We report the world-leading performance of a 1.3 GHz cryomodule equipped with eight 9-cell superconducting radio-frequency cavities that underwent a medium-temperature furnace baking process.During continuous wave hor...We report the world-leading performance of a 1.3 GHz cryomodule equipped with eight 9-cell superconducting radio-frequency cavities that underwent a medium-temperature furnace baking process.During continuous wave horizontal testing,these cavities achieved unprecedented average intrinsic quality factors of 4.0×10^(10)at 20 MV/m and 3.2×10^(10)at 29 MV/m,with no instances of field emission.The cryomodule demonstrates near-complete preservation of ultra-high quality factors and ultra-high accelerating gradients from vertical to horizontal testing,marking a significant milestone in continuous-wave superconducting radio-frequency accelerator technology.This letter presents the cryomodule development experience,includ-ing cavity preparation,cryomodule assembly,degaussing,fast cooldown,and performance testing.展开更多
Alcohol oxidation is a widely used green chemical reaction.The reaction process produces flammable and explosive hydrogen,so the design of the reactor must meet stringent safety requirements.Based on the limited exper...Alcohol oxidation is a widely used green chemical reaction.The reaction process produces flammable and explosive hydrogen,so the design of the reactor must meet stringent safety requirements.Based on the limited experimental data,utilizing the traditional numerical method of computational fluid dynamics(CFD)to simulate the gas-liquid two-phase flow reactor can mitigate the risk of danger under varying working conditions.However,the calculation process is highly time-consuming.Therefore,by integrating process simulation,computational fluid dynamics,and deep learning technologies,an intelligent hybrid chemical model based on machine learning was proposed to expedite CFD calculations,enhance the prediction of flow fields,conversion rates,and concentrations inside the reactor,and offer insights for designing and optimizing the reactor for the alcohol oxidation system.The results show that the hybrid model based on the long and short-term memory neural network achieves 99.8%accuracy in conversion rate prediction and 99.9%accuracy in product concentration prediction.Through validation,the hybrid model is accelerated by about 360 times compared with instrumental analysis in conversion rate prediction and about 45 times compared with CFD calculation in concentration distribution prediction.This hybrid model can quickly predict the conversion rate and product concentration distribution in the gas-liquid two-phase flow reactor and provide a model reference for fast prediction and accurate control in the actual chemical production process.展开更多
Very high-energy electrons(VHEEs)are potential candidates for FLASH radiotherapy for deep-seated tumors.We proposed a compact VHEE facility based on an X-band high-gradient high-power technique.In this study,we invest...Very high-energy electrons(VHEEs)are potential candidates for FLASH radiotherapy for deep-seated tumors.We proposed a compact VHEE facility based on an X-band high-gradient high-power technique.In this study,we investigated and realized the first X-band backward traveling-wave(BTW)accelerating structure as the buncher for a VHEE facility.A method for calculating the parameters of single cell from the field distribution was introduced to simplify the design of the BTW structure.Time-domain circuit equations were applied to calculate the transient beam parameters of the buncher in the unsteady state.A prototype of the BTW structure with a thermionic cathode-diode electron gun was designed,fabricated,and tested at high power at the Tsinghua X-band high-power test stand.The structure successfully operated with 5-MW microwave pulses from the pulse compressor and outputted electron bunches with an energy of 8 MeV and a pulsed current of 108 mA.展开更多
In order to design the relief system size of di-tert-butyl peroxide(DTBP) storage tanks,the runaway re-action of DTBP was simulated by accelerating rate calorimeter(ARC).The results indicated that under adiabatic cond...In order to design the relief system size of di-tert-butyl peroxide(DTBP) storage tanks,the runaway re-action of DTBP was simulated by accelerating rate calorimeter(ARC).The results indicated that under adiabatic conditions the initial exothermic temperature was 102.6 ℃,the maximum self-heating rate was 3.095×107 ℃·min-1,the maximum self-heating temperature was 375.9 ℃,and the pressure produced by unit mass was 4.512 MPa·g-1.Judged by ARC test,the emergency relief system for DTBP was a hybrid system.Based on Design Institute for Emergency Relief System(DIERS) method,the releasing mass flow rate W was determined by Leung methods,and the mass velocity G was calculated by two modified Omega methods.The two relief sizes calculated by monograph Omega method and arithmetic Omega method are close,with only 0.63% relative error.The monograph Omega method is more convenient to apply.展开更多
There are many accelerating convergence factors (ACFs) for limit periodic continued fraction K(an/1)(an→a≠0). In this paper, some characteristics and comparative theorems are ob tained on ACFs. Two results are given...There are many accelerating convergence factors (ACFs) for limit periodic continued fraction K(an/1)(an→a≠0). In this paper, some characteristics and comparative theorems are ob tained on ACFs. Two results are given for most frequently used ACFs.展开更多
