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RSS2016 Vol. 28, No. 08
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2016,
28: 080101.
doi: 10.11884/HPLPB201628.160111
Abstract:
Initial laser indirect-driven integrated experiment was carried out on the new-established Shenguang Ⅲ laser facility. The shaped laser pulses from multi-rings were injected into a hohlraum and converted to X-ray emissions. According to the control of the drive asymmetry by the optimization of the laser parameter, the quasi one-dimensional imploding performance of DT capsule was demonstrated with the dominant inertial compression and 10-15 convergence ratio. Meanwhile, the physical guide line for high yield over clean (YOC) and high neutron yield was accomplished. For vacuum hohlraum, the highest neutron yield is 1.91012 while YOC is about 60%; For hohlraum filled with gas, the highest neutron yield is 2.41012 while YOC is about 70%. These experimental results provide a foundation for the imploding integrated experiments with multi-step drive and higher convergence ratio in the near future.
Initial laser indirect-driven integrated experiment was carried out on the new-established Shenguang Ⅲ laser facility. The shaped laser pulses from multi-rings were injected into a hohlraum and converted to X-ray emissions. According to the control of the drive asymmetry by the optimization of the laser parameter, the quasi one-dimensional imploding performance of DT capsule was demonstrated with the dominant inertial compression and 10-15 convergence ratio. Meanwhile, the physical guide line for high yield over clean (YOC) and high neutron yield was accomplished. For vacuum hohlraum, the highest neutron yield is 1.91012 while YOC is about 60%; For hohlraum filled with gas, the highest neutron yield is 2.41012 while YOC is about 70%. These experimental results provide a foundation for the imploding integrated experiments with multi-step drive and higher convergence ratio in the near future.
2016,
28: 081001.
doi: 10.11884/HPLPB201628.151290
Abstract:
The annular Gaussian beams having different initial energies propagation in air are numerically studied by two models, the linear model and the nonlinear model. Numerical results show that (i) at the beginning of the propagation the nonlinear Kerr effect slightly suppresses the focusing caused by the spatial chirp, and (ii) the focusing caused by the spatial chirp generates a high intensity core making the beam shape near the axis similar to the Gaussian shape and this can enhance the Kerr self-focusing, and (iii) the initial energy of the annular beams can influence the nonlinear foci, filamentation length, and the fluence of the propagation. The nonlinear foci decrease with the initial energy, but the foci are not inversely proportional to the square root of the initial peak power, which is not the same as the Gaussian beam. The filamentation length increases with the initial input energy.
The annular Gaussian beams having different initial energies propagation in air are numerically studied by two models, the linear model and the nonlinear model. Numerical results show that (i) at the beginning of the propagation the nonlinear Kerr effect slightly suppresses the focusing caused by the spatial chirp, and (ii) the focusing caused by the spatial chirp generates a high intensity core making the beam shape near the axis similar to the Gaussian shape and this can enhance the Kerr self-focusing, and (iii) the initial energy of the annular beams can influence the nonlinear foci, filamentation length, and the fluence of the propagation. The nonlinear foci decrease with the initial energy, but the foci are not inversely proportional to the square root of the initial peak power, which is not the same as the Gaussian beam. The filamentation length increases with the initial input energy.
2016,
28: 081002.
doi: 10.11884/HPLPB201628.151147
Abstract:
Packaging technology for semiconductor laser diodes influences significantly on their output characteristics, such as lifetime. Selections of solders and welding process are very important. Using a semi-automatic welding system, mini-bar was directly welded on Cu heat sink with indium solder. By improving the welding system, optimizing software and slowing imaging procedures, the welding with high accuracy and high reliability was achieved. Measurements of the laser performances show that power for the welding is stable, its welded precision is 20 m, smile effect can be controlled less than 0.5 m.
Packaging technology for semiconductor laser diodes influences significantly on their output characteristics, such as lifetime. Selections of solders and welding process are very important. Using a semi-automatic welding system, mini-bar was directly welded on Cu heat sink with indium solder. By improving the welding system, optimizing software and slowing imaging procedures, the welding with high accuracy and high reliability was achieved. Measurements of the laser performances show that power for the welding is stable, its welded precision is 20 m, smile effect can be controlled less than 0.5 m.
2016,
28: 081003.
doi: 10.11884/HPLPB201628.151111
Abstract:
The design and performance of a non-chain transverse excited HF laser with ultraviolet spark is described. It has high energy implantation and great energy output, and takes a high power excitation system with thyratron combined magnetic pulse compression switch. The laser pulse energy was studied in different gas pressure and fractions of the media SF6 and H2. The maximal output energy 1.3 J was achieved under the condition of 88 kPa gas pressure with 10% H2 and 90% SF6. Laser electro-optical conversion efficiency 5.3% were obtained.
The design and performance of a non-chain transverse excited HF laser with ultraviolet spark is described. It has high energy implantation and great energy output, and takes a high power excitation system with thyratron combined magnetic pulse compression switch. The laser pulse energy was studied in different gas pressure and fractions of the media SF6 and H2. The maximal output energy 1.3 J was achieved under the condition of 88 kPa gas pressure with 10% H2 and 90% SF6. Laser electro-optical conversion efficiency 5.3% were obtained.
2016,
28: 081004.
doi: 10.11884/HPLPB201628.151266
Abstract:
In order to explore the elements of trace impurities in fused silica and the change of them during HF acid etching process, the static etching experiments of 24 h, 48 h, 72 h, 96 h were performed by the mass fraction of 1% HF acid solution. The results of TOF-SIMS and XPS show that, the fused silica surface mainly contains eight trace impurity elements, including B, F, K, Ca, Na, Al, Zn, Ca, and Cr; most of these elements are in the Beiby layer, and K and Ca impurity elements are detected in the subsurface defect layer; fluosilicate salts of K, Na are generated. By analysis, during the process of HF acid etching, a part of the impurity elements will be removed, and a portion of the impurity elements and the fluosilicate salts will diffuse gradually from the surface of the fused silica to the depth with the etching liquid while some will be absorbed by fused silica surface and deposit, and the contents of them reduce gradually with the increase of the depth.
In order to explore the elements of trace impurities in fused silica and the change of them during HF acid etching process, the static etching experiments of 24 h, 48 h, 72 h, 96 h were performed by the mass fraction of 1% HF acid solution. The results of TOF-SIMS and XPS show that, the fused silica surface mainly contains eight trace impurity elements, including B, F, K, Ca, Na, Al, Zn, Ca, and Cr; most of these elements are in the Beiby layer, and K and Ca impurity elements are detected in the subsurface defect layer; fluosilicate salts of K, Na are generated. By analysis, during the process of HF acid etching, a part of the impurity elements will be removed, and a portion of the impurity elements and the fluosilicate salts will diffuse gradually from the surface of the fused silica to the depth with the etching liquid while some will be absorbed by fused silica surface and deposit, and the contents of them reduce gradually with the increase of the depth.
