A high performance current and voltage measurement system has been developed in power system. The system is composed of two parts: one current measurement element and one voltage measurement element. A Rogowski coil ...A high performance current and voltage measurement system has been developed in power system. The system is composed of two parts: one current measurement element and one voltage measurement element. A Rogowski coil and a capacitive voltage divider are used respectively for the line current and voltage measurements. Active electronic components are used to modulate signal, and power supply for these components is drawn from power line via an auxiliary current transformer. Measurement signal is transmitted by optical fibers, which is resistant to electromagnetic induction and noise. With careful design and the use of digital signal processing technology, the whole system can meet 0.5% accuracy for metering and provides large dynamic range coupled with good accuracy for protective relaying use.展开更多
In this study, compounded surface modification technology-high current pulsed electron beam (HCPEB) + micro-plasma oxidation (MPO) was applied to treat ZK60 Mg alloys. The characteristics of the microstructure of...In this study, compounded surface modification technology-high current pulsed electron beam (HCPEB) + micro-plasma oxidation (MPO) was applied to treat ZK60 Mg alloys. The characteristics of the microstructure of ZK60 Mg alloy after single MPO and HCPEB+MPO compounded treatment were investigated by SEM. The results showed that the density of the ceramic layer of HCPEB+MPO-treated ZK60 Mg alloy was improved and defects were reduced compared to that under MPO treatment alone. Surface modified layer of ZK60 Mg alloys treated by HCPEB+MPO was divided into three zones, namely the top loose ceramic zone, middle compact zone and inside HCPEB-induced melted zone. Corrosion resistance of ZK60 Mg alloy before and after the compounded surface modification was measured in a solution of 3.5% NaCl by potentiodynamic polarization curves. It was found that the corrosion current density of ZK60 Mg alloys could be reduced by about three orders of magnitude, from 311μA/cm^2 of the original sample to 0.2μA/cm^2 of the HCPEB+MPO-treated sample. This indicates the great application potential of the HCPEB+MPO compounded surface modification technology in improving the corrosion resistance of ZK60 Mg alloys in the future.展开更多
The optimized synergy conditions between electron cyclotron current drive (ECCD) and lower hybrid current drive (LHCD) with normal parameters of the EAST tokamak are studied by using the C3PO/LUKE code based on th...The optimized synergy conditions between electron cyclotron current drive (ECCD) and lower hybrid current drive (LHCD) with normal parameters of the EAST tokamak are studied by using the C3PO/LUKE code based on the under- standing of the synergy mechanisms so as to obtain a higher synergistic current and provide theoretical reference for the synergistic effect in the EAST experiment. The dependences of the synergistic effect on the parameters of two waves (lower hybrid wave (LHW) and electron cyclotron wave (ECW)), including the radial position of the power deposition, the power value of the LH and EC waves, and the parallel refractive indices of the LHW (Nr) are oresented and discussed.展开更多
This paper describes a prototype power delivery system developed for high voltage electronic current transformer (ECT) that uses laser light to transfer power to and communicates with the primary converter. The desi...This paper describes a prototype power delivery system developed for high voltage electronic current transformer (ECT) that uses laser light to transfer power to and communicates with the primary converter. The design is based on optical-to-electrical power converters, solid-state diode lasers and optical fibers. Command signals are transmitted via the same up-fiber used to send power from secondary power supply to primary converter. The upward data transmission is completed during the brief interruption of power delivery without affecting steady power-supply. A simple comparator added to the primary converter can take the command data. Experimental results show that the fibers can provide reliable up-link for data transmission at 200 kb/s from the secondary to the primary converter. Based on the delivery system, the secondary converter can control three auxiliary channels to provide additional information. These monitoring channels are used in a time-multiplexing mode to provide information about the operation temperature, voltage and current at the remote unit for monitoring the ECT. This preventive maintenance or built-in test can increase reliability by giving early warning for necessary maintenance request.展开更多
