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RSS2016 Vol. 28, No. 09
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2016,
28: 090201.
doi: 10.11884/HPLPB201628.160058
Abstract:
In near infrared high reflectors, nodular defects are the main factor inducing the laser damage of optical coatings. In order to improve the laser-induced damage threshold (LIDT) of the optical coatings, it is necessary to study the damage characteristics of nodules. In this paper, the studies on laser-induced damage of nodular defects is reviewed from two aspects: the real nodules and the artificial nodules. For real nodules, the geometries of nodular defects were established and the preliminary understanding of the damage mechanisms of nodular defects was achieved. The finite-difference time-domain (FDTD) technique has been successfully used to simulate the electric-field intensity enhancement in nodules, which helps to explain the damage mechanism of nodules. The experimental methods of eliminating the seeds and laser conditioning have been proposed to control nodular defects and to improve LIDT. However, the properties of real nodules, such as the diameters, absorption and lodging depth of seeds, are quite diverse and very difficult to predict, control and reproduce. This makes the systematical and quantitative study of nodular damage quite challenging, and the understanding of the nodular damage mechanisms is still insufficient. Artificial nodules offered the opportunity to study their damage behaviors systematically, quantitatively or even in a single factor manner, which greatly improved the efficiency and reliability of the experimental studies. In addition, a direct comparison between the experimental results and theoretical simulation results could be achieved using the well-controlled artificial nodules. The damage morphologies of artificial nodules were almost the same with the FDTD simulated electric-field intensity distributions, which not only demonstrates the correctness of the simulated results but also further illustrates that the electric field enhancement is the main mechanism of inducing nodular damage. After having a deeper understanding of the nodular damage mechanisms, the broadband coating and planarization technique have been used to suppress the electric field enhancement and to improve the LIDT of nodules. This extends the ideas and methods dealing with nodular defects, from solely removing nodular defects to controlling nodular defects, which opens up new directions for improving the LIDT of laser coatings.
In near infrared high reflectors, nodular defects are the main factor inducing the laser damage of optical coatings. In order to improve the laser-induced damage threshold (LIDT) of the optical coatings, it is necessary to study the damage characteristics of nodules. In this paper, the studies on laser-induced damage of nodular defects is reviewed from two aspects: the real nodules and the artificial nodules. For real nodules, the geometries of nodular defects were established and the preliminary understanding of the damage mechanisms of nodular defects was achieved. The finite-difference time-domain (FDTD) technique has been successfully used to simulate the electric-field intensity enhancement in nodules, which helps to explain the damage mechanism of nodules. The experimental methods of eliminating the seeds and laser conditioning have been proposed to control nodular defects and to improve LIDT. However, the properties of real nodules, such as the diameters, absorption and lodging depth of seeds, are quite diverse and very difficult to predict, control and reproduce. This makes the systematical and quantitative study of nodular damage quite challenging, and the understanding of the nodular damage mechanisms is still insufficient. Artificial nodules offered the opportunity to study their damage behaviors systematically, quantitatively or even in a single factor manner, which greatly improved the efficiency and reliability of the experimental studies. In addition, a direct comparison between the experimental results and theoretical simulation results could be achieved using the well-controlled artificial nodules. The damage morphologies of artificial nodules were almost the same with the FDTD simulated electric-field intensity distributions, which not only demonstrates the correctness of the simulated results but also further illustrates that the electric field enhancement is the main mechanism of inducing nodular damage. After having a deeper understanding of the nodular damage mechanisms, the broadband coating and planarization technique have been used to suppress the electric field enhancement and to improve the LIDT of nodules. This extends the ideas and methods dealing with nodular defects, from solely removing nodular defects to controlling nodular defects, which opens up new directions for improving the LIDT of laser coatings.
2016,
28: 091001.
doi: 10.11884/HPLPB201628.160046
Abstract:
For structured light decoding, we propose a universal decoding method for periodic wave patterns based on traditional phase measuring profilometry(PMP). By applying PMP phase computation algorithm in such periodic wave patterns, as triangular, sawtooth and square wave patterns, we could achieved accurate final phases by temporally unwrapping phases of the patterns with sufficiently high frequency. Experiments using a white wall as the testing surface and reconstructing a white plaster statue demonstrate that, the proposed method is valid as it can achieve comparable accuracy.
For structured light decoding, we propose a universal decoding method for periodic wave patterns based on traditional phase measuring profilometry(PMP). By applying PMP phase computation algorithm in such periodic wave patterns, as triangular, sawtooth and square wave patterns, we could achieved accurate final phases by temporally unwrapping phases of the patterns with sufficiently high frequency. Experiments using a white wall as the testing surface and reconstructing a white plaster statue demonstrate that, the proposed method is valid as it can achieve comparable accuracy.
2016,
28: 091002.
doi: 10.11884/HPLPB201628.160011
Abstract:
Two main problems must be solved in order to obtain a reliable slab laser gain medium module with large size and low wave-front distortion during high power working condition. The first problem is the formation of a large connection area with low thermal resistance and free voids. The second problem is how to get a low stress connection with low transmission wave-front distortion. The indium metal was chosen as a welding material for its outstanding ductile property and its optimal thickness was found through experiments. A reliable connection area greater than 40 cm2 has been established between slab laser gain medium and cooling unit by improved welding technique. The repetitiveness of this improved craft with voids ratio less than 0.5% and voids area less than 1 mm2 is over 90%. The ones whose static transmission wave-front distortion is less than 1 m of slab laser gain medium with the size of 150.2 mm30 mm2.5 mm is over 80%, while those with the static transmission wave-front distortion less than 1.5 m is nearly 100%. A 4000 W-output Nd: YAG slab laser has been achieved based on improved packaging technology.