An S-band high-gradient accelerating structure is designed for a proton therapy linear accelerator(linac)to accommodate the new development of compact,singleroom facilities and ultra-high dose rate(FLASH)radiotherapy....An S-band high-gradient accelerating structure is designed for a proton therapy linear accelerator(linac)to accommodate the new development of compact,singleroom facilities and ultra-high dose rate(FLASH)radiotherapy.To optimize the design,an efficient optimization scheme is applied to improve the simulation efficiency.An S-band accelerating structure with 2856 MHz is designed with a low beta of 0.38,which is a difficult structure to achieve for a linac accelerating proton particles from 70 to 250 MeV,as a high gradient up to 50 MV/m is required.A special design involving a dual-feed coupler eliminates the dipole field effect.This paper presents all the details pertaining to the design,fabrication,and cold test results of the S-band high-gradient accelerating structure.展开更多
To investigate the principal resonance in transverse nonlinear parametric vibration of an axially accelerating viscoelastic string,the method of multiple scales is applied directly to the nonlinear partial differentia...To investigate the principal resonance in transverse nonlinear parametric vibration of an axially accelerating viscoelastic string,the method of multiple scales is applied directly to the nonlinear partial differential equation that governs the transverse vibration of the string.To derive the governing equation,Newton's second law,Lagrangean strain,and Kelvin's model are respectively used to account the dynamical relation,geometric nonlinearity and the viscoelasticity of the string material. Based on the solvability condition of eliminating the secular terms,closed form solutions are obtained for the amplitude and the existence conditions of nontrivial steady-state response of the principal parametric resonance.The Lyapunov linearized stability theory is employed to analyze the stability of the trivial and nontrivial solutions in the principal parametric resonance.Some numerical examples are presented to show the effects of the mean transport speed,the amplitude and the frequency of speed variation.展开更多
The physical design and cooling test of a C-band 2MeV standing wave （SW） accelerating tube are described in this paper. The designed accelerating structure consists of 3-cell buncher and 4-cell accelerating section ...The physical design and cooling test of a C-band 2MeV standing wave （SW） accelerating tube are described in this paper. The designed accelerating structure consists of 3-cell buncher and 4-cell accelerating section with a total length of about 163mm, excited with 1MW magnetron. Dynamic simulation presents that about 150mA beam pulse current and 30% capture efficiency can be achieved. By means of nonlinear Gauss fit on electron transverse distribution, the diameter of beam spot FWHM （full width at half maximum of density distribution） is about 0.55mm. Cooling test results of the accelerating tube show that frequencies of cavities are tuned to 5527MHz and the field distribution of bunching section is about 3：9：10.展开更多
The development of a high-gradient accelerating structure is underway to construct a compact proton linear accelerator for cancer treatment.Extensive experiments and numerous studies are being conducted to develop com...The development of a high-gradient accelerating structure is underway to construct a compact proton linear accelerator for cancer treatment.Extensive experiments and numerous studies are being conducted to develop compact linear accelerators for proton therapy.Optimization of the electromagnetic and mechanical design has been performed to simplify the manufacturing process and reduce costs.A novel high-gradient structure with a low relativistic proton velocity(β),v/c=0.38,was designed,fabricated,and tested at high power.The first full-scale prototype was also successfully tested with high radio frequency(RF)power,a repetition rate of 50 Hz,and pulse length of 3μs to reach a high-gradient of 46 MV/m using a 50 MW S-band klystron power supply obtained from the Shanghai Soft X-ray Free Electron Laser Facility.This is the first high-power test in China,which is in line with the expected experimental goal.This study presents preliminary high-power testing of S-band standing wave accelerating structures with 11 cells.This work aims to verify the feasibility of using a high-gradient RF accelerating structure in compact proton therapy facilities.The cold test of the prototype cavity was completed in advance.Details of the high-power RF test setup,the process of RF conditioning,and the high-power results are described.展开更多
Two 650 MHz single-cell superconducting radio-frequency(SRF)cavities used for the Circular Electron Positron Collider(CEPC)were studied to achieve a high accelerating gradient(E_(acc))and high intrinsic quality factor...Two 650 MHz single-cell superconducting radio-frequency(SRF)cavities used for the Circular Electron Positron Collider(CEPC)were studied to achieve a high accelerating gradient(E_(acc))and high intrinsic quality factor(Q_(0)).The 650 MHz single-cell cavities were subjected to a combination of buffered chemical polishing(BCP)and electropolishing(EP),and their E_(acc) exceeded40 MV/m.Such a high E_(acc) may result from the cold EP with more uniform removal.BCP is easy,cheap,and rough,whereas EP is complicated,expensive,and precise Therefore,the combination of BCP and EP investigated in this study is suitable for surface treatments of mass SRF cavities.Medium temperature(mid-T)furnace baking was also conducted,which demonstrated an ultrahigh Q_(0) of 8×10^(10) at 22 MV/m for both cavities,and an extremely low BCS resistance(R_(BCS))of~1.0 nΩwas achieved a2.0 K.展开更多
