Precise transverse emittance assessment in electron beams is crucial for advancing high-brightness beam injectors.As opposed to intricate methodologies that use specialized devices,quadrupole focusing strength scannin...Precise transverse emittance assessment in electron beams is crucial for advancing high-brightness beam injectors.As opposed to intricate methodologies that use specialized devices,quadrupole focusing strength scanning(Q-scanning)techniques offer notable advantages for various injectors owing to their inherent convenience and cost-effectiveness.However,their stringent approximation conditions lead to inevitable errors in practical operation,thereby limiting their widespread application.This study addressed these challenges by revisiting the analytical derivation procedure and investigating the effects of the underlying approximation conditions.Preliminary corrections were explored through a combination of data processing analysis and numerical simulations.Furthermore,based on theoretical derivations,virtual measurements using beam dynamics calculations were employed to evaluate the correction reliability.Subsequent experimental validations were performed at the Huazhong University of Science and Technology injector to verify the effectiveness of the proposed compensation method.Both the virtual and experimental results confirm the feasibility and reliability of the enhanced Q-scanning-based diagnosis for transverse emittance in typical beam injectors operating under common conditions.Through the integration of these corrections and compensations,enhanced Q-scanning-based techniques emerge as promising alternatives to traditional emittance diagnosis methods.展开更多
Without knowing the emittance value, it is difficult to optimize ion beam optics for minimum beam loss during transmission, especially considering the very high emittance values of electron cyclotron resonance(ECR) io...Without knowing the emittance value, it is difficult to optimize ion beam optics for minimum beam loss during transmission, especially considering the very high emittance values of electron cyclotron resonance(ECR) ion sources.With this in mind, to measure the emittance of the ion beams produced by the mVINIS ECR, which is part of the FAMA facility at the Vin?a Institute of Nuclear Sciences, we have developed a pepper-pot scintillator screen system combined with a CMOS camera. The application, developed on the Lab VIEW platform, allows us to control the camera's main attribute settings, such as the shutter speed and the gain, record the images in the region of interest, and process and filter the images in real time. To analyze the data from the obtained image, we have developed an algorithm called measurement and analysis of ion beam luminosity(MAIBL) to reconstruct the four-dimensional(4D) beam profile and calculate the root mean square(RMS) emittance. Before measuring emittance, we performed a simulated experiment using the pepper-pot simulation(PPS) program. An exported file(PPS) gives a numerically generated raw image(mock image) of a beam with a predefined emittance value after it has passed through a pepper-pot mask. By analyzing data from mock images instead of the image obtained by the camera and putting it into the MAIBL algorithm, we can compare the calculated emittance with PPS's initial emittance value. In this paper, we present our computational tools and explain the method for verifying the correctness of the calculated emittance values.展开更多
This paper presents an analytical description for the growth of the projected emittanee （here just referred to the transverse emittance） based on the concept of the slice emittance in an RF photoinjector. In the RF ...This paper presents an analytical description for the growth of the projected emittanee （here just referred to the transverse emittance） based on the concept of the slice emittance in an RF photoinjector. In the RF photoinjector, the slice emittance undergoes small changes, but the projected emittance changes significantly even in the drift space after the injector. Carefully adjusting the parameters of the RF photoinjector, which usually means emittance compensation, the projected emittance can be minimized to the value of the slice emittance. The relation between slice emittance and projected emittance is explained in this paper. An emittance function, which shows such a relation, is also introduced. A model about the emittance growth in the RF photoinjector is established, which accords with the particle simulation results by using the code ASTRA. The condition to minimize the emittance is also given by using the emittance function, which means the emittance compensation in the RF photoinjector.展开更多
