A cylindrical gates model of the static induction transistor is proposed and mirror method is used to calculate the distribution of electric potential.The results show that:the potential barrier is directly determined...A cylindrical gates model of the static induction transistor is proposed and mirror method is used to calculate the distribution of electric potential.The results show that:the potential barrier is directly determined by channel over pinched-off factor;gate efficiency η decreases as the gate dimension α 2 and shifted gate voltage are minished,and what differs from the first-order theory is that η will tend to zero at the shifted gate voltage tends to zero when V D=0;at low current,the voltage amplification factor μ increases as the drain current rising.When the drain current reaches certain degree,the voltage amplification factor keeps almost constant.In the end,an analytical description of SIT’s characteristic suited to both triode-like and mixed I-V characteristics are obtained.The predicted I-V curves are consistent perfectly with the reported experimental ones.展开更多
A method using multiple mirror images of point charges is put forward to analyze the polarization of two identical conductor spheres in a uniform electrostatic field.By use of the method,the electric field distributio...A method using multiple mirror images of point charges is put forward to analyze the polarization of two identical conductor spheres in a uniform electrostatic field.By use of the method,the electric field distribution and the interaction force between two spheres can be calculated accurately even for very small gap between two spheres.Our results show that the magnitude of the product of the gap between two spheres and the local electric field in the center of the gap is approximately in the same order and the interaction between two spheres increases very fast as the two spheres are close to each other.We also show that the interaction force between two conductor spheres is almost same with that between two dielectric spheres with high permittivity.展开更多
Magnetic mirror used as an efficient tool to confine plasma has been widely adopted in many different areas especially in recent cusped field thrusters. In order to check the influence of magnetic mirror effect on the...Magnetic mirror used as an efficient tool to confine plasma has been widely adopted in many different areas especially in recent cusped field thrusters. In order to check the influence of magnetic mirror effect on the plasma distribution in a cusped field thruster, three different radii of the discharge channel(6 mm, 4 mm, and 2 mm) in a cusped field thruster are investigated by using Particle-in-Cell Plus Monte Carlo(PIC-MCC) simulated method, under the condition of a fixed axial length of the discharge channel and the same operating parameters. It is found that magnetic cusps inside the small radius discharge channel cannot confine electrons very well. Thus, the electric field is hard to establish. With the reduction of the discharge channel’s diameter, more electrons will escape from cusps to the centerline area near the anode due to a lower magnetic mirror ratio. Meanwhile, the leak width of the cusped magnetic field will increase at the cusp. By increasing the magnetic field strength in a small radius model of a cusped field thruster, the negative effect caused by the weak magnetic mirror effect can be partially compensated. Therefore, according to engineering design, the increase of magnetic field strength can contribute to obtaining a good performance, when the radial distance between the magnets and the inner surface of the discharge channel is relatively big.展开更多
Particle Image Velocimetry(PIV)is a well-developed and contactless technique in experimental fluid mechanics,but the strong velocity gradient and streamline curvature near the wall substantially limits its accuracy im...Particle Image Velocimetry(PIV)is a well-developed and contactless technique in experimental fluid mechanics,but the strong velocity gradient and streamline curvature near the wall substantially limits its accuracy improvement.This paper presents a data processing procedure combining conventional PIV and newly developed Mirror Interchange(MI)based Interface-PIV for the measurement of the boundary layer parameter development in the blade leading edge region.The synthetic particle images are used to analyze the measurement errors in the entire procedure.Overall,three types of errors,namely the errors caused by the Window Deformation Iterative Multigrid(WIDIM)algorithm,the discrete data interpolation and integration,and the wall offset uncertainty,comprise the main measurement error.Specifically,the errors due to the discrete data interpolation and integration and the WIDIM algorithm comprise the mean bias,which can be corrected through the error analysis method proposed in the present work.Meanwhile,the errors due to the WIDIM algorithm and the wall offset uncertainty contribute to the measurement uncertainty.Computational fluid dynamics-based synthetic particle flows were generated to verify the newly developed PIV data processing procedure and the corresponding error analysis method.Results showed that the data processing method could improve the accuracy of PIV measurements for boundary layer flows with high curvature and acceleration and even with significant flow separation bubbles.Finally,the data processing method is also applied in a PIV experiment to investigate the boundary layer flows around a compressor blade leading edge,and several credible boundary flow parameters were obtained.展开更多
Primary mirror is one of the key components in the space remote sensing system. To minimize the mass of the mirror without compromising its stiffness and decrease the deformation of the mirror surface at the different...Primary mirror is one of the key components in the space remote sensing system. To minimize the mass of the mirror without compromising its stiffness and decrease the deformation of the mirror surface at the different temperatures are the mainly two objects in the development of the primary mirror. Silicon carbide (SiC), the most promising optical material, was used as the material of the primary mirror with triangle lightmass structure in a Cassegrain system. By using finite element method, the properties of the SiC mirror were compared with that of the traditional Be mirror and fused silica mirror. The results of static, dynamic and thermo-mechanical analysis indicate that the deformation of the mirror surface caused by temperature field is much bigger than that caused by gravity field. The SiC mirror has the best overall properties, and the SiC material is much suitable for the primary mirror.展开更多
First mirrors are the facing components of plasma optical diagnostics system for superconductivity and other fusion devices. Due to high level of neutron and gamma radiation, the lifetime and optical state of first mi...First mirrors are the facing components of plasma optical diagnostics system for superconductivity and other fusion devices. Due to high level of neutron and gamma radiation, the lifetime and optical state of first mirror will face an enormous challenge. The degradation of the optical character on the mirror surface mainly comes from the two opposite processes, one is erosion, the other is re-deposition. Which proces plays more important role need testing in present machines. Before 2001 the experimental studies mainly put on material character simulation in a laboratory. Recently, the sample of the first mirror has been investigated in actual fusion device and modification of mirror optical properties was made. But how to protect mirror and make the lifetime longer will be an issue need solving urgently.展开更多
文摘A cylindrical gates model of the static induction transistor is proposed and mirror method is used to calculate the distribution of electric potential.The results show that:the potential barrier is directly determined by channel over pinched-off factor;gate efficiency η decreases as the gate dimension α 2 and shifted gate voltage are minished,and what differs from the first-order theory is that η will tend to zero at the shifted gate voltage tends to zero when V D=0;at low current,the voltage amplification factor μ increases as the drain current rising.When the drain current reaches certain degree,the voltage amplification factor keeps almost constant.In the end,an analytical description of SIT’s characteristic suited to both triode-like and mixed I-V characteristics are obtained.The predicted I-V curves are consistent perfectly with the reported experimental ones.
