Shanghai high-repetition-rate XFEL and extreme light facility (SHINE), the first hard XFEL based on a superconducting accelerated structure in China, is now under development at the Shanghai Institute of Applied Physi...Shanghai high-repetition-rate XFEL and extreme light facility (SHINE), the first hard XFEL based on a superconducting accelerated structure in China, is now under development at the Shanghai Institute of Applied Physics, Chinese Academy of Sciences. In this paper, power losses caused by trapped longitudinal high-order modes (HOM), steady-state loss, and transient loss generated by untrapped HOMs in the 1.3-GHz SHINE cryomodule are investigated and calculated. The heat load generated by resistive wall wakefields is considered as well. Results are presented for power losses of every element in the 1.3-GHz cryomodule, caused by HOM excitation in the acceleration RF system of the continuouswave linac of SHINE.展开更多
Besides the original seeded undulator line,in the soft X-ray free-electron laser(SXFEL) user facility in Shanghai,a second undulator line based on self-amplified spontaneous emission is proposed to achieve 2-nm laser ...Besides the original seeded undulator line,in the soft X-ray free-electron laser(SXFEL) user facility in Shanghai,a second undulator line based on self-amplified spontaneous emission is proposed to achieve 2-nm laser pulse with extremely high brightness.In this paper,the beam energy deviation induced by the undulator wakefields is numerically calculated,and 3D and 2D results agree well with each other.The beam energy loss along the undulator degrades the expected FEL output performances,i.e.,the pulse energy,radiation power and spectrum,which can be compensated with a proper taper in the undulator.Using the planned time-resolved diagnostic,a novel experiment is proposed to measure the SXFEL longitudinal wakefields.展开更多
Different operating conditions （e.g. design and off-design） may lead to a significant difference in the hydrodynamics performance of a ship, especially in the total resistance and wake field of ships. This work inve...Different operating conditions （e.g. design and off-design） may lead to a significant difference in the hydrodynamics performance of a ship, especially in the total resistance and wake field of ships. This work investigated the hydrodynamic performance of the well-known KRISO 3600 TEU Container Ship （KCS） under three different operating conditions by means of Particle Image Velocimetry （P/V） and Computational Fluid Dynamics （CFD）. The comparison results show that the use of PIV to measure a ship＇s nominal wake field is an important method which has the advantages of being contactless and highly accurate. Acceptable agreements between the results obtained by the two different methods are achieved. Results indicate that the total resistances of the KCS model under two off-design conditions are 23.88% and 13.92% larger than that under the designed condition, respectively.展开更多
The research and development of a C-band (5712 MHz) high gradient traveling-wave accelerating structure has been in progress for some years at the Shanghai Institute of Applied Physics, Chinese Academy of Sciences. Co...The research and development of a C-band (5712 MHz) high gradient traveling-wave accelerating structure has been in progress for some years at the Shanghai Institute of Applied Physics, Chinese Academy of Sciences. Conceptual design of the accelerating structure has been accomplished, and verified by cold testing an experimental model. The first prototype structure is now ready for high RF power tests. To develop a robust high gradient C-band accelerating structure, an optimized constant gradient structure with a 4 /5 operating mode for future X-ray Free Electron Laser facilities is proposed in this paper. This scheme can improve the breakdown stability and beam quality. The high power RF system, four operating modes and disk iris shape are analyzed and optimized.展开更多
Polarized electron beam production via laser wakefield acceleration in pre-polarized plasma is investigated by particlein-cell simulations.The evolution of the electron beam polarization is studied based on the Thomas...Polarized electron beam production via laser wakefield acceleration in pre-polarized plasma is investigated by particlein-cell simulations.The evolution of the electron beam polarization is studied based on the Thomas±Bargmann±Michel±Telegdi equation for the transverse and longitudinal self-injection,and the depolarization process is found to be influenced by the injection schemes.In the case of transverse self-injection,as found typically in the bubble regime,the spin precession of the accelerated electrons is mainly influenced by the wakefield.However,in the case of longitudinal injection in the quasi-1D regime(for example,F.Y.Li et al.,Phys.Rev.Lett.110,135002(2013)),the direction of electron spin oscillates in the laser field.Since the electrons move around the laser axis,the net influence of the laser field is nearly zero and the contribution of the wakefield can be ignored.Finally,an ultra-short electron beam with polarization of 99%can be obtained using longitudinal self-injection.展开更多