The transverse emittance of the extracted beam from the heavy ion medical machine cyclotron is measured and then optimized for injection into the synchrotron.For the purposes of cross-validation,three methods,i.e.,sli...The transverse emittance of the extracted beam from the heavy ion medical machine cyclotron is measured and then optimized for injection into the synchrotron.For the purposes of cross-validation,three methods,i.e.,slit-grid,Q-scan,and 3-grid,are used to measure the emittance.In the slit-grid technique,an automatic selection of the region of interest is adopted to isolate the major noise from the beam phase space,which is an improvement over the traditional technique.After iterating over the contour level,an unbiased measurement of the emittance can be obtained.An improvement in the thin lens technique is implemented in the Q-scan method.The results of these measurements are presented.展开更多
Beam emittance reduction is an effective method to increase the brightness of a synchrotron light source.Robinson wiggler can play a role in the beam emittance reduction by increasing the horizontal damping partition ...Beam emittance reduction is an effective method to increase the brightness of a synchrotron light source.Robinson wiggler can play a role in the beam emittance reduction by increasing the horizontal damping partition number.A replacement of the quadrupoles in the arc section with short combined function dipoles will construct a single-periodic Robinson wiggler in the SSRF storage ring.This scheme provides a lower beam emittance,without occupying any straight section.Detailed analysis is presented in this paper.展开更多
The La-Sr-Mn-O films were deposited on Si（100） substrates by DC magnetron sputtering and followed by air annealing at 973 K for I h. The microstructure and temperature dependence of total hemispherical emittance （...The La-Sr-Mn-O films were deposited on Si（100） substrates by DC magnetron sputtering and followed by air annealing at 973 K for I h. The microstructure and temperature dependence of total hemispherical emittance （εH） of the annealed La-Sr-Mn-O films prepared at various processing parameters were investigated. The results indicated the films deposited at lower sputtering pressure and lower O2（O2＋Ar） volume proportion （R0） were present in rhombohedral .perovskite structure and the length of MnO bond was shorter. The metal-insulator transition temperature （TMI） was higher. All of the annealed films showed the unique feature of variable emittance based on metal-insulator transition. The films showed low emittance at low temperature but high emittance at high temperature. Moreover, the εH significantly changed in the vicinity of TMI. The variability of total hemispherical emittance （△ε） and the temperature range with obvious emittance change could be adjusted by changing the processing parameters. The Aε could be 0.45 and △ε/ε355 （ε355 is the εH at 355K） exceeded 50% for the annealed La-Sr-Mn-O films. Therefore, the annealed La-Sr-Mn-O films showed much potential for thermal control applications as smart thermochromic variable emittance materials.展开更多
Based on the multi-slit method, a new method is introduced to measure the nonlinear force caused emittance growth in a RF photoinjector. It is possible to reconstruct the phase space of a beam under some conditions by...Based on the multi-slit method, a new method is introduced to measure the nonlinear force caused emittance growth in a RF photoinjector. It is possible to reconstruct the phase space of a beam under some conditions by the multi-slit method. Based on the reconstructed phase space, besides the emittance, the emittance growth from the distortion of the phase space can also be measured. The emittance growth results from the effects of nonlinear force acting on electron, which is very important for the high quality beam in a RF photoinjector.展开更多
The nonlinear space charge effect of bunched beam in linac is one of the im-portant factors that induces the emittance growth due to the conversion of the field en-ergy to kinetic energy.In this paper,the internal fie...The nonlinear space charge effect of bunched beam in linac is one of the im-portant factors that induces the emittance growth due to the conversion of the field en-ergy to kinetic energy.In this paper,the internal field energies associated with sometransverse nonuniform space charge distributions of a bunched beam,such as Gaussiandistribution,waterbag distribution and parabolic distribution,are worked out.And theemittance growth caused by these nonuniformities are obtained.展开更多
The enhancement of trapping and the optimization of beam quality are two key issues of Laser Wakefield Acceleration (LWFA). The effect of a homogenous constant magnetic field B0, parallel to the direction of propagati...The enhancement of trapping and the optimization of beam quality are two key issues of Laser Wakefield Acceleration (LWFA). The effect of a homogenous constant magnetic field B0, parallel to the direction of propagation of the pump pulse, is studied in the blowout regime via 2Dx3Dv Particle-In-Cell simulations. Electrons are injected into the wake using a counter-propagating low amplitude laser. Transverse currents are generated at the rim of the bubble, which results in the amplification of the B0 field at the rear of the bubble. Therefore the dynamics of the beam is modified, the main effect is the reduction of the transverse emittance when B0 is raised. Depending on beam loading effects the low energy tail, observed in the non-magnetized case, can be suppressed when B0 is applied, which provides a mono-energetic beam.展开更多