2016,
28: 081005.
doi: 10.11884/HPLPB201628.151303
Abstract:
The discrete step-type phase modulation and pixel gaps of liquid crystal spatial light modulator (LC-SLM) are the main distortion reasons for the 4f pulse shaping system. Based on the analysis of the above factors, the 4f pulse shaping system mathematical model is established and simulated with different modulation rates, different pixel sizes, different gap sizes and different dispersion relations. The simulation results show that step-type phase modulation can lead to replica pulses, the modulation rate or pixel size is larger, the intensity of the replica pulses is stronger, and the distortion of shaped pulse is more serious; the pixel gaps can also lead to replica pulses, the gap size is larger, the intensity of the replica pulses is stronger, and the distortion of shaped pulse is more serious. The interval of the replica pulses is a constant determined by the frequency separation of adjacent pixels. The nonlinear spectral dispersion can reduce the intensity while causing chirp effect of replica pulses.
The discrete step-type phase modulation and pixel gaps of liquid crystal spatial light modulator (LC-SLM) are the main distortion reasons for the 4f pulse shaping system. Based on the analysis of the above factors, the 4f pulse shaping system mathematical model is established and simulated with different modulation rates, different pixel sizes, different gap sizes and different dispersion relations. The simulation results show that step-type phase modulation can lead to replica pulses, the modulation rate or pixel size is larger, the intensity of the replica pulses is stronger, and the distortion of shaped pulse is more serious; the pixel gaps can also lead to replica pulses, the gap size is larger, the intensity of the replica pulses is stronger, and the distortion of shaped pulse is more serious. The interval of the replica pulses is a constant determined by the frequency separation of adjacent pixels. The nonlinear spectral dispersion can reduce the intensity while causing chirp effect of replica pulses.
2016,
28: 082001.
doi: 10.11884/HPLPB201628.150989
Abstract:
The laser clipping effect and the consequent background X-ray are researched by planar hole-target on Shenguang-Ⅲ and Shenguang-Ⅲ prototype. A laser energy detector is used to measure the laser clipping ratio directly, an X-ray pinhole camera attains the spatial image of the background X-ray, and flat-response X-ray detectors measure the intensity of the background X-ray. The experiment result shows that the ratio of the background X-ray to the X-ray exiting from a hohlraum is about 1.2% by X-ray pinhole camera with 800 m LEH on Shenguang-Ⅲ prototype; the background X-ray contributes about 2.7% overestimation on the X-ray exiting from a hohlraum and the laser clipping ratio is about 2.6% by flat-response X-ray detectors with 1000 m LEH on Shenguang-Ⅲ. In addition, the laser clipping ratio and the consequent background X-ray are simulated according to the condition of Shenguang-Ⅲ. Comparison to the experiment result illustrates the validity of the simple model. So, the model could be used to estimate the laser clipping ratio and the consequent background X-ray, and the model could guide to choose the size of the LEH.
The laser clipping effect and the consequent background X-ray are researched by planar hole-target on Shenguang-Ⅲ and Shenguang-Ⅲ prototype. A laser energy detector is used to measure the laser clipping ratio directly, an X-ray pinhole camera attains the spatial image of the background X-ray, and flat-response X-ray detectors measure the intensity of the background X-ray. The experiment result shows that the ratio of the background X-ray to the X-ray exiting from a hohlraum is about 1.2% by X-ray pinhole camera with 800 m LEH on Shenguang-Ⅲ prototype; the background X-ray contributes about 2.7% overestimation on the X-ray exiting from a hohlraum and the laser clipping ratio is about 2.6% by flat-response X-ray detectors with 1000 m LEH on Shenguang-Ⅲ. In addition, the laser clipping ratio and the consequent background X-ray are simulated according to the condition of Shenguang-Ⅲ. Comparison to the experiment result illustrates the validity of the simple model. So, the model could be used to estimate the laser clipping ratio and the consequent background X-ray, and the model could guide to choose the size of the LEH.
2016,
28: 082002.
doi: 10.11884/HPLPB201628.150929
Abstract:
This paper presents the study on the enhancement mechanism of laser-induced breakdown spectroscopy on cobalt sample with double femtosecond pulse. The double-pulse experiments were carried out in the collinear beam geometry in air. The influence of the delay between the two collinear laser pulses was investigated by changing the pulses path length. In cases of no delay between the two pulses, the laser-induced breakdown spectroscopy is equivalent to that induced by a single pulse laser with energy equals to the sum of the double collinear pulse energy. The obtained results show that with an optimized delay, the double-pulse laser-induced breakdown spectroscopy has a very clear enhancement comparing with the single-pulse laser induced breakdown spectroscopy. In addition, the dependence of the electron temperature obtained by linear Boltzmann method on the pulse interval was investigated. The experiment shows that the dependence of spectral enhancement factor on the pulse interval is the same as that of the electron temperature, both of them go through two obvious changing processes. Analysing by the Boltzmann equation, we draw the conclusion that the spectral signal enhancement depends on the electron temperature.
This paper presents the study on the enhancement mechanism of laser-induced breakdown spectroscopy on cobalt sample with double femtosecond pulse. The double-pulse experiments were carried out in the collinear beam geometry in air. The influence of the delay between the two collinear laser pulses was investigated by changing the pulses path length. In cases of no delay between the two pulses, the laser-induced breakdown spectroscopy is equivalent to that induced by a single pulse laser with energy equals to the sum of the double collinear pulse energy. The obtained results show that with an optimized delay, the double-pulse laser-induced breakdown spectroscopy has a very clear enhancement comparing with the single-pulse laser induced breakdown spectroscopy. In addition, the dependence of the electron temperature obtained by linear Boltzmann method on the pulse interval was investigated. The experiment shows that the dependence of spectral enhancement factor on the pulse interval is the same as that of the electron temperature, both of them go through two obvious changing processes. Analysing by the Boltzmann equation, we draw the conclusion that the spectral signal enhancement depends on the electron temperature.
2016,
28: 083001.
doi: 10.11884/HPLPB201628.151271
Abstract:
Based on 2.1 m diameter parabolic reflector, the parameters of TEM horn-feed and coplanar-feed IRA were optimized, and the characteristics of these two antennas were compared in this paper. A physical model of IRA was built and the radiation center movement principle of V-shaped dipole was investigated. The analytic radiating solution of these two antennas was got by different approximation measurement. From theoretic calculation and numerical simulation, the field distribution of the reflector aperture was obtained. And with different width of excitation impulse, the radiation waveform of these two antennas exhibited regular transformation. With GW peak power capacity, the TEM horn and coplanar-feed IRA were fabricated. The experiment results agree well with the conclusion achieved above.