Two main problems must be solved in order to obtain a reliable slab laser gain medium module with large size and low wave-front distortion during high power working condition. The first problem is the formation of a large connection area with low thermal resistance and free voids. The second problem is how to get a low stress connection with low transmission wave-front distortion. The indium metal was chosen as a welding material for its outstanding ductile property and its optimal thickness was found through experiments. A reliable connection area greater than 40 cm2 has been established between slab laser gain medium and cooling unit by improved welding technique. The repetitiveness of this improved craft with voids ratio less than 0.5% and voids area less than 1 mm2 is over 90%. The ones whose static transmission wave-front distortion is less than 1 m of slab laser gain medium with the size of 150.2 mm30 mm2.5 mm is over 80%, while those with the static transmission wave-front distortion less than 1.5 m is nearly 100%. A 4000 W-output Nd: YAG slab laser has been achieved based on improved packaging technology.
2016,
28: 091003.
doi: 10.11884/HPLPB201628.151225
Abstract:
This paper presents a physical model about the temperature distribution of a silicon preform exposed to a 10.6 m CO2 laser in consideration of air convection and environmental radiation heat transfer. In the meantime, an approach of heating the preform by the laser combining with graphite furnace is suggested. Simulation results show that the temperature distribution is strongly dependent on the parameters of the CO2 laser and the preform, and laser heating is appropriate for preform with diameter less than 10 mm when the laser spot radius is 3 mm and laser power is 400 W. Heating combining with graphite furnace can modulate the temperature gradient effectively and build the correct temperature field for silicon core fiber drawing.
This paper presents a physical model about the temperature distribution of a silicon preform exposed to a 10.6 m CO2 laser in consideration of air convection and environmental radiation heat transfer. In the meantime, an approach of heating the preform by the laser combining with graphite furnace is suggested. Simulation results show that the temperature distribution is strongly dependent on the parameters of the CO2 laser and the preform, and laser heating is appropriate for preform with diameter less than 10 mm when the laser spot radius is 3 mm and laser power is 400 W. Heating combining with graphite furnace can modulate the temperature gradient effectively and build the correct temperature field for silicon core fiber drawing.
2016,
28: 091004.
doi: 10.11884/HPLPB201628.151288
Abstract:
A novel method of 3-D visual reconstruction without system calibration, which is based on phase map, is proposed to solve the problem of the dependency on calibration information in traditional 3-D reconstruction. Firstly, the phase map of the scanned object is obtained by structured light illumination. Then the horizontal and vertical spatial distortions of the phase image are used to calculate the relative depth of the scanned object. Finally, the 3-D visual reconstruction of the scanned object is realized. This method can be applied in some 3-D applications where the calibration information cant be obtained. Experiment results show good 3-D visual reconstruction result when the surface structure of the scanned object is simple. Comparing with the traditional 3-D reconstruction results, it is proved that this algorithm is valid.
A novel method of 3-D visual reconstruction without system calibration, which is based on phase map, is proposed to solve the problem of the dependency on calibration information in traditional 3-D reconstruction. Firstly, the phase map of the scanned object is obtained by structured light illumination. Then the horizontal and vertical spatial distortions of the phase image are used to calculate the relative depth of the scanned object. Finally, the 3-D visual reconstruction of the scanned object is realized. This method can be applied in some 3-D applications where the calibration information cant be obtained. Experiment results show good 3-D visual reconstruction result when the surface structure of the scanned object is simple. Comparing with the traditional 3-D reconstruction results, it is proved that this algorithm is valid.
2016,
28: 092001.
doi: 10.11884/HPLPB201628.160037
Abstract:
Alkali borosilicate glasses are used in inertial confinement fusion (ICF) as materials of hollow glass microspheres (HGMs). In this work, classical molecular dynamic simulation was addressed to study this kind of glass. Then the microstructure including bond lengths, bond angles, coordinate number and void sites distribution with different K (molar ratio of SiO2 to B2O3) and R (molar ratio of Na2O to B2O3) were gotten. After simulation, in the glass with different K and R, the network of silicate atoms keeps stable, and the network of boron atoms changes with the composition. At the same time, when we comes to the actual use of Ar-filled glass in the experiment of ICF, through simulation, if K is 40.5, R is 17.4, 8.5, 4.2, there are much more void sites in the glass for argon atoms to diffuse.
Alkali borosilicate glasses are used in inertial confinement fusion (ICF) as materials of hollow glass microspheres (HGMs). In this work, classical molecular dynamic simulation was addressed to study this kind of glass. Then the microstructure including bond lengths, bond angles, coordinate number and void sites distribution with different K (molar ratio of SiO2 to B2O3) and R (molar ratio of Na2O to B2O3) were gotten. After simulation, in the glass with different K and R, the network of silicate atoms keeps stable, and the network of boron atoms changes with the composition. At the same time, when we comes to the actual use of Ar-filled glass in the experiment of ICF, through simulation, if K is 40.5, R is 17.4, 8.5, 4.2, there are much more void sites in the glass for argon atoms to diffuse.
An Abel inversion method based on basis set expansion for discontinuous radial distribution problems
2016,
28: 092002.
doi: 10.11884/HPLPB201628.151262
Abstract:
Diagnostics of fusion capsule plasma which usually has a discontinuous radial distribution is a basic problem in laser fusion plasma researches. An Abel inversion method based on basis set expansion was proposed to handle this discontinuous Abel inverse problem. This method expands the radial distribution on a set of basis functions, and then the measurement data can be approximated by a linear combination of Abel transforms of the basis functions. The weighted coefficients of the basis functions were obtained by projected Landweber iteration method. Numerical simulations demonstrate that the proposed method is sufficiently accurate to reconstruct discontinuous radial distribution, and variance of reconstructed result can reach 10-4 for ideal signal. Although some noise were added in measurement data, the inversion result can still reflect discontinuous property of radial distribution accurately.
Diagnostics of fusion capsule plasma which usually has a discontinuous radial distribution is a basic problem in laser fusion plasma researches. An Abel inversion method based on basis set expansion was proposed to handle this discontinuous Abel inverse problem. This method expands the radial distribution on a set of basis functions, and then the measurement data can be approximated by a linear combination of Abel transforms of the basis functions. The weighted coefficients of the basis functions were obtained by projected Landweber iteration method. Numerical simulations demonstrate that the proposed method is sufficiently accurate to reconstruct discontinuous radial distribution, and variance of reconstructed result can reach 10-4 for ideal signal. Although some noise were added in measurement data, the inversion result can still reflect discontinuous property of radial distribution accurately.
