FELiChEM is a new experimental facility under construction at the University of Science and Technology of China（USTC）. Its core device is two free electron laser oscillators generating middle-infrared and far-infrar...FELiChEM is a new experimental facility under construction at the University of Science and Technology of China（USTC）. Its core device is two free electron laser oscillators generating middle-infrared and far-infrared laser and covering the spectral range of 2.5–200 μm. It will be a dedicated infrared light source aiming at energy chemistry research. We present the brief design of the FEL oscillators, with the emphasis put on the middle-infrared oscillator.Most of the basic parameters are determined and the anticipated performance of the output radiation is given. The first light of FELiChEM is targeted for the end of 2017.展开更多
In order to meet the requirements of the synchrotron radiation users, a fully coherent VUV free electron laser （FEL） has been preliminarily designed. One important goal of this design is that the radiation wavelengt...In order to meet the requirements of the synchrotron radiation users, a fully coherent VUV free electron laser （FEL） has been preliminarily designed. One important goal of this design is that the radiation wavelength can be easily tuned in a broad range （70 170 nm）. In the light of the users＇ demand and our actual conditions, the self-seeding scheme is adopted for this proposal. Firstly, we attempted to fix the electron energy and only changed the undulator gap to vary the radiation wavelength; however, our analysis implies that this is difficult because of the great difference of the power gain length and FEL efficiency at different wavelengths. Therefore, we have considered dividing the wavelength range into three subareas. In each subarea, a constant electron energy is used and the wavelength tuning is realized only by adjusting the undulator gap. The simulation results show that this scheme has an acceptable performance.展开更多
The enhanced high gain harmonic generation （EHGHG） scheme has been proposed and shown to be able to significantly enhance the performance of HGHG FEL. In this paper we investigate the EHGHG scheme with negative disp...The enhanced high gain harmonic generation （EHGHG） scheme has been proposed and shown to be able to significantly enhance the performance of HGHG FEL. In this paper we investigate the EHGHG scheme with negative dispersion. The bunching factor at the entrance of the radiator is analyzed, which indicates that the scheme with negative dispersion can further weaken the negative effect of the dispersive strength on the energy spread correction factor. The numerical results from GENESIS （3D-code） are presented, and are in good agreement with our analysis. Then we comparatively study the effects of the initial beam energy spread and the relative phase shift on the radiation power. The results show that the EHGHG scheme with negative dispersion has a larger tolerance on the initial beam energy spread and a nearly equal wide good region of the relative phase shift compared with the case of positive dispersion.展开更多
We put forward a method to optimize the single-step tapering amplitude of undulator strength and initial energy tuning of electron beam to maximize the saturation power of high gain free-electron lasers （FELs）, base...We put forward a method to optimize the single-step tapering amplitude of undulator strength and initial energy tuning of electron beam to maximize the saturation power of high gain free-electron lasers （FELs）, based on the physics of longitudinal electron beam phase space. Using the FEL simulation code GENESIS, we numerically demonstrate the accuracy of the estimations for parameters corresponding to the linac coherent light source and the Tesla test facility.展开更多
There is an empirical formula describing the relationship between the peak magnetic field and the undulator structure parameters for a uniform-parameter hybrid undulator. In this paper, we investigate the relationship...There is an empirical formula describing the relationship between the peak magnetic field and the undulator structure parameters for a uniform-parameter hybrid undulator. In this paper, we investigate the relationship for a linearly tapered undulator through numerical calculation by using the code RADIA, and check it with the empirical formula. The results imply that this empirical formula is also effective for linearly tapered undulators at a big enough scope for the requirements of normal FEL experiments. Therefore, for a linearly tapered undulator, we can use the empirical formula to design the variation of the undulator gap. For the tapering rate demanded by normal FEL experiments, the gap of a linearly tapered undulator increases almost linearly, and the tapering rate will keep constant while adjusting the undulator gap with the same variation for each undulator period.展开更多