A combined unit, which has the ability to measure the current and emittance of the high intensity direct current（DC）ion beam, is developed at Peking University（PKU）. It is a multi-slit single-wire（MSSW）-type bea...A combined unit, which has the ability to measure the current and emittance of the high intensity direct current（DC）ion beam, is developed at Peking University（PKU）. It is a multi-slit single-wire（MSSW）-type beam emittance meter combined with a water-cooled Faraday Cup, named high intensity beam emittance measurement unit-6（HIBEMU-6）. It takes about 15 seconds to complete one measurement of the beam current and its emittance. The emittance of a 50-mA@50-kV DC proton beam is measured.展开更多
The nonlinear space charge effect of bunched beam in linac is one of theimportant factors that induces the emittance growth due to the conversion of thefield energy to kinetic energy. Using a cylinder model of space c...The nonlinear space charge effect of bunched beam in linac is one of theimportant factors that induces the emittance growth due to the conversion of thefield energy to kinetic energy. Using a cylinder model of space charge in a linac,we derive the internal energy for a bunched beam with some nonuniform spacecharge distributions, such as Gaussian, waterbag and parabolic distributions inboth the longitudinal and transverse directions. And the emittance growth causedby these nonuniformities is worked out.展开更多
RF effect and space charge effect are the main sources of the emittance growth in the RF elec-tron gun.The single particle dynamics near the cathode is discussed,and the emittance growth due to RFnonlinear force and t...RF effect and space charge effect are the main sources of the emittance growth in the RF elec-tron gun.The single particle dynamics near the cathode is discussed,and the emittance growth due to RFnonlinear force and time-dependent force are studied in detail.Comparison with the emittance at the gunexit shows that the emittanca growth due to nonlinear RF effect near the cathode can not be neglected.展开更多
The nonlinear space charge effect of bunched beam in linac is one of the important factors thatinduces the emittance growth due to the conversion of the field energy to kinetic energy.In this paper,us-ing a cylinder m...The nonlinear space charge effect of bunched beam in linac is one of the important factors thatinduces the emittance growth due to the conversion of the field energy to kinetic energy.In this paper,us-ing a cylinder model of space charge in linac,we derived the internal energy for a bunched beam withsome nonuniform space charge distributions,such as longitudinal Gaussian distribution combined withKapchinskij-Vladimirski1,waterbag,parabolic or Gaussian transverse distribution.And the emittancegrowth caused by the above distributions is worked out.展开更多
Emittance is a key figure of merit for charged particle beams,and various diagnostic techniques have been developed to try to measure it accurately.To measure the transverse emittance,a traditional emittance measureme...Emittance is a key figure of merit for charged particle beams,and various diagnostic techniques have been developed to try to measure it accurately.To measure the transverse emittance,a traditional emittance measurement device,which consists of slits and wire scanners,is installed at the MEBT section of the Ci-ADS injector Ⅱ.展开更多
Fast electron generation and transport in high-intensity laser–solid interactions induces X-ray emission and drives ion acceleration.Effective production of these sources hinges on an efficient laser absorption into ...Fast electron generation and transport in high-intensity laser–solid interactions induces X-ray emission and drives ion acceleration.Effective production of these sources hinges on an efficient laser absorption into the fast electron population and control of divergence as the beam propagates through the target.Nanowire targets can be employed to increase the laser absorption,but it is not yet clear how the fast electron beam properties are modified.Here we present novel measurements of the emittance of the exiting fast electron beam from irradiated solid planar and nanowire targets via a pepper-pot diagnostic.The measurements indicate a greater fast electron emittance is obtained from nanowire targets.Two-dimensional particle-in-cell simulations support this conclusion,revealing beam defocusing at the wire–substrate boundary,a higher fast electron temperature and transverse oscillatory motion around the wires.展开更多
