The helical undulator is in high demand in synchrotron radiation facilities for circular polarization generation.Owing to the higher field strength provided by the superconducting undulator compared to the conventiona...The helical undulator is in high demand in synchrotron radiation facilities for circular polarization generation.Owing to the higher field strength provided by the superconducting undulator compared to the conventional permanent-magnet undulator,greater research efforts should be directed toward this area.The helical superconducting undulator holds great potential in synchrotron radiation facilities,especially in low-energy storage rings that seek circularly polarized radiation with the highest possible radiation flux.Following the successful development of planar superconducting undulators,the Institute of High Energy Physics conducted research and development for the helical superconducting undulator.A 0.5-m-long Deltatype superconducting undulator prototype was developed and tested.Detailed information on the design,fabrication,and cryogenic testing of the prototype is presented and discussed.展开更多
Looking for new light sources, especially short wavelength laser light sources has attracted widespread attention. This paper analytically describes the radiation of a crystalline undulator field by the sine-squared p...Looking for new light sources, especially short wavelength laser light sources has attracted widespread attention. This paper analytically describes the radiation of a crystalline undulator field by the sine-squared potential. In the classical mechanics and the dipole approximation, the motion equation of a particle is reduced to a generalized pendulum equation with a damping term and a forcing term. The bifurcation behavior of periodic orbits is analyzed by using the Melnikov method and the numerical method, and the stability of the system is discussed. The results show that, in principle, the stability of the system relates to its parameters, and only by adjusting these parameters appropriately can the occurrence of bifurcation be avoided or suppressed.展开更多
The angular spectrum of spontaneous emission in a two-dimensional undulator free-electron laser is analyzed theoretically. Numerical calculation shows that the 3-th harmonic spontaneous emission power density can be g...The angular spectrum of spontaneous emission in a two-dimensional undulator free-electron laser is analyzed theoretically. Numerical calculation shows that the 3-th harmonic spontaneous emission power density can be greatly enhanced by using a two-dimensional undulator, for which l=s, so the harmonic number can be selected by selecting l. Therefore, the higher harmonic operation of a free-electron laser can be realized selectively.展开更多
APPLE-Knot undulator can effectively solve the on-axis heat load problem and is proven to perform well in VUV beamline and soft x-ray beamline in high energy storage ring. However, for soft x-ray beamline in a medium ...APPLE-Knot undulator can effectively solve the on-axis heat load problem and is proven to perform well in VUV beamline and soft x-ray beamline in high energy storage ring. However, for soft x-ray beamline in a medium energy ring,whether the APPLE-Knot undulator excels the APPLE undulator is still a question. Here, a merged APPLE-Knot undulator is studied to generate soft x-ray in a medium energy ring. Its advantages and problems are discussed. Though the on-axis heat load of the APPLE-Knot undulator is lower in linear polarization modes compared to the APPLE undulator, its flux is lower. The APPLE-Knot undulator shows no advantage when only fundamental harmonic is needed. However, in circular polarization mode, the APPLE-Knot undulator shows the ability to cover a broader energy range which can remedy the notable shortcoming of the APPLE undulator.展开更多
A numerical method for the optimum motion of an undulatory swimming plate is presented. The optimum problem is stated as minimizing the power input under the condition of fixed thrust. The problem is singular for the ...A numerical method for the optimum motion of an undulatory swimming plate is presented. The optimum problem is stated as minimizing the power input under the condition of fixed thrust. The problem is singular for the invisible modes, and therefore the commonly used Lagrange multiplier method cannot predict an optimum solution but just a saddle point. To eliminate the singularity, an additional amplitude inequality constraint is added to the problem. A numerical optimization code with a sequential quadratic programming method is used to solve the problem. The method is applied to several cases of the motion of two-dimensional and three-dimensional undulatory plates, and the optimum results are obtained.展开更多