X-ray Talbot-Lau interferometer has been used most widely to perform x-ray phase-contrast imaging with a con- ventional low-brilliance x-ray source, and it yields high-sensitivity phase and dark-field images of sample...X-ray Talbot-Lau interferometer has been used most widely to perform x-ray phase-contrast imaging with a con- ventional low-brilliance x-ray source, and it yields high-sensitivity phase and dark-field images of samples producing low absorption contrast, thus beating tremendous potential for future clinical diagnosis. In this work, by changing the accel- erating voltage of the x-ray tube from 35 kV to 45 kV, x-ray phase-contrast imaging of a test sample is performed at each integer value of the accelerating voltage to investigate the characteristic of an x-ray Talbot-Lau interferometer （located in the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan） versus tube voltage. Ex- perimental results and data analysis show that within a range this x-ray Talbot-Lau interferometer is not sensitive to the accelerating voltage of the tube with a constant fringe visibility of ~ 44%. This x-ray Talbot-Lau interferometer research demonstrates the feasibility of a new dual energy phase-contrast x-ray imaging strategy and the possibility to collect a refraction spectrum.展开更多
The main measures to accelerate leaching sulfide ore are large spraying intensity,manual oxygen supply,temperature control,and acclimated bacteria.The indoor experiment accelerating sulfide ore leaching detected the t...The main measures to accelerate leaching sulfide ore are large spraying intensity,manual oxygen supply,temperature control,and acclimated bacteria.The indoor experiment accelerating sulfide ore leaching detected the temperature during leaching process,dissolvability of oxygen,bacterial concentration,Cu concentration and slag grade.At the same time,this paper also analyzed the effect of four factors,which are bacterial diversity cultivation stage,spraying intensity,air supply,and whether to control temperature,on the leaching efficiency of copper.The results indicate that the oxygen content of leach solution has a close relationship with temperature but it is rarely affected by air supply.The bacterial concentration preserves from 106 to 107 mL^-1,and temperature has a great effect on the bacterial activity under the condition of proper temperature and oxygen supply,and the lack of nutrition prevents the bacterial concentration from rising in the late stage.The relationships of the copper leaching efficiency to temperature,air feed,and spraying intensity are directly proportional.The leaching efficiencies of the cultivated bacteria and acclimation bacteria are 1.2 and 1.4 times as large as that of the original bacteria.展开更多
The infiltration kinetics of the metal melt into a fibrous preform in centrifugal accelerating field is analyzed on the basis of Darcy's law and the assumption that the fibrous preform is treated as 'bundle of...The infiltration kinetics of the metal melt into a fibrous preform in centrifugal accelerating field is analyzed on the basis of Darcy's law and the assumption that the fibrous preform is treated as 'bundle of capillaries' The critical rotating speed is analyzed with the established model The influences of the metal melt mass,the rotating speed of the equipment,the casting height, the original outer radius of the metal melt and the fibrous volume fraction in fibrous preform on infilatration are studied The results show that the critical rotating speed is dependent on critical pressure, casting height, metal melt mass and the character of fibrous preform With the increase in the metal melt mass, rotating speed of the equipment and original outer radius of the metal melt, or the decrease in casting height and fibrous volume fraction in fibrous of the metal melt,or the decrease in casting height and fibrous volume fraction in fibrous preform,infiltration of metal melt for fibrous preform becomes easier.展开更多
Based on continuum theory and moving law of particles, a model is presentedto obtain gradient distribution of particles in centrifugal accelerating field, by which theparticle distribution in gradient composite materi...Based on continuum theory and moving law of particles, a model is presentedto obtain gradient distribution of particles in centrifugal accelerating field, by which theparticle distribution in gradient composite material can be predicted. The simulation shows withincreases in rotating time, four regions gradually appear from the internal periphery to theexternal one, they are free region, transition region, steady region and surface reinforced region,and the latest three regions are defined as a rich region. Finally, the steady region disappears,and the rich region only includes transition region and surface reinforced region. The influences ofcentrifugal acceleration coefficient G, primary volume fraction phi_0, pouring temperature theta_pand density difference between the particle and the metal matrix on particles gradient distributionare studied in detail. The results of the theoretical analysis agree with experiment ones. Both ofanalysis and experiment results indicate that with the increase in G and theta_p the particledistribution becomes more centralized and the consistence of particle in the surface peripherybecomes larger.展开更多
Given the importance of lithium-ion cell safety,a comprehensive review on the thermal stability of lithium-ion cells investigated by accelerating rate calorimetry(ARC),is provided in the present work.The operating mec...Given the importance of lithium-ion cell safety,a comprehensive review on the thermal stability of lithium-ion cells investigated by accelerating rate calorimetry(ARC),is provided in the present work.The operating mechanism of ARC is discussed first,including the usage and the reaction kinetics.Besides that,the thermal stability of the cathode/anode materials at elevated temperatures is revealed by examining the impacts of some significant factors,i.e.,the lithium content,particle size,material density,lithium salt,solvent,additive,binder and initial heating temperature.A comparison of the common cathode materials indicates that the presence of Mn and polyanion could significantly enhance the thermal stability of cathode materials,while the doping of Al also helps to restrain the reactivity.Except for their high capacity,some alloy materials demonstrate more competitive safety than traditional carbon anode materials.Furthermore,the thermal behaviors of full cells under abusive conditions are reviewed here.Due to the sensitivity of ARC to the kinetic parameters,a reaction kinetic modeling can be built on the basis of ARC profiles,to predict the thermal behaviors of cell components and cells.Herein,a shortcircuit modeling is exampled.展开更多
