. In this paper, a two-dimensional magneto-hydrodynamic code MPF-2D is used to study the formation process of field reversed configuration on Ying-Guang 1 device, which is constructed by the Institute of Fluid Physics, China Academy of Engineering Physics. The influence of experimental parameters is studied in details, and three groups of experimental input parameters are suggested for the incoming experiment, of which the bias fields are 0.3 T, the initial densities are 71015 cm-3, the cusp fields are from -1.0 T to -2.0 T and the main fields are from -3.0 T to -4.0 T.
2015,
27: 045007.
doi: 10.11884/HPLPB201527.045007
Abstract:
The characteristics of the pulsed plasma have been measured using the triple probe method, and the temporal evolution of the plasma characteristics has been diagnosed in a single pulse. Electromagnetism disturbance has been controlled by metal shield and battery power supply for oscillograph. A code has been made to deal with data of triple probe method based on Labview. According to the characteristics of mixed ion components and supersonic ion velocities for pulsed plasma, the theory of the triple probe has been revised. Results show that during the pulse discharge time, the electron temperature Te is between 2-4 eV and the ion density ni is between 1017-1018 m-3 at the high voltage extraction interface, which is consistent with Langmuir single probes results.
The characteristics of the pulsed plasma have been measured using the triple probe method, and the temporal evolution of the plasma characteristics has been diagnosed in a single pulse. Electromagnetism disturbance has been controlled by metal shield and battery power supply for oscillograph. A code has been made to deal with data of triple probe method based on Labview. According to the characteristics of mixed ion components and supersonic ion velocities for pulsed plasma, the theory of the triple probe has been revised. Results show that during the pulse discharge time, the electron temperature Te is between 2-4 eV and the ion density ni is between 1017-1018 m-3 at the high voltage extraction interface, which is consistent with Langmuir single probes results.
2015,
27: 045008.
doi: 10.11884/HPLPB201527.045008
Abstract:
A novel spiral pulse forming line with oscillating and variable impedance is presented, which can neutralize fast-wave oscillation in previous spiral line with inner conductor and outer shield. Offsetting conduction of two fast waves respectively induced by reflected fast wave and reflected slow wave in such a spiral line is analyzed. Some relationship formulas, such as slow-wave coefficients and turns densities, of two variable impedance spiral sections are given. Simulative results show that such method can effectively neutralize the fast wave influence on the output pulse of the previous spiral line.
A novel spiral pulse forming line with oscillating and variable impedance is presented, which can neutralize fast-wave oscillation in previous spiral line with inner conductor and outer shield. Offsetting conduction of two fast waves respectively induced by reflected fast wave and reflected slow wave in such a spiral line is analyzed. Some relationship formulas, such as slow-wave coefficients and turns densities, of two variable impedance spiral sections are given. Simulative results show that such method can effectively neutralize the fast wave influence on the output pulse of the previous spiral line.
2015,
27: 045009.
doi: 10.11884/HPLPB201527.045009
Abstract:
Experiments about the laser-triggered water switch under microsecond rise-time pulse were done. Relation between the jitter of trigger breakdown delay time and the length of laser-induced water breakdown arc, laser energy and trigger time was researched. A water gap was designed for these experiments. The gap has two electrodes, one is a hemispheroid and the other is a plate. A hole in the hemispheroid electrode is designed for the laser. From self-breakdown experiments results, self-breakdown voltage of the water switch is about 133 kV, and jitter of self-breakdown delay time is about 263 ns. The jitter of breakdown delay time was reduced to less than 30 ns by laser-triggering. The laser energy has little influence on the jitter of breakdown delay time when the energy is higher than 19 mJ in the experiments.
Experiments about the laser-triggered water switch under microsecond rise-time pulse were done. Relation between the jitter of trigger breakdown delay time and the length of laser-induced water breakdown arc, laser energy and trigger time was researched. A water gap was designed for these experiments. The gap has two electrodes, one is a hemispheroid and the other is a plate. A hole in the hemispheroid electrode is designed for the laser. From self-breakdown experiments results, self-breakdown voltage of the water switch is about 133 kV, and jitter of self-breakdown delay time is about 263 ns. The jitter of breakdown delay time was reduced to less than 30 ns by laser-triggering. The laser energy has little influence on the jitter of breakdown delay time when the energy is higher than 19 mJ in the experiments.