Background Nineteen undulators of various types are being fabricated for high-energy photon source(HEPS).In order to ensure the optical performance of the undulators,the girder deformation is usually carefully optimiz...Background Nineteen undulators of various types are being fabricated for high-energy photon source(HEPS).In order to ensure the optical performance of the undulators,the girder deformation is usually carefully optimized during the structural design stage.Purpose Optimization of magnet girder deformation is one of the key points to ensure undulator magneticfield performance.To reduce magnet girder deformation,base plate,feet and strong back should be designed carefully.In the HEPS undulator design and manufacturing stage,it is found that under special circumstances,such as after the height of the feet is adjusted,or after the undulator is lifted to other place,the base plate and girder may deform more than expected.Methods Therefore based on ANSYS simulation and experimental test results,the factors causing the deformation of the girders are carefully analyzed.Base plate and feet were optimized for different types of undulators to avoid girder deformation.Related simulation and laser tracker measurement were performed tofind out the reason in this paper.Results and conclusion Results show that the base plate of C-frame undulators will collapse and deform under the action of magnetic force.Asymmetric sagged base plate is the main reason of girder deformation.Increasing the thickness of the base plate and increasing the number of feet can both reduce that deformation.Optimization of magnet girder deformation is one of the key points to ensure undulator magneticfield performance.To reduce magnet girder deformation,base plate,feet and strong back should be designed carefully.展开更多
The undulator is the key component in the compact THz radiation source based on FEL.By matching the adjustable period magnetic field of the undulator with the optical resonance cavity,the passing electron beam will ge...The undulator is the key component in the compact THz radiation source based on FEL.By matching the adjustable period magnetic field of the undulator with the optical resonance cavity,the passing electron beam will generate coherent radiation with gain,and the radiation power required by THz source can be achieved finally. Compared with the pure permanent magnet type,the hybrid type undulator can decrease the field errors caused by non-homogeneous magnetization of magnetic blocks,and provide higher magnetic field.The conceptual design of a hybrid undulator used for THz radiation source is introduced.We use the FEM code OPERA/TOSCA to simulate 3D magnetic field of the undulator.After optimizing the end structure of the hybrid undulator,the first field integrals is controlled within 0.01Gs.m,and the deviation of the electron beam is less than 0.02mm.展开更多
In this paper we discuss the theory of undulator radiation in an electromagnet undulator. We discuss the spectral properties of undulator radiation when electrons are injected off the undulator axis. This paper highli...In this paper we discuss the theory of undulator radiation in an electromagnet undulator. We discuss the spectral properties of undulator radiation when electrons are injected off the undulator axis. This paper highlights the distinctive features of the radiation spectrum from electromagnet undulators, as compared to PPM undulators.展开更多
Background High energy photon source(HEPS)is the fourth-generation light source,which uses a large number of highperformance insertion devices to generate synchrotron radiation.The control system is an important part ...Background High energy photon source(HEPS)is the fourth-generation light source,which uses a large number of highperformance insertion devices to generate synchrotron radiation.The control system is an important part of the insertion device(ID).Purpose Cryogenic permanent magnet undulator(CPMU)is one kind of IDs that works in liquid nitrogen temperature and ultra-high vacuum environment,and its control system is more difficult and complex than in-air ID.The design of the control system for CPMU will be introduced in detail.Method The sub-systems include high-precision magnetic gap control,safety protection,measurement and compensation of magnetic gap at cryogenic temperature and cryogenic temperature monitoring.Mature,reliable,stable technical schemes are designed to meet the technical specifications of sub-systems.Results The experiment results show that the magnetic gap motion accuracy can be controlled within 0.2–0.3μm under the step size of 1μm.The safety protection system has been tested in turn,and the predetermined protection can be achieved.The average value of magnetic gap cold contraction is 1.512 mm measured by optical micrometer,and the compensation is realized by software.The average temperature of the main magnet structure measured by the temperature sensors is 81.0 K,and the temperature gradient is 0.7 K/m.The temperature monitoring is reliable and stable.Conclusion The CPMU control system which is based on EPICS has been successfully applied to the CPMU prototype,and the test results have met the design specifications.展开更多
For the success of PAL-XFEL, two critical systems, namely a low emittance injector and a variable gap out-vacuum undulator, are under development. In order to realize the target emittance of the PAL-XFEL injector we c...For the success of PAL-XFEL, two critical systems, namely a low emittance injector and a variable gap out-vacuum undulator, are under development. In order to realize the target emittance of the PAL-XFEL injector we carried out an optimization study of various parameters, such as the laser beam transverse profile, the laser pulse length, the laser phase,and the gun energy. The transverse emittance measured at the Injector Test Facility(ITF) is εx=0.48±0.01 mm mrad.An undulator prototype based on the EU-XFEL design and modified for PAL-XFEL was built and tested. A local-K pole tuning procedure was developed and tested. A significant reduction(90%) of the local-K fluctuation was observed. The requirement of undulator field reproducibility better than 2×10-4and the undulator gap setting accuracy below 1 μm were achieved for the prototype. The optical phase jitter after the pole height tuning at the tuning gap was calculated to be 2.6? rms, which satisfies the requirement of 5.0?.展开更多