Based on 2.1 m diameter parabolic reflector, the parameters of TEM horn-feed and coplanar-feed IRA were optimized, and the characteristics of these two antennas were compared in this paper. A physical model of IRA was built and the radiation center movement principle of V-shaped dipole was investigated. The analytic radiating solution of these two antennas was got by different approximation measurement. From theoretic calculation and numerical simulation, the field distribution of the reflector aperture was obtained. And with different width of excitation impulse, the radiation waveform of these two antennas exhibited regular transformation. With GW peak power capacity, the TEM horn and coplanar-feed IRA were fabricated. The experiment results agree well with the conclusion achieved above.
2016,
28: 083002.
doi: 10.11884/HPLPB201628.150866
Abstract:
A free electron laser based on a coaxial static magnetic undulator utilizes annular electron beam interacting with TE mode to coherently generate electromagnetic radiation, which is an important millimeter wave radiation source. The influencing laws of the coaxial inner and outer radii, the operation mode, the beam voltage and the period of the undulator on the radiation frequency are analyzed. The main principles to choose the electron average radius and the designing method of beam wave interaction cavity are studied. Based on theoretical analysis, a coaxial static magnetic free electron laser at W band is designed and simulated by PIC simulation. The radiation wave at 107 GHz and 35 MW power are acquired. The beam wave power conversation efficiency is 4.9%. The length of the undulator is shorter than 200 mm, and the magnetic field of the undulator is 0.34 T.
A free electron laser based on a coaxial static magnetic undulator utilizes annular electron beam interacting with TE mode to coherently generate electromagnetic radiation, which is an important millimeter wave radiation source. The influencing laws of the coaxial inner and outer radii, the operation mode, the beam voltage and the period of the undulator on the radiation frequency are analyzed. The main principles to choose the electron average radius and the designing method of beam wave interaction cavity are studied. Based on theoretical analysis, a coaxial static magnetic free electron laser at W band is designed and simulated by PIC simulation. The radiation wave at 107 GHz and 35 MW power are acquired. The beam wave power conversation efficiency is 4.9%. The length of the undulator is shorter than 200 mm, and the magnetic field of the undulator is 0.34 T.
2016,
28: 083003.
doi: 10.11884/HPLPB201628.151244
Abstract:
A shaped scheme based on geometric optics for offset-fed dual-reflector focus antenna is presented. The main reflector is a shaped antenna based on conservation of energy along a ray tube, Snells law, uniform phase and equal path length. Only Snells law is imposed on the sub-reflector. Based on this design solution, theoretical analysis, numerical simulation and experimental test are carried out for a 110 cm dish baseline system with an angle of 20 between x axis and the beam. The experiment shows that at 95 GHz, the antenna has a well focusing through phase measurement with an angle of 20 between x axis and the beam.
A shaped scheme based on geometric optics for offset-fed dual-reflector focus antenna is presented. The main reflector is a shaped antenna based on conservation of energy along a ray tube, Snells law, uniform phase and equal path length. Only Snells law is imposed on the sub-reflector. Based on this design solution, theoretical analysis, numerical simulation and experimental test are carried out for a 110 cm dish baseline system with an angle of 20 between x axis and the beam. The experiment shows that at 95 GHz, the antenna has a well focusing through phase measurement with an angle of 20 between x axis and the beam.
2016,
28: 083004.
doi: 10.11884/HPLPB201628.150974
Abstract:
To control the antenna array with numerous elements，a multi level communication system based on controller area network (CAN) bus is designed. Firstly, CAN bus topology is analyzed and the basic CAN network structure is derived from the capacity of a single CAN channel. Then, CAN node hardware based on Nios II soft core is proposed. Lastly, application layer communication protocol and application software for array antenna work function are compiled based on CAN 2.0B. Experiment shows that this CAN network can work at baud rate higher than 500k bps, and its jitter time is less than 1 ms. Moreover, this CAN network controls array antennas steadily in high power environment at GW level.
To control the antenna array with numerous elements，a multi level communication system based on controller area network (CAN) bus is designed. Firstly, CAN bus topology is analyzed and the basic CAN network structure is derived from the capacity of a single CAN channel. Then, CAN node hardware based on Nios II soft core is proposed. Lastly, application layer communication protocol and application software for array antenna work function are compiled based on CAN 2.0B. Experiment shows that this CAN network can work at baud rate higher than 500k bps, and its jitter time is less than 1 ms. Moreover, this CAN network controls array antennas steadily in high power environment at GW level.
2016,
28: 083005.
doi: 10.11884/HPLPB201628.151037
Abstract:
The radiation characters of conical horn antennas excited by TE1n /TM1n modes are studied. Measuring the E- and H-plane power density patterns of a horn, one can get the horns radiation power by respectively integrating the two patterns on the spherical surface and taking their average. The effects of the measuring points range and number on the power calculations are discussed, and a data fitting method is presented to reduce the error caused by numbered measuring points. A principle to choose the range and number of the measuring points is given: the range may be 15 dB-beamwidth or 18 dB-beamwidth, and the number is about 15.
The radiation characters of conical horn antennas excited by TE1n /TM1n modes are studied. Measuring the E- and H-plane power density patterns of a horn, one can get the horns radiation power by respectively integrating the two patterns on the spherical surface and taking their average. The effects of the measuring points range and number on the power calculations are discussed, and a data fitting method is presented to reduce the error caused by numbered measuring points. A principle to choose the range and number of the measuring points is given: the range may be 15 dB-beamwidth or 18 dB-beamwidth, and the number is about 15.
2016,
28: 083006.
doi: 10.11884/HPLPB201628.151095
Abstract:
A parallel waveguide structure for high power phase shifter is proposed. The ferrite phase shifter at present can achieve high power capacity with dual-toroids structure. The influence on the propagation, phase shift efficiency and power capacity of the dual toroids ferrite phase shifter of its parameters is simulated and analyzed in this paper. The peak power capacity can reach hundred kW level after optimization. By using parallel waveguide in parallel structure based on the dual-toroids form, it can be increased to MW level. After matching design, VSWR of the shifter is less than 1.4 from 9.25 to 9.8 GHz. The saturation differential phase shift is about 390 degrees. So this design can achieve 360 degrees electronically controlled phase shift above MW level in X band.