The rate and cycling performances of the electrode materials are affected by many factors in a practical complicated electrode process. Learning about the limiting step in a practical electrochemical reaction is very ...The rate and cycling performances of the electrode materials are affected by many factors in a practical complicated electrode process. Learning about the limiting step in a practical electrochemical reaction is very important to effectively improve the electrochemical performances of the electrode materials. Li4Ti5O12, as a zero-strain material, has been considered as a promising anode material for long life Li-ion batteries. In this study, our results show that the Li4Ti5O12 pasted on Cu or graphite felt current collector exhibits unexpectedly higher rate performance than on A1 current collector. For Li4Ti5O12, the electron transfer between current collector and active material is the critical factor that affects its rate and cycling performances.展开更多
Surface modification of magnesium alloy AZ91HP (9wt%Al, 0.5wt%Zn, 0.5wt%Mn, Mg remaining percentage) by high current pulsed electron beam (HCPEB) treatment was studied in this paper. The secondary phase MgnAln is near...Surface modification of magnesium alloy AZ91HP (9wt%Al, 0.5wt%Zn, 0.5wt%Mn, Mg remaining percentage) by high current pulsed electron beam (HCPEB) treatment was studied in this paper. The secondary phase MgnAln is nearly completely dissolved and as a result, a super-saturated solid solution forms on the re-melted surface. The microhardness is increased both in and far beyond the heat-affected zone (HAZ), reaching about 250um. Measurements on sliding wear have shown that the wear resistance of the treated samples was improved by a factor of about 2.4 as compared to the as-received sample. It is also found that the sliding wear resistance can be further improved by surface alloying with TiN.展开更多
Electron cyclotron current drive (ECCD) will be applied in the EAST tokamak during its the new campaign. In order to provide theoretical predictions for relevant physical experiments, some numerical simulations of E...Electron cyclotron current drive (ECCD) will be applied in the EAST tokamak during its the new campaign. In order to provide theoretical predictions for relevant physical experiments, some numerical simulations of ECCD with the parameters of EAST have been can'ied out by using TORAY-GA code based on the understanding of ECCD mechanisms. ECCD efficiencies achieved in different plasma and electron cyclotron (EC) wave parameters are given. The dependences of ECCD characteristics on EC wave injection angle, toroidal magnetic field, plasma density, and temperature are presented and discussed.展开更多
The surface modification of magnesium alloys (AZ31 and AZ91HP) was studied by a high current pulsed electron beam(HCPEB). The results show that the cross-sectional microhardness of treated samples increases not only i...The surface modification of magnesium alloys (AZ31 and AZ91HP) was studied by a high current pulsed electron beam(HCPEB). The results show that the cross-sectional microhardness of treated samples increases not only in the heat affected zone(HAZ), but also beyond HAZ, reaching over 250μm. This is due to the action of quasi-static thermal stress and the shock thermal stress wave with materials, which result in its fast deformation on the surface layer and so increases microhardness. For the AZ91HP alloy, a nearly complete dissolution of the intermetallic phase Mg_ 17Al_ 12 is observed, and a super-saturated solid solution forms on the re-melted surface, which is due to the solute trapping effect during the fast solidification process. Measurements on sliding wear show that wear resistance is improved by approximately 5.6 and 2.4 times for the AZ31 and AZ91HP respectively, as compared with as-received samples.展开更多
Investigation of neoclassical tearing mode and its suppression by electron cyclotron current drive(ECCD)has been carried out in HL-2 M tokamak.The current driving capability of the electron cyclotron wave is evaluated...Investigation of neoclassical tearing mode and its suppression by electron cyclotron current drive(ECCD)has been carried out in HL-2 M tokamak.The current driving capability of the electron cyclotron wave is evaluated.It is found that the deposition location can be effectively controlled by changing the poloidal angle.The validation of electron cyclotron wave heating and current driving has been demonstrated for the upper launcher port.We show that 3.0 MW and2.5 MW modulated ECCD can completely stabilize(2,1)and(3,2)NTMs,respectively.The non-modulated ECCD,radial misalignment as well as current profile broadening have deleterious effect on the NTM stabilization.The time required for suppression of(3,2)mode is shorter than that required for the suppression of(2,1)mode.Moreover,the time needed for complete stabilization at different initial island width has been quantitatively presented and analyzed.展开更多