A simple analysis is given for the optimum length of undulator in a self-seeding free electron laser （FEL）. The obtained relations show the correlation between the undulator length and the system parameters. The pow...A simple analysis is given for the optimum length of undulator in a self-seeding free electron laser （FEL）. The obtained relations show the correlation between the undulator length and the system parameters. The power required for the seeding in the second part of the undulator and the overall efficiency of monochromatizating the seeding determine the length of the first part of the undulator; the magnitude of seeding power dominates the length of the second part of the undulator; the whole length of the undulator in a self-seeding FEL is determined by the overall efficiency for getting coherent seed, and is about half as long again as that of SASE, not including the dispersion section. The requirement of the dispersion section strength is also analyzed.展开更多
Introduction A novel type of pure permanent cryogenic Delta–Knot Undulator was developed at IHEP to supply a high flux of full adjustable polarization synchrotron radiation with low on-axis power density.This prototy...Introduction A novel type of pure permanent cryogenic Delta–Knot Undulator was developed at IHEP to supply a high flux of full adjustable polarization synchrotron radiation with low on-axis power density.This prototype was an active attempt and early exploration for future APPLE–Knot undulator,which will be used at high energy photon source(HEPS).Materials and methods There are several challenges to develop a cryogenic delta undulator,such as the complicated structure,the influence of large magnetic force,and the magnetic measurement difficulty due to the very small gap.In this paper,the mechanical design for overcoming these difficulties will be presented in detail.Conclusion A special hall measuring system is developed,and the preliminary results agree with the theoretical results.This undulator prototype will provide valuable experience for angle magnetization technology,intricate magnetic attraction structure design,and magnetic field measurement under closed small space.展开更多
A new stretched-wire system is built for a cryogenic permanent magnet undulator in High Energy Photon Source Testing Facility.The system has two functions:integral field measurement and magnet gap measurement.Integral...A new stretched-wire system is built for a cryogenic permanent magnet undulator in High Energy Photon Source Testing Facility.The system has two functions:integral field measurement and magnet gap measurement.Integral field measurement and gap measurement are important for evaluation and optimization of the magnetic performance of the undulator in cryogenic-vacuum environment.Two high-precision,high-load motion stages are used for accurate positioning.A special fix structure of stretched wire is adopted for vacuum environment.To reduce the deflection of the 3-meter-long wire,constant tension is maintained along the wire.The measurement repeatability of field integral and magnetic gap is the key performance which depends on the stability of wire and suppression of the electric noise.Strategy of improving the measurement accuracy and stability is presented.展开更多
Purpose A new in-vacuum three-dimensional Hall probe magnetic measurement system is under fabrication for characterizing the magnetic performance of the Cryogenic Permanent Magnet Undulator(CPMU).In order to fit the s...Purpose A new in-vacuum three-dimensional Hall probe magnetic measurement system is under fabrication for characterizing the magnetic performance of the Cryogenic Permanent Magnet Undulator(CPMU).In order to fit the small gap(5 mm)of magnetic structure and vacuum environment,a small three-dimensional Hall probe has been manufactured.The angular and positional misalignment errors of the Hall sensors play an important role in the measurement accuracy of the CPMU.In order to minimize the misalignment errors,a method of calibrating angle error and relative assembly displacements of a three-dimensional Hall probe is carried out.Methods The angle error of Hall sensors will be calibrated by a standard dipole magnet and a five-dimensional Hall bench.The standard dipole magnet will generate a single direction and uniform magnetic field.And the fivedimensional Hall bench is used to rotate the Hall probe which is put in the center of magnet.Based on the relationship between angle and magnetic field strength,the angle error of each Hall sensor will be obtained.The relative position between the sensitive areas of the Hall sensors will be calibrated by a two-dimensional magnetic field undulator section.Based on Maxwell’s equations,through the calculation of measurement magnetic field strength,the relative assembly displacements of the three Hall sensors can be derived.Results The details of the calibration methods and the data processing of angle error and relative assembly displacements of a three-dimensional Hall probe are presented.The three-dimensional magnetic fields of a cryogenic permanent magnet undulator can be received accurately by correcting these angle errors and position errors of Hall sensors.Conclusions This paper illustrates the relative position and angle calibration procedures and the data processing of a three-dimensional Hall probe.Now the design of a smaller Hall probe is in process.The calibration of the angle errors and position errors will be carried out after the fabrication of the standard dipole magnet.展开更多