2016,
28: 092003.
doi: 10.11884/HPLPB201628.151128
Abstract:
Based on emission mode of transmit cathode and the principle of FXRD, a transmit cathode for XRD was designed and manufactured. A sample with a cathode made up of 550 nm CH and 50 nm Au was used for preliminary experiments on SG-Ⅲ prototype facility. Firstly the influence of direct X-ray was evaluated using an XRD with reflective cathode. The results show that the XRD with -1500 V bias voltage could eliminate the influence of X-ray arrived at the anode for XRD with transmission cathode. Then when main lasers and the ninth laser were operating on SG-Ⅲ prototype facility, the transmission cathode XRD with negative bias voltage captured normal signals. The results show that the second peak signal delay 3.01 ns by the first peak, which is in accord with the time sequence of main lasers and the ninth laser. The capability of temporal resolution can satisfy requirements of experiments.
Based on emission mode of transmit cathode and the principle of FXRD, a transmit cathode for XRD was designed and manufactured. A sample with a cathode made up of 550 nm CH and 50 nm Au was used for preliminary experiments on SG-Ⅲ prototype facility. Firstly the influence of direct X-ray was evaluated using an XRD with reflective cathode. The results show that the XRD with -1500 V bias voltage could eliminate the influence of X-ray arrived at the anode for XRD with transmission cathode. Then when main lasers and the ninth laser were operating on SG-Ⅲ prototype facility, the transmission cathode XRD with negative bias voltage captured normal signals. The results show that the second peak signal delay 3.01 ns by the first peak, which is in accord with the time sequence of main lasers and the ninth laser. The capability of temporal resolution can satisfy requirements of experiments.
2016,
28: 092004.
doi: 10.11884/HPLPB201628.160078
Abstract:
The hydrocarbon glow discharge polymer (GDP) shells fabricated by plasma polymerization technology were used as the ablators for ICF targets. In order to understand the properties of hydrocarbon plasma for GDP deposition, plasmas of trans-two-butane and H2 (T2B/H2) were investigated by Langmuir probe and mass spectrometer in the diffusion region. Several parameters, such as electron energy probability functions, electron densities, electron temperature were analyzed. The relationship between the properties of plasma and the discharge parameters were also discussed. It was found that there was a significant modulating effect of the radio frequency (RF) powers on the plasma parameters. The electron density was found to be nearly proportional to the discharge power in the range of 10 W to 35 W. As the RF power increased, the electron temperature and plasma potential decreased at first then increased with discharge power, which was governed by a two-step ionization mechanism. The small and stable fragments, found by mass spectrometer, indicated that the polymerization was suppressed in the gas phase at high RF power.
The hydrocarbon glow discharge polymer (GDP) shells fabricated by plasma polymerization technology were used as the ablators for ICF targets. In order to understand the properties of hydrocarbon plasma for GDP deposition, plasmas of trans-two-butane and H2 (T2B/H2) were investigated by Langmuir probe and mass spectrometer in the diffusion region. Several parameters, such as electron energy probability functions, electron densities, electron temperature were analyzed. The relationship between the properties of plasma and the discharge parameters were also discussed. It was found that there was a significant modulating effect of the radio frequency (RF) powers on the plasma parameters. The electron density was found to be nearly proportional to the discharge power in the range of 10 W to 35 W. As the RF power increased, the electron temperature and plasma potential decreased at first then increased with discharge power, which was governed by a two-step ionization mechanism. The small and stable fragments, found by mass spectrometer, indicated that the polymerization was suppressed in the gas phase at high RF power.
2016,
28: 093001.
doi: 10.11884/HPLPB201628.151272
Abstract:
The influence of equivalent surface currents was introduced and the farfield directivity was amended which was more adaptive to describe the aperture radiation characteristics. It was concluded that wide impulse, small aperture, severe tapered field in aperture, or obvious spherical wavefront would lead to bad directivity. By holding the spherical wavefront in proper extent, it could achieve a farfield with flat lobe around boresight and sharp falling at certain angle. By investigating the radiation characteristics of different aperture in time domain, it was easier to analyze the practical impulse antenna in a short time.
The influence of equivalent surface currents was introduced and the farfield directivity was amended which was more adaptive to describe the aperture radiation characteristics. It was concluded that wide impulse, small aperture, severe tapered field in aperture, or obvious spherical wavefront would lead to bad directivity. By holding the spherical wavefront in proper extent, it could achieve a farfield with flat lobe around boresight and sharp falling at certain angle. By investigating the radiation characteristics of different aperture in time domain, it was easier to analyze the practical impulse antenna in a short time.
2016,
28: 093002.
doi: 10.11884/HPLPB201628.151098
Abstract:
A Ku band coaxial relativistic backward wave oscillator (RBWO) with low magnetic field is presented in this paper. This RBWO works at coaxial TM01-mode which contains two-segment slow wave structures (SWSs). The first segment SWS mainly modulates the intense electron and the second one mainly extracts the microwave energy. By introducing pre-modulate using an asymmetry reflector, the modulation depth is improved. By optimizing the length of the drift between SWSs, the field distribution is optimized and the axial electric field intension of the extract SWS is farther improved. The efficiency of the RBWO is improved. Finally ,when the magnetic field is 0.6 T，the diode voltage is 490 kV，the diode current is 7.5 kA, a 1.27 GW microwave is obtained with an efficiency of 35% and a frequency of 14.7 GHz.