In J-TEXT tokamak,fast electron bremsstrahlung diagnostic with 9 chords equipped with multichannel analyzer enables detailed studies of the generation and transport of fast electrons.The spatial profiles and energy sp...In J-TEXT tokamak,fast electron bremsstrahlung diagnostic with 9 chords equipped with multichannel analyzer enables detailed studies of the generation and transport of fast electrons.The spatial profiles and energy spectrum of the fast electrons have been measured in two ECCD cases with either on-axis or off-axis injection,and the profiles processed by Abel-inversion are consistent with the calculated power deposition locations.Moreover,it is observed that the energy of fast electrons increases rapidly after turning off the ECCD,which may be attributed to the acceleration by the recovered loop voltage at low electron density.展开更多
High current pulsed electron beam(HCPEB) is now developing as a useful tool for surface modification of materials.When concentrated electron flux transferring its energy into the surface layer of target material withi...High current pulsed electron beam(HCPEB) is now developing as a useful tool for surface modification of materials.When concentrated electron flux transferring its energy into the surface layer of target material within a short pulse time,coupled thermal and stress processes would lead to the formation of metastalbe microstructure with improved properties.In the present work,HCPEB treatment of 316L stainless steel(SS) was carried out and the microstructural changes in modified surface layer were characterized with optical microscopy,X-ray diffractometry and electron backscatter diffractometry(EBSD) techniques.The corrosion resistance of modified surface was measured in a 5wt.% salt solution.The evolution regularity of surface craters and grain refinement effect,as well as the preferred orientation of(111) crystal plane occurring in the HCPEB treatment under different working parameters were discussed along with their influence on corrosion resistance.展开更多
Electron cyclotron current drive(ECCD) efficiency research is of great importance for the neoclassical tearing mode(NTM) stabilization.Improving ECCD efficiency is beneficial for the NTM stabilization and the ECCD pow...Electron cyclotron current drive(ECCD) efficiency research is of great importance for the neoclassical tearing mode(NTM) stabilization.Improving ECCD efficiency is beneficial for the NTM stabilization and the ECCD power threshold reduction.ECCD efficiency has been investigated on the J-TEXT tokamak.The electron cyclotron wave(ECW) power scan was performed to obtain the current drive efficiency.The current drive efficiency is derived to be approximately η_(0)=(0.06-0.16)×10^(19)A m^(-2)W^(-1)on the J-TEXT tokamak.The effect of the residual toroidal electric field has been included in the determination of the current drive efficiency,which will enhance the ECCD efficiency.At the plasma current of I_(p)=100 kA and electron density of n_(e)=1.5×10^(19)m^(-3),the ratio of Spitzer conductivity between omhic(OH)and ECCD phases is considered and the experimental data have been corrected.The correction results show that the current drive efficiency η_(1)caused by the fast electron hot conductivity decreases by approximately 79%.It can be estimated that the driven current is approximately 24 kA at 300 kW ECW power.展开更多
Nb/Ta multilayer films deposited on Ti6A14V substrate with Nb and Ta monolayer thicknesses of 30 nm, 120 nm, and 240 nm were irradiated by a high current pulse electron beam (HCPEB) to prepare Nb-Ta alloyed layers. ...Nb/Ta multilayer films deposited on Ti6A14V substrate with Nb and Ta monolayer thicknesses of 30 nm, 120 nm, and 240 nm were irradiated by a high current pulse electron beam (HCPEB) to prepare Nb-Ta alloyed layers. The mi- crostructure and the composition of the outmost surface of melted alloyed layers were investigated using a transmission electron microscope (TEM) equipped with an X-ray energy dispersive spectrometer (EDS) attachment. The Ta content of the alloyed surface layer prepared from the monolayer of thickness 30 nm, 120 nm, and 240 nm was- 27.7 at.%, 6.37 at.%, and 0 at.%, respectively. It was found that the Ta content in the alloyed layer plays a dominant role in the microstructure of the films. The hardness and the wear rate of the alloyed layers decrease with the increasing content of Ta in the surface laver.展开更多
Five new electronically-controllable second order current-mode sinusoidal oscillators using three mul-ti-output operational transconductance amplifiers (MO-OTAs) and two grounded capacitors (GC) have been presented. S...Five new electronically-controllable second order current-mode sinusoidal oscillators using three mul-ti-output operational transconductance amplifiers (MO-OTAs) and two grounded capacitors (GC) have been presented. Simulation results are included to confirm the theoretical analysis based upon CMOS OTAs implementable in 0.5 μm technology.展开更多
Dielectric wall accelerator(DWA), towards high gradient acceleration field(30 MeV/m–100 MeV/m), is under development at Institute of Modern Physics. A prototype was designed and constructed to prove the principle. Th...Dielectric wall accelerator(DWA), towards high gradient acceleration field(30 MeV/m–100 MeV/m), is under development at Institute of Modern Physics. A prototype was designed and constructed to prove the principle. This needs a short pulse high current electron source to match the acceleration field generated by the Blumlein-type pulse forming lines(PFLs). In this paper, we report the design and test of a new type short pulse high current electron gun based on principle of vacuum arc discharge. Electron beams of 100 mA with pulse width of 10 ns were obtained.展开更多