The design and development status of Sm2Co17 magnet blocks for two in-vacuum undulators （IVU20） at the SSRF with the same hybrid design has been described. By the technological improvement of some processes and comp...The design and development status of Sm2Co17 magnet blocks for two in-vacuum undulators （IVU20） at the SSRF with the same hybrid design has been described. By the technological improvement of some processes and comparison with the experimental Sm2Co17 magnet blocks for the IVU25A, magnetic properties such as the intrinsic coercive force Hci and the average magnetic moment M are increased, the bend point magnetic field Hk value and pass rate are significantly increased, and the magnetic field uniformity of the magnet blocks are significantly improved. The basic developmental method of high uniformity Sm2Co17 magnet blocks for IVU20 is presented. The magnetic field qualities of the magnet blocks, including the magnetic property, the magnetic moment distribution, the magnetization deviation angle and the magnetic field uniformity, basically satisfy the specifications of the two IVU20 in-vacuum undulators.展开更多
Since the beta function of the electron beam within the undulator has a great influence on the power gain of the free electron laser（FEL）,optimization of the undulator lattice becomes important.In this paper,the tra...Since the beta function of the electron beam within the undulator has a great influence on the power gain of the free electron laser（FEL）,optimization of the undulator lattice becomes important.In this paper,the transfer matrix of the planar undulator is obtained from differential equations of the electron motion.Based on this,the lattice function of the planar undulator in a terahertz FEL oscillator proposed by Huazhong University of Science and Technology（HUST-FEL） is optimized and the expressions of the average beta function are derived.The accuracy of the optimization result was confirmed well by the numerical method.The application range of this analytical method is given as well.At last,the emittance growth in the horizontal direction due to the attenuation of the magnetic field is discussed.展开更多
The magnetic field stability of the PrFeB magnets is one of the key points which affect its application in such devices as cryogenic permanent magnet undulators. In this study, the magnetic properties and micro struct...The magnetic field stability of the PrFeB magnets is one of the key points which affect its application in such devices as cryogenic permanent magnet undulators. In this study, the magnetic properties and micro structure of PrFeB magnets, which were developed by the grain boundary diffusion, were examined. The demagnetizing field distribution of the cryogenic permanent magnet undulator made using the PrFeB magnets was simulated by Radia, and the change mechanism of the irreversible demagnetization following treatments at high temperatures was experimentally studied, The results show that the intrinsic coercivity of the PrFeB magnets can be increased by diffusion of Tb. Meanwhile, the remanence of the magnets displays almost no loss, and the increasing range is closely related to the orientation thickness of the PrFeB magnet, Therefore, the PrFeB magnets developed using grain boundary diffusion are found to have extremely high comprehensive magnetic properties, The irreversible demagnetization of the PrFeB magnets developed by grain boundary diffusion for the CPMU is determined to be significantly improved following high-temperature treatments.展开更多
We propose a proof-of-principle experiment to test a new scheme to produce a single-cycle radiation pulse in free-electron lasers(FELs). Here, a few α-BBO crystals will be first used to produce an equally spaced lase...We propose a proof-of-principle experiment to test a new scheme to produce a single-cycle radiation pulse in free-electron lasers(FELs). Here, a few α-BBO crystals will be first used to produce an equally spaced laser pulse train.Then, the laser pulse train illuminates the cathode to produce a frequency-chirped electron bunch train in a photocathode rf gun. Finally, the frequency-chirped electron bunch train passes through a tapered undulator to produce a quasi-single-cycle THz pulse. This experiment should allow comparison and confirmation of predictive models and scaling laws, and the preliminary experimental results will also be discussed.展开更多
Undulators are key devices to produce brilliant synchrotron radiation at the synchrotron radiation facilities. In this paper we present a numerical computing method, including the computing program that has been devel...Undulators are key devices to produce brilliant synchrotron radiation at the synchrotron radiation facilities. In this paper we present a numerical computing method, including the computing program that has been developed to calculate the spontaneous radiation emitted from relativistic electrons in undulators by simulating the electrons＇ trajectory. The effects of electron beam emittance and energy spread have also been taken into account. Comparing with other computing methods available at present, this method has a few advantages with respect to several aspects. It can adopt any measured or arbitrarily simulated 3D magnetic field and arbitrary electron beam pattern for the calculation and it＇s able to analyze undulators of any type of magnetic structure. It＇s expected to predict precisely the practical radiation spectrum. The calculation results of a short period in-vacuum undulator and an Elliptically Polarized Undulator （EPU） at Shanghai Synchrotron Radiation Facility （SSRF） are presented as examples.展开更多