2015,
27: 045101.
doi: 10.11884/HPLPB201527.045101
Abstract:
The GaAs photocathode high-voltage DC injector has been demonstrated as one of the most important electron sources for future high-repetition short-wave free electron lasers (FELs) and energy recovery linacs (ERLs). In this paper, recent progress of the GaAs high-voltage (HV) photo-injector for the FEL-THz facility is presented, and the chance of which for driving a future high-repetition short-wave FEL is discussed. All the factors that affect the GaAs photocathode operation life-time are considered and a qualitative physical model is proposed. Under the guidance of this model and with some optimization strategies, a 5 mA/32 min CW output is reached in the HV DC injector. Some electron beam parameters are measured, including normalized emittance under 4.8 mA output that is about 6.0 mmmrad, thermal emittance about 0.6mmmrad, intrinsic transverse energy about 92 meV, and root-mean-squared length with 250 keV kinetic energy that is 11.5 ps at 90.6 cm after the cathode. The state of the injector now meets the needs of FEL-THz electron source requirements preliminarily.
The GaAs photocathode high-voltage DC injector has been demonstrated as one of the most important electron sources for future high-repetition short-wave free electron lasers (FELs) and energy recovery linacs (ERLs). In this paper, recent progress of the GaAs high-voltage (HV) photo-injector for the FEL-THz facility is presented, and the chance of which for driving a future high-repetition short-wave FEL is discussed. All the factors that affect the GaAs photocathode operation life-time are considered and a qualitative physical model is proposed. Under the guidance of this model and with some optimization strategies, a 5 mA/32 min CW output is reached in the HV DC injector. Some electron beam parameters are measured, including normalized emittance under 4.8 mA output that is about 6.0 mmmrad, thermal emittance about 0.6mmmrad, intrinsic transverse energy about 92 meV, and root-mean-squared length with 250 keV kinetic energy that is 11.5 ps at 90.6 cm after the cathode. The state of the injector now meets the needs of FEL-THz electron source requirements preliminarily.
2015,
27: 045102.
doi: 10.11884/HPLPB201527.045102
Abstract:
The wiggler magnetic measurement system is designed according to theoretical analysis and manufacture technology level. The main parameters which affect the character of the magnetic measurement are described and analyzed in detail. Accurate orientation and measure of Hall probe with synchronous acquisition of the position and magnetic field data are the main function of the magnetic field measurement device which is made up of air-thrust bearings, Magnetic instrument and control system. In z direction, the positioning accuracy and repeat positioning accuracy are less than 5 m and 2 m respectively. Measuring precision, repeat measuring precision and response frequency of Hall probe are 0.05%, 0.01% and 1 kHz respectively. Sampling rate of data acquisition card is more than 1000.
The wiggler magnetic measurement system is designed according to theoretical analysis and manufacture technology level. The main parameters which affect the character of the magnetic measurement are described and analyzed in detail. Accurate orientation and measure of Hall probe with synchronous acquisition of the position and magnetic field data are the main function of the magnetic field measurement device which is made up of air-thrust bearings, Magnetic instrument and control system. In z direction, the positioning accuracy and repeat positioning accuracy are less than 5 m and 2 m respectively. Measuring precision, repeat measuring precision and response frequency of Hall probe are 0.05%, 0.01% and 1 kHz respectively. Sampling rate of data acquisition card is more than 1000.
2015,
27: 045103.
doi: 10.11884/HPLPB201527.045103
Abstract:
Based on the output effect of the circuit, the study used the charge transfer principle to describe the relative complex physical processes of balanced Cockcroft-Walton(C-W) circuit. Given the periodically turning model to mathematical analysis is equivalent to nonlinear conduction properties of the diode, theoretical model output formulas of ripple voltage and load-dropping output voltage that describe the output characteristics of C-W circuit are derivated. With circuit simulation software, the ripple voltage and the output voltage waveforms of the basic and balanced C-W circuit are simulated, and it illustrates that the ripple voltage of the balanced topology is far less than the basic, approximately the value percentage of 8%. The outputs of the theoretical model established in this paper are verified, and the results show that the calculated ripple voltage from the theoretical model is slightly lower than the simulation values, and the relative error between the calculated output voltage and simulation values is less than 10%.