The present paper reports the rapid surface alloying induced by the bombardment of high-current pulsed electron beam. Two kinds of substrate materials were examined to show this effect. The first sample was a pure Al ...The present paper reports the rapid surface alloying induced by the bombardment of high-current pulsed electron beam. Two kinds of substrate materials were examined to show this effect. The first sample was a pure Al metal pre-coated with fine carbon powders prior to the bombardment, and the second alloy is the D2-Crl2MolVl mould steel pre-coated with Cr, Ti, and TiN powders. The surface elements diffuse about several micrometers into the substrate materials only after several bombardments. Tribological behaviors of these samples were characterized and significant improvement in wear resistance was found. Finally, a TEM analysis reveals the presence of stress waves generated by coupled thermal and stress fields, which was considered as the main cause of the enhanced properties.展开更多
The effect of applied longitudinal magnetic field on the self-pinched critical current in the intense electron beam diode is discussed. The self-pinched critical current is derived and its validity is tested by numeri...The effect of applied longitudinal magnetic field on the self-pinched critical current in the intense electron beam diode is discussed. The self-pinched critical current is derived and its validity is tested by numerical simulations. The results shows that an applied longitudinal magnetic field tends to increase the self-pinched critical current. Without the effect of anode plasma, the maximal diode current approximately equals the self-pinched critical current with the longitudinal magnetic field applied; when self-pinched occurs, the diode current approaches the self-pinched critical current.展开更多
This paper investigates the impact of electrical degradation and current collapse on different thickness SiNx passivated AlGaN/GaN high electron mobility transistors. It finds that higher thickness SiNx passivation ca...This paper investigates the impact of electrical degradation and current collapse on different thickness SiNx passivated AlGaN/GaN high electron mobility transistors. It finds that higher thickness SiNx passivation can significantly improve the high-electric-field reliability of a device. The degradation mechanism of the SiNx passivation layer under ON-state stress has also been discussed in detail. Under the ON-state stress, the strong electric-field led to degradation of SiNx passivation located in the gate-drain region. As the thickness of SiNx passivation increases, the density of the surface state will be increased to some extent. Meanwhile, it is found that the high NH3 flow in the plasma enhanced chemical vapour deposition process could reduce the surface state and suppress the current collapse.展开更多
The modified microstructure of Al-Si-Pb alloys irradiated by high current electron beam (HCPEB) reveals three distinct regions: a molten zone, an overlapped zone of heat-affected and quasistatic thermal stress-affecte...The modified microstructure of Al-Si-Pb alloys irradiated by high current electron beam (HCPEB) reveals three distinct regions: a molten zone, an overlapped zone of heat-affected and quasistatic thermal stress-affected zone, and a transition zone followed by the substrate. The hardness and wear properties of the alloys were significantly improved. To better understand these changes in microstructure and properties, the physical model for the simulation of temperature and quasistatic stress fields was established. Based on experimental investigation and physical models, the temperature field and stress field were simulated for Al-Si-Pb alloy. The starting melting position, largest crater depth, melting layer thickness, and quasistatic stress distribution were obtained. These results reveal the mechanism of crater formation on the surface and improvement of hardness and wear resistance.展开更多
文摘A high performance current and voltage measurement system has been developed in power system. The system is composed of two parts: one current measurement element and one voltage measurement element. A Rogowski coil and a capacitive voltage divider are used respectively for the line current and voltage measurements. Active electronic components are used to modulate signal, and power supply for these components is drawn from power line via an auxiliary current transformer. Measurement signal is transmitted by optical fibers, which is resistant to electromagnetic induction and noise. With careful design and the use of digital signal processing technology, the whole system can meet 0.5% accuracy for metering and provides large dynamic range coupled with good accuracy for protective relaying use.