A Ku band coaxial relativistic backward wave oscillator (RBWO) with low magnetic field is presented in this paper. This RBWO works at coaxial TM01-mode which contains two-segment slow wave structures (SWSs). The first segment SWS mainly modulates the intense electron and the second one mainly extracts the microwave energy. By introducing pre-modulate using an asymmetry reflector, the modulation depth is improved. By optimizing the length of the drift between SWSs, the field distribution is optimized and the axial electric field intension of the extract SWS is farther improved. The efficiency of the RBWO is improved. Finally ,when the magnetic field is 0.6 T，the diode voltage is 490 kV，the diode current is 7.5 kA, a 1.27 GW microwave is obtained with an efficiency of 35% and a frequency of 14.7 GHz.
2016,
28: 093003.
doi: 10.11884/HPLPB201628.151187
Abstract:
A metallic metamaterial high power microwave (HPM) mode converter which converts cylindrical TEM mode to TE11 mode is presented. Metallic sector grid elements are periodically arranged both in the azimuthal and longitudinal directions to gain high refractive index to act as phase shifter in the convertor. The mode converter is simulated by 3D commercial electromagnetic simulation software CST Microwave Studio. Simulation results show that the converter has high conversion efficiency with a relative bandwidth of about 4%. The radiation antenna with a metamaterial mode converter is simulated. The mode convertor is simulated combined with an L-band MILO tube using a particle-in-cell software, and a TE11 mode HPM is obtained in the outlet of the tube.
A metallic metamaterial high power microwave (HPM) mode converter which converts cylindrical TEM mode to TE11 mode is presented. Metallic sector grid elements are periodically arranged both in the azimuthal and longitudinal directions to gain high refractive index to act as phase shifter in the convertor. The mode converter is simulated by 3D commercial electromagnetic simulation software CST Microwave Studio. Simulation results show that the converter has high conversion efficiency with a relative bandwidth of about 4%. The radiation antenna with a metamaterial mode converter is simulated. The mode convertor is simulated combined with an L-band MILO tube using a particle-in-cell software, and a TE11 mode HPM is obtained in the outlet of the tube.
2016,
28: 093004.
doi: 10.11884/HPLPB201628.160002
Abstract:
By elaborately designing the slow wave structure (SWS), an oversized terahertz backward wave oscillator(BWO) with high output power and high beam-wave conversion efficiency is presented and the 2.5-D particle-in-cell simulations are carried out using a PIC code. Under the condition of 280 kV voltage and 320 A current, the output power of 130 MW at frequency of 121.8 GHz is achieved when the strength of the guiding magnetic field is 3 T, and the beam-wave power efficiency of 14.5 % is obtained.
By elaborately designing the slow wave structure (SWS), an oversized terahertz backward wave oscillator(BWO) with high output power and high beam-wave conversion efficiency is presented and the 2.5-D particle-in-cell simulations are carried out using a PIC code. Under the condition of 280 kV voltage and 320 A current, the output power of 130 MW at frequency of 121.8 GHz is achieved when the strength of the guiding magnetic field is 3 T, and the beam-wave power efficiency of 14.5 % is obtained.
2016,
28: 093005.
doi: 10.11884/HPLPB201628.160025
Abstract:
A new slow-wave structure with two rectangular helixes is described in this paper. The high-frequency characteristics including dispersion characteristic and coupling impedance are calculated using 3D electromagnetic simulation software. The result shows that, compared with single rectangular helix SWS, double rectangular helix SWS is capable of higher coupling impedance in the same position with little dispersion characteristic change. Meanwhile, sheet electron beam can be set in the region containing these positions to further improve the output power. Key words: double rectangular helix slow-wave structure; micro-electro-mechanical system technology; sheet
A new slow-wave structure with two rectangular helixes is described in this paper. The high-frequency characteristics including dispersion characteristic and coupling impedance are calculated using 3D electromagnetic simulation software. The result shows that, compared with single rectangular helix SWS, double rectangular helix SWS is capable of higher coupling impedance in the same position with little dispersion characteristic change. Meanwhile, sheet electron beam can be set in the region containing these positions to further improve the output power. Key words: double rectangular helix slow-wave structure; micro-electro-mechanical system technology; sheet
2016,
28: 093006.
doi: 10.11884/HPLPB201628.150842
Abstract:
A V-band mode-selective coupler is designed for measuring the output power of overmoded high power millimeter-wave generators. The small-hole coupling theory and infinitesimal dividing method are adopted to analyze the coupling characteristics of the diamond aperture which is applied to decrease the length of the coupler and increase the operating bandwidth. Meanwhile, mode selection can be achieved by setting two identical apertures. At the frequency of 60 GHz, the simulation results show that the coupling coefficient and directivity of TM01 mode are 50 dB and 75 dB respectively, and the suppression of TM02 mode is more than 10 dB. Besides, a coupler for measuring the output power of generators operating in high order mode is also presented in this paper, which is used to couple TM01 mode and suppress TM02 mode. The numerical calculation and simulation results show a good coherency.
A V-band mode-selective coupler is designed for measuring the output power of overmoded high power millimeter-wave generators. The small-hole coupling theory and infinitesimal dividing method are adopted to analyze the coupling characteristics of the diamond aperture which is applied to decrease the length of the coupler and increase the operating bandwidth. Meanwhile, mode selection can be achieved by setting two identical apertures. At the frequency of 60 GHz, the simulation results show that the coupling coefficient and directivity of TM01 mode are 50 dB and 75 dB respectively, and the suppression of TM02 mode is more than 10 dB. Besides, a coupler for measuring the output power of generators operating in high order mode is also presented in this paper, which is used to couple TM01 mode and suppress TM02 mode. The numerical calculation and simulation results show a good coherency.
2016,
28: 093007.
doi: 10.11884/HPLPB201628.151205
Abstract:
A new type of test system has been designed for the research on microwave radiation characteristics of large-aperture antenna excited by short pulses. The system is made of a pulse-width tuning microwave source (the shortest pulse-width is 0.5 ns) and a receiving system whose dynamic range is up to 52 dB. Based on such test system, the changing curve of antenna pattern and the pulse-width of antennas radiation field waveform were obtained under the condition of different microwave pulse-width. The results show that in far field, there is no significant influence on the radiation waveform in the principal axis, by changing microwave pulse-width; it was found that radiation waveforms deviated from the principal axis in different angles could present pulse widening and amplitude decreasing, the greater the angle deviated, the more obvious the phenomenon could be.