Based on the output effect of the circuit, the study used the charge transfer principle to describe the relative complex physical processes of balanced Cockcroft-Walton(C-W) circuit. Given the periodically turning model to mathematical analysis is equivalent to nonlinear conduction properties of the diode, theoretical model output formulas of ripple voltage and load-dropping output voltage that describe the output characteristics of C-W circuit are derivated. With circuit simulation software, the ripple voltage and the output voltage waveforms of the basic and balanced C-W circuit are simulated, and it illustrates that the ripple voltage of the balanced topology is far less than the basic, approximately the value percentage of 8%. The outputs of the theoretical model established in this paper are verified, and the results show that the calculated ripple voltage from the theoretical model is slightly lower than the simulation values, and the relative error between the calculated output voltage and simulation values is less than 10%.
2015,
27: 045104.
doi: 10.11884/HPLPB201527.045104
Abstract:
About 120 magnets would be installed and aligned in the HLSⅡ upgrade project. In order to make sure the project to be completed smoothly, according to the structure characteristics of HLSⅡ, the primary control network is measured by several different instruments and softwares. The magnets are installed and aligned in the coordinate of themselves, it benefits to the efficiency and accuracy of magnets installation and alignment. After three times installation and alignment, all magnets are properly positioned, and the accuracy meets the requirement.
About 120 magnets would be installed and aligned in the HLSⅡ upgrade project. In order to make sure the project to be completed smoothly, according to the structure characteristics of HLSⅡ, the primary control network is measured by several different instruments and softwares. The magnets are installed and aligned in the coordinate of themselves, it benefits to the efficiency and accuracy of magnets installation and alignment. After three times installation and alignment, all magnets are properly positioned, and the accuracy meets the requirement.
2015,
27: 045105.
doi: 10.11884/HPLPB201527.045105
Abstract:
The storage ring at Shanghai Synchrotron Radiation Facility (SSRF) is operating at the top-up mode, which is injected every 10 minutes. The transverse betatron oscillation introduced during the injection can be used to calculate the tune of the machine. A real-time tune measurement system has been built where the Fast Fourier Transformation (FFT) of the turn-by-turn beam position data from digital BPM processors is calculated at injection rate. Long-term results of the first half of 2014 show that the system is capable of monitoring tune shift effectively, and can be used to evaluate the best tune performance of the storage ring. Meanwhile, the system can detect operation abnormality in time and locate the malfunction causes effectively after analyzing related systems. It is an effective tool for the operation and optimization of the machine.
The storage ring at Shanghai Synchrotron Radiation Facility (SSRF) is operating at the top-up mode, which is injected every 10 minutes. The transverse betatron oscillation introduced during the injection can be used to calculate the tune of the machine. A real-time tune measurement system has been built where the Fast Fourier Transformation (FFT) of the turn-by-turn beam position data from digital BPM processors is calculated at injection rate. Long-term results of the first half of 2014 show that the system is capable of monitoring tune shift effectively, and can be used to evaluate the best tune performance of the storage ring. Meanwhile, the system can detect operation abnormality in time and locate the malfunction causes effectively after analyzing related systems. It is an effective tool for the operation and optimization of the machine.
2015,
27: 045106.
doi: 10.11884/HPLPB201527.045106
Abstract:
The upgrade project of HLSⅡ is almost finished and the new injector has achieved the goal of full energy injection. To satisfy the need of measuring the new injector beam intensity, a beam intensity measurement (BIM) system is designed, which has 3 fast current transformers (FCT) and 2 integrating current transformers (ICT) installed in the vacuum chamber to non-destructively and real-timely measure beam current and beam charge. To acquire beam parameters accurately, the article elaborates the on-line and off-line calibration method of long transmission coaxial cable. Then two low noise pre-amplifiers used to amplify the output signal of ICT to improve SNR are designed and appropriate algorithms of reducing the low frequency harmonic noise and kicker noise in software are proposed. In the end, some on-line experiment results are presented, which show that beam transmission efficiency is about 27.4% and injection efficiency is approximately 44.3%.