Synchrotron radiation(SR)sources are immensely useful tools for scientific researches and many practical applications.Currently,the state-of-the-art synchrotrons rely on conventional accelerators,where electrons are a...Synchrotron radiation(SR)sources are immensely useful tools for scientific researches and many practical applications.Currently,the state-of-the-art synchrotrons rely on conventional accelerators,where electrons are accelerated in a straight line and radiate in bending magnets or other insertion devices.However,these facilities are usually large and costly.Here,we study a compact all optical synchrotron-like radiation source based on laser-plasma acceleration either in a straight or a curved plasma channel.With the laser pulse off-axially injected,its centroid oscillates transversely in the plasma channel.This results in a wiggler motion of the whole accelerating structure and the self-trapped electrons behind the laser pulse,leading to strong synchrotron-like radiations with tunable spectra.It is further shown that a palmtop ring-shaped synchrotron is possible with current high power laser technologies.With its potential of high flexibility and tunability,such light sources once realized would find applications in wide areas and make up the shortage of large SR facilities.展开更多
Purpose X-ray free-electron laser facilities require high-repetition and high-energy electron beams,which makes the radiation safety become an important issue due to beam loss.Beam collimation is used to protect the u...Purpose X-ray free-electron laser facilities require high-repetition and high-energy electron beams,which makes the radiation safety become an important issue due to beam loss.Beam collimation is used to protect the undulator and other devices by removing the beam halo in operation,as well as absorbing the off-axis beam in the case of machine failure.Method In this paper,the beam collimation system in the switchyard of the SHINE is presented.Results and conclusion Tracking with an expanded initial beam distribution,the efficiency of the collimation system is shown,and the detailed collimation performance is simulated to evaluate the available limitation from the acceptance of the undulator.Moreover,the accidental beam loss and wakefield effects are also considered to ensure the reliability of the collimation.展开更多
Terahertz(THz)radiation finds important applications in various fields,making the study of THz sources significant.Among different approaches,electron accelerator-based THz sources hold notable advantages in generatin...Terahertz(THz)radiation finds important applications in various fields,making the study of THz sources significant.Among different approaches,electron accelerator-based THz sources hold notable advantages in generating THz radiation with narrow bandwidth,high brightness,high peak power,and high repetition rate.To further improve the THz radiation energy,the bunching factor of the free electron bunch train needs to be increased.We propose and numerically reveal that,by adding an additional short-pulse drive beam before the main beam as the excitation source of nonlinear plasma wake,the bunching factor of the main beam can be further increased to∼0.94,even though with a relatively low charge,low current,and relatively diffused electron beam.Two such electron beams with loose requirements can be easily generated using typical photoinjectors.Our work provides a way for a new THz source with enhanced radiation energy.展开更多
X-ray sources with tunable energy spectra have a wide range of applications in different scenarios due to their different penetration depths.However,existing x-ray sources face difficulties in terms of energy regulati...X-ray sources with tunable energy spectra have a wide range of applications in different scenarios due to their different penetration depths.However,existing x-ray sources face difficulties in terms of energy regulation.In this paper,we present a scheme for tuning the energy spectrum of a betatron x-ray generated from a relativistic electron bunch oscillating in a plasma wakefield.The center energy of the x-ray source can be tuned from several keV to several hundred keV by changing the plasma density,thereby extending the control range by an order of magnitude.At different central energies,the brightness of the betatron radiation is in the range of 3.7×10^(22)to 5.5×10^(22)photons/(0.1%BW·s·mm^(2)·mrad^(2))and the photon divergence angle is about 2 mrad.This high-brightness,energy-controlled betatron source could pave the way to a wide range of applications requiring photons of specific energy,such as phase-contrast imaging in medicine,non-destructive testing and material analysis in industry,and imaging in nuclear physics.展开更多