This paper presents a novel optimal Motion Cueing Algorithm(MCA)to control the rotations of a Human Centrifuge(HC)and achieve the best simulation of a Space Craft(SC)motion.Relations of the specific forces sensed by a...This paper presents a novel optimal Motion Cueing Algorithm(MCA)to control the rotations of a Human Centrifuge(HC)and achieve the best simulation of a Space Craft(SC)motion.Relations of the specific forces sensed by astronauts of the SC and the HC have been derived and linearized.A Linear Quadratic Regulator(LQR)controller is implemented for the problem which tends to minimize the error between the two sensed specific forces as well as control input in a cost function.It results in control inputs of the HC to generate its sensed specific force as close as possible to the one in the SC.The algorithm is implemented for both linearized and nonlinear portions of a US space shuttle mission trajectory as a verification using MATLAB.In longitudinal direction,the proposed MCA,works well when the acceleration is less than 2 g in which the tracking error does not exceed 12%.In lateral direction the tracking is much better even in nonlinear region since the error remains less than 7%for tilting up to 50°.Finally,the effect of weight matrixes in the LQR cost function on overall weight and power of the HC motion system is discussed.展开更多
To implement the Tsinghua Thomson Scattering X-ray Source upgrade plan and the Very Compact Inverse Compton Scattering Gamma-ray Source (VIGAS) program, a new 1.5-m traveling-wave accelerating structure was designed t...To implement the Tsinghua Thomson Scattering X-ray Source upgrade plan and the Very Compact Inverse Compton Scattering Gamma-ray Source (VIGAS) program, a new 1.5-m traveling-wave accelerating structure was designed to replace the old 3-m SLAC-type structure with the aim of increasing the accelerating gradient from15 to 30 MV/m. The new type of structure works in the 3π/4 mode with a comparatively low group velocity varying from 0.007c to 0.003c to increase the accelerating gradient at a given power. An elliptical iris was employed to reduce the surface field enhancement. The filling process of the low-group-velocity structure was analyzed using a circuit model. After fabrication, the structure was precisely tuned using the non-contact tuning method, followed by detailed low-power radiofrequency measurements. The structure was first installed and utilized at a beamline for the terahertz experiment at Tsinghua University. After 120 h of conditioning, it is now operating at a gradient of 24.2 MV/m and a 20.7-MW input power, with the klystron operating at its full power. It is expected to generate an accelerating gradient of 30 MV/m when the klystron power is upgraded to 30 MW in the near future.展开更多
X-band high-gradient linear accelerators are a challenging and attractive technology for compact electron linear-accelerator facilities.The Very Compact Inverse Compton Scattering Gamma-ray Source(VIGAS)program at Tsi...X-band high-gradient linear accelerators are a challenging and attractive technology for compact electron linear-accelerator facilities.The Very Compact Inverse Compton Scattering Gamma-ray Source(VIGAS)program at Tsinghua University will utilize X-band high-gradient accelerating structures to boost the electron beam from 50 to 350 MeV over a short distance.A constant-impedance traveling-wave structure consisting of 72 cells working in the 2π/3 mode was designed and fabricated for this project.Precise tuning and detailed measurements were successfully applied to the structure.After 180 h of conditioning in the Tsinghua high-power test stand,the structure reached a target gradient of 80 MV/m.The breakdown rate versus gradient of this structure was measured and analyzed.展开更多
In this paper, we present the design and optimization of a side-coupled accelerating structure with an energy switch. The beam parameters are optimized, and the electric field asymmetry in the first cell is analyzed. ...In this paper, we present the design and optimization of a side-coupled accelerating structure with an energy switch. The beam parameters are optimized, and the electric field asymmetry in the first cell is analyzed. The new structure we designed has an improvement of 10 times in the accelerating field symmetry. Thermo-mechanical analysis is performed based on the electromagnetic results. The highest temperature is 72.5 ℃ at the nose cone, and the maximal deformation is 73 μm at the outer edge of the coupling cavity.展开更多
The effects of accelerating agent on the deposition speed of Electroless Nickel Plating, the stability of solution and the corrosion resistant of The EN coatings were studied. The influence of A1 content on EN activat...The effects of accelerating agent on the deposition speed of Electroless Nickel Plating, the stability of solution and the corrosion resistant of The EN coatings were studied. The influence of A1 content on EN activation energy, the rest potential and polarization cures are measured. The mechanism of the acceleration effect of A1 on the EN plating was proposed.展开更多
基金supported by Zhangjiang Laboratory,the SHINE R&D project(No.2017SHZDZX02)the SHINE projectthe National Natural Science Foundation of China(No.12125508).