A new type of test system has been designed for the research on microwave radiation characteristics of large-aperture antenna excited by short pulses. The system is made of a pulse-width tuning microwave source (the shortest pulse-width is 0.5 ns) and a receiving system whose dynamic range is up to 52 dB. Based on such test system, the changing curve of antenna pattern and the pulse-width of antennas radiation field waveform were obtained under the condition of different microwave pulse-width. The results show that in far field, there is no significant influence on the radiation waveform in the principal axis, by changing microwave pulse-width; it was found that radiation waveforms deviated from the principal axis in different angles could present pulse widening and amplitude decreasing, the greater the angle deviated, the more obvious the phenomenon could be.
2016,
28: 093008.
doi: 10.11884/HPLPB201628.160027
Abstract:
This paper proposes a compact balanced Wilkinson power divider based on artificial transmission lines using double-sided parallel-strip lines. The design consists of artificial transmission lines to replace conventional transmission lines to save circuit size. In the meantime, the structure of double-sided parallel-strip lines is introduced to achieve balanced function. The proposed power divider is about 25% the place of a conventional divider. The measurements show that such a balanced Wilkinson power divider at operational frequency ranging from 0.83 GHz to 1.05 GHz has 1.28 phase balance and 0.17 dB amplitude balance. At all ports return losses are more than 16.79 dB and good isolation between the two output ports is greater than 16.21 dB. The measurements agree well with simulation results, demonstrating that this power divider has good performance.
This paper proposes a compact balanced Wilkinson power divider based on artificial transmission lines using double-sided parallel-strip lines. The design consists of artificial transmission lines to replace conventional transmission lines to save circuit size. In the meantime, the structure of double-sided parallel-strip lines is introduced to achieve balanced function. The proposed power divider is about 25% the place of a conventional divider. The measurements show that such a balanced Wilkinson power divider at operational frequency ranging from 0.83 GHz to 1.05 GHz has 1.28 phase balance and 0.17 dB amplitude balance. At all ports return losses are more than 16.79 dB and good isolation between the two output ports is greater than 16.21 dB. The measurements agree well with simulation results, demonstrating that this power divider has good performance.
2016,
28: 093009.
doi: 10.11884/HPLPB201628.151261
Abstract:
A variable pulse generation and radiation system working at high-power very high frequency(VHF) band was investigated. Based on optimization, radiation output with pulse width between several nanoseconds and tens of nanoseconds was obtained under laboratory conditions. To realize the adjustability of the pulse width, the open-circuit capacitive antenna was loaded with a variable inductor. By introducing the large inductor in parallel, little pulse tail and high efficiency are also achieved. Besides, high-power and short-pulsed source was applied in discharge circuit for energy storage and discharge, which reduced the synchronization jitter between the radiation pulses.
A variable pulse generation and radiation system working at high-power very high frequency(VHF) band was investigated. Based on optimization, radiation output with pulse width between several nanoseconds and tens of nanoseconds was obtained under laboratory conditions. To realize the adjustability of the pulse width, the open-circuit capacitive antenna was loaded with a variable inductor. By introducing the large inductor in parallel, little pulse tail and high efficiency are also achieved. Besides, high-power and short-pulsed source was applied in discharge circuit for energy storage and discharge, which reduced the synchronization jitter between the radiation pulses.
2016,
28: 094001.
doi: 10.11884/HPLPB201628.150642
Abstract:
In muon tomography based on multiple Coulomb scattering, the scattering properties of cosmic-ray muons are distinctive even for the same target due to their different momentum distribution, which, to some extent, cast down the imaging resolution. For the purpose of suppressing or eliminating this effect, a multi-group model (MGM) of the momentum spectra of cosmic-ray muons was set up and validated by measuring the thicknesses of Pb slabs and by identifying the materials of unknown slabs. The results show that MGM can give a precise calculation of Pb slab thickness in the range of 1-16 cm, within an error of 5%. Moreover, MGM can also identify the materials of slabs by calculating the corresponding radiation lengths, which is especially effective for high-Z materials with an calculation error below 4%.
In muon tomography based on multiple Coulomb scattering, the scattering properties of cosmic-ray muons are distinctive even for the same target due to their different momentum distribution, which, to some extent, cast down the imaging resolution. For the purpose of suppressing or eliminating this effect, a multi-group model (MGM) of the momentum spectra of cosmic-ray muons was set up and validated by measuring the thicknesses of Pb slabs and by identifying the materials of unknown slabs. The results show that MGM can give a precise calculation of Pb slab thickness in the range of 1-16 cm, within an error of 5%. Moreover, MGM can also identify the materials of slabs by calculating the corresponding radiation lengths, which is especially effective for high-Z materials with an calculation error below 4%.
2016,
28: 094002.
doi: 10.11884/HPLPB201628.150498
Abstract:
Blurring and noise are serious problems in hydro-test with high-energy X-ray radiography and make it difficult to reconstruct density distributions from radiographic images. A constrained optimization reconstruction method to decrease the blurring and noise impact is proposed. In this method, the parallel-beam X-ray projections are modeled by inserting a blurring matrix in. The optimization reconstruction problem is minimized by steepest descent method, and a preconditioned matrix has been adopted to improve the reconstruction efficiency. We focus on the topographic reconstruction of piecewise smooth objects involving sharp edges, so the algorithm is based on generalized-variation-minimization constraints, piecewise constraints and the non-negative density values constraints. We applied the reconstruction algorithm to reconstruct computer-synthesized images of the French Test Object (FTO) and a hydro-test object image. The results show that our method is beneficial to improve the quality of reconstructed image with better performance of noise smoothing and better edge preserving as well.