Thanks to a rapid progress of high-power lasers since the birth of laser by T.H.Maiman in 1960,intense lasers have been developed mainly for studying the scientific feasibility of laser fusion.Inertial confinement fus...Thanks to a rapid progress of high-power lasers since the birth of laser by T.H.Maiman in 1960,intense lasers have been developed mainly for studying the scientific feasibility of laser fusion.Inertial confinement fusion with an intense laser has attracted attention as a new future energy source after two oil crises in the 1970s and 1980s.From the beginning,the most challenging physics is known to be the hydrodynamic instability to realize the spherical implosion to achieve more than 1000 times the solid density.Many studies have been performed theoretically and experimentally on the hydrodynamic instability and resultant turbulent mixing of compressible fluids.During such activities in the laboratory,the explosion of supernova SN1987A was observed in the sky on 23 February 1987.The X-ray satellites have revealed that the hydrodynamic instability is a key issue to understand the physics of supernova explosion.After collaboration between laser plasma researchers and astrophysicists,the laboratory astrophysics with intense lasers was proposed and promoted around the end of the 1990s.The original subject was mainly related to hydrodynamic instabilities.However,after two decades of laboratory astrophysics research,we can now find a diversity of research topics.It has been demonstrated theoretically and experimentally that a variety of nonlinear physics of collisionless plasmas can be studied in laser ablation plasmas in the last decade.In the present paper,we shed light on the recent 10 topics studied intensively in laboratory experiments.A brief review is given by citing recent papers.Then,modeling cosmic-ray acceleration with lasers is reviewed in a following session as a special topic to be the future main topic in laboratory astrophysics research.展开更多
X-band accelerators for multi-bunches are a new way to produce high luminosity and energy efficiency bunches. The smaller the size and the more bunches, the more severe is the wakefield in the X-band accelerators, unl...X-band accelerators for multi-bunches are a new way to produce high luminosity and energy efficiency bunches. The smaller the size and the more bunches, the more severe is the wakefield in the X-band accelerators, unless some means of strongly suppressing the transverse wakefield is adopted in the design of the accelerating structure. Here, the derivation of the wakefield function of the double circuit model and its application to the designed accelerator structure have been demonstrated.展开更多
It is found that there is an upper-limit critical power for self-guided propagation of intense lasers in plasma in addition to the well-known lower-limit critical power set by the relativistic effect.Above this upper-...It is found that there is an upper-limit critical power for self-guided propagation of intense lasers in plasma in addition to the well-known lower-limit critical power set by the relativistic effect.Above this upper-limit critical power,the laser pulse experiences defocusing due to expulsion of local plasma electrons by the transverse ponderomotive force.Associated with the upper-limit power,a lower-limit critical plasma density is also found for a given laser spot size,below which self-focusing does not occur for any laser power.Both the upper-limit power and the lower-limit density are derived theoretically and verified by two-dimensional particle-in-cell simulations.The present study provides new guidance for experimental designs,where self-guided propagation of lasers is essential.展开更多
Recently, intense research into laser plasma accelerators has achieved great progress in the production of high-energy,high-quality electron beams with Ge V-level energies in a cm-scale plasma. These electron beams op...Recently, intense research into laser plasma accelerators has achieved great progress in the production of high-energy,high-quality electron beams with Ge V-level energies in a cm-scale plasma. These electron beams open the door for broad applications in fundamental, medical, and industrial sciences. Here we present conceptual designs of an extreme ultraviolet radiation source for next-generation lithography and a laser Compton Gamma-beam source for nuclear physics research on a table-top scale.展开更多