文摘We report the world-leading performance of a 1.3 GHz cryomodule equipped with eight 9-cell superconducting radio-frequency cavities that underwent a medium-temperature furnace baking process.During continuous wave horizontal testing,these cavities achieved unprecedented average intrinsic quality factors of 4.0×10^(10)at 20 MV/m and 3.2×10^(10)at 29 MV/m,with no instances of field emission.The cryomodule demonstrates near-complete preservation of ultra-high quality factors and ultra-high accelerating gradients from vertical to horizontal testing,marking a significant milestone in continuous-wave superconducting radio-frequency accelerator technology.This letter presents the cryomodule development experience,includ-ing cavity preparation,cryomodule assembly,degaussing,fast cooldown,and performance testing.
基金the support from the National Natural Science Foundation of China(22478429)the Special Project Fund of Taishan-Scholars(tsqn202408101)+3 种基金the Natural Science Foundation of Shandong Province(ZR2023YQ009)CNPC Innovation Found(2024DQ02-0504)Fundamental Research Funds for the Central Universities,Ocean University of China(202364004)the State Key Laboratory of Heavy Oil Processing(SKLHOP202403003)。
文摘Alcohol oxidation is a widely used green chemical reaction.The reaction process produces flammable and explosive hydrogen,so the design of the reactor must meet stringent safety requirements.Based on the limited experimental data,utilizing the traditional numerical method of computational fluid dynamics(CFD)to simulate the gas-liquid two-phase flow reactor can mitigate the risk of danger under varying working conditions.However,the calculation process is highly time-consuming.Therefore,by integrating process simulation,computational fluid dynamics,and deep learning technologies,an intelligent hybrid chemical model based on machine learning was proposed to expedite CFD calculations,enhance the prediction of flow fields,conversion rates,and concentrations inside the reactor,and offer insights for designing and optimizing the reactor for the alcohol oxidation system.The results show that the hybrid model based on the long and short-term memory neural network achieves 99.8%accuracy in conversion rate prediction and 99.9%accuracy in product concentration prediction.Through validation,the hybrid model is accelerated by about 360 times compared with instrumental analysis in conversion rate prediction and about 45 times compared with CFD calculation in concentration distribution prediction.This hybrid model can quickly predict the conversion rate and product concentration distribution in the gas-liquid two-phase flow reactor and provide a model reference for fast prediction and accurate control in the actual chemical production process.
基金supported by the National Natural Science Foundation of China(No.11922504).
文摘Very high-energy electrons(VHEEs)are potential candidates for FLASH radiotherapy for deep-seated tumors.We proposed a compact VHEE facility based on an X-band high-gradient high-power technique.In this study,we investigated and realized the first X-band backward traveling-wave(BTW)accelerating structure as the buncher for a VHEE facility.A method for calculating the parameters of single cell from the field distribution was introduced to simplify the design of the BTW structure.Time-domain circuit equations were applied to calculate the transient beam parameters of the buncher in the unsteady state.A prototype of the BTW structure with a thermionic cathode-diode electron gun was designed,fabricated,and tested at high power at the Tsinghua X-band high-power test stand.The structure successfully operated with 5-MW microwave pulses from the pulse compressor and outputted electron bunches with an energy of 8 MeV and a pulsed current of 108 mA.
文摘In order to design the relief system size of di-tert-butyl peroxide(DTBP) storage tanks,the runaway re-action of DTBP was simulated by accelerating rate calorimeter(ARC).The results indicated that under adiabatic conditions the initial exothermic temperature was 102.6 ℃,the maximum self-heating rate was 3.095×107 ℃·min-1,the maximum self-heating temperature was 375.9 ℃,and the pressure produced by unit mass was 4.512 MPa·g-1.Judged by ARC test,the emergency relief system for DTBP was a hybrid system.Based on Design Institute for Emergency Relief System(DIERS) method,the releasing mass flow rate W was determined by Leung methods,and the mass velocity G was calculated by two modified Omega methods.The two relief sizes calculated by monograph Omega method and arithmetic Omega method are close,with only 0.63% relative error.The monograph Omega method is more convenient to apply.