Indus-2 is an Indian synchrotron light source, operating at 2.5 Ge V and generating synchrotron radiation from its bending magnets. In order to provide more intense synchrotron radiation to the synchrotron users, ther...Indus-2 is an Indian synchrotron light source, operating at 2.5 Ge V and generating synchrotron radiation from its bending magnets. In order to provide more intense synchrotron radiation to the synchrotron users, there is a plan to install five insertion devices in the Indus-2 storage ring. In the first phase of installation of insertion devices, there is a proposal to install two out- vacuum pure permanent magnet linearly polarized undulators in long straight sections of the Indus-2 storage ring. The presence of the insertion devices in the ring has inevitable effects on beam parameters like betatron tune, betatron amplitude function, closed orbit, emittance, energy spread and dynamic aperture etc. In this paper, the effect of two undulators on the above mentioned parameters of the Indus-2stored electron beam at 2.5 Ge V is presented. Moreover a correction scheme for the restoration of the betatron tune and amplitude function is also presented.展开更多
基金supported by the National Natural Science Foundation of China(No.E1113R5C10)。
文摘The helical undulator is in high demand in synchrotron radiation facilities for circular polarization generation.Owing to the higher field strength provided by the superconducting undulator compared to the conventional permanent-magnet undulator,greater research efforts should be directed toward this area.The helical superconducting undulator holds great potential in synchrotron radiation facilities,especially in low-energy storage rings that seek circularly polarized radiation with the highest possible radiation flux.Following the successful development of planar superconducting undulators,the Institute of High Energy Physics conducted research and development for the helical superconducting undulator.A 0.5-m-long Deltatype superconducting undulator prototype was developed and tested.Detailed information on the design,fabrication,and cryogenic testing of the prototype is presented and discussed.
文摘Looking for new light sources, especially short wavelength laser light sources has attracted widespread attention. This paper analytically describes the radiation of a crystalline undulator field by the sine-squared potential. In the classical mechanics and the dipole approximation, the motion equation of a particle is reduced to a generalized pendulum equation with a damping term and a forcing term. The bifurcation behavior of periodic orbits is analyzed by using the Melnikov method and the numerical method, and the stability of the system is discussed. The results show that, in principle, the stability of the system relates to its parameters, and only by adjusting these parameters appropriately can the occurrence of bifurcation be avoided or suppressed.
文摘The angular spectrum of spontaneous emission in a two-dimensional undulator free-electron laser is analyzed theoretically. Numerical calculation shows that the 3-th harmonic spontaneous emission power density can be greatly enhanced by using a two-dimensional undulator, for which l=s, so the harmonic number can be selected by selecting l. Therefore, the higher harmonic operation of a free-electron laser can be realized selectively.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. U1632266, 11927807, and U2032207)。
文摘APPLE-Knot undulator can effectively solve the on-axis heat load problem and is proven to perform well in VUV beamline and soft x-ray beamline in high energy storage ring. However, for soft x-ray beamline in a medium energy ring,whether the APPLE-Knot undulator excels the APPLE undulator is still a question. Here, a merged APPLE-Knot undulator is studied to generate soft x-ray in a medium energy ring. Its advantages and problems are discussed. Though the on-axis heat load of the APPLE-Knot undulator is lower in linear polarization modes compared to the APPLE undulator, its flux is lower. The APPLE-Knot undulator shows no advantage when only fundamental harmonic is needed. However, in circular polarization mode, the APPLE-Knot undulator shows the ability to cover a broader energy range which can remedy the notable shortcoming of the APPLE undulator.
文摘A numerical method for the optimum motion of an undulatory swimming plate is presented. The optimum problem is stated as minimizing the power input under the condition of fixed thrust. The problem is singular for the invisible modes, and therefore the commonly used Lagrange multiplier method cannot predict an optimum solution but just a saddle point. To eliminate the singularity, an additional amplitude inequality constraint is added to the problem. A numerical optimization code with a sequential quadratic programming method is used to solve the problem. The method is applied to several cases of the motion of two-dimensional and three-dimensional undulatory plates, and the optimum results are obtained.