Passive radiative cooling is a promising passive cooling technology that emits heat to deep space without energy consumption.Nevertheless,the persistent challenge of overcooling in static radiative techniques has rais...Passive radiative cooling is a promising passive cooling technology that emits heat to deep space without energy consumption.Nevertheless,the persistent challenge of overcooling in static radiative techniques has raised concerns.Although a desirable solution is suggested based on vanadium dioxide(VO_(2))in the form of a Fabry-Perot(F-P)resonant cavity,the inherent contradiction between desired high emissivity(ε)and low solar absorptance(α_(sol))remains a notable limitation.Here,we employed a simple mask-filling technique to develop a temperature-adaptive metasurface radiative cooling device(ATMRD)for dynamic thermal regulation.Simulation and experimental results substantially evidenced that multiple localized polariton resonances were induced by the VO_(2)metasurface,significantly enhancing the thermal emittance of the ATMRDs.The engineered ATMRD achieved an amazing switch of the atmospheric window emittance from 0.13 to 0.85 when the surface temperature exceeds a pre-set transition temperature,accompanied by a commendableα_(sol)of 27.71%.The mechanism of multiple localized polariton resonances is discussed in detail to understand the enhanced performance based on the investigation of the relationship between the metasurface structure and multiple localized polariton resonances.We demonstrate an efficient smart radiative technique achieved by a simple micro/nanoprocess and,most importantly,contribute a valuable reference for the design of radiative devices,which is crucial in various areas such as passive cooling,smart windows,multifunctional electromagnetic response,and space application technologies.展开更多
One should pay attention to quite a lot of factors when the emittance of high-current ion beam is measured. The background subtraction and threshold setting,the measuring method of pulsed beam emittance,as well as the...One should pay attention to quite a lot of factors when the emittance of high-current ion beam is measured. The background subtraction and threshold setting,the measuring method of pulsed beam emittance,as well as the error sources in the emittance measurements and its elimination or correction are discussed based on the experience during the R&D of three emittance measurement units for high-current ion beams at Peking University.展开更多
Further studies on beam emittance measurement have been made to improve the emittance measurement precision at BEPCⅡ linac.Some problems in the measurement are solved and a code for beam emittance calculation is deve...Further studies on beam emittance measurement have been made to improve the emittance measurement precision at BEPCⅡ linac.Some problems in the measurement are solved and a code for beam emittance calculation is developed.With these improvements,the emittance measurement precision was upgraded.展开更多
One kind of instantaneous electron beam emittance measurement system based on the optical transition radiation principle and double imaging optical method has been set up. It is mainly adopted in the test for the inte...One kind of instantaneous electron beam emittance measurement system based on the optical transition radiation principle and double imaging optical method has been set up. It is mainly adopted in the test for the intense electron-beam produced by a linear induction accelerator. The system features two characteristics. The first one concerns the system synchronization signal triggered by the following edge of the main output waveform from a Blumlein switch. The synchronous precision of about 1 ns between the electron beam and the image capture time can be reached in this way so that the electron beam emittance at the desired time point can be obtained. The other advantage of the system is the ability to obtain the beam spot and beam divergence in one measurement so that the calculated result is the true beam emittance at that time, which can explain the electron beam condition. It provides to be a powerful beam diagnostic method for a 2.5 kA, 18.5 MeV, 90 ns （FWHM） electron beam pulse produced by Dragon I. The ability of the instantaneous measurement is about 3 ns and it can measure the beam emittance at any time point during one beam pulse. A series of beam emittances have been obtained for Dragon I. The typical beam spot is 9.0 mm （FWHM） in diameter and the corresponding beam divergence is about 10.5 mrad.展开更多
Three sets of High Intensity Beam Emittance Measurement Units (HIBEMUs) are being developed at Peking University. They are HIBEMU-2 (slit-wire type, one direction), HIBEMU-3 (Allison scanner type, one direction) and H...Three sets of High Intensity Beam Emittance Measurement Units (HIBEMUs) are being developed at Peking University. They are HIBEMU-2 (slit-wire type, one direction), HIBEMU-3 (Allison scanner type, one direction) and HIBEMU-4 (slit-wire type, two directions). For HIBEMU-2 and HIBEMU-3, more recent work has been done on software redesign in order to measure beam emittance and to draw phase diagram more efficiently and precisely. Software for control and data processing of them were developed in Labveiw environment, trying to improve calculation rationality and to offer user-friendly interface. Mechanical modification was also done for HIBEMU-3, mainly concentrating on the protection of Faraday cups from being overheated by the high intensity beam and also from interference of secondary electrons. This paper will also cover the mechanical structure as well as the software development of HIBEMU-4, which is a two-direction emittance scanner newly designed and manufactured for the high energy beam transport (HEBT) of Peking University Neutron Imaging FaciliTY (PKUNIFTY). At the end of this paper, comparison and analysis of the three HIBEMUs are given to draw forth better design of the future emittance measurement facility.展开更多