A wakefield driven by a short intense laser pulse in a perpendicularly magnetized underdense plasma is studied analytically and numerically for both weakly relativistic and highly relativistic situations. Owing to the...A wakefield driven by a short intense laser pulse in a perpendicularly magnetized underdense plasma is studied analytically and numerically for both weakly relativistic and highly relativistic situations. Owing to the DC magnetic field, a transverse component of the electric fields associated with the wakefield appears, while the longitudinal wave is not greatly affected by the magnetic field up to 22 Tesla. Moreover, the scaling law of the transverse field versus the longitudinal field is derived. One-dimensional particle-in-cell simulation results confirm the analytical results. Wakefield transmission through the plasma-vacuum boundary, where electromagnetic emission into vacuum occurs, is also investigated numerically. These results are useful for the generation of terahertz radiation and the diagnosis of laser wakefields.展开更多
Ionization-induced electron injection in laser wakefield accelerators, which was recently proposed to lower the laser intensity threshold for electron trapping into the wake wave, has the drawback of generating electr...Ionization-induced electron injection in laser wakefield accelerators, which was recently proposed to lower the laser intensity threshold for electron trapping into the wake wave, has the drawback of generating electron beams with large and continuous energy spreads, severely limiting their future applications. Complex target designs based on separating the electron trapping and acceleration stages were proposed as the only way for getting small energy-spread electron beams. Here, based on the self-truncated ionization-injection concept which requires the use of unmatched laser–plasma parameters and by using tens of TW laser pulses focused onto a gas jet of helium mixed with low concentrations of nitrogen, we demonstrate single-stage laser wakefield acceleration of multi-hundred MeV electron bunches with energy spreads of a few percent. The experimental results are verified by PIC simulations.展开更多
Laser wakefield accelerators（LWFAs） are compact accelerators which can produce femtosecond high-energy electron beams on a much smaller scale than the conventional radiofrequency accelerators. It is attributed to th...Laser wakefield accelerators（LWFAs） are compact accelerators which can produce femtosecond high-energy electron beams on a much smaller scale than the conventional radiofrequency accelerators. It is attributed to their high acceleration gradient which is about 3 orders of magnitude larger than the traditional ones. The past decade has witnessed the major breakthroughs and progress in developing the laser wakfield accelerators. To achieve the LWFAs suitable for applications,more and more attention has been paid to optimize the LWFAs for high-quality electron beams. A single-staged LWFA does not favor generating controllable electron beams beyond 1 Ge V since electron injection and acceleration are coupled and cannot be independently controlled. Staged LWFAs provide a promising route to overcome this disadvantage by decoupling injection from acceleration and thus the electron-beam quality as well as the stability can be greatly improved.This paper provides an overview of the physical conceptions of the LWFA, as well as the major breakthroughs and progress in developing LWFAs from single-stage to two-stage LWFAs.展开更多
基金supported by the Frontier Research of Large Science Installation(2016YFA0401902)the Youth Innovation Promotion Association CAS(No.2018300)
文摘Shanghai high-repetition-rate XFEL and extreme light facility (SHINE), the first hard XFEL based on a superconducting accelerated structure in China, is now under development at the Shanghai Institute of Applied Physics, Chinese Academy of Sciences. In this paper, power losses caused by trapped longitudinal high-order modes (HOM), steady-state loss, and transient loss generated by untrapped HOMs in the 1.3-GHz SHINE cryomodule are investigated and calculated. The heat load generated by resistive wall wakefields is considered as well. Results are presented for power losses of every element in the 1.3-GHz cryomodule, caused by HOM excitation in the acceleration RF system of the continuouswave linac of SHINE.
基金supported by the National Natural Science Foundation of China(Nos.11475250 and 11322550)Ten Thousand Talent Program
文摘Besides the original seeded undulator line,in the soft X-ray free-electron laser(SXFEL) user facility in Shanghai,a second undulator line based on self-amplified spontaneous emission is proposed to achieve 2-nm laser pulse with extremely high brightness.In this paper,the beam energy deviation induced by the undulator wakefields is numerically calculated,and 3D and 2D results agree well with each other.The beam energy loss along the undulator degrades the expected FEL output performances,i.e.,the pulse energy,radiation power and spectrum,which can be compensated with a proper taper in the undulator.Using the planned time-resolved diagnostic,a novel experiment is proposed to measure the SXFEL longitudinal wakefields.