基金Supported by the National Natural Science Foundation of china
文摘There are many accelerating convergence factors (ACFs) for limit periodic continued fraction K(an/1)(an→a≠0). In this paper, some characteristics and comparative theorems are ob tained on ACFs. Two results are given for most frequently used ACFs.
基金This work was supported by the Alliance of International Science Organizations(No.ANSO-CR-KP-2020-16).
文摘An S-band high-gradient accelerating structure is designed for a proton therapy linear accelerator(linac)to accommodate the new development of compact,singleroom facilities and ultra-high dose rate(FLASH)radiotherapy.To optimize the design,an efficient optimization scheme is applied to improve the simulation efficiency.An S-band accelerating structure with 2856 MHz is designed with a low beta of 0.38,which is a difficult structure to achieve for a linac accelerating proton particles from 70 to 250 MeV,as a high gradient up to 50 MV/m is required.A special design involving a dual-feed coupler eliminates the dipole field effect.This paper presents all the details pertaining to the design,fabrication,and cold test results of the S-band high-gradient accelerating structure.
基金The project supported by the National Natural Science Foundation of China (10172056)
文摘To investigate the principal resonance in transverse nonlinear parametric vibration of an axially accelerating viscoelastic string,the method of multiple scales is applied directly to the nonlinear partial differential equation that governs the transverse vibration of the string.To derive the governing equation,Newton's second law,Lagrangean strain,and Kelvin's model are respectively used to account the dynamical relation,geometric nonlinearity and the viscoelasticity of the string material. Based on the solvability condition of eliminating the secular terms,closed form solutions are obtained for the amplitude and the existence conditions of nontrivial steady-state response of the principal parametric resonance.The Lyapunov linearized stability theory is employed to analyze the stability of the trivial and nontrivial solutions in the principal parametric resonance.Some numerical examples are presented to show the effects of the mean transport speed,the amplitude and the frequency of speed variation.
文摘The physical design and cooling test of a C-band 2MeV standing wave （SW） accelerating tube are described in this paper. The designed accelerating structure consists of 3-cell buncher and 4-cell accelerating section with a total length of about 163mm, excited with 1MW magnetron. Dynamic simulation presents that about 150mA beam pulse current and 30% capture efficiency can be achieved. By means of nonlinear Gauss fit on electron transverse distribution, the diameter of beam spot FWHM （full width at half maximum of density distribution） is about 0.55mm. Cooling test results of the accelerating tube show that frequencies of cavities are tuned to 5527MHz and the field distribution of bunching section is about 3：9：10.
基金supported by National Key R&D Program of China(No.2018YFF0109203)。
文摘The development of a high-gradient accelerating structure is underway to construct a compact proton linear accelerator for cancer treatment.Extensive experiments and numerous studies are being conducted to develop compact linear accelerators for proton therapy.Optimization of the electromagnetic and mechanical design has been performed to simplify the manufacturing process and reduce costs.A novel high-gradient structure with a low relativistic proton velocity(β),v/c=0.38,was designed,fabricated,and tested at high power.The first full-scale prototype was also successfully tested with high radio frequency(RF)power,a repetition rate of 50 Hz,and pulse length of 3μs to reach a high-gradient of 46 MV/m using a 50 MW S-band klystron power supply obtained from the Shanghai Soft X-ray Free Electron Laser Facility.This is the first high-power test in China,which is in line with the expected experimental goal.This study presents preliminary high-power testing of S-band standing wave accelerating structures with 11 cells.This work aims to verify the feasibility of using a high-gradient RF accelerating structure in compact proton therapy facilities.The cold test of the prototype cavity was completed in advance.Details of the high-power RF test setup,the process of RF conditioning,and the high-power results are described.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB25000000)the National Natural Science Foundation of China(No.12075270)the Platform of Advanced Photon Source Technology R&D。
文摘Two 650 MHz single-cell superconducting radio-frequency(SRF)cavities used for the Circular Electron Positron Collider(CEPC)were studied to achieve a high accelerating gradient(E_(acc))and high intrinsic quality factor(Q_(0)).The 650 MHz single-cell cavities were subjected to a combination of buffered chemical polishing(BCP)and electropolishing(EP),and their E_(acc) exceeded40 MV/m.Such a high E_(acc) may result from the cold EP with more uniform removal.BCP is easy,cheap,and rough,whereas EP is complicated,expensive,and precise Therefore,the combination of BCP and EP investigated in this study is suitable for surface treatments of mass SRF cavities.Medium temperature(mid-T)furnace baking was also conducted,which demonstrated an ultrahigh Q_(0) of 8×10^(10) at 22 MV/m for both cavities,and an extremely low BCS resistance(R_(BCS))of~1.0 nΩwas achieved a2.0 K.