基金supported by the National Natural Science Foundation of China(Nos.12341501 and 11905074)。
文摘Precise transverse emittance assessment in electron beams is crucial for advancing high-brightness beam injectors.As opposed to intricate methodologies that use specialized devices,quadrupole focusing strength scanning(Q-scanning)techniques offer notable advantages for various injectors owing to their inherent convenience and cost-effectiveness.However,their stringent approximation conditions lead to inevitable errors in practical operation,thereby limiting their widespread application.This study addressed these challenges by revisiting the analytical derivation procedure and investigating the effects of the underlying approximation conditions.Preliminary corrections were explored through a combination of data processing analysis and numerical simulations.Furthermore,based on theoretical derivations,virtual measurements using beam dynamics calculations were employed to evaluate the correction reliability.Subsequent experimental validations were performed at the Huazhong University of Science and Technology injector to verify the effectiveness of the proposed compensation method.Both the virtual and experimental results confirm the feasibility and reliability of the enhanced Q-scanning-based diagnosis for transverse emittance in typical beam injectors operating under common conditions.Through the integration of these corrections and compensations,enhanced Q-scanning-based techniques emerge as promising alternatives to traditional emittance diagnosis methods.
基金funded by the Ministry of Education, Science and Technological Development of the Republic of Serbia via the FAMA project (research topic “Physics and chemistry with ion beams”)。
文摘Without knowing the emittance value, it is difficult to optimize ion beam optics for minimum beam loss during transmission, especially considering the very high emittance values of electron cyclotron resonance(ECR) ion sources.With this in mind, to measure the emittance of the ion beams produced by the mVINIS ECR, which is part of the FAMA facility at the Vin?a Institute of Nuclear Sciences, we have developed a pepper-pot scintillator screen system combined with a CMOS camera. The application, developed on the Lab VIEW platform, allows us to control the camera's main attribute settings, such as the shutter speed and the gain, record the images in the region of interest, and process and filter the images in real time. To analyze the data from the obtained image, we have developed an algorithm called measurement and analysis of ion beam luminosity(MAIBL) to reconstruct the four-dimensional(4D) beam profile and calculate the root mean square(RMS) emittance. Before measuring emittance, we performed a simulated experiment using the pepper-pot simulation(PPS) program. An exported file(PPS) gives a numerically generated raw image(mock image) of a beam with a predefined emittance value after it has passed through a pepper-pot mask. By analyzing data from mock images instead of the image obtained by the camera and putting it into the MAIBL algorithm, we can compare the calculated emittance with PPS's initial emittance value. In this paper, we present our computational tools and explain the method for verifying the correctness of the calculated emittance values.
文摘This paper presents an analytical description for the growth of the projected emittanee （here just referred to the transverse emittance） based on the concept of the slice emittance in an RF photoinjector. In the RF photoinjector, the slice emittance undergoes small changes, but the projected emittance changes significantly even in the drift space after the injector. Carefully adjusting the parameters of the RF photoinjector, which usually means emittance compensation, the projected emittance can be minimized to the value of the slice emittance. The relation between slice emittance and projected emittance is explained in this paper. An emittance function, which shows such a relation, is also introduced. A model about the emittance growth in the RF photoinjector is established, which accords with the particle simulation results by using the code ASTRA. The condition to minimize the emittance is also given by using the emittance function, which means the emittance compensation in the RF photoinjector.