The upgrade project of HLSⅡ is almost finished and the new injector has achieved the goal of full energy injection. To satisfy the need of measuring the new injector beam intensity, a beam intensity measurement (BIM) system is designed, which has 3 fast current transformers (FCT) and 2 integrating current transformers (ICT) installed in the vacuum chamber to non-destructively and real-timely measure beam current and beam charge. To acquire beam parameters accurately, the article elaborates the on-line and off-line calibration method of long transmission coaxial cable. Then two low noise pre-amplifiers used to amplify the output signal of ICT to improve SNR are designed and appropriate algorithms of reducing the low frequency harmonic noise and kicker noise in software are proposed. In the end, some on-line experiment results are presented, which show that beam transmission efficiency is about 27.4% and injection efficiency is approximately 44.3%.
2015,
27: 045107.
doi: 10.11884/HPLPB201527.045107
Abstract:
XFEL light source which produces hard X-ray from radiation character of electron bunch in undulator will be researched in CAEP. According to theoretical analysis and numerical simulation, an undulator line is designed on the condition that the beam energy can reach 12 GeV at present. The out vacuum undulaor line is composed of 25 segments and the length of each segment is 3.86 m. The period length of undulator is 25.4 mm and the peak magnetic field is 0.636-1.03 T, while the gap changes from 7 mm to 10 mm. The total undulator line is about 120 m. The radiation energy designed is from 3 keV to 25 keV.
XFEL light source which produces hard X-ray from radiation character of electron bunch in undulator will be researched in CAEP. According to theoretical analysis and numerical simulation, an undulator line is designed on the condition that the beam energy can reach 12 GeV at present. The out vacuum undulaor line is composed of 25 segments and the length of each segment is 3.86 m. The period length of undulator is 25.4 mm and the peak magnetic field is 0.636-1.03 T, while the gap changes from 7 mm to 10 mm. The total undulator line is about 120 m. The radiation energy designed is from 3 keV to 25 keV.
2015,
27: 045108.
doi: 10.11884/HPLPB201527.045108
Abstract:
A new generation of ring-based light source, called diffraction-limited storage ring (DLSR), has attracted increasing attention from accelerator scientists worldwide. This article introduces the progress in the physical design and optimization of DLSR at home and abroad in the past few years. In the linear optics design multi-bend achromats with compact layout are usually adopted, so as to achieve ultralow emittance within a reasonable circumference. In the nonlinear optimization, phase manipulation technique, theoretical and numerical optimization methods are usually used to minimize the strong nonlinearities caused by the chromatic sextupoles. Associated with the small acceptance of a DLSR, off-axis injection with pulsed multipoles and on-axis injection with fast kickers are considered. Collective effects, especially the intrabeam scattering and the Touschek effects, become significant as emittance decreases, requiring methods of bunch lengthening and transverse feedback to ensure the stability of the particle motion.
A new generation of ring-based light source, called diffraction-limited storage ring (DLSR), has attracted increasing attention from accelerator scientists worldwide. This article introduces the progress in the physical design and optimization of DLSR at home and abroad in the past few years. In the linear optics design multi-bend achromats with compact layout are usually adopted, so as to achieve ultralow emittance within a reasonable circumference. In the nonlinear optimization, phase manipulation technique, theoretical and numerical optimization methods are usually used to minimize the strong nonlinearities caused by the chromatic sextupoles. Associated with the small acceptance of a DLSR, off-axis injection with pulsed multipoles and on-axis injection with fast kickers are considered. Collective effects, especially the intrabeam scattering and the Touschek effects, become significant as emittance decreases, requiring methods of bunch lengthening and transverse feedback to ensure the stability of the particle motion.