基金Project supported by the Major State Basic Research Development Program of China(Grant No.2012CB825800)the Science Fund for Creative Research Groups,China(Grant No.11321503)+1 种基金the National Natural Science Foundation of China(Grant Nos.11179004,10979055,11205189,and 11205157)the Japan–Asia Youth Exchange Program in Science(SAKURA Exchange Program in Science)Administered by the Japan Science and Technology Agency
文摘X-ray Talbot-Lau interferometer has been used most widely to perform x-ray phase-contrast imaging with a con- ventional low-brilliance x-ray source, and it yields high-sensitivity phase and dark-field images of samples producing low absorption contrast, thus beating tremendous potential for future clinical diagnosis. In this work, by changing the accel- erating voltage of the x-ray tube from 35 kV to 45 kV, x-ray phase-contrast imaging of a test sample is performed at each integer value of the accelerating voltage to investigate the characteristic of an x-ray Talbot-Lau interferometer （located in the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan） versus tube voltage. Ex- perimental results and data analysis show that within a range this x-ray Talbot-Lau interferometer is not sensitive to the accelerating voltage of the tube with a constant fringe visibility of ~ 44%. This x-ray Talbot-Lau interferometer research demonstrates the feasibility of a new dual energy phase-contrast x-ray imaging strategy and the possibility to collect a refraction spectrum.
基金supported by the Major Research Development Program of China(No.2004CB612905)the National Science Fund for Distinguished Young Scholars(No.50325415)+1 种基金the National Originality Innovation Population Project(No.50321402)the National Natural Science Foundation of China(No.50774011).
文摘The main measures to accelerate leaching sulfide ore are large spraying intensity,manual oxygen supply,temperature control,and acclimated bacteria.The indoor experiment accelerating sulfide ore leaching detected the temperature during leaching process,dissolvability of oxygen,bacterial concentration,Cu concentration and slag grade.At the same time,this paper also analyzed the effect of four factors,which are bacterial diversity cultivation stage,spraying intensity,air supply,and whether to control temperature,on the leaching efficiency of copper.The results indicate that the oxygen content of leach solution has a close relationship with temperature but it is rarely affected by air supply.The bacterial concentration preserves from 106 to 107 mL^-1,and temperature has a great effect on the bacterial activity under the condition of proper temperature and oxygen supply,and the lack of nutrition prevents the bacterial concentration from rising in the late stage.The relationships of the copper leaching efficiency to temperature,air feed,and spraying intensity are directly proportional.The leaching efficiencies of the cultivated bacteria and acclimation bacteria are 1.2 and 1.4 times as large as that of the original bacteria.
基金This project is supported by National Natural Science Foundation of China(No.59771055).
文摘The infiltration kinetics of the metal melt into a fibrous preform in centrifugal accelerating field is analyzed on the basis of Darcy's law and the assumption that the fibrous preform is treated as 'bundle of capillaries' The critical rotating speed is analyzed with the established model The influences of the metal melt mass,the rotating speed of the equipment,the casting height, the original outer radius of the metal melt and the fibrous volume fraction in fibrous preform on infilatration are studied The results show that the critical rotating speed is dependent on critical pressure, casting height, metal melt mass and the character of fibrous preform With the increase in the metal melt mass, rotating speed of the equipment and original outer radius of the metal melt, or the decrease in casting height and fibrous volume fraction in fibrous of the metal melt,or the decrease in casting height and fibrous volume fraction in fibrous preform,infiltration of metal melt for fibrous preform becomes easier.
基金This project is supported by Provincial Department of ScienceTechnology of Jilin.
文摘Based on continuum theory and moving law of particles, a model is presentedto obtain gradient distribution of particles in centrifugal accelerating field, by which theparticle distribution in gradient composite material can be predicted. The simulation shows withincreases in rotating time, four regions gradually appear from the internal periphery to theexternal one, they are free region, transition region, steady region and surface reinforced region,and the latest three regions are defined as a rich region. Finally, the steady region disappears,and the rich region only includes transition region and surface reinforced region. The influences ofcentrifugal acceleration coefficient G, primary volume fraction phi_0, pouring temperature theta_pand density difference between the particle and the metal matrix on particles gradient distributionare studied in detail. The results of the theoretical analysis agree with experiment ones. Both ofanalysis and experiment results indicate that with the increase in G and theta_p the particledistribution becomes more centralized and the consistence of particle in the surface peripherybecomes larger.