A parallel waveguide structure for high power phase shifter is proposed. The ferrite phase shifter at present can achieve high power capacity with dual-toroids structure. The influence on the propagation, phase shift efficiency and power capacity of the dual toroids ferrite phase shifter of its parameters is simulated and analyzed in this paper. The peak power capacity can reach hundred kW level after optimization. By using parallel waveguide in parallel structure based on the dual-toroids form, it can be increased to MW level. After matching design, VSWR of the shifter is less than 1.4 from 9.25 to 9.8 GHz. The saturation differential phase shift is about 390 degrees. So this design can achieve 360 degrees electronically controlled phase shift above MW level in X band.
2016,
28: 083007.
doi: 10.11884/HPLPB201628.150832
Abstract:
The sectorial waveguide can be used as an element of high power microwave(HPM) cylindrically conformal slotted waveguide array antenna. In this paper, the field components for the domination mode in a sectorial waveguide are investigated. According to the practicality applied area, the field components of domination mode can be reasonably approximated. By the reciprocity theorem, the amplitudes of forward or backward scattered mode can be expressed by the transverse field components of waveguide and the field components in slot. By the transmission line theorem, the longitudinal shunt slot is equivalent to a shunt obstacle on a two-wire transmission line. According to the boundary condition, the resonant normalized conductance of the slot is expressed by the amplitudes of scattered domination mode. The radiation resistance of half wavelength slot is obtained from the complementary half wavelength dipole. The amplitudes of scattered domination mode are expressed by radiation power of slot. The analytic formula of the resonant conductance for longitudinal shunt slots cut in the curved broad face of the waveguide is derived with the parameters of offset angle from the center line, the width of slot, the wavelength and guide wavelength and the dimension of inner cavity of waveguide. An example is presented and the result obtained in the middle area of waveguide is satisfactory.
The sectorial waveguide can be used as an element of high power microwave(HPM) cylindrically conformal slotted waveguide array antenna. In this paper, the field components for the domination mode in a sectorial waveguide are investigated. According to the practicality applied area, the field components of domination mode can be reasonably approximated. By the reciprocity theorem, the amplitudes of forward or backward scattered mode can be expressed by the transverse field components of waveguide and the field components in slot. By the transmission line theorem, the longitudinal shunt slot is equivalent to a shunt obstacle on a two-wire transmission line. According to the boundary condition, the resonant normalized conductance of the slot is expressed by the amplitudes of scattered domination mode. The radiation resistance of half wavelength slot is obtained from the complementary half wavelength dipole. The amplitudes of scattered domination mode are expressed by radiation power of slot. The analytic formula of the resonant conductance for longitudinal shunt slots cut in the curved broad face of the waveguide is derived with the parameters of offset angle from the center line, the width of slot, the wavelength and guide wavelength and the dimension of inner cavity of waveguide. An example is presented and the result obtained in the middle area of waveguide is satisfactory.
2016,
28: 083101.
doi: 10.11884/HPLPB201628.151073
Abstract:
With the research and development of hypersonic vehicles technology, the issues of ionization blackout have become increasing prominent during hypersonic flight. And there is the superiority of millimeter wave atmospheric window in atmospheric transmission. According to the data provided by radio attenuation measurement C (RAM C) voyage experiment, double-exponential distribution, Epstein distribution and Gaussian distribution models of plasma sheath were established. The principle of interaction between atmospheric window of millimeter wave and plasma was analyzed through Z-FDTD algorithm, getting the attenuation properties of atmospheric window of millimeter wave propagation in plasma sheath. The analysis by synthesis shows that the 35 GHz, the window of atmosphere in Ka waveband can be selected as communication waveband used in near space main communication platform, and subsidiary of 220 GHz in terahertz waveband airspace-based communication platform. It will carry on the real-time measurement and control when the reentering vehicles and hypersonic aerocraft voyage in the near space.
With the research and development of hypersonic vehicles technology, the issues of ionization blackout have become increasing prominent during hypersonic flight. And there is the superiority of millimeter wave atmospheric window in atmospheric transmission. According to the data provided by radio attenuation measurement C (RAM C) voyage experiment, double-exponential distribution, Epstein distribution and Gaussian distribution models of plasma sheath were established. The principle of interaction between atmospheric window of millimeter wave and plasma was analyzed through Z-FDTD algorithm, getting the attenuation properties of atmospheric window of millimeter wave propagation in plasma sheath. The analysis by synthesis shows that the 35 GHz, the window of atmosphere in Ka waveband can be selected as communication waveband used in near space main communication platform, and subsidiary of 220 GHz in terahertz waveband airspace-based communication platform. It will carry on the real-time measurement and control when the reentering vehicles and hypersonic aerocraft voyage in the near space.
2016,
28: 083201.
doi: 10.11884/HPLPB201628.150410
Abstract:
The electromagnetic wave reflectivity and transmissivity of plain concrete, steel wire mesh and steel wire mesh concrete were numerically studied. Firstly, model simulation results were compared with experimental data of reflectivity and transmissivity and the discrepancy was analyzed. Secondly, two different steel wire meshes were simulated and compared with experimental results, and parameters including wire diameter, mesh diameter and number of layers were studied. Lastly, the steel wires and the influence of their positions on the reflectivity and transmissivity were studied. In this paper, a numerical simulation tool Ansoft HFSS 15.0 was used. When the diameters of steel wires are the same, the larger the mesh diameter is, the lower the reflectivity is. Joining steel wires has little effect on the average reflectivity of concrete, but could affect the harmonicity of the reflectivity curve.
The electromagnetic wave reflectivity and transmissivity of plain concrete, steel wire mesh and steel wire mesh concrete were numerically studied. Firstly, model simulation results were compared with experimental data of reflectivity and transmissivity and the discrepancy was analyzed. Secondly, two different steel wire meshes were simulated and compared with experimental results, and parameters including wire diameter, mesh diameter and number of layers were studied. Lastly, the steel wires and the influence of their positions on the reflectivity and transmissivity were studied. In this paper, a numerical simulation tool Ansoft HFSS 15.0 was used. When the diameters of steel wires are the same, the larger the mesh diameter is, the lower the reflectivity is. Joining steel wires has little effect on the average reflectivity of concrete, but could affect the harmonicity of the reflectivity curve.