FELiChEM is an infrared free electron laser（FEL） facility currently under construction, which consists of two oscillators generating middle-infrared and far-infrared laser covering the spectral range of 2.5–200 μm...FELiChEM is an infrared free electron laser（FEL） facility currently under construction, which consists of two oscillators generating middle-infrared and far-infrared laser covering the spectral range of 2.5–200 μm. In this paper, we numerically study the output characteristics of the middle-infrared oscillator with accurate cavity length detuning. Emphasis is put on the temporal structure of the micropulse and the corresponding spectral bandwidth.Taking the radiation wavelengths of 50 μm and 5 μm as examples, we show that the output pulse duration can be tuned in the range of 1–6 ps with corresponding bandwidth of 13%–0.2% by adjusting the cavity length detuning.In addition, a special discussion on the comb structure is presented, and it is indicated that the comb structure may arise in the output optical pulse when the normalized slippage length is much smaller than unity. This work has reference value for the operation of FELiChEM and other FEL oscillators.展开更多
We investigate storage ring-based Echo-Enabled Harmonic Generation（EEHG） superradiant undulator radiation as a possible scheme to obtain shorter wavelengths at the HLS-Ⅱ（Hefei Light Source-Ⅱ） storage ring. In th...We investigate storage ring-based Echo-Enabled Harmonic Generation（EEHG） superradiant undulator radiation as a possible scheme to obtain shorter wavelengths at the HLS-Ⅱ（Hefei Light Source-Ⅱ） storage ring. In this paper we give the designation of the storage ring based EEHG up to the 26 th harmonic, where 31 nm vacuum ultraviolet light is radiated from an 800 nm seeded laser. The novelty of our design is that both the two dispersion sections of EEHG are realized by the storage ring＇s own magnet structure. In particular, the whole ring is used as the first dispersion section, and two modulators of the traditional EEHG can be done with the same undulator. These two dispersion sections are realized by changing the superperiod of the present lattice structure, and more precisely by changing the focusing strengths of the present structure. Since no additional magnets and chicanes are used,the beam circulates around the storage ring repeatedly, and thus this storage ring-based EEHG can have a higher repetition rate than a linac-based EEHG.展开更多
In this paper, the harmonics suppression effect of quasi-periodic undulators （QPUs） in self-amplified spontaneous emission free-electron laser （SASE FEL） is investigated. The numerical results show that the harmon...In this paper, the harmonics suppression effect of quasi-periodic undulators （QPUs） in self-amplified spontaneous emission free-electron laser （SASE FEL） is investigated. The numerical results show that the harmonics power is reduced by using QPUs, but the fundamental radiation power also has a pronounced decrease as the saturation length gets very long. The cases of employing QPUs as parts of undulators are studied. The calculations show that if the fraction of QPUs and their offgap are appropriate in an undulator system, the harmonics radiation could be suppressed remarkably, meanwhile the fundamental saturation length does not increase too much.展开更多
An easy-to-implement scheme called Enhanced High Gain Harmonic Generation is expected to be able to significantly enhance the performance of HG-FEL. In this paper we investigate the effects of the system parameters in...An easy-to-implement scheme called Enhanced High Gain Harmonic Generation is expected to be able to significantly enhance the performance of HG-FEL. In this paper we investigate the effects of the system parameters in the new scheme, including the electron energy detuning, initial electron-beam energy spread, seeding laser power, dispersive field strength and amount of the phase shift, etc. The numerical results from GENESIS （3D-code） are presented and show that the new scheme has acceptable parameters tolerance requirements and is no more or even less sensitive to the system parameters than that of the existing scheme; With the electron energy above the resonance, the efficiency is enhanced for both the new scheme and the existing scheme compared with the resonant energy case.展开更多
基金Supported by National Natural Science Foundation of China(21327901)
文摘FELiChEM is a new experimental facility under construction at the University of Science and Technology of China（USTC）. Its core device is two free electron laser oscillators generating middle-infrared and far-infrared laser and covering the spectral range of 2.5–200 μm. It will be a dedicated infrared light source aiming at energy chemistry research. We present the brief design of the FEL oscillators, with the emphasis put on the middle-infrared oscillator.Most of the basic parameters are determined and the anticipated performance of the output radiation is given. The first light of FELiChEM is targeted for the end of 2017.
基金Supported by Major State Basic Research Development Program of China(2011CB808301)National Natural Science Foundation of China.(11205156)
文摘In order to meet the requirements of the synchrotron radiation users, a fully coherent VUV free electron laser （FEL） has been preliminarily designed. One important goal of this design is that the radiation wavelength can be easily tuned in a broad range （70 170 nm）. In the light of the users＇ demand and our actual conditions, the self-seeding scheme is adopted for this proposal. Firstly, we attempted to fix the electron energy and only changed the undulator gap to vary the radiation wavelength; however, our analysis implies that this is difficult because of the great difference of the power gain length and FEL efficiency at different wavelengths. Therefore, we have considered dividing the wavelength range into three subareas. In each subarea, a constant electron energy is used and the wavelength tuning is realized only by adjusting the undulator gap. The simulation results show that this scheme has an acceptable performance.