文摘Background Nineteen undulators of various types are being fabricated for high-energy photon source(HEPS).In order to ensure the optical performance of the undulators,the girder deformation is usually carefully optimized during the structural design stage.Purpose Optimization of magnet girder deformation is one of the key points to ensure undulator magneticfield performance.To reduce magnet girder deformation,base plate,feet and strong back should be designed carefully.In the HEPS undulator design and manufacturing stage,it is found that under special circumstances,such as after the height of the feet is adjusted,or after the undulator is lifted to other place,the base plate and girder may deform more than expected.Methods Therefore based on ANSYS simulation and experimental test results,the factors causing the deformation of the girders are carefully analyzed.Base plate and feet were optimized for different types of undulators to avoid girder deformation.Related simulation and laser tracker measurement were performed tofind out the reason in this paper.Results and conclusion Results show that the base plate of C-frame undulators will collapse and deform under the action of magnetic force.Asymmetric sagged base plate is the main reason of girder deformation.Increasing the thickness of the base plate and increasing the number of feet can both reduce that deformation.Optimization of magnet girder deformation is one of the key points to ensure undulator magneticfield performance.To reduce magnet girder deformation,base plate,feet and strong back should be designed carefully.
文摘The undulator is the key component in the compact THz radiation source based on FEL.By matching the adjustable period magnetic field of the undulator with the optical resonance cavity,the passing electron beam will generate coherent radiation with gain,and the radiation power required by THz source can be achieved finally. Compared with the pure permanent magnet type,the hybrid type undulator can decrease the field errors caused by non-homogeneous magnetization of magnetic blocks,and provide higher magnetic field.The conceptual design of a hybrid undulator used for THz radiation source is introduced.We use the FEM code OPERA/TOSCA to simulate 3D magnetic field of the undulator.After optimizing the end structure of the hybrid undulator,the first field integrals is controlled within 0.01Gs.m,and the deviation of the electron beam is less than 0.02mm.
文摘In this paper we discuss the theory of undulator radiation in an electromagnet undulator. We discuss the spectral properties of undulator radiation when electrons are injected off the undulator axis. This paper highlights the distinctive features of the radiation spectrum from electromagnet undulators, as compared to PPM undulators.
文摘Background High energy photon source(HEPS)is the fourth-generation light source,which uses a large number of highperformance insertion devices to generate synchrotron radiation.The control system is an important part of the insertion device(ID).Purpose Cryogenic permanent magnet undulator(CPMU)is one kind of IDs that works in liquid nitrogen temperature and ultra-high vacuum environment,and its control system is more difficult and complex than in-air ID.The design of the control system for CPMU will be introduced in detail.Method The sub-systems include high-precision magnetic gap control,safety protection,measurement and compensation of magnetic gap at cryogenic temperature and cryogenic temperature monitoring.Mature,reliable,stable technical schemes are designed to meet the technical specifications of sub-systems.Results The experiment results show that the magnetic gap motion accuracy can be controlled within 0.2–0.3μm under the step size of 1μm.The safety protection system has been tested in turn,and the predetermined protection can be achieved.The average value of magnetic gap cold contraction is 1.512 mm measured by optical micrometer,and the compensation is realized by software.The average temperature of the main magnet structure measured by the temperature sensors is 81.0 K,and the temperature gradient is 0.7 K/m.The temperature monitoring is reliable and stable.Conclusion The CPMU control system which is based on EPICS has been successfully applied to the CPMU prototype,and the test results have met the design specifications.
基金supported by the Ministry of Science,ICT and Future Planning of Korea
文摘For the success of PAL-XFEL, two critical systems, namely a low emittance injector and a variable gap out-vacuum undulator, are under development. In order to realize the target emittance of the PAL-XFEL injector we carried out an optimization study of various parameters, such as the laser beam transverse profile, the laser pulse length, the laser phase,and the gun energy. The transverse emittance measured at the Injector Test Facility(ITF) is εx=0.48±0.01 mm mrad.An undulator prototype based on the EU-XFEL design and modified for PAL-XFEL was built and tested. A local-K pole tuning procedure was developed and tested. A significant reduction(90%) of the local-K fluctuation was observed. The requirement of undulator field reproducibility better than 2×10-4and the undulator gap setting accuracy below 1 μm were achieved for the prototype. The optical phase jitter after the pole height tuning at the tuning gap was calculated to be 2.6? rms, which satisfies the requirement of 5.0?.