基金supported by the National Natural Science Foundation of China(No.11775281)
文摘The transverse emittance of the extracted beam from the heavy ion medical machine cyclotron is measured and then optimized for injection into the synchrotron.For the purposes of cross-validation,three methods,i.e.,slit-grid,Q-scan,and 3-grid,are used to measure the emittance.In the slit-grid technique,an automatic selection of the region of interest is adopted to isolate the major noise from the beam phase space,which is an improvement over the traditional technique.After iterating over the contour level,an unbiased measurement of the emittance can be obtained.An improvement in the thin lens technique is implemented in the Q-scan method.The results of these measurements are presented.
基金supported by the Beamline Project of Shanghai Synchrotron Radiation Facility
文摘Beam emittance reduction is an effective method to increase the brightness of a synchrotron light source.Robinson wiggler can play a role in the beam emittance reduction by increasing the horizontal damping partition number.A replacement of the quadrupoles in the arc section with short combined function dipoles will construct a single-periodic Robinson wiggler in the SSRF storage ring.This scheme provides a lower beam emittance,without occupying any straight section.Detailed analysis is presented in this paper.
基金Project supported by the Scientific Research Start-up Fund Project of Hohai University (20080403)Natural Science Fund of Hohai University (2008427911)Natural Scienctific Research Innovation Foundation in Harbin Institute of Technology (HIT NSRIF 2009030)
文摘The La-Sr-Mn-O films were deposited on Si（100） substrates by DC magnetron sputtering and followed by air annealing at 973 K for I h. The microstructure and temperature dependence of total hemispherical emittance （εH） of the annealed La-Sr-Mn-O films prepared at various processing parameters were investigated. The results indicated the films deposited at lower sputtering pressure and lower O2（O2＋Ar） volume proportion （R0） were present in rhombohedral .perovskite structure and the length of MnO bond was shorter. The metal-insulator transition temperature （TMI） was higher. All of the annealed films showed the unique feature of variable emittance based on metal-insulator transition. The films showed low emittance at low temperature but high emittance at high temperature. Moreover, the εH significantly changed in the vicinity of TMI. The variability of total hemispherical emittance （△ε） and the temperature range with obvious emittance change could be adjusted by changing the processing parameters. The Aε could be 0.45 and △ε/ε355 （ε355 is the εH at 355K） exceeded 50% for the annealed La-Sr-Mn-O films. Therefore, the annealed La-Sr-Mn-O films showed much potential for thermal control applications as smart thermochromic variable emittance materials.
基金Project supported by the National Natural Science Foundation of China （Grant No 10347009）.
文摘Based on the multi-slit method, a new method is introduced to measure the nonlinear force caused emittance growth in a RF photoinjector. It is possible to reconstruct the phase space of a beam under some conditions by the multi-slit method. Based on the reconstructed phase space, besides the emittance, the emittance growth from the distortion of the phase space can also be measured. The emittance growth results from the effects of nonlinear force acting on electron, which is very important for the high quality beam in a RF photoinjector.
基金The project supported by China Science Foundation of Nuclear Industry
文摘The nonlinear space charge effect of bunched beam in linac is one of the im-portant factors that induces the emittance growth due to the conversion of the field en-ergy to kinetic energy.In this paper,the internal field energies associated with sometransverse nonuniform space charge distributions of a bunched beam,such as Gaussiandistribution,waterbag distribution and parabolic distribution,are worked out.And theemittance growth caused by these nonuniformities are obtained.
文摘The enhancement of trapping and the optimization of beam quality are two key issues of Laser Wakefield Acceleration (LWFA). The effect of a homogenous constant magnetic field B0, parallel to the direction of propagation of the pump pulse, is studied in the blowout regime via 2Dx3Dv Particle-In-Cell simulations. Electrons are injected into the wake using a counter-propagating low amplitude laser. Transverse currents are generated at the rim of the bubble, which results in the amplification of the B0 field at the rear of the bubble. Therefore the dynamics of the beam is modified, the main effect is the reduction of the transverse emittance when B0 is raised. Depending on beam loading effects the low energy tail, observed in the non-magnetized case, can be suppressed when B0 is applied, which provides a mono-energetic beam.