基金Supported by National Natural Science Foundation of China (10975137)
文摘The enhanced high gain harmonic generation （EHGHG） scheme has been proposed and shown to be able to significantly enhance the performance of HGHG FEL. In this paper we investigate the EHGHG scheme with negative dispersion. The bunching factor at the entrance of the radiator is analyzed, which indicates that the scheme with negative dispersion can further weaken the negative effect of the dispersive strength on the energy spread correction factor. The numerical results from GENESIS （3D-code） are presented, and are in good agreement with our analysis. Then we comparatively study the effects of the initial beam energy spread and the relative phase shift on the radiation power. The results show that the EHGHG scheme with negative dispersion has a larger tolerance on the initial beam energy spread and a nearly equal wide good region of the relative phase shift compared with the case of positive dispersion.
基金Supported by Major State Basic Research Development Program(2011CB808301)National Natural Science Foundation of China(11205156)
文摘We put forward a method to optimize the single-step tapering amplitude of undulator strength and initial energy tuning of electron beam to maximize the saturation power of high gain free-electron lasers （FELs）, based on the physics of longitudinal electron beam phase space. Using the FEL simulation code GENESIS, we numerically demonstrate the accuracy of the estimations for parameters corresponding to the linac coherent light source and the Tesla test facility.
基金Supported by National Natural Science Foundation of China(11205156)Major State Basic Research Development Program(2011CB808301)
文摘There is an empirical formula describing the relationship between the peak magnetic field and the undulator structure parameters for a uniform-parameter hybrid undulator. In this paper, we investigate the relationship for a linearly tapered undulator through numerical calculation by using the code RADIA, and check it with the empirical formula. The results imply that this empirical formula is also effective for linearly tapered undulators at a big enough scope for the requirements of normal FEL experiments. Therefore, for a linearly tapered undulator, we can use the empirical formula to design the variation of the undulator gap. For the tapering rate demanded by normal FEL experiments, the gap of a linearly tapered undulator increases almost linearly, and the tapering rate will keep constant while adjusting the undulator gap with the same variation for each undulator period.
基金Supported by National Natural Science Foundation of China(21327901,11205156)
文摘FELiChEM is an infrared free electron laser（FEL） facility currently under construction, which consists of two oscillators generating middle-infrared and far-infrared laser covering the spectral range of 2.5–200 μm. In this paper, we numerically study the output characteristics of the middle-infrared oscillator with accurate cavity length detuning. Emphasis is put on the temporal structure of the micropulse and the corresponding spectral bandwidth.Taking the radiation wavelengths of 50 μm and 5 μm as examples, we show that the output pulse duration can be tuned in the range of 1–6 ps with corresponding bandwidth of 13%–0.2% by adjusting the cavity length detuning.In addition, a special discussion on the comb structure is presented, and it is indicated that the comb structure may arise in the output optical pulse when the normalized slippage length is much smaller than unity. This work has reference value for the operation of FELiChEM and other FEL oscillators.
基金Supported by National Natural Science Foundation of China(11305170)
文摘We investigate storage ring-based Echo-Enabled Harmonic Generation（EEHG） superradiant undulator radiation as a possible scheme to obtain shorter wavelengths at the HLS-Ⅱ（Hefei Light Source-Ⅱ） storage ring. In this paper we give the designation of the storage ring based EEHG up to the 26 th harmonic, where 31 nm vacuum ultraviolet light is radiated from an 800 nm seeded laser. The novelty of our design is that both the two dispersion sections of EEHG are realized by the storage ring＇s own magnet structure. In particular, the whole ring is used as the first dispersion section, and two modulators of the traditional EEHG can be done with the same undulator. These two dispersion sections are realized by changing the superperiod of the present lattice structure, and more precisely by changing the focusing strengths of the present structure. Since no additional magnets and chicanes are used,the beam circulates around the storage ring repeatedly, and thus this storage ring-based EEHG can have a higher repetition rate than a linac-based EEHG.
文摘In this paper, the harmonics suppression effect of quasi-periodic undulators （QPUs） in self-amplified spontaneous emission free-electron laser （SASE FEL） is investigated. The numerical results show that the harmonics power is reduced by using QPUs, but the fundamental radiation power also has a pronounced decrease as the saturation length gets very long. The cases of employing QPUs as parts of undulators are studied. The calculations show that if the fraction of QPUs and their offgap are appropriate in an undulator system, the harmonics radiation could be suppressed remarkably, meanwhile the fundamental saturation length does not increase too much.
文摘An easy-to-implement scheme called Enhanced High Gain Harmonic Generation is expected to be able to significantly enhance the performance of HG-FEL. In this paper we investigate the effects of the system parameters in the new scheme, including the electron energy detuning, initial electron-beam energy spread, seeding laser power, dispersive field strength and amount of the phase shift, etc. The numerical results from GENESIS （3D-code） are presented and show that the new scheme has acceptable parameters tolerance requirements and is no more or even less sensitive to the system parameters than that of the existing scheme; With the electron energy above the resonance, the efficiency is enhanced for both the new scheme and the existing scheme compared with the resonant energy case.