2016,
28: 083202.
doi: 10.11884/HPLPB201628.150877
Abstract:
When a vehicle flies at high velocity, the high temperature gas in shock layer undergoes strong physical and chemical change along with substantive optical radiation which will directly affect the imaging quality of an infrared seeker. Fluid dynamics Navier-Stokes equations with thermo-chemical non-equilibrium models were used to simulate the high temperature gas flow. Narrowband model accounting for both electronic and vibrational-rotational transition mechanisms was employed to obtain gas radiative characteristics. Radiative transfer equation was computed by finite volume method to acquire radiative intensity distribution. Based on validation of flow solver, radiative parameter calculation and radiative transportation computation, hypersonic flight vehicles were simulated. Flow structures and parameters and particles distributions were obtained. Emission coefficients in specific wavelength range were solved through the flow parameter. The distribution of the coefficients shows that is very similar to shock wave shape and gas temperature contours behind the shock. Gas radiative noises on optics window are axisymmetric, which is strongly related to flow velocity, gas species and so on. When Mach number increases, the gas radiative noises grow rapidly.
When a vehicle flies at high velocity, the high temperature gas in shock layer undergoes strong physical and chemical change along with substantive optical radiation which will directly affect the imaging quality of an infrared seeker. Fluid dynamics Navier-Stokes equations with thermo-chemical non-equilibrium models were used to simulate the high temperature gas flow. Narrowband model accounting for both electronic and vibrational-rotational transition mechanisms was employed to obtain gas radiative characteristics. Radiative transfer equation was computed by finite volume method to acquire radiative intensity distribution. Based on validation of flow solver, radiative parameter calculation and radiative transportation computation, hypersonic flight vehicles were simulated. Flow structures and parameters and particles distributions were obtained. Emission coefficients in specific wavelength range were solved through the flow parameter. The distribution of the coefficients shows that is very similar to shock wave shape and gas temperature contours behind the shock. Gas radiative noises on optics window are axisymmetric, which is strongly related to flow velocity, gas species and so on. When Mach number increases, the gas radiative noises grow rapidly.
2016,
28: 083203.
doi: 10.11884/HPLPB201628.160052
Abstract:
Based on low-frequency partial element equivalent circuit (PEEC) method, the current and potential distribution of the ground loop is presented, and the mechanism of common ground conduction interference is analyzed in this paper. Our proposed low-frequency PEEC model is achieved based on mixed potential integral equation (MPIE), and its accuracy is verified by comparing with the results of boundary element method. By realizing the three-dimensional current distribution calculation with the PEEC model, the current distribution of a typical large conductor ground loop and the effects on the current distribution due to frequency are achieved. The results demonstrate that current distribution of ground conductor is mainly concentrated in the vicinity of the ground electrode, and a potential difference is observed between two ground electrodes because of the influence of inductance, which reveals the mechanism of common ground conduction interference in the ground loop.
Based on low-frequency partial element equivalent circuit (PEEC) method, the current and potential distribution of the ground loop is presented, and the mechanism of common ground conduction interference is analyzed in this paper. Our proposed low-frequency PEEC model is achieved based on mixed potential integral equation (MPIE), and its accuracy is verified by comparing with the results of boundary element method. By realizing the three-dimensional current distribution calculation with the PEEC model, the current distribution of a typical large conductor ground loop and the effects on the current distribution due to frequency are achieved. The results demonstrate that current distribution of ground conductor is mainly concentrated in the vicinity of the ground electrode, and a potential difference is observed between two ground electrodes because of the influence of inductance, which reveals the mechanism of common ground conduction interference in the ground loop.
2016,
28: 083204.
doi: 10.11884/HPLPB201628.151145
Abstract:
In order to study the characteristics of the needle-plate corona discharge induced by the electromagnetic field in the vacuum environment, a simulation test system of corona discharge induced by the electromagnetic fields, such as the electromagnetic field generator, the vacuum system, the high voltage power supply, and the dynamic potential tester, is developed. The system can realize a low vacuum environment of 80 Pa, and we can use the system to carry out the corona discharge test under the action of the electromagnetic field. The change laws of the threshold voltage of corona discharge induced by electromagnetic field are obtained. The experimental results show that when the temperature, humidity and other environmental factors keep unchanged, the normal discharge threshold is -590 V. When the pressure of the vacuum tube is 80 Pa, the negative high voltage of electrostatic discharge could release a voltage from 10 kV to 20 kV. The electromagnetic pulse acts on the inner of the vacuum tube in the charging area, the discharge threshold will reduce 90-180 V.
In order to study the characteristics of the needle-plate corona discharge induced by the electromagnetic field in the vacuum environment, a simulation test system of corona discharge induced by the electromagnetic fields, such as the electromagnetic field generator, the vacuum system, the high voltage power supply, and the dynamic potential tester, is developed. The system can realize a low vacuum environment of 80 Pa, and we can use the system to carry out the corona discharge test under the action of the electromagnetic field. The change laws of the threshold voltage of corona discharge induced by electromagnetic field are obtained. The experimental results show that when the temperature, humidity and other environmental factors keep unchanged, the normal discharge threshold is -590 V. When the pressure of the vacuum tube is 80 Pa, the negative high voltage of electrostatic discharge could release a voltage from 10 kV to 20 kV. The electromagnetic pulse acts on the inner of the vacuum tube in the charging area, the discharge threshold will reduce 90-180 V.
2016,
28: 084001.
doi: 10.11884/HPLPB201628.150695
Abstract:
A method based on the simulation of system state is proposed to assess radiation hardened performance of electronic system. Based on radiation effects of devices of system, the system output is simulated using behavioral models which describe the electrical circuit behavior and its dependence on the radiation dose. By using Monte Carlo method, the uncertainty of system performance is calculated, then the margin and uncertainty of the system are determined. Applying the method to evaluate the radiation hardness performance of an A/D circuit illustrates the using steps of the method. The radiation experiment of the A/D circuit is performed to compare with the result given by the method.
A method based on the simulation of system state is proposed to assess radiation hardened performance of electronic system. Based on radiation effects of devices of system, the system output is simulated using behavioral models which describe the electrical circuit behavior and its dependence on the radiation dose. By using Monte Carlo method, the uncertainty of system performance is calculated, then the margin and uncertainty of the system are determined. Applying the method to evaluate the radiation hardness performance of an A/D circuit illustrates the using steps of the method. The radiation experiment of the A/D circuit is performed to compare with the result given by the method.
2016,
28: 084002.
doi: 10.11884/HPLPB201628.151259
Abstract:
The alpha energy-loss method is an effective and novel way to measure film thickness and thickness uniformity. But this kind of measurement should be carried out in a vacuum chamber. How to choose the appropriate vacuum degree is of great importance for improving the measurement precision and reducing the construction cost of the vacuum system. In this paper, we simulate the process of alpha particles with a power of 5.486 MeV going through air by using the software SRIM, calculate the energy loss of particles coming from Am-241 through different air distances between the source and the detector with different vacuum degrees and obtain the relationship between the energy loss and the vacuum degree. According to this relationship, combined with the stability and repeatability of the measurement of alpha spectrometer, we have found the method of determining the required vacuum degree in the chamber for measuring the film thickness with alpha particles. Based on the result, we get a conclusion that a vacuum degree less than 100 Pa will completely meet the requirement of sufficient accuracy when the distance between the source and the detector is 2-8 cm.
