Emission of the electromagnetic pulses （EMP） due to laser-target interaction in laser facility had been evaluated using a cone antenna in this work. The microwave in frequencies ranging from several hundreds of MHz ...Emission of the electromagnetic pulses （EMP） due to laser-target interaction in laser facility had been evaluated using a cone antenna in this work. The microwave in frequencies ranging from several hundreds of MHz to 2 GHz was recorded when long-pulse lasers with several thousands of joules illuminated the solid targets, meanwhile the voltage signals from 1V to 4V were captured as functions of laser energy and backlight laser, where the corresponding electric field strengths were obtained by simulating the cone antenna in combination with conducting a mathematical process （Tiknohov Regularization with L curve）. All the typical coupled voltage oscillations displayed multiple peaks and had duration of up to 80ns before decaying into noise and mechanisms of the EMP generation was schematically interpreted in basis of the practical measuring environments. The resultant data were expected to offer basic know-how to achieve inertial confinement fusion.展开更多
The maximum flyer impact velocity based on a dynamic solidification cracking mechanism is proposed to describe the upper limit of collision welding process windows.Thus,the upper limit of the weld window is governed b...The maximum flyer impact velocity based on a dynamic solidification cracking mechanism is proposed to describe the upper limit of collision welding process windows.Thus,the upper limit of the weld window is governed by the evolution of dynamic stresses and temperatures at the weld interface.Current formulations for the upper limit of the collision weld window assume that both the flyer and target are made of the same material and approximate stress propagation velocities using the acoustic velocity or the shear wave velocity of the weld material.However,collision welding fundamentally depends on the impacts that generate shockwaves in weld members,which can dominate the stress propagation velocities in thin weld sections.Therefore,this study proposes an alternative weld window upper limit that approximates stress propagation using shock velocities calculated from modified 1-D Rankine-Hugoniot relations.The shock upper limit is validated against the experimental and simulation data in the collision welding literature,and offers a design tool to rapidly predict more accurate optimal collision weld process limits for similar and dissimilar weld couples compared to existing models without the cost or complexity of high-fidelity simulations.展开更多
为了研究激光推进技术中液体工质的最优掺杂浓度,进行了激光烧蚀掺杂甘油液体工质的冲量耦合特性实验研究。实验中采用10ns脉宽的Nd:YAG激光器烧蚀粘性液体甘油,在甘油中混合了不同浓度的纳米碳粉作为掺杂剂,以提高对激光能量的吸收。...为了研究激光推进技术中液体工质的最优掺杂浓度,进行了激光烧蚀掺杂甘油液体工质的冲量耦合特性实验研究。实验中采用10ns脉宽的Nd:YAG激光器烧蚀粘性液体甘油,在甘油中混合了不同浓度的纳米碳粉作为掺杂剂,以提高对激光能量的吸收。运用阴影测量法观测了激光烧蚀羽流的喷射过程,对不同掺杂浓度甘油的烧蚀产物、等离子体膨胀、激波传播、飞溅现象进行了对比分析;运用激光干涉扭摆法测量了烧蚀冲量,并分析了掺杂浓度对冲量耦合系数的影响。实验结果表明,掺碳后甘油的喷射行为、激波速度和冲量都发生了改变,而且掺碳后甘油的冲量耦合系数和比冲有了显著提高。综合分析得到1%浓度碳粉是甘油的最优掺杂浓度,此时冲量耦合系数从无掺杂时的67 m N·s/J提高到1250m N·s/J。展开更多
基金We would like to thank Dr. Peng Wang at University of Electric Science and Technology of China （UESTC） and Dr. Ziyu Chen at China Academy of Engineering Physics for their help in processing the data and understanding the potential mechanisms. This work was financially supported by the Fundamental Research Funds for the Central Universities （No. ZYGX2015J108） and National Natural Science Foundation of China （Nos. 11575166 and 5158 1140）.
文摘Emission of the electromagnetic pulses （EMP） due to laser-target interaction in laser facility had been evaluated using a cone antenna in this work. The microwave in frequencies ranging from several hundreds of MHz to 2 GHz was recorded when long-pulse lasers with several thousands of joules illuminated the solid targets, meanwhile the voltage signals from 1V to 4V were captured as functions of laser energy and backlight laser, where the corresponding electric field strengths were obtained by simulating the cone antenna in combination with conducting a mathematical process （Tiknohov Regularization with L curve）. All the typical coupled voltage oscillations displayed multiple peaks and had duration of up to 80ns before decaying into noise and mechanisms of the EMP generation was schematically interpreted in basis of the practical measuring environments. The resultant data were expected to offer basic know-how to achieve inertial confinement fusion.
基金support of the DEVCOM Army Research Laboratory and the Department of Defense SMART scholarship-for-service program.
文摘The maximum flyer impact velocity based on a dynamic solidification cracking mechanism is proposed to describe the upper limit of collision welding process windows.Thus,the upper limit of the weld window is governed by the evolution of dynamic stresses and temperatures at the weld interface.Current formulations for the upper limit of the collision weld window assume that both the flyer and target are made of the same material and approximate stress propagation velocities using the acoustic velocity or the shear wave velocity of the weld material.However,collision welding fundamentally depends on the impacts that generate shockwaves in weld members,which can dominate the stress propagation velocities in thin weld sections.Therefore,this study proposes an alternative weld window upper limit that approximates stress propagation using shock velocities calculated from modified 1-D Rankine-Hugoniot relations.The shock upper limit is validated against the experimental and simulation data in the collision welding literature,and offers a design tool to rapidly predict more accurate optimal collision weld process limits for similar and dissimilar weld couples compared to existing models without the cost or complexity of high-fidelity simulations.
文摘为了研究激光推进技术中液体工质的最优掺杂浓度,进行了激光烧蚀掺杂甘油液体工质的冲量耦合特性实验研究。实验中采用10ns脉宽的Nd:YAG激光器烧蚀粘性液体甘油,在甘油中混合了不同浓度的纳米碳粉作为掺杂剂,以提高对激光能量的吸收。运用阴影测量法观测了激光烧蚀羽流的喷射过程,对不同掺杂浓度甘油的烧蚀产物、等离子体膨胀、激波传播、飞溅现象进行了对比分析;运用激光干涉扭摆法测量了烧蚀冲量,并分析了掺杂浓度对冲量耦合系数的影响。实验结果表明,掺碳后甘油的喷射行为、激波速度和冲量都发生了改变,而且掺碳后甘油的冲量耦合系数和比冲有了显著提高。综合分析得到1%浓度碳粉是甘油的最优掺杂浓度,此时冲量耦合系数从无掺杂时的67 m N·s/J提高到1250m N·s/J。