2015,
27: 045109.
doi: 10.11884/HPLPB201527.045109
Abstract:
With the development of the required gradient of the waveguide coupled TW accelerating structure, for preventing the undesirable transverse momentum contributions being imparted to the beam during traversal of the linac coupler cavities, the use of symmetric dual feed cylindrical cavities which have diametrically opposed side wall coupling apertures has been widely accepted. As one type of the dual feed cylindrical cavities, the prototype of the S-band J-type waveguide feeding accelerating structure developed has got a top accelerating gradient of 30 MV per meter during RF conditioning. However, the transverse gradient of the amplitude and the phase of the longitudinal electric field caused by the existence of the quadrupolar field in the dual feed cylindrical cavity, will also degrade the beam emittance. So the J-type waveguide feeding racetrack cavity is studied theoretically. With comparison of the simulation results to the cylindrical cavity, the racetrack cavity can improve the rotational symmetry of the longitudinal electric field in the non-near axis area in the transverse plane very well, which will reduce the impact of the quadrupolar field. More importantly, the J-type waveguide feeding racetrack cavity is easier in the aspect of mechanical fabrication and measurement, which seems to be a very good direction for the future dual feed accelerating structures.
With the development of the required gradient of the waveguide coupled TW accelerating structure, for preventing the undesirable transverse momentum contributions being imparted to the beam during traversal of the linac coupler cavities, the use of symmetric dual feed cylindrical cavities which have diametrically opposed side wall coupling apertures has been widely accepted. As one type of the dual feed cylindrical cavities, the prototype of the S-band J-type waveguide feeding accelerating structure developed has got a top accelerating gradient of 30 MV per meter during RF conditioning. However, the transverse gradient of the amplitude and the phase of the longitudinal electric field caused by the existence of the quadrupolar field in the dual feed cylindrical cavity, will also degrade the beam emittance. So the J-type waveguide feeding racetrack cavity is studied theoretically. With comparison of the simulation results to the cylindrical cavity, the racetrack cavity can improve the rotational symmetry of the longitudinal electric field in the non-near axis area in the transverse plane very well, which will reduce the impact of the quadrupolar field. More importantly, the J-type waveguide feeding racetrack cavity is easier in the aspect of mechanical fabrication and measurement, which seems to be a very good direction for the future dual feed accelerating structures.
2015,
27: 045110.
doi: 10.11884/HPLPB201527.045110
Abstract:
An interlock control system based on a new redundant Programmable Logic Controller (PLC) and PROFINET protocol is developed as one of the key systems in China Accelerator Driven Sub-critical System (C-ADS) injector Ⅰ for machine control and personnel protection. Signals from critical accelerator components are sent to this system for safety protection. Fault-tolerance and redundancy for high reliability are considered through the whole design, and reliability analysis of both redundant and non-redundant systems is done to meet the strict requirement. A control interface of Experimental Physics and Industrial Control System (EPICS) is developed and successfully used online.
An interlock control system based on a new redundant Programmable Logic Controller (PLC) and PROFINET protocol is developed as one of the key systems in China Accelerator Driven Sub-critical System (C-ADS) injector Ⅰ for machine control and personnel protection. Signals from critical accelerator components are sent to this system for safety protection. Fault-tolerance and redundancy for high reliability are considered through the whole design, and reliability analysis of both redundant and non-redundant systems is done to meet the strict requirement. A control interface of Experimental Physics and Industrial Control System (EPICS) is developed and successfully used online.
2015,
27: 046001.
doi: 10.11884/HPLPB201527.046001
Abstract:
Based on the result of physics and pyrology design, the design of subcritical blanket fission fuel zone structure is given for the fusion-fission hybrid reactor. This scheme includes longitudinal bone support structure, fuel zone structure and zirconium cladding structure. Using Pro/e CAD software, the subcritical blanket fuel zone structure model is established, at the same time, the preliminary mechanical analysis for the longitudinal bone style support structure is carried out by ANSYS-workbench mechanical finite software. Accordingly, the maximal Tresca stress value, the stress distribution contours and the total deformation are obtained, the maximal stress and deformation are respectively 87.04 MPa and 0.17 mm. In the light of the third strength theory, the above calculation results show that the longitudinal bone style subcritical blanket fuel zone structure can satisfy the strength requirements.