基金supported by Liaoning BaiQianWan Talents Program of China (No. 2008921028)Doctoral Fund of Ministry of Education of China (No. 200801451082)
文摘In this study, compounded surface modification technology-high current pulsed electron beam (HCPEB) + micro-plasma oxidation (MPO) was applied to treat ZK60 Mg alloys. The characteristics of the microstructure of ZK60 Mg alloy after single MPO and HCPEB+MPO compounded treatment were investigated by SEM. The results showed that the density of the ceramic layer of HCPEB+MPO-treated ZK60 Mg alloy was improved and defects were reduced compared to that under MPO treatment alone. Surface modified layer of ZK60 Mg alloys treated by HCPEB+MPO was divided into three zones, namely the top loose ceramic zone, middle compact zone and inside HCPEB-induced melted zone. Corrosion resistance of ZK60 Mg alloy before and after the compounded surface modification was measured in a solution of 3.5% NaCl by potentiodynamic polarization curves. It was found that the corrosion current density of ZK60 Mg alloys could be reduced by about three orders of magnitude, from 311μA/cm^2 of the original sample to 0.2μA/cm^2 of the HCPEB+MPO-treated sample. This indicates the great application potential of the HCPEB+MPO compounded surface modification technology in improving the corrosion resistance of ZK60 Mg alloys in the future.
基金supported by the National Magnetic Confinement Fusion Science Program of China(Grant Nos.2011GB102000,2012GB103000,2013GB106001,and2015GB102003)the National Natural Science Foundation of China(Grant Nos.11175206 and 11305211)+1 种基金the JSPS-NRF-NSFC A3 Foresight Program in the Field of Plasma Physics(Grant No.11261140328)the Fundamental Research Funds for the Central Universities of China(Grant No.JZ2015HGBZ0472)
文摘The optimized synergy conditions between electron cyclotron current drive (ECCD) and lower hybrid current drive (LHCD) with normal parameters of the EAST tokamak are studied by using the C3PO/LUKE code based on the under- standing of the synergy mechanisms so as to obtain a higher synergistic current and provide theoretical reference for the synergistic effect in the EAST experiment. The dependences of the synergistic effect on the parameters of two waves (lower hybrid wave (LHW) and electron cyclotron wave (ECW)), including the radial position of the power deposition, the power value of the LH and EC waves, and the parallel refractive indices of the LHW (Nr) are oresented and discussed.
基金Project supported by the National Natural Science Foundation of China (Grant No.50447006)
文摘This paper describes a prototype power delivery system developed for high voltage electronic current transformer (ECT) that uses laser light to transfer power to and communicates with the primary converter. The design is based on optical-to-electrical power converters, solid-state diode lasers and optical fibers. Command signals are transmitted via the same up-fiber used to send power from secondary power supply to primary converter. The upward data transmission is completed during the brief interruption of power delivery without affecting steady power-supply. A simple comparator added to the primary converter can take the command data. Experimental results show that the fibers can provide reliable up-link for data transmission at 200 kb/s from the secondary to the primary converter. Based on the delivery system, the secondary converter can control three auxiliary channels to provide additional information. These monitoring channels are used in a time-multiplexing mode to provide information about the operation temperature, voltage and current at the remote unit for monitoring the ECT. This preventive maintenance or built-in test can increase reliability by giving early warning for necessary maintenance request.