The alpha energy-loss method is an effective and novel way to measure film thickness and thickness uniformity. But this kind of measurement should be carried out in a vacuum chamber. How to choose the appropriate vacuum degree is of great importance for improving the measurement precision and reducing the construction cost of the vacuum system. In this paper, we simulate the process of alpha particles with a power of 5.486 MeV going through air by using the software SRIM, calculate the energy loss of particles coming from Am-241 through different air distances between the source and the detector with different vacuum degrees and obtain the relationship between the energy loss and the vacuum degree. According to this relationship, combined with the stability and repeatability of the measurement of alpha spectrometer, we have found the method of determining the required vacuum degree in the chamber for measuring the film thickness with alpha particles. Based on the result, we get a conclusion that a vacuum degree less than 100 Pa will completely meet the requirement of sufficient accuracy when the distance between the source and the detector is 2-8 cm.
2016,
28: 084003.
doi: 10.11884/HPLPB201628.151143
Abstract:
Dynamic fragmentation of material under superhigh strain rate is a topic of increasing interest in shock physics. However, due to diagnosis technique limits, high-quality experimental data of particle size of the fragmentation are quite sparse. Recently, based on in-line holography, we have explored a technique to diagnose the dynamic fragmentation process and measure particle size of fragmentation. Using this diagnosis system, an experiment of laser-shock-melted aluminum has been successfully performed, in-situ data of fragment particles have been obtained in melted aluminum for strain rate ranging from 107～108/s, which gives confidence to our measurement technique for dynamic fragments with high precision.
Dynamic fragmentation of material under superhigh strain rate is a topic of increasing interest in shock physics. However, due to diagnosis technique limits, high-quality experimental data of particle size of the fragmentation are quite sparse. Recently, based on in-line holography, we have explored a technique to diagnose the dynamic fragmentation process and measure particle size of fragmentation. Using this diagnosis system, an experiment of laser-shock-melted aluminum has been successfully performed, in-situ data of fragment particles have been obtained in melted aluminum for strain rate ranging from 107～108/s, which gives confidence to our measurement technique for dynamic fragments with high precision.
2016,
28: 084004.
doi: 10.11884/HPLPB201628.150892
Abstract:
A single-event experiment is carried out for the industrial Ethernet chip KSZ8851-16MLLJ by using a heavy ion source in order to evaluate and study the adaptability of the chip in the space environment. The single-event experimental plan is formulated according to the structure and function of the Ethernet chip to get experimental data which will be arranged and researched. Some results are shown about the experiment and research as follows. The chip has some anti-single-event radiation ability, the probability of single-event upset is different under different network transmission conditions, the chip will produce a current step in the continuous single-event radiation and the single event is locked when the second current step happens, and thus the radiation level of the chip is monitored by the current step in engineering application.
A single-event experiment is carried out for the industrial Ethernet chip KSZ8851-16MLLJ by using a heavy ion source in order to evaluate and study the adaptability of the chip in the space environment. The single-event experimental plan is formulated according to the structure and function of the Ethernet chip to get experimental data which will be arranged and researched. Some results are shown about the experiment and research as follows. The chip has some anti-single-event radiation ability, the probability of single-event upset is different under different network transmission conditions, the chip will produce a current step in the continuous single-event radiation and the single event is locked when the second current step happens, and thus the radiation level of the chip is monitored by the current step in engineering application.
2016,
28: 084005.
doi: 10.11884/HPLPB201628.151015
Abstract:
The research aims at assessing the relationship between the excitation light intensity and the image signal of the all optical high-speed camera system based on the transient grating and the viability of establishing a high-speed camera based on InP. This paper theoretically analyzes the physical quantity relationship of photons and excited carriers, carrier concentration and refractive index, refractive index and diffraction efficiency. In experiments, the image detection system based on collecting diffracted light was established to obtain the transient grating distribution in InP. Theoretical results provide the relationship between excitation light intensity and carrier concentration when the semiconductor is InP, the relationship between carrier concentration and refractive index when the wavelength of the probe beam is 1064 nm, and the relationship between refractive index and diffraction efficiency when the transient grating is rectangular grating. Theoretical results also indicate that the sensitivity of the all optical high-speed camera with 1 ps time resolution based on InP and a probe beam of 1064 nm is about 1.3105 Wcm-2 when it is excited by the photons of 532 nm bean. Experimental results indicate that it is viable to establish all optical high-speed camera system based on InP and 1064 nm beam. According to the image obtained in experiments the spatial resolution of the system is better than 5.04 lp/mm.
The research aims at assessing the relationship between the excitation light intensity and the image signal of the all optical high-speed camera system based on the transient grating and the viability of establishing a high-speed camera based on InP. This paper theoretically analyzes the physical quantity relationship of photons and excited carriers, carrier concentration and refractive index, refractive index and diffraction efficiency. In experiments, the image detection system based on collecting diffracted light was established to obtain the transient grating distribution in InP. Theoretical results provide the relationship between excitation light intensity and carrier concentration when the semiconductor is InP, the relationship between carrier concentration and refractive index when the wavelength of the probe beam is 1064 nm, and the relationship between refractive index and diffraction efficiency when the transient grating is rectangular grating. Theoretical results also indicate that the sensitivity of the all optical high-speed camera with 1 ps time resolution based on InP and a probe beam of 1064 nm is about 1.3105 Wcm-2 when it is excited by the photons of 532 nm bean. Experimental results indicate that it is viable to establish all optical high-speed camera system based on InP and 1064 nm beam. According to the image obtained in experiments the spatial resolution of the system is better than 5.04 lp/mm.
2016,
28: 084101.
doi: 10.11884/HPLPB201628.160013
Abstract:
The experimental platform for electrical explosion of wire was built and iron wire was electrically exploded in air to produce metal nanoparticles. The total energy deposited in the wire was estimated by time integration using the product of voltage and current waveforms measured by voltage divider and Rogowski coil, respectively. The light emission from the plasma was recorded by photoelectric detector. The composition and morphology of the electrical explosion product were tested by the high-multiple microscope, scanning electronic microscope (SEM), transmission electron microscopy (TEM), the energy dispersive spectroscope (EDS) and X-ray diffractometry (XRD) to analyze the products phase characteristics. The results show that during the process of electrical explosion, when iron wire goes from liquid phase to gas phase, current hardly flows through the wire and load voltage of wire approaches the initial charge voltage of capacitor due to rapid increase of wire resistance. With energy deposited into wire, arc plasma is formed in the chamber. Meanwhile, current can flow through the low resistance arc plasma, which leads to voltage as well as current waveforms evolving into underdamped sinusoidal waveforms. The product of iron wire electrical explosion is composed of Fe3O4 nanoparticles and most of them are in good spherical shape. The particle size ranges mainly from 30 to 60 nm and obeys the log-normal distribution.