Based on the result of physics and pyrology design, the design of subcritical blanket fission fuel zone structure is given for the fusion-fission hybrid reactor. This scheme includes longitudinal bone support structure, fuel zone structure and zirconium cladding structure. Using Pro/e CAD software, the subcritical blanket fuel zone structure model is established, at the same time, the preliminary mechanical analysis for the longitudinal bone style support structure is carried out by ANSYS-workbench mechanical finite software. Accordingly, the maximal Tresca stress value, the stress distribution contours and the total deformation are obtained, the maximal stress and deformation are respectively 87.04 MPa and 0.17 mm. In the light of the third strength theory, the above calculation results show that the longitudinal bone style subcritical blanket fuel zone structure can satisfy the strength requirements.
2015,
27: 046002.
doi: 10.11884/HPLPB201527.046002
Abstract:
According to the working principle of EAST-NBI deflection system, the basic transmission process of the beam and characteristics of the deflection system were analyzed. Using Monte Carlo method, computer programs were developed to simulate the transmission of the neutral beam in the deflecting region. The results show EAST-NBI magnetic deflection system can strip the residual ions out of the beam passage; The loss of reionization in the beam deflection region is about 2.43%; Because of line focusing process caused by the 180 degrees deflection of the beam, the pole shields of the deflection magnet have high heat flux density.
According to the working principle of EAST-NBI deflection system, the basic transmission process of the beam and characteristics of the deflection system were analyzed. Using Monte Carlo method, computer programs were developed to simulate the transmission of the neutral beam in the deflecting region. The results show EAST-NBI magnetic deflection system can strip the residual ions out of the beam passage; The loss of reionization in the beam deflection region is about 2.43%; Because of line focusing process caused by the 180 degrees deflection of the beam, the pole shields of the deflection magnet have high heat flux density.
2015,
27: 049001.
doi: 10.11884/HPLPB201527.049001
Abstract:
The vibrothermography technique was applied to detect: The surface temperature distribution of flat-panel component under different endogenous heat sources (instantaneous and periodical) was studied. The heating at the different forms of damage, including surface crack, subsurface delamination and internal debond, was simulated under vibration excitation by numerical finite element method. Typical composite component specimens with different types of damage including impact and fatigue were designed and produced, then detected by vibrothermography method with ultrasonic generator and infrared camera. The results prove the feasibility and advantages of the vibrothermography method for detecting interface damage in composite materials.
The vibrothermography technique was applied to detect: The surface temperature distribution of flat-panel component under different endogenous heat sources (instantaneous and periodical) was studied. The heating at the different forms of damage, including surface crack, subsurface delamination and internal debond, was simulated under vibration excitation by numerical finite element method. Typical composite component specimens with different types of damage including impact and fatigue were designed and produced, then detected by vibrothermography method with ultrasonic generator and infrared camera. The results prove the feasibility and advantages of the vibrothermography method for detecting interface damage in composite materials.
2015,
27: 041016.
doi: 10.11884/HPLPB201527.041016
Abstract:
Closed circulation is an important way to achieve miniaturization and practicability of high-power pulsed HF lasers. To obtain stable output energy of closed circulation pulsed HF laser, the characteristics of the closed circulation HF laser is studied, and the numerical model of the laser duct is established. Based on the ANSYS application software , the flow rate distribution of the gas medium inside the gain region is analyzed. To acquire better distribution uniformity, different structures of the injection section and transmit section are developed, and corresponding flow fields are simulated and analyzed. A circulation duct with improved distribution uniformity is designed, and the flow rate distribution of the gain region is measured. The results of the experiment and the simulation are consistent.
Closed circulation is an important way to achieve miniaturization and practicability of high-power pulsed HF lasers. To obtain stable output energy of closed circulation pulsed HF laser, the characteristics of the closed circulation HF laser is studied, and the numerical model of the laser duct is established. Based on the ANSYS application software , the flow rate distribution of the gas medium inside the gain region is analyzed. To acquire better distribution uniformity, different structures of the injection section and transmit section are developed, and corresponding flow fields are simulated and analyzed. A circulation duct with improved distribution uniformity is designed, and the flow rate distribution of the gain region is measured. The results of the experiment and the simulation are consistent.