基金Project supported by the National Basic Research Program of China(Grant No.2014CB845502)the National Natural Science Foundation of China(Grant No.91126004)
文摘A combined unit, which has the ability to measure the current and emittance of the high intensity direct current（DC）ion beam, is developed at Peking University（PKU）. It is a multi-slit single-wire（MSSW）-type beam emittance meter combined with a water-cooled Faraday Cup, named high intensity beam emittance measurement unit-6（HIBEMU-6）. It takes about 15 seconds to complete one measurement of the beam current and its emittance. The emittance of a 50-mA@50-kV DC proton beam is measured.
基金The project supported by the National Natural Science Foundation of China(NSFC) the Science Foundation of Chinese Nuclear Industry
文摘The nonlinear space charge effect of bunched beam in linac is one of theimportant factors that induces the emittance growth due to the conversion of thefield energy to kinetic energy. Using a cylinder model of space charge in a linac,we derive the internal energy for a bunched beam with some nonuniform spacecharge distributions, such as Gaussian, waterbag and parabolic distributions inboth the longitudinal and transverse directions. And the emittance growth causedby these nonuniformities is worked out.
基金The project supported by the Nuclear Science Foundation of China
文摘RF effect and space charge effect are the main sources of the emittance growth in the RF elec-tron gun.The single particle dynamics near the cathode is discussed,and the emittance growth due to RFnonlinear force and time-dependent force are studied in detail.Comparison with the emittance at the gunexit shows that the emittanca growth due to nonlinear RF effect near the cathode can not be neglected.
基金The project supported by the National Natural Science Foundation of China and the Sciences Foundation of Chinese Nuclear Industry
文摘The nonlinear space charge effect of bunched beam in linac is one of the important factors thatinduces the emittance growth due to the conversion of the field energy to kinetic energy.In this paper,us-ing a cylinder model of space charge in linac,we derived the internal energy for a bunched beam withsome nonuniform space charge distributions,such as longitudinal Gaussian distribution combined withKapchinskij-Vladimirski1,waterbag,parabolic or Gaussian transverse distribution.And the emittancegrowth caused by the above distributions is worked out.
文摘Emittance is a key figure of merit for charged particle beams,and various diagnostic techniques have been developed to try to measure it accurately.To measure the transverse emittance,a traditional emittance measurement device,which consists of slits and wire scanners,is installed at the MEBT section of the Ci-ADS injector Ⅱ.
基金the NextGenerationEU(PNRR)Integrated Infrastructure Initiative in Photonic and Quantum Sciences(IPHOQS)(CUP B53C22001750006,ID D2B8D520,IR0000016)EuPRAXIA Advanced Photon Sources(EuAPS)(CUP I93C21000160006,IR0000030)+3 种基金funding from the Engineering and Physical Sciences Research Council(EP/L01663X/1)the Royal Society International Exchange(IES/R3/170248)Computing resources were provided by STFC Scientific Computing Department’s SCARF clusterfunded by the UK EPSRC(grants EP/G054950/1,EP/G056803/1,EP/G055165/1 and EP/M022463/1).
文摘Fast electron generation and transport in high-intensity laser–solid interactions induces X-ray emission and drives ion acceleration.Effective production of these sources hinges on an efficient laser absorption into the fast electron population and control of divergence as the beam propagates through the target.Nanowire targets can be employed to increase the laser absorption,but it is not yet clear how the fast electron beam properties are modified.Here we present novel measurements of the emittance of the exiting fast electron beam from irradiated solid planar and nanowire targets via a pepper-pot diagnostic.The measurements indicate a greater fast electron emittance is obtained from nanowire targets.Two-dimensional particle-in-cell simulations support this conclusion,revealing beam defocusing at the wire–substrate boundary,a higher fast electron temperature and transverse oscillatory motion around the wires.