基金supported by the "Hundred Talent Project" of the Chinese Academy of Sciencesthe National High Technology Research and Development Program of China(Grant No.2009AA033101)+3 种基金the National Basic Research Program of China(Grant Nos.2007CB936500 and 2010CB833102)the National Natural Science Foundation of China(Grant No.50972164)the Science and Technology Planning Project of Guangdong Province,China(Grant No.2010A090602001)the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No.KJCX2-YW-W26)
文摘The rate and cycling performances of the electrode materials are affected by many factors in a practical complicated electrode process. Learning about the limiting step in a practical electrochemical reaction is very important to effectively improve the electrochemical performances of the electrode materials. Li4Ti5O12, as a zero-strain material, has been considered as a promising anode material for long life Li-ion batteries. In this study, our results show that the Li4Ti5O12 pasted on Cu or graphite felt current collector exhibits unexpectedly higher rate performance than on A1 current collector. For Li4Ti5O12, the electron transfer between current collector and active material is the critical factor that affects its rate and cycling performances.
文摘Surface modification of magnesium alloy AZ91HP (9wt%Al, 0.5wt%Zn, 0.5wt%Mn, Mg remaining percentage) by high current pulsed electron beam (HCPEB) treatment was studied in this paper. The secondary phase MgnAln is nearly completely dissolved and as a result, a super-saturated solid solution forms on the re-melted surface. The microhardness is increased both in and far beyond the heat-affected zone (HAZ), reaching about 250um. Measurements on sliding wear have shown that the wear resistance of the treated samples was improved by a factor of about 2.4 as compared to the as-received sample. It is also found that the sliding wear resistance can be further improved by surface alloying with TiN.
基金Project supported by the National Magnetic Confinement Fusion Science Program of China(Grant No.2011GB102000)the National Natural Science Foundation of China(Grant Nos.11175206 and 11305211)
文摘Electron cyclotron current drive (ECCD) will be applied in the EAST tokamak during its the new campaign. In order to provide theoretical predictions for relevant physical experiments, some numerical simulations of ECCD with the parameters of EAST have been can'ied out by using TORAY-GA code based on the understanding of ECCD mechanisms. ECCD efficiencies achieved in different plasma and electron cyclotron (EC) wave parameters are given. The dependences of ECCD characteristics on EC wave injection angle, toroidal magnetic field, plasma density, and temperature are presented and discussed.
文摘The surface modification of magnesium alloys (AZ31 and AZ91HP) was studied by a high current pulsed electron beam(HCPEB). The results show that the cross-sectional microhardness of treated samples increases not only in the heat affected zone(HAZ), but also beyond HAZ, reaching over 250μm. This is due to the action of quasi-static thermal stress and the shock thermal stress wave with materials, which result in its fast deformation on the surface layer and so increases microhardness. For the AZ91HP alloy, a nearly complete dissolution of the intermetallic phase Mg_ 17Al_ 12 is observed, and a super-saturated solid solution forms on the re-melted surface, which is due to the solute trapping effect during the fast solidification process. Measurements on sliding wear show that wear resistance is improved by approximately 5.6 and 2.4 times for the AZ31 and AZ91HP respectively, as compared with as-received samples.
基金the National Key Research and Development Program of China(Grant Nos.2018YFE0303102,2018YFE0301100,and2017YFE0301702)the National Natural Science Foundation of China(Grant Nos.11905109 and 11947238)+1 种基金U.S.DOE Sci DAC ISEP,users with Excellence Program(on EAST tokamak)of Hefei Science Center CAS under(Grant No.2021HSC-UE017)the Center for Computational Science and Engineering of Southern University of Science and Technology。
文摘Investigation of neoclassical tearing mode and its suppression by electron cyclotron current drive(ECCD)has been carried out in HL-2 M tokamak.The current driving capability of the electron cyclotron wave is evaluated.It is found that the deposition location can be effectively controlled by changing the poloidal angle.The validation of electron cyclotron wave heating and current driving has been demonstrated for the upper launcher port.We show that 3.0 MW and2.5 MW modulated ECCD can completely stabilize(2,1)and(3,2)NTMs,respectively.The non-modulated ECCD,radial misalignment as well as current profile broadening have deleterious effect on the NTM stabilization.The time required for suppression of(3,2)mode is shorter than that required for the suppression of(2,1)mode.Moreover,the time needed for complete stabilization at different initial island width has been quantitatively presented and analyzed.
