The Shanghai High Repetition Rate XFEL and Extreme Light Facility(SHINE)project will use 6001.3 GHz fundamental power couplers,which are modified based on TTF-Ⅲ power couplers,for continuous-wave operation with input...The Shanghai High Repetition Rate XFEL and Extreme Light Facility(SHINE)project will use 6001.3 GHz fundamental power couplers,which are modified based on TTF-Ⅲ power couplers,for continuous-wave operation with input power up to approximately 7 kW.The first batch of 20 sets of 1.3 GHz coupler prototypes was fabricated from three domestic manufacturers for the SHINE project.To better characterize the radio frequency conditioning phenomena for validating the performance of power couplers,a room temperature test stand was designed,constructed,and commissioned for the SHINE 1.3 GHz power couplers.In addition,a horizontal test cryostat was built to test the 1.3 GHz superconducting cavities,fundamental power couplers,tuners,and other components as a set.The results of these tests indicate that the 1.3 GHz couplers are capable of handling up to 14 kW continuous waves.Herein,the main aspects of the radio frequency design and construction of the test stand,along with the test results of the high-power conditioning of the 1.3 GHz couplers,are described.展开更多
The research and development of high temperature superconducting （HTS） films, especially ReBa2Cu3- O7-δ （REBCO or RE123; RE=Y, Gd, or other rare earths） yttrium-based coated conductors, has generated widespread i...The research and development of high temperature superconducting （HTS） films, especially ReBa2Cu3- O7-δ （REBCO or RE123; RE=Y, Gd, or other rare earths） yttrium-based coated conductors, has generated widespread interest for the potential applications of the second generation superconducting films. In view of commercialization, however, the maximum superconducting currents for coated conductors should be increased further. Unfortunately, it has been frequently observed that the average critical current density Jc decreases with an increase in film thickness. The thickness effect is still a hurdle for largescale production, especially in pulsed laser deposition and metal organic deposition processes. An engineering current of more than 1 000 A/cm is desired owing to the high cost of 2G superconducting materials. The present work attempts to review the evolution of various issues subject to the thickness effect, including the microstructure, epitaxial texture, surface roughness, pinning force, oxygen deficiency, residual stress, copper-rich layers, and segregation of elements. Furthermore, recent progress in enhancing the performance of superconductors especially in terms of critical current density is illustrated, such as the use of heavy doping. Further understanding of the thickness effect is extremely important for large-scale commercial development of the second generation high temperature superconductors.展开更多
We propose a medium access control(MAC) protocol for uplink transmissions in wireless local area networks(WLANs),where both stations and access points(APs) are equipped with multiple antennas. The protocol solves some...We propose a medium access control(MAC) protocol for uplink transmissions in wireless local area networks(WLANs),where both stations and access points(APs) are equipped with multiple antennas. The protocol solves some common problems in utilizing multiple input multiple output(MIMO) under the 802.11 protocol,e.g.,how to deploy preamble(training sequence) used for channel estimation and how to enable simultaneous data transmissions,and facilitates two simultaneous uplink data transmissions via a cross-layer approach. Furthermore,we develop a 3D discrete-time Markov model to analyze the per-formance of the proposed WLAN scheme. The analytical results are verified by simulation,and numerical results show that the system throughput can be significantly improved by our proposed scheme as compared with conventional schemes.展开更多
基金supported by Shanghai Municipal Science and Technology Major Project(No.2017SHZDZX02)。
文摘The Shanghai High Repetition Rate XFEL and Extreme Light Facility(SHINE)project will use 6001.3 GHz fundamental power couplers,which are modified based on TTF-Ⅲ power couplers,for continuous-wave operation with input power up to approximately 7 kW.The first batch of 20 sets of 1.3 GHz coupler prototypes was fabricated from three domestic manufacturers for the SHINE project.To better characterize the radio frequency conditioning phenomena for validating the performance of power couplers,a room temperature test stand was designed,constructed,and commissioned for the SHINE 1.3 GHz power couplers.In addition,a horizontal test cryostat was built to test the 1.3 GHz superconducting cavities,fundamental power couplers,tuners,and other components as a set.The results of these tests indicate that the 1.3 GHz couplers are capable of handling up to 14 kW continuous waves.Herein,the main aspects of the radio frequency design and construction of the test stand,along with the test results of the high-power conditioning of the 1.3 GHz couplers,are described.
基金Project supported by the National Key Research and Development Program of China(No.2018YFD0400305)the Modern Agro-industry Technology Research System of China(No.CARS-40-K26)the“One Belt and One Road”International Science and Technology Cooperation Program of Zhejiang,China(No.2019C04022)。
基金This work was supported in part by Shanghai Key Laboratory of High Temperature Superconductors （Grant No. 14DZ2260700）, the Science and Technology Commission of Shanghai Municipality （Grant Nos. 13111102300 and 14521102800）, and the National Natural Science Foundation of China （Grant Nos. 51572165, 11174193 and 51202141）.
文摘The research and development of high temperature superconducting （HTS） films, especially ReBa2Cu3- O7-δ （REBCO or RE123; RE=Y, Gd, or other rare earths） yttrium-based coated conductors, has generated widespread interest for the potential applications of the second generation superconducting films. In view of commercialization, however, the maximum superconducting currents for coated conductors should be increased further. Unfortunately, it has been frequently observed that the average critical current density Jc decreases with an increase in film thickness. The thickness effect is still a hurdle for largescale production, especially in pulsed laser deposition and metal organic deposition processes. An engineering current of more than 1 000 A/cm is desired owing to the high cost of 2G superconducting materials. The present work attempts to review the evolution of various issues subject to the thickness effect, including the microstructure, epitaxial texture, surface roughness, pinning force, oxygen deficiency, residual stress, copper-rich layers, and segregation of elements. Furthermore, recent progress in enhancing the performance of superconductors especially in terms of critical current density is illustrated, such as the use of heavy doping. Further understanding of the thickness effect is extremely important for large-scale commercial development of the second generation high temperature superconductors.
基金supported by the National Natural Science Foundation of China (No. 60832008)the Research Grants Council Joint Research Scheme National Natural Science Foundation of China (No. 60731160013)
文摘We propose a medium access control(MAC) protocol for uplink transmissions in wireless local area networks(WLANs),where both stations and access points(APs) are equipped with multiple antennas. The protocol solves some common problems in utilizing multiple input multiple output(MIMO) under the 802.11 protocol,e.g.,how to deploy preamble(training sequence) used for channel estimation and how to enable simultaneous data transmissions,and facilitates two simultaneous uplink data transmissions via a cross-layer approach. Furthermore,we develop a 3D discrete-time Markov model to analyze the per-formance of the proposed WLAN scheme. The analytical results are verified by simulation,and numerical results show that the system throughput can be significantly improved by our proposed scheme as compared with conventional schemes.