基金supported by the National Natural Science Foundation of China(Grant No.52371176)
文摘Passive radiative cooling is a promising passive cooling technology that emits heat to deep space without energy consumption.Nevertheless,the persistent challenge of overcooling in static radiative techniques has raised concerns.Although a desirable solution is suggested based on vanadium dioxide(VO_(2))in the form of a Fabry-Perot(F-P)resonant cavity,the inherent contradiction between desired high emissivity(ε)and low solar absorptance(α_(sol))remains a notable limitation.Here,we employed a simple mask-filling technique to develop a temperature-adaptive metasurface radiative cooling device(ATMRD)for dynamic thermal regulation.Simulation and experimental results substantially evidenced that multiple localized polariton resonances were induced by the VO_(2)metasurface,significantly enhancing the thermal emittance of the ATMRDs.The engineered ATMRD achieved an amazing switch of the atmospheric window emittance from 0.13 to 0.85 when the surface temperature exceeds a pre-set transition temperature,accompanied by a commendableα_(sol)of 27.71%.The mechanism of multiple localized polariton resonances is discussed in detail to understand the enhanced performance based on the investigation of the relationship between the metasurface structure and multiple localized polariton resonances.We demonstrate an efficient smart radiative technique achieved by a simple micro/nanoprocess and,most importantly,contribute a valuable reference for the design of radiative devices,which is crucial in various areas such as passive cooling,smart windows,multifunctional electromagnetic response,and space application technologies.
文摘One should pay attention to quite a lot of factors when the emittance of high-current ion beam is measured. The background subtraction and threshold setting,the measuring method of pulsed beam emittance,as well as the error sources in the emittance measurements and its elimination or correction are discussed based on the experience during the R&D of three emittance measurement units for high-current ion beams at Peking University.
文摘Further studies on beam emittance measurement have been made to improve the emittance measurement precision at BEPCⅡ linac.Some problems in the measurement are solved and a code for beam emittance calculation is developed.With these improvements,the emittance measurement precision was upgraded.
基金Supported by National Natural Science Foundation of China(10675104)
文摘One kind of instantaneous electron beam emittance measurement system based on the optical transition radiation principle and double imaging optical method has been set up. It is mainly adopted in the test for the intense electron-beam produced by a linear induction accelerator. The system features two characteristics. The first one concerns the system synchronization signal triggered by the following edge of the main output waveform from a Blumlein switch. The synchronous precision of about 1 ns between the electron beam and the image capture time can be reached in this way so that the electron beam emittance at the desired time point can be obtained. The other advantage of the system is the ability to obtain the beam spot and beam divergence in one measurement so that the calculated result is the true beam emittance at that time, which can explain the electron beam condition. It provides to be a powerful beam diagnostic method for a 2.5 kA, 18.5 MeV, 90 ns （FWHM） electron beam pulse produced by Dragon I. The ability of the instantaneous measurement is about 3 ns and it can measure the beam emittance at any time point during one beam pulse. A series of beam emittances have been obtained for Dragon I. The typical beam spot is 9.0 mm （FWHM） in diameter and the corresponding beam divergence is about 10.5 mrad.
基金supported by the National Natural Science Foudation of China (Grant No. 11075008)
文摘Three sets of High Intensity Beam Emittance Measurement Units (HIBEMUs) are being developed at Peking University. They are HIBEMU-2 (slit-wire type, one direction), HIBEMU-3 (Allison scanner type, one direction) and HIBEMU-4 (slit-wire type, two directions). For HIBEMU-2 and HIBEMU-3, more recent work has been done on software redesign in order to measure beam emittance and to draw phase diagram more efficiently and precisely. Software for control and data processing of them were developed in Labveiw environment, trying to improve calculation rationality and to offer user-friendly interface. Mechanical modification was also done for HIBEMU-3, mainly concentrating on the protection of Faraday cups from being overheated by the high intensity beam and also from interference of secondary electrons. This paper will also cover the mechanical structure as well as the software development of HIBEMU-4, which is a two-direction emittance scanner newly designed and manufactured for the high energy beam transport (HEBT) of Peking University Neutron Imaging FaciliTY (PKUNIFTY). At the end of this paper, comparison and analysis of the three HIBEMUs are given to draw forth better design of the future emittance measurement facility.