Blurring and noise are serious problems in hydro-test with high-energy X-ray radiography and make it difficult to reconstruct density distributions from radiographic images. A constrained optimization reconstruction method to decrease the blurring and noise impact is proposed. In this method, the parallel-beam X-ray projections are modeled by inserting a blurring matrix in. The optimization reconstruction problem is minimized by steepest descent method, and a preconditioned matrix has been adopted to improve the reconstruction efficiency. We focus on the topographic reconstruction of piecewise smooth objects involving sharp edges, so the algorithm is based on generalized-variation-minimization constraints, piecewise constraints and the non-negative density values constraints. We applied the reconstruction algorithm to reconstruct computer-synthesized images of the French Test Object (FTO) and a hydro-test object image. The results show that our method is beneficial to improve the quality of reconstructed image with better performance of noise smoothing and better edge preserving as well.
2016,
28: 095001.
doi: 10.11884/HPLPB201628.160072
Abstract:
Experiments about single wire exploding were carried out on the fast linear transformer driver(FLTD), which provides a current of about 100 ns rising time and about 100 kA maximum amplitude. Laser probe and visible framing camera have been set up for plasma diagnostics. In addition, visible detector PIN and XRD were used to measure the characteristic of radiation for single wire exploding. A series of images for single tungsten wire（15 m W） and coated tungsten wire (15 m W+2 m Polyimide)exploding experiments have been obtained, which show the evolution of wire ablating and the instability development of ablated plasma. The results show that wire coating will add more energy to the wire at the initial phase, hence improve the characteristics of wire exploding .
Experiments about single wire exploding were carried out on the fast linear transformer driver(FLTD), which provides a current of about 100 ns rising time and about 100 kA maximum amplitude. Laser probe and visible framing camera have been set up for plasma diagnostics. In addition, visible detector PIN and XRD were used to measure the characteristic of radiation for single wire exploding. A series of images for single tungsten wire（15 m W） and coated tungsten wire (15 m W+2 m Polyimide)exploding experiments have been obtained, which show the evolution of wire ablating and the instability development of ablated plasma. The results show that wire coating will add more energy to the wire at the initial phase, hence improve the characteristics of wire exploding .
2016,
28: 095002.
doi: 10.11884/HPLPB201628.151077
Abstract:
In order to track the plasma rapid change in the vertical displacement, an H-bridge quick response power supply based on IGBT has been developed, rating of the power supply parameters for +500 V/+3 kA. Due to the structure and control strategy, the old quick response power supply has some deficiencies such as IGBT turn-off overvoltage, low working frequency, wide pulse voltage of uncontrolled flyback process. Aiming to solve these deficiencies, firstly, a new H-bridge quick response power supply redesigns the structure to reduce the power of the parasitic inductance, which brings down the IGBT turn-off overvoltage. Secondly, through changing the control mode of power supply, the working frequency of the power supply is two times the IGBT switch frequency, and the frequency of the power supply output voltage is increased, equivalent to improve the fast response ability of the power supply. At the same time, a kind of controllable flyback mode is designed, which changes the flyback circuit with IGBT to make the flyback process under control. Tested by the experimental study, the response time of the power supply is 125 s. The power supply has a quick response when the displacement of plasma changes, ensuring the normal discharge of tokamak, and with the new freewheeling control mode, the wide voltage pulse will not happen again, thus the output voltage can effectively track the given voltage change.
In order to track the plasma rapid change in the vertical displacement, an H-bridge quick response power supply based on IGBT has been developed, rating of the power supply parameters for +500 V/+3 kA. Due to the structure and control strategy, the old quick response power supply has some deficiencies such as IGBT turn-off overvoltage, low working frequency, wide pulse voltage of uncontrolled flyback process. Aiming to solve these deficiencies, firstly, a new H-bridge quick response power supply redesigns the structure to reduce the power of the parasitic inductance, which brings down the IGBT turn-off overvoltage. Secondly, through changing the control mode of power supply, the working frequency of the power supply is two times the IGBT switch frequency, and the frequency of the power supply output voltage is increased, equivalent to improve the fast response ability of the power supply. At the same time, a kind of controllable flyback mode is designed, which changes the flyback circuit with IGBT to make the flyback process under control. Tested by the experimental study, the response time of the power supply is 125 s. The power supply has a quick response when the displacement of plasma changes, ensuring the normal discharge of tokamak, and with the new freewheeling control mode, the wide voltage pulse will not happen again, thus the output voltage can effectively track the given voltage change.
2016,
28: 095003.
doi: 10.11884/HPLPB201628.150883
Abstract:
A new kind of high-power pulse laser diode has been researched, and it is mainly used for triggering high-gain gallium arsenide photoconductive semiconductor switch (GaAs PCSS) in experiments. The driver of the laser diode is based on RF MOSFET and it provides an ultra-fast pulse drive current for the laser diode, and the rise-time, FWHM and peak current of the drive current are 4 ns, 20 ns and 130 A, respectively. The characteristics of the laser diode have been researched, including laser pulse waveform, energy, power, optical field distribution, and so on. In the Blumlein transmission line structure, the influences of bias voltage, laser spot size, laser energy and laser power on the on-state resistance and jitter of the GaAs PCSS are analyzed. Experiment shows that, lager and more uniform laser spot, higher laser energy and power all help to improve the performance of PCSS.
A new kind of high-power pulse laser diode has been researched, and it is mainly used for triggering high-gain gallium arsenide photoconductive semiconductor switch (GaAs PCSS) in experiments. The driver of the laser diode is based on RF MOSFET and it provides an ultra-fast pulse drive current for the laser diode, and the rise-time, FWHM and peak current of the drive current are 4 ns, 20 ns and 130 A, respectively. The characteristics of the laser diode have been researched, including laser pulse waveform, energy, power, optical field distribution, and so on. In the Blumlein transmission line structure, the influences of bias voltage, laser spot size, laser energy and laser power on the on-state resistance and jitter of the GaAs PCSS are analyzed. Experiment shows that, lager and more uniform laser spot, higher laser energy and power all help to improve the performance of PCSS.