基金the National Key R&D Program of China(Nos.2017YFE0302000,2018YFE0309103,2019YFE030-10004,2017YFE0300501,2018YFE0310300,2018YFE0309100)National Natural Science Foundation of China(Nos.11775089,51821005,11905077 and 11575068)the China Postdoctoral Science Foundation(No.2019M652615)。
文摘In J-TEXT tokamak,fast electron bremsstrahlung diagnostic with 9 chords equipped with multichannel analyzer enables detailed studies of the generation and transport of fast electrons.The spatial profiles and energy spectrum of the fast electrons have been measured in two ECCD cases with either on-axis or off-axis injection,and the profiles processed by Abel-inversion are consistent with the calculated power deposition locations.Moreover,it is observed that the energy of fast electrons increases rapidly after turning off the ECCD,which may be attributed to the acceleration by the recovered loop voltage at low electron density.
基金This work is financially supported by Scientific Research Foundation for the Returned Overseas Chinese Scholars and Franco-China Cooperative Research Program between University of Metz and Dalian Uni-versity of Technology(2004)
文摘High current pulsed electron beam(HCPEB) is now developing as a useful tool for surface modification of materials.When concentrated electron flux transferring its energy into the surface layer of target material within a short pulse time,coupled thermal and stress processes would lead to the formation of metastalbe microstructure with improved properties.In the present work,HCPEB treatment of 316L stainless steel(SS) was carried out and the microstructural changes in modified surface layer were characterized with optical microscopy,X-ray diffractometry and electron backscatter diffractometry(EBSD) techniques.The corrosion resistance of modified surface was measured in a 5wt.% salt solution.The evolution regularity of surface craters and grain refinement effect,as well as the preferred orientation of(111) crystal plane occurring in the HCPEB treatment under different working parameters were discussed along with their influence on corrosion resistance.
基金supported by the National Magnetic Confinement Fusion Energy R&D Program of China(No.2019YFE03010004)the National Key R&D Program ofChina(No.2018YFE0309100)National Natural Science Foundation of China(Nos.11775089,11905077,51821005)
文摘Electron cyclotron current drive(ECCD) efficiency research is of great importance for the neoclassical tearing mode(NTM) stabilization.Improving ECCD efficiency is beneficial for the NTM stabilization and the ECCD power threshold reduction.ECCD efficiency has been investigated on the J-TEXT tokamak.The electron cyclotron wave(ECW) power scan was performed to obtain the current drive efficiency.The current drive efficiency is derived to be approximately η_(0)=(0.06-0.16)×10^(19)A m^(-2)W^(-1)on the J-TEXT tokamak.The effect of the residual toroidal electric field has been included in the determination of the current drive efficiency,which will enhance the ECCD efficiency.At the plasma current of I_(p)=100 kA and electron density of n_(e)=1.5×10^(19)m^(-3),the ratio of Spitzer conductivity between omhic(OH)and ECCD phases is considered and the experimental data have been corrected.The correction results show that the current drive efficiency η_(1)caused by the fast electron hot conductivity decreases by approximately 79%.It can be estimated that the driven current is approximately 24 kA at 300 kW ECW power.
基金Project supported by the National Basic Research Program of China (Grant No. 2013CB632305)the Guangdong Province University-Industry Cooperation Project of the Ministry of Education, China (Grant No. 2010B090400444)+1 种基金the Guangdong International Cooperation Projects, China (Grant No. 2010B050900003)the Guangdong Science and Technology Plan Projects, China (Grant No. 2010A070500002)
文摘Nb/Ta multilayer films deposited on Ti6A14V substrate with Nb and Ta monolayer thicknesses of 30 nm, 120 nm, and 240 nm were irradiated by a high current pulse electron beam (HCPEB) to prepare Nb-Ta alloyed layers. The mi- crostructure and the composition of the outmost surface of melted alloyed layers were investigated using a transmission electron microscope (TEM) equipped with an X-ray energy dispersive spectrometer (EDS) attachment. The Ta content of the alloyed surface layer prepared from the monolayer of thickness 30 nm, 120 nm, and 240 nm was- 27.7 at.%, 6.37 at.%, and 0 at.%, respectively. It was found that the Ta content in the alloyed layer plays a dominant role in the microstructure of the films. The hardness and the wear rate of the alloyed layers decrease with the increasing content of Ta in the surface laver.