基金Supported by Major State Basic Research Development Program(2011CB808301)National Natural Science Foundation of China(11375199)
文摘A simple analysis is given for the optimum length of undulator in a self-seeding free electron laser （FEL）. The obtained relations show the correlation between the undulator length and the system parameters. The power required for the seeding in the second part of the undulator and the overall efficiency of monochromatizating the seeding determine the length of the first part of the undulator; the magnitude of seeding power dominates the length of the second part of the undulator; the whole length of the undulator in a self-seeding FEL is determined by the overall efficiency for getting coherent seed, and is about half as long again as that of SASE, not including the dispersion section. The requirement of the dispersion section strength is also analyzed.
基金The Grant No.is 11675207.Project name:The Physical and Technical Study of Quasi-eriodic DELTA Undulator working at liquid nitrogen temperature.
文摘Introduction A novel type of pure permanent cryogenic Delta–Knot Undulator was developed at IHEP to supply a high flux of full adjustable polarization synchrotron radiation with low on-axis power density.This prototype was an active attempt and early exploration for future APPLE–Knot undulator,which will be used at high energy photon source(HEPS).Materials and methods There are several challenges to develop a cryogenic delta undulator,such as the complicated structure,the influence of large magnetic force,and the magnetic measurement difficulty due to the very small gap.In this paper,the mechanical design for overcoming these difficulties will be presented in detail.Conclusion A special hall measuring system is developed,and the preliminary results agree with the theoretical results.This undulator prototype will provide valuable experience for angle magnetization technology,intricate magnetic attraction structure design,and magnetic field measurement under closed small space.
文摘A new stretched-wire system is built for a cryogenic permanent magnet undulator in High Energy Photon Source Testing Facility.The system has two functions:integral field measurement and magnet gap measurement.Integral field measurement and gap measurement are important for evaluation and optimization of the magnetic performance of the undulator in cryogenic-vacuum environment.Two high-precision,high-load motion stages are used for accurate positioning.A special fix structure of stretched wire is adopted for vacuum environment.To reduce the deflection of the 3-meter-long wire,constant tension is maintained along the wire.The measurement repeatability of field integral and magnetic gap is the key performance which depends on the stability of wire and suppression of the electric noise.Strategy of improving the measurement accuracy and stability is presented.
文摘Purpose A new in-vacuum three-dimensional Hall probe magnetic measurement system is under fabrication for characterizing the magnetic performance of the Cryogenic Permanent Magnet Undulator(CPMU).In order to fit the small gap(5 mm)of magnetic structure and vacuum environment,a small three-dimensional Hall probe has been manufactured.The angular and positional misalignment errors of the Hall sensors play an important role in the measurement accuracy of the CPMU.In order to minimize the misalignment errors,a method of calibrating angle error and relative assembly displacements of a three-dimensional Hall probe is carried out.Methods The angle error of Hall sensors will be calibrated by a standard dipole magnet and a five-dimensional Hall bench.The standard dipole magnet will generate a single direction and uniform magnetic field.And the fivedimensional Hall bench is used to rotate the Hall probe which is put in the center of magnet.Based on the relationship between angle and magnetic field strength,the angle error of each Hall sensor will be obtained.The relative position between the sensitive areas of the Hall sensors will be calibrated by a two-dimensional magnetic field undulator section.Based on Maxwell’s equations,through the calculation of measurement magnetic field strength,the relative assembly displacements of the three Hall sensors can be derived.Results The details of the calibration methods and the data processing of angle error and relative assembly displacements of a three-dimensional Hall probe are presented.The three-dimensional magnetic fields of a cryogenic permanent magnet undulator can be received accurately by correcting these angle errors and position errors of Hall sensors.Conclusions This paper illustrates the relative position and angle calibration procedures and the data processing of a three-dimensional Hall probe.Now the design of a smaller Hall probe is in process.The calibration of the angle errors and position errors will be carried out after the fabrication of the standard dipole magnet.
基金Supported by National Important Project on Science of SSRF
文摘The design and development status of Sm2Co17 magnet blocks for two in-vacuum undulators （IVU20） at the SSRF with the same hybrid design has been described. By the technological improvement of some processes and comparison with the experimental Sm2Co17 magnet blocks for the IVU25A, magnetic properties such as the intrinsic coercive force Hci and the average magnetic moment M are increased, the bend point magnetic field Hk value and pass rate are significantly increased, and the magnetic field uniformity of the magnet blocks are significantly improved. The basic developmental method of high uniformity Sm2Co17 magnet blocks for IVU20 is presented. The magnetic field qualities of the magnet blocks, including the magnetic property, the magnetic moment distribution, the magnetization deviation angle and the magnetic field uniformity, basically satisfy the specifications of the two IVU20 in-vacuum undulators.