2016,
28: 095004.
doi: 10.11884/HPLPB201628.151091
Abstract:
The electric field emission and thermal emission around the junction of triple point and the secondary electron emission are believed to play a major role in the initialization and the development stages of the surface flashover. We have extended OPAL, a parallel framework for charged particle optics in accelerator structures and beam lines, with the necessary particle-boundary collision test model, field emission model as well as secondary emission models to simulate the initialization and development of surface flashover in an X-pinch load case with complex geometry. The discharge experiment shows that the silicon oil coated case has a stronger return current than the not-coated case. Accordingly, possible way of flashover suppression is discussed.
The electric field emission and thermal emission around the junction of triple point and the secondary electron emission are believed to play a major role in the initialization and the development stages of the surface flashover. We have extended OPAL, a parallel framework for charged particle optics in accelerator structures and beam lines, with the necessary particle-boundary collision test model, field emission model as well as secondary emission models to simulate the initialization and development of surface flashover in an X-pinch load case with complex geometry. The discharge experiment shows that the silicon oil coated case has a stronger return current than the not-coated case. Accordingly, possible way of flashover suppression is discussed.
2016,
28: 095101.
doi: 10.11884/HPLPB201628.150950
Abstract:
Two types of flashover phenomenons were discovered during the high voltage test of Dragon-Ⅱ linear induction accelerator insulator ring, which was made by cross-linked polystyrene. One type of the flashover was initialized from cathode and the other one was initialized from anode. The mechanism of the phenomenon was analyzed by comparing breakdown voltage waveform and discharge trace，and calculating electric field combination with flashover experiment on little insulator samples. It is assumed that the cooperating problem of the insulator and cathode caused the difference between accelerator and injector insulator ring flashover.
Two types of flashover phenomenons were discovered during the high voltage test of Dragon-Ⅱ linear induction accelerator insulator ring, which was made by cross-linked polystyrene. One type of the flashover was initialized from cathode and the other one was initialized from anode. The mechanism of the phenomenon was analyzed by comparing breakdown voltage waveform and discharge trace，and calculating electric field combination with flashover experiment on little insulator samples. It is assumed that the cooperating problem of the insulator and cathode caused the difference between accelerator and injector insulator ring flashover.
2016,
28: 095102.
doi: 10.11884/HPLPB201628.151292
Abstract:
The electron cloud instability is believed to be an obstacle for the high intensity proton accelerators. The secondary electron multipacting is responsible for the development of the electron cloud. It can be explained by the energy gain and motion of electrons. For acquiring the density and the distribution of the electron cloud, a program has been developed to simulate the evolution of the electron cloud. This paper analyzes the motion of electrons under beam force, and proposes the reason for the secondary electron multipacting. The analyses are in agreement with the simulation result.
The electron cloud instability is believed to be an obstacle for the high intensity proton accelerators. The secondary electron multipacting is responsible for the development of the electron cloud. It can be explained by the energy gain and motion of electrons. For acquiring the density and the distribution of the electron cloud, a program has been developed to simulate the evolution of the electron cloud. This paper analyzes the motion of electrons under beam force, and proposes the reason for the secondary electron multipacting. The analyses are in agreement with the simulation result.
2016,
28: 095103.
doi: 10.11884/HPLPB201628.151286
Abstract:
Beam signal stretching is significant for bunch-by-bunch position measurements on a storage ring. This paper presents a signal stretching method using the low-pass filter and envelope detection through analysis of beam signal characteristics on the storage ring at Shanghai Synchrotron Radiation Facility. With the consideration of the need to delay the signal in picosecond order, a circuit based on microstrip transmission was adopted to implement this method. Microstrip transmission line equivalent to lumped LC elements was derived for the low-pass filter design and the impedance matching scheme was given to implement the broadband power splitter and combiner. The simulation and experimental results show that the design can stretch beam signal effectively.
Beam signal stretching is significant for bunch-by-bunch position measurements on a storage ring. This paper presents a signal stretching method using the low-pass filter and envelope detection through analysis of beam signal characteristics on the storage ring at Shanghai Synchrotron Radiation Facility. With the consideration of the need to delay the signal in picosecond order, a circuit based on microstrip transmission was adopted to implement this method. Microstrip transmission line equivalent to lumped LC elements was derived for the low-pass filter design and the impedance matching scheme was given to implement the broadband power splitter and combiner. The simulation and experimental results show that the design can stretch beam signal effectively.
2016,
28: 095104.
doi: 10.11884/HPLPB201628.160112
Abstract:
This paper proposes an improved bunch length measurement method based on high order mode cavity. Different from traditional ways, the new method uses the cavity that resonates with higher order mode TM0n0 instead of fundamental mode TM010. The operating mode of this new method is alterable, which means that harmonic cavities with larger radius are available and working frequency restriction caused by beam pipe radius is removed. A two-cavity monitor was designed for the linac of future National Synchrotron Radiation Laboratory(NSRL) positron source. Operating frequency selection is discussed and calculation formula of bunch length is derived. The bunch length measurement cavity resonates with mode TM020 at 14.28 GHz, which provides much larger radius than TM010 mode. A simulation measurement was conducted in CST Particle Studio and the result shows a fairly high accuracy (better than 7%).
This paper proposes an improved bunch length measurement method based on high order mode cavity. Different from traditional ways, the new method uses the cavity that resonates with higher order mode TM0n0 instead of fundamental mode TM010. The operating mode of this new method is alterable, which means that harmonic cavities with larger radius are available and working frequency restriction caused by beam pipe radius is removed. A two-cavity monitor was designed for the linac of future National Synchrotron Radiation Laboratory(NSRL) positron source. Operating frequency selection is discussed and calculation formula of bunch length is derived. The bunch length measurement cavity resonates with mode TM020 at 14.28 GHz, which provides much larger radius than TM010 mode. A simulation measurement was conducted in CST Particle Studio and the result shows a fairly high accuracy (better than 7%).