基金supported by the National Natural Science Foundation of China(Grant Nos.41176074,51209048,51379043,and 51409063)the High Technology Ship Scientific Research Project of Ministry of Industry and Information Technology of China(Grant No.G014613002)
文摘Different operating conditions （e.g. design and off-design） may lead to a significant difference in the hydrodynamics performance of a ship, especially in the total resistance and wake field of ships. This work investigated the hydrodynamic performance of the well-known KRISO 3600 TEU Container Ship （KCS） under three different operating conditions by means of Particle Image Velocimetry （P/V） and Computational Fluid Dynamics （CFD）. The comparison results show that the use of PIV to measure a ship＇s nominal wake field is an important method which has the advantages of being contactless and highly accurate. Acceptable agreements between the results obtained by the two different methods are achieved. Results indicate that the total resistances of the KCS model under two off-design conditions are 23.88% and 13.92% larger than that under the designed condition, respectively.
基金supported by the Program of the Shanghai Subject Chief Scientist-Natural Science Foundation (08XD1405400)
文摘The research and development of a C-band (5712 MHz) high gradient traveling-wave accelerating structure has been in progress for some years at the Shanghai Institute of Applied Physics, Chinese Academy of Sciences. Conceptual design of the accelerating structure has been accomplished, and verified by cold testing an experimental model. The first prototype structure is now ready for high RF power tests. To develop a robust high gradient C-band accelerating structure, an optimized constant gradient structure with a 4 /5 operating mode for future X-ray Free Electron Laser facilities is proposed in this paper. This scheme can improve the breakdown stability and beam quality. The high power RF system, four operating modes and disk iris shape are analyzed and optimized.
基金supported by the National Natural Science Foundation of China(Nos.11804348,11775056,11975154 and 11991074)the Science Challenge Project(No.TZ2018005).X.F.Li was also supported by the Shanghai Pujiang Program(No.23PJ1414600)。
文摘Polarized electron beam production via laser wakefield acceleration in pre-polarized plasma is investigated by particlein-cell simulations.The evolution of the electron beam polarization is studied based on the Thomas±Bargmann±Michel±Telegdi equation for the transverse and longitudinal self-injection,and the depolarization process is found to be influenced by the injection schemes.In the case of transverse self-injection,as found typically in the bubble regime,the spin precession of the accelerated electrons is mainly influenced by the wakefield.However,in the case of longitudinal injection in the quasi-1D regime(for example,F.Y.Li et al.,Phys.Rev.Lett.110,135002(2013)),the direction of electron spin oscillates in the laser field.Since the electrons move around the laser axis,the net influence of the laser field is nearly zero and the contribution of the wakefield can be ignored.Finally,an ultra-short electron beam with polarization of 99%can be obtained using longitudinal self-injection.
基金supported in part by the National Basic Research Program of China(Grant No 2013CBA01504)Major State Basic Research Development Program of China(2015CB859700)+2 种基金the National Science Foundation of China(Grant Nos.11421064,11374209,11374210)supports from National 1000 Young Talent Programthe support of the University of Strathclyde and helpful comments from Prof。
文摘Synchrotron radiation(SR)sources are immensely useful tools for scientific researches and many practical applications.Currently,the state-of-the-art synchrotrons rely on conventional accelerators,where electrons are accelerated in a straight line and radiate in bending magnets or other insertion devices.However,these facilities are usually large and costly.Here,we study a compact all optical synchrotron-like radiation source based on laser-plasma acceleration either in a straight or a curved plasma channel.With the laser pulse off-axially injected,its centroid oscillates transversely in the plasma channel.This results in a wiggler motion of the whole accelerating structure and the self-trapped electrons behind the laser pulse,leading to strong synchrotron-like radiations with tunable spectra.It is further shown that a palmtop ring-shaped synchrotron is possible with current high power laser technologies.With its potential of high flexibility and tunability,such light sources once realized would find applications in wide areas and make up the shortage of large SR facilities.
基金supported by the CAS Project for Young Scientists in Basic Research(YSBR-042)the National Natural Science Foundation of China(12125508,11935020)+1 种基金Program of Shanghai Academic/Technology Research Leader(21XD1404100)Shanghai Pilot Program for Basic Research—Chinese Academy of Sciences,Shanghai Branch(JCYJ-SHFY-2021-010).