文摘Five new electronically-controllable second order current-mode sinusoidal oscillators using three mul-ti-output operational transconductance amplifiers (MO-OTAs) and two grounded capacitors (GC) have been presented. Simulation results are included to confirm the theoretical analysis based upon CMOS OTAs implementable in 0.5 μm technology.
基金Supported by knowledge innovation project of Chinese academy of sciences(No.Y115280YZD)the National Natural Science Foundation of China(No.11105195 and No.11105197)
文摘Dielectric wall accelerator(DWA), towards high gradient acceleration field(30 MeV/m–100 MeV/m), is under development at Institute of Modern Physics. A prototype was designed and constructed to prove the principle. This needs a short pulse high current electron source to match the acceleration field generated by the Blumlein-type pulse forming lines(PFLs). In this paper, we report the design and test of a new type short pulse high current electron gun based on principle of vacuum arc discharge. Electron beams of 100 mA with pulse width of 10 ns were obtained.
文摘The present paper reports the rapid surface alloying induced by the bombardment of high-current pulsed electron beam. Two kinds of substrate materials were examined to show this effect. The first sample was a pure Al metal pre-coated with fine carbon powders prior to the bombardment, and the second alloy is the D2-Crl2MolVl mould steel pre-coated with Cr, Ti, and TiN powders. The surface elements diffuse about several micrometers into the substrate materials only after several bombardments. Tribological behaviors of these samples were characterized and significant improvement in wear resistance was found. Finally, a TEM analysis reveals the presence of stress waves generated by coupled thermal and stress fields, which was considered as the main cause of the enhanced properties.
文摘The effect of applied longitudinal magnetic field on the self-pinched critical current in the intense electron beam diode is discussed. The self-pinched critical current is derived and its validity is tested by numerical simulations. The results shows that an applied longitudinal magnetic field tends to increase the self-pinched critical current. Without the effect of anode plasma, the maximal diode current approximately equals the self-pinched critical current with the longitudinal magnetic field applied; when self-pinched occurs, the diode current approaches the self-pinched critical current.
基金Project supported by the State Key Program of National Natural Science Foundation of China (Grant No. 60736033)
文摘This paper investigates the impact of electrical degradation and current collapse on different thickness SiNx passivated AlGaN/GaN high electron mobility transistors. It finds that higher thickness SiNx passivation can significantly improve the high-electric-field reliability of a device. The degradation mechanism of the SiNx passivation layer under ON-state stress has also been discussed in detail. Under the ON-state stress, the strong electric-field led to degradation of SiNx passivation located in the gate-drain region. As the thickness of SiNx passivation increases, the density of the surface state will be increased to some extent. Meanwhile, it is found that the high NH3 flow in the plasma enhanced chemical vapour deposition process could reduce the surface state and suppress the current collapse.
基金Project(50375063) supported by the National Natural Science Foundation of China
文摘The modified microstructure of Al-Si-Pb alloys irradiated by high current electron beam (HCPEB) reveals three distinct regions: a molten zone, an overlapped zone of heat-affected and quasistatic thermal stress-affected zone, and a transition zone followed by the substrate. The hardness and wear properties of the alloys were significantly improved. To better understand these changes in microstructure and properties, the physical model for the simulation of temperature and quasistatic stress fields was established. Based on experimental investigation and physical models, the temperature field and stress field were simulated for Al-Si-Pb alloy. The starting melting position, largest crater depth, melting layer thickness, and quasistatic stress distribution were obtained. These results reveal the mechanism of crater formation on the surface and improvement of hardness and wear resistance.