文摘Since the beta function of the electron beam within the undulator has a great influence on the power gain of the free electron laser（FEL）,optimization of the undulator lattice becomes important.In this paper,the transfer matrix of the planar undulator is obtained from differential equations of the electron motion.Based on this,the lattice function of the planar undulator in a terahertz FEL oscillator proposed by Huazhong University of Science and Technology（HUST-FEL） is optimized and the expressions of the average beta function are derived.The accuracy of the optimization result was confirmed well by the numerical method.The application range of this analytical method is given as well.At last,the emittance growth in the horizontal direction due to the attenuation of the magnetic field is discussed.
基金Project supported by the Natural Science Foundation of Shanghai(15ZR1448000)the State Key Lab of Advanced Metals and Materials(2016-Z03)
文摘The magnetic field stability of the PrFeB magnets is one of the key points which affect its application in such devices as cryogenic permanent magnet undulators. In this study, the magnetic properties and micro structure of PrFeB magnets, which were developed by the grain boundary diffusion, were examined. The demagnetizing field distribution of the cryogenic permanent magnet undulator made using the PrFeB magnets was simulated by Radia, and the change mechanism of the irreversible demagnetization following treatments at high temperatures was experimentally studied, The results show that the intrinsic coercivity of the PrFeB magnets can be increased by diffusion of Tb. Meanwhile, the remanence of the magnets displays almost no loss, and the increasing range is closely related to the orientation thickness of the PrFeB magnet, Therefore, the PrFeB magnets developed using grain boundary diffusion are found to have extremely high comprehensive magnetic properties, The irreversible demagnetization of the PrFeB magnets developed by grain boundary diffusion for the CPMU is determined to be significantly improved following high-temperature treatments.
基金supported by the Major State Basic Research Development Program of China (grants no.2015CB859700)by the National Natural Science Foundation of China (grants no.11327902)Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning (no.SHDP201507)
文摘We propose a proof-of-principle experiment to test a new scheme to produce a single-cycle radiation pulse in free-electron lasers(FELs). Here, a few α-BBO crystals will be first used to produce an equally spaced laser pulse train.Then, the laser pulse train illuminates the cathode to produce a frequency-chirped electron bunch train in a photocathode rf gun. Finally, the frequency-chirped electron bunch train passes through a tapered undulator to produce a quasi-single-cycle THz pulse. This experiment should allow comparison and confirmation of predictive models and scaling laws, and the preliminary experimental results will also be discussed.
文摘Undulators are key devices to produce brilliant synchrotron radiation at the synchrotron radiation facilities. In this paper we present a numerical computing method, including the computing program that has been developed to calculate the spontaneous radiation emitted from relativistic electrons in undulators by simulating the electrons＇ trajectory. The effects of electron beam emittance and energy spread have also been taken into account. Comparing with other computing methods available at present, this method has a few advantages with respect to several aspects. It can adopt any measured or arbitrarily simulated 3D magnetic field and arbitrary electron beam pattern for the calculation and it＇s able to analyze undulators of any type of magnetic structure. It＇s expected to predict precisely the practical radiation spectrum. The calculation results of a short period in-vacuum undulator and an Elliptically Polarized Undulator （EPU） at Shanghai Synchrotron Radiation Facility （SSRF） are presented as examples.
文摘Indus-2 is an Indian synchrotron light source, operating at 2.5 Ge V and generating synchrotron radiation from its bending magnets. In order to provide more intense synchrotron radiation to the synchrotron users, there is a plan to install five insertion devices in the Indus-2 storage ring. In the first phase of installation of insertion devices, there is a proposal to install two out- vacuum pure permanent magnet linearly polarized undulators in long straight sections of the Indus-2 storage ring. The presence of the insertion devices in the ring has inevitable effects on beam parameters like betatron tune, betatron amplitude function, closed orbit, emittance, energy spread and dynamic aperture etc. In this paper, the effect of two undulators on the above mentioned parameters of the Indus-2stored electron beam at 2.5 Ge V is presented. Moreover a correction scheme for the restoration of the betatron tune and amplitude function is also presented.