The experimental platform for electrical explosion of wire was built and iron wire was electrically exploded in air to produce metal nanoparticles. The total energy deposited in the wire was estimated by time integration using the product of voltage and current waveforms measured by voltage divider and Rogowski coil, respectively. The light emission from the plasma was recorded by photoelectric detector. The composition and morphology of the electrical explosion product were tested by the high-multiple microscope, scanning electronic microscope (SEM), transmission electron microscopy (TEM), the energy dispersive spectroscope (EDS) and X-ray diffractometry (XRD) to analyze the products phase characteristics. The results show that during the process of electrical explosion, when iron wire goes from liquid phase to gas phase, current hardly flows through the wire and load voltage of wire approaches the initial charge voltage of capacitor due to rapid increase of wire resistance. With energy deposited into wire, arc plasma is formed in the chamber. Meanwhile, current can flow through the low resistance arc plasma, which leads to voltage as well as current waveforms evolving into underdamped sinusoidal waveforms. The product of iron wire electrical explosion is composed of Fe3O4 nanoparticles and most of them are in good spherical shape. The particle size ranges mainly from 30 to 60 nm and obeys the log-normal distribution.
2016,
28: 085001.
doi: 10.11884/HPLPB201628.151294
Abstract:
Based on the equivalent circuit and simplified model of disk explosive magnetic generator (DEMG), the code MDEMG was compiled with Matlab. To analyze the variation of parameters, such as current, induction, distribution of voltage, detonation pressure and magnetic pressure, and the influences of different initial currents and different shapes of disk on output characteristic of generator, the operation of 240 mm disk explosive magnetic generator was simulated with MDEMG. The results of the simulation include three conclusions as following: this type of generator can output current 40 MA on a 1.5 nH inductive load with a characteristic rise time of 3 s, which corresponds to the experiment results of Russian researcher; Output current increases with the increase of initial current, but output current has a limitation because of the quick increase of magnetic pressure; Conical disk can produce much higher power than that of flat disk. This paper can provide theoretical reference for further domestic study of DEMG.
Based on the equivalent circuit and simplified model of disk explosive magnetic generator (DEMG), the code MDEMG was compiled with Matlab. To analyze the variation of parameters, such as current, induction, distribution of voltage, detonation pressure and magnetic pressure, and the influences of different initial currents and different shapes of disk on output characteristic of generator, the operation of 240 mm disk explosive magnetic generator was simulated with MDEMG. The results of the simulation include three conclusions as following: this type of generator can output current 40 MA on a 1.5 nH inductive load with a characteristic rise time of 3 s, which corresponds to the experiment results of Russian researcher; Output current increases with the increase of initial current, but output current has a limitation because of the quick increase of magnetic pressure; Conical disk can produce much higher power than that of flat disk. This paper can provide theoretical reference for further domestic study of DEMG.
2016,
28: 085002.
doi: 10.11884/HPLPB201628.150913
Abstract:
In Z-pinch experiments carried on Primary Test Stand（PTS）, we used a multi-channel filtered X-ray diode (XRD) array to measure the soft X-ray total radiant energy, power and energy spectrum emitted from Z-pinches. This paper reports on the theory, performance and major parameters of multi-channel XRD array, and the unfolding calculation. The measurement results and the data analysis are also presented. At last, the spectra measured by multi-channel XRD array are compared with those by transmission grating spectrograph, the total yield data achieved by multi-channel XRD array, bolometer, and flat-response XRD detector, are also compared.
In Z-pinch experiments carried on Primary Test Stand（PTS）, we used a multi-channel filtered X-ray diode (XRD) array to measure the soft X-ray total radiant energy, power and energy spectrum emitted from Z-pinches. This paper reports on the theory, performance and major parameters of multi-channel XRD array, and the unfolding calculation. The measurement results and the data analysis are also presented. At last, the spectra measured by multi-channel XRD array are compared with those by transmission grating spectrograph, the total yield data achieved by multi-channel XRD array, bolometer, and flat-response XRD detector, are also compared.
2016,
28: 085003.
doi: 10.11884/HPLPB201628.151295
Abstract:
In consideration of the mutual coupling, the active element pattern (AEP) theory is adopted to calculate the time-domain radiation field of large pulsed antenna arrays. The AEPs of a large array can be transformed into those of a small array under similar mutual coupling condition, and the radiation field of the large array is obtained by superposing AEPs of all the elements. On this basis, an improved method is proposed combined with time-domain radiation theory. By formula deriving, the analysis of a large linear array or a large planar array can be respectively converted into that of two small linear arrays or four small planar arrays. In comparison with the original method, calculating all AEPs of subarray is avoided. A 13 linear array and an 1113 planar array are calculated for verification, the results agree well with software simulation results. Compared with the original method, the calculation is reduced by 56.8% for the linear array and 81.17% for the planar array.
In consideration of the mutual coupling, the active element pattern (AEP) theory is adopted to calculate the time-domain radiation field of large pulsed antenna arrays. The AEPs of a large array can be transformed into those of a small array under similar mutual coupling condition, and the radiation field of the large array is obtained by superposing AEPs of all the elements. On this basis, an improved method is proposed combined with time-domain radiation theory. By formula deriving, the analysis of a large linear array or a large planar array can be respectively converted into that of two small linear arrays or four small planar arrays. In comparison with the original method, calculating all AEPs of subarray is avoided. A 13 linear array and an 1113 planar array are calculated for verification, the results agree well with software simulation results. Compared with the original method, the calculation is reduced by 56.8% for the linear array and 81.17% for the planar array.
2016,
28: 085101.
doi: 10.11884/HPLPB201628.151013
Abstract:
The China Spallation Neutron Source accelerator is designed to accelerate proton beam pulses to 1.6 GeV at 25 Hz repetition rate, striking a solid metal target to produce spallation neutrons. The accelerator provides a beam power of 100 kW on the target in the first phase. The linac is designed with beam energy of 81 MeV and a peak current of 15 mA. It consists of RFQ, two bunchers of medium energy beam transmission line, four DTL tanks, and one debuncher of linac-to-ring beam transmission line. Correspondingly eight online RF power sources are used to power these accelerators. So far, all RD prototypes of the CSNS linac RF power sources have been completed, and the performance meets the design requirements. Mass production, equipment installation and commissioning are still under way.