基金Supported by Guizhou Provincial Science and Technology Foundation (Z103167)Youth Foundation of Guizhou University (X092012)+1 种基金the National Basic Research Program of China under Grant No. 2009CB930800National Natural Science Foundation of China under Grant Nos. 10674157 and 10875166
文摘A method using multiple mirror images of point charges is put forward to analyze the polarization of two identical conductor spheres in a uniform electrostatic field.By use of the method,the electric field distribution and the interaction force between two spheres can be calculated accurately even for very small gap between two spheres.Our results show that the magnitude of the product of the gap between two spheres and the local electric field in the center of the gap is approximately in the same order and the interaction between two spheres increases very fast as the two spheres are close to each other.We also show that the interaction force between two conductor spheres is almost same with that between two dielectric spheres with high permittivity.
基金supported by the National Natural Science Foundation of China(Grant No.51006028)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(Grant No.51121004)
文摘Magnetic mirror used as an efficient tool to confine plasma has been widely adopted in many different areas especially in recent cusped field thrusters. In order to check the influence of magnetic mirror effect on the plasma distribution in a cusped field thruster, three different radii of the discharge channel(6 mm, 4 mm, and 2 mm) in a cusped field thruster are investigated by using Particle-in-Cell Plus Monte Carlo(PIC-MCC) simulated method, under the condition of a fixed axial length of the discharge channel and the same operating parameters. It is found that magnetic cusps inside the small radius discharge channel cannot confine electrons very well. Thus, the electric field is hard to establish. With the reduction of the discharge channel’s diameter, more electrons will escape from cusps to the centerline area near the anode due to a lower magnetic mirror ratio. Meanwhile, the leak width of the cusped magnetic field will increase at the cusp. By increasing the magnetic field strength in a small radius model of a cusped field thruster, the negative effect caused by the weak magnetic mirror effect can be partially compensated. Therefore, according to engineering design, the increase of magnetic field strength can contribute to obtaining a good performance, when the radial distance between the magnets and the inner surface of the discharge channel is relatively big.
基金funded by the National Natural Science Foundation of China(Nos.51790511 and 51806004)the National Science and Technology Major Project,China(No.2017-II-0001-0013).
文摘Particle Image Velocimetry(PIV)is a well-developed and contactless technique in experimental fluid mechanics,but the strong velocity gradient and streamline curvature near the wall substantially limits its accuracy improvement.This paper presents a data processing procedure combining conventional PIV and newly developed Mirror Interchange(MI)based Interface-PIV for the measurement of the boundary layer parameter development in the blade leading edge region.The synthetic particle images are used to analyze the measurement errors in the entire procedure.Overall,three types of errors,namely the errors caused by the Window Deformation Iterative Multigrid(WIDIM)algorithm,the discrete data interpolation and integration,and the wall offset uncertainty,comprise the main measurement error.Specifically,the errors due to the discrete data interpolation and integration and the WIDIM algorithm comprise the mean bias,which can be corrected through the error analysis method proposed in the present work.Meanwhile,the errors due to the WIDIM algorithm and the wall offset uncertainty contribute to the measurement uncertainty.Computational fluid dynamics-based synthetic particle flows were generated to verify the newly developed PIV data processing procedure and the corresponding error analysis method.Results showed that the data processing method could improve the accuracy of PIV measurements for boundary layer flows with high curvature and acceleration and even with significant flow separation bubbles.Finally,the data processing method is also applied in a PIV experiment to investigate the boundary layer flows around a compressor blade leading edge,and several credible boundary flow parameters were obtained.
文摘Primary mirror is one of the key components in the space remote sensing system. To minimize the mass of the mirror without compromising its stiffness and decrease the deformation of the mirror surface at the different temperatures are the mainly two objects in the development of the primary mirror. Silicon carbide (SiC), the most promising optical material, was used as the material of the primary mirror with triangle lightmass structure in a Cassegrain system. By using finite element method, the properties of the SiC mirror were compared with that of the traditional Be mirror and fused silica mirror. The results of static, dynamic and thermo-mechanical analysis indicate that the deformation of the mirror surface caused by temperature field is much bigger than that caused by gravity field. The SiC mirror has the best overall properties, and the SiC material is much suitable for the primary mirror.
文摘First mirrors are the facing components of plasma optical diagnostics system for superconductivity and other fusion devices. Due to high level of neutron and gamma radiation, the lifetime and optical state of first mirror will face an enormous challenge. The degradation of the optical character on the mirror surface mainly comes from the two opposite processes, one is erosion, the other is re-deposition. Which proces plays more important role need testing in present machines. Before 2001 the experimental studies mainly put on material character simulation in a laboratory. Recently, the sample of the first mirror has been investigated in actual fusion device and modification of mirror optical properties was made. But how to protect mirror and make the lifetime longer will be an issue need solving urgently.