2016,
28: 096001.
doi: 10.11884/HPLPB201628.151260
Abstract:
It is crucial to calculate the electric field distribution using Finite Element Analysis (FEA) program so as to do high efficiency simulation works for TPC gaseous detectors. A FEA program combined with the nodes positioning method has been employed to do the electric field calculation for TPC detectors, which basically have the geometry of multi-wire and multi-strip. After the tests of the nodes positioning method, we finished the electric field calculation and drift simulations for SRIT-TPC, which had been constructed by MSU and other institutions. The calculation and simulation results agree well with those calculated by GARFIELD. Furthermore, 3D electric field calculation and the simulation for TPC detectors can also be done in a similar way.
It is crucial to calculate the electric field distribution using Finite Element Analysis (FEA) program so as to do high efficiency simulation works for TPC gaseous detectors. A FEA program combined with the nodes positioning method has been employed to do the electric field calculation for TPC detectors, which basically have the geometry of multi-wire and multi-strip. After the tests of the nodes positioning method, we finished the electric field calculation and drift simulations for SRIT-TPC, which had been constructed by MSU and other institutions. The calculation and simulation results agree well with those calculated by GARFIELD. Furthermore, 3D electric field calculation and the simulation for TPC detectors can also be done in a similar way.
2016,
28: 096002.
doi: 10.11884/HPLPB201628.151241
Abstract:
Scintillation detectors based on LaBr3 are the new type of detectors for measuring -rays in a mixed /n pulsed radiation field with high intensity. It owns superior properties such as fast response time, small nonproportionality, and high scintillation yield. As the fluence rate linear response limit of LaBr3 scintillator is not available in literature, an experiment which studies the high fluence rate response behavior of LaBr3 scintillators is introduced in this paper. Lissajous figure method is used in the experiment. The result shows that the fluence rate linear response limit is about 2.01018 MeV/(cm2s).
Scintillation detectors based on LaBr3 are the new type of detectors for measuring -rays in a mixed /n pulsed radiation field with high intensity. It owns superior properties such as fast response time, small nonproportionality, and high scintillation yield. As the fluence rate linear response limit of LaBr3 scintillator is not available in literature, an experiment which studies the high fluence rate response behavior of LaBr3 scintillators is introduced in this paper. Lissajous figure method is used in the experiment. The result shows that the fluence rate linear response limit is about 2.01018 MeV/(cm2s).
2016,
28: 096003.
doi: 10.11884/HPLPB201628.151204
Abstract:
When using SDEF card in MCNP code to describe source information of fixed sources, it is necessary to input the distribution of the source. MCNP code offers SP card to input the distribution probability. The V option of SP card is for cell distributions only. Recent research discovers that there is a bug when using this option, which may lead to wrong calculation results. Making up a typical model, a comparison between the results using V option and not using V option was made. The comparison shows that the bug really exists. The effectiveness of the solutions proposed was also validated.
When using SDEF card in MCNP code to describe source information of fixed sources, it is necessary to input the distribution of the source. MCNP code offers SP card to input the distribution probability. The V option of SP card is for cell distributions only. Recent research discovers that there is a bug when using this option, which may lead to wrong calculation results. Making up a typical model, a comparison between the results using V option and not using V option was made. The comparison shows that the bug really exists. The effectiveness of the solutions proposed was also validated.
2016,
28: 096004.
doi: 10.11884/HPLPB201628.160018
Abstract:
When applied the minitype reference radiation (MRR) to calibrate gamma ray dosimeters, the shielding structure of the MRR should meet the shielding technique demand, in which the limit dose rate of the outside surface of the MRR must be lower than 5 Sv/h. In order to optimize the shielding design of the MRR, Monte Carlo particle transport code MCNP is employed to simulate and analyze the dose distribution of the outside surface of the MRR. The results show that the dose distribution of each surface of the MRR can be described in detail with MCNP and it is conducive to complete shielding design. The lead-steel composite material is applied to increase the strength and reduce the weight of the MRR. The optimized weight of the MRR is about 271.9 kg.
When applied the minitype reference radiation (MRR) to calibrate gamma ray dosimeters, the shielding structure of the MRR should meet the shielding technique demand, in which the limit dose rate of the outside surface of the MRR must be lower than 5 Sv/h. In order to optimize the shielding design of the MRR, Monte Carlo particle transport code MCNP is employed to simulate and analyze the dose distribution of the outside surface of the MRR. The results show that the dose distribution of each surface of the MRR can be described in detail with MCNP and it is conducive to complete shielding design. The lead-steel composite material is applied to increase the strength and reduce the weight of the MRR. The optimized weight of the MRR is about 271.9 kg.
2016,
28: 099001.
doi: 10.11884/HPLPB201628.160048
Abstract:
Based on the fact that surface textured cutting tool can effectively improve the cutting performance, taking broach material into consideration a processing method of micro-textured broach was put forward. Laser processing technology was used to generate a micro-texture on the flank of broach, and the influence of various processing parameters was researched. The influence of Q frequency, power, scanning speed and processing times on the texture formation and wetting was investigated. The experimental results show that with the increase of the Q frequency, the texture boundaries are more clear, recast area will be larger with the increase of power, the depth of micro texture is proportional to the processing times, and the scanning speed has to be lower than a certain speed to remove material adequately. In the initial stage of the preparation, the energy remains on the surface of the texture will make the hydrophobic texture appear hydrophilic.
Based on the fact that surface textured cutting tool can effectively improve the cutting performance, taking broach material into consideration a processing method of micro-textured broach was put forward. Laser processing technology was used to generate a micro-texture on the flank of broach, and the influence of various processing parameters was researched. The influence of Q frequency, power, scanning speed and processing times on the texture formation and wetting was investigated. The experimental results show that with the increase of the Q frequency, the texture boundaries are more clear, recast area will be larger with the increase of power, the depth of micro texture is proportional to the processing times, and the scanning speed has to be lower than a certain speed to remove material adequately. In the initial stage of the preparation, the energy remains on the surface of the texture will make the hydrophobic texture appear hydrophilic.