The China Spallation Neutron Source accelerator is designed to accelerate proton beam pulses to 1.6 GeV at 25 Hz repetition rate, striking a solid metal target to produce spallation neutrons. The accelerator provides a beam power of 100 kW on the target in the first phase. The linac is designed with beam energy of 81 MeV and a peak current of 15 mA. It consists of RFQ, two bunchers of medium energy beam transmission line, four DTL tanks, and one debuncher of linac-to-ring beam transmission line. Correspondingly eight online RF power sources are used to power these accelerators. So far, all RD prototypes of the CSNS linac RF power sources have been completed, and the performance meets the design requirements. Mass production, equipment installation and commissioning are still under way.
2016,
28: 085102.
doi: 10.11884/HPLPB201628.151229
Abstract:
In flash-radiography, scattering photons will decrease the definition of receiving images, which limits the resolving power of the interface and the density of the object for radiography. The anti-scatter grid camera is able to improve the picture resolving power due to a great reduction of scattering photons, which, in the meantime, demands a much more stable spatial position of the X-ray source in order to reduce the loss of signal photons in the anti-scatter grid structure. The pinhole imaging method is applied to measure the spatial distribution of the Dragon-I LIA X-ray source, by which the centroid and the FWHM of the spot can be calculated, and to analyze the influence of the electron beam focusing to the displacement and the size of the source spot. Experimental results demonstrate that a variation in electron beam focusing will lead to a distinct change of the spatial position and the size of the radiographic source. It can also be seen that the jitter of the source centroid and the change of the spot size can be kept in a small range when the focusing of the electron beam remains invariant.
In flash-radiography, scattering photons will decrease the definition of receiving images, which limits the resolving power of the interface and the density of the object for radiography. The anti-scatter grid camera is able to improve the picture resolving power due to a great reduction of scattering photons, which, in the meantime, demands a much more stable spatial position of the X-ray source in order to reduce the loss of signal photons in the anti-scatter grid structure. The pinhole imaging method is applied to measure the spatial distribution of the Dragon-I LIA X-ray source, by which the centroid and the FWHM of the spot can be calculated, and to analyze the influence of the electron beam focusing to the displacement and the size of the source spot. Experimental results demonstrate that a variation in electron beam focusing will lead to a distinct change of the spatial position and the size of the radiographic source. It can also be seen that the jitter of the source centroid and the change of the spot size can be kept in a small range when the focusing of the electron beam remains invariant.
2016,
28: 085103.
doi: 10.11884/HPLPB201628.151020
Abstract:
Dragon Ⅱ is a linear induction accelerator which can shoot 3 coaxial pulsed high intense current electron beams at one time. The distinguished beam parameters between electron beam pulses should be achieved at least for its multi-pulsed electron beams. The high time-resolved beam parameters inside an electron beam pulse are important. One set of complicated electron beam parameters measurement system has been specially developed recently for Dragon Ⅱ LIA. The optics layout for beam profile measurement and beam emittance measurement individually being carried out is developed from the structure of instantaneous electron beam emittance measurement system based on the optical transition radiation principle. Multi framing cameras are adopted in the system. This system features very flexible assembled measurement ability. It meets the diversified demands for very difficult debugging work and beam parameters measurement of Dragon Ⅱ LIA. The highest time-resolved ability is up to 2 ns and at least 8 results of time-resolved beam parameters inside one pulse can be obtained at one time.
Dragon Ⅱ is a linear induction accelerator which can shoot 3 coaxial pulsed high intense current electron beams at one time. The distinguished beam parameters between electron beam pulses should be achieved at least for its multi-pulsed electron beams. The high time-resolved beam parameters inside an electron beam pulse are important. One set of complicated electron beam parameters measurement system has been specially developed recently for Dragon Ⅱ LIA. The optics layout for beam profile measurement and beam emittance measurement individually being carried out is developed from the structure of instantaneous electron beam emittance measurement system based on the optical transition radiation principle. Multi framing cameras are adopted in the system. This system features very flexible assembled measurement ability. It meets the diversified demands for very difficult debugging work and beam parameters measurement of Dragon Ⅱ LIA. The highest time-resolved ability is up to 2 ns and at least 8 results of time-resolved beam parameters inside one pulse can be obtained at one time.
2016,
28: 089001.
doi: 10.11884/HPLPB201628.150690
Abstract:
Autogenous laser welding of aluminum-lithium alloy often results in bad weld appearance and serious porosity. This paper investigates the influence of different laser welding positions on the welding quality of 5A90 Al-Li alloy. The weld appearance and the porosity are compared with the flat welding, the horizontal welding and the vertical welding respectively. The formation and suppression mechanism of defects in different welding positions are analyzed and discussed considering the force state of the melt pool, the liquid metal flow and the keyhole behavior. The experimental results show that the weld seams suffer from excessive penetration in the flat welding, and serious metallic spatters, discontinuous weld bead in the horizontal welding, the concave defects in the back weld in the vertical-up welding. The optimal weld appearance and least porosity defects could be obtained in the vertical-down welding position. The porosity is closely related to the welding positions due to the change of dynamic characteristics of the keyhole and the flow behavior of the melt pool. The porosity changes in a similar trend with the increase of the heat input in different welding positions. The pores increase at first then decrease, and a maximum value is reached when the weld is incompletely penetrated. The number of pores and their average size could both be suppressed into minimums in the vertical-down welding, and the pores formed mainly in the centerline of the seam while they distribute chaotically around the weld seam in other welding positions.
Autogenous laser welding of aluminum-lithium alloy often results in bad weld appearance and serious porosity. This paper investigates the influence of different laser welding positions on the welding quality of 5A90 Al-Li alloy. The weld appearance and the porosity are compared with the flat welding, the horizontal welding and the vertical welding respectively. The formation and suppression mechanism of defects in different welding positions are analyzed and discussed considering the force state of the melt pool, the liquid metal flow and the keyhole behavior. The experimental results show that the weld seams suffer from excessive penetration in the flat welding, and serious metallic spatters, discontinuous weld bead in the horizontal welding, the concave defects in the back weld in the vertical-up welding. The optimal weld appearance and least porosity defects could be obtained in the vertical-down welding position. The porosity is closely related to the welding positions due to the change of dynamic characteristics of the keyhole and the flow behavior of the melt pool. The porosity changes in a similar trend with the increase of the heat input in different welding positions. The pores increase at first then decrease, and a maximum value is reached when the weld is incompletely penetrated. The number of pores and their average size could both be suppressed into minimums in the vertical-down welding, and the pores formed mainly in the centerline of the seam while they distribute chaotically around the weld seam in other welding positions.