基金supported by NSERC,Tesla Motors,the National Natural Science Foundation of China (No.52204213,52272396)the China Postdoctoral Science Foundation (No.2022M711602)+2 种基金the Opening Fund of State Key Laboratory of Fire Science (SKLFS) (No.HZ2022-KF07)the Jiangsu Project Plan for Outstanding Talents Team in Six Research Fields (No.TD-XNYQC-002)the support of the China Scholarship Council。
文摘Given the importance of lithium-ion cell safety,a comprehensive review on the thermal stability of lithium-ion cells investigated by accelerating rate calorimetry(ARC),is provided in the present work.The operating mechanism of ARC is discussed first,including the usage and the reaction kinetics.Besides that,the thermal stability of the cathode/anode materials at elevated temperatures is revealed by examining the impacts of some significant factors,i.e.,the lithium content,particle size,material density,lithium salt,solvent,additive,binder and initial heating temperature.A comparison of the common cathode materials indicates that the presence of Mn and polyanion could significantly enhance the thermal stability of cathode materials,while the doping of Al also helps to restrain the reactivity.Except for their high capacity,some alloy materials demonstrate more competitive safety than traditional carbon anode materials.Furthermore,the thermal behaviors of full cells under abusive conditions are reviewed here.Due to the sensitivity of ARC to the kinetic parameters,a reaction kinetic modeling can be built on the basis of ARC profiles,to predict the thermal behaviors of cell components and cells.Herein,a shortcircuit modeling is exampled.
文摘This paper presents a novel optimal Motion Cueing Algorithm(MCA)to control the rotations of a Human Centrifuge(HC)and achieve the best simulation of a Space Craft(SC)motion.Relations of the specific forces sensed by astronauts of the SC and the HC have been derived and linearized.A Linear Quadratic Regulator(LQR)controller is implemented for the problem which tends to minimize the error between the two sensed specific forces as well as control input in a cost function.It results in control inputs of the HC to generate its sensed specific force as close as possible to the one in the SC.The algorithm is implemented for both linearized and nonlinear portions of a US space shuttle mission trajectory as a verification using MATLAB.In longitudinal direction,the proposed MCA,works well when the acceleration is less than 2 g in which the tracking error does not exceed 12%.In lateral direction the tracking is much better even in nonlinear region since the error remains less than 7%for tilting up to 50°.Finally,the effect of weight matrixes in the LQR cost function on overall weight and power of the HC motion system is discussed.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.11922504 and 12027902).
文摘To implement the Tsinghua Thomson Scattering X-ray Source upgrade plan and the Very Compact Inverse Compton Scattering Gamma-ray Source (VIGAS) program, a new 1.5-m traveling-wave accelerating structure was designed to replace the old 3-m SLAC-type structure with the aim of increasing the accelerating gradient from15 to 30 MV/m. The new type of structure works in the 3π/4 mode with a comparatively low group velocity varying from 0.007c to 0.003c to increase the accelerating gradient at a given power. An elliptical iris was employed to reduce the surface field enhancement. The filling process of the low-group-velocity structure was analyzed using a circuit model. After fabrication, the structure was precisely tuned using the non-contact tuning method, followed by detailed low-power radiofrequency measurements. The structure was first installed and utilized at a beamline for the terahertz experiment at Tsinghua University. After 120 h of conditioning, it is now operating at a gradient of 24.2 MV/m and a 20.7-MW input power, with the klystron operating at its full power. It is expected to generate an accelerating gradient of 30 MV/m when the klystron power is upgraded to 30 MW in the near future.
基金supported by the National Natural Science Foundation of China (Nos. 11922504 and 12027902)
文摘X-band high-gradient linear accelerators are a challenging and attractive technology for compact electron linear-accelerator facilities.The Very Compact Inverse Compton Scattering Gamma-ray Source(VIGAS)program at Tsinghua University will utilize X-band high-gradient accelerating structures to boost the electron beam from 50 to 350 MeV over a short distance.A constant-impedance traveling-wave structure consisting of 72 cells working in the 2π/3 mode was designed and fabricated for this project.Precise tuning and detailed measurements were successfully applied to the structure.After 180 h of conditioning in the Tsinghua high-power test stand,the structure reached a target gradient of 80 MV/m.The breakdown rate versus gradient of this structure was measured and analyzed.
文摘In this paper, we present the design and optimization of a side-coupled accelerating structure with an energy switch. The beam parameters are optimized, and the electric field asymmetry in the first cell is analyzed. The new structure we designed has an improvement of 10 times in the accelerating field symmetry. Thermo-mechanical analysis is performed based on the electromagnetic results. The highest temperature is 72.5 ℃ at the nose cone, and the maximal deformation is 73 μm at the outer edge of the coupling cavity.
文摘The effects of accelerating agent on the deposition speed of Electroless Nickel Plating, the stability of solution and the corrosion resistant of The EN coatings were studied. The influence of A1 content on EN activation energy, the rest potential and polarization cures are measured. The mechanism of the acceleration effect of A1 on the EN plating was proposed.