文摘Purpose X-ray free-electron laser facilities require high-repetition and high-energy electron beams,which makes the radiation safety become an important issue due to beam loss.Beam collimation is used to protect the undulator and other devices by removing the beam halo in operation,as well as absorbing the off-axis beam in the case of machine failure.Method In this paper,the beam collimation system in the switchyard of the SHINE is presented.Results and conclusion Tracking with an expanded initial beam distribution,the efficiency of the collimation system is shown,and the detailed collimation performance is simulated to evaluate the available limitation from the acceptance of the undulator.Moreover,the accidental beam loss and wakefield effects are also considered to ensure the reliability of the collimation.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFB2806703)the National Natural Science Foundation of China(Grant Nos.U22A6004,62301294,and 11835004)was funded by the National Key Laboratory of Science and Technology on Vacuum Electronics.
文摘Terahertz(THz)radiation finds important applications in various fields,making the study of THz sources significant.Among different approaches,electron accelerator-based THz sources hold notable advantages in generating THz radiation with narrow bandwidth,high brightness,high peak power,and high repetition rate.To further improve the THz radiation energy,the bunching factor of the free electron bunch train needs to be increased.We propose and numerically reveal that,by adding an additional short-pulse drive beam before the main beam as the excitation source of nonlinear plasma wake,the bunching factor of the main beam can be further increased to∼0.94,even though with a relatively low charge,low current,and relatively diffused electron beam.Two such electron beams with loose requirements can be easily generated using typical photoinjectors.Our work provides a way for a new THz source with enhanced radiation energy.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11921006 and 12175058)the Beijing Distinguished Young Scientist Program and National Grand Instrument Project (Grant No.SQ2019YFF01014400)+1 种基金the Beijing Municipal Science&Technology Commission,Administrative Commission of Zhongguancun Science Park (Grant No.Z231100006023003)in part funded by United Kingdom EPSRC (Grant Nos.EP/G054950/1,EP/G056803/1,EP/G055165/1,and EP/M022463/1)。
文摘X-ray sources with tunable energy spectra have a wide range of applications in different scenarios due to their different penetration depths.However,existing x-ray sources face difficulties in terms of energy regulation.In this paper,we present a scheme for tuning the energy spectrum of a betatron x-ray generated from a relativistic electron bunch oscillating in a plasma wakefield.The center energy of the x-ray source can be tuned from several keV to several hundred keV by changing the plasma density,thereby extending the control range by an order of magnitude.At different central energies,the brightness of the betatron radiation is in the range of 3.7×10^(22)to 5.5×10^(22)photons/(0.1%BW·s·mm^(2)·mrad^(2))and the photon divergence angle is about 2 mrad.This high-brightness,energy-controlled betatron source could pave the way to a wide range of applications requiring photons of specific energy,such as phase-contrast imaging in medicine,non-destructive testing and material analysis in industry,and imaging in nuclear physics.
基金supported by the JSPS KAKENHI under Grant Nos.19K21865,19H00668,and 20KK0064。
文摘Thanks to a rapid progress of high-power lasers since the birth of laser by T.H.Maiman in 1960,intense lasers have been developed mainly for studying the scientific feasibility of laser fusion.Inertial confinement fusion with an intense laser has attracted attention as a new future energy source after two oil crises in the 1970s and 1980s.From the beginning,the most challenging physics is known to be the hydrodynamic instability to realize the spherical implosion to achieve more than 1000 times the solid density.Many studies have been performed theoretically and experimentally on the hydrodynamic instability and resultant turbulent mixing of compressible fluids.During such activities in the laboratory,the explosion of supernova SN1987A was observed in the sky on 23 February 1987.The X-ray satellites have revealed that the hydrodynamic instability is a key issue to understand the physics of supernova explosion.After collaboration between laser plasma researchers and astrophysicists,the laboratory astrophysics with intense lasers was proposed and promoted around the end of the 1990s.The original subject was mainly related to hydrodynamic instabilities.However,after two decades of laboratory astrophysics research,we can now find a diversity of research topics.It has been demonstrated theoretically and experimentally that a variety of nonlinear physics of collisionless plasmas can be studied in laser ablation plasmas in the last decade.In the present paper,we shed light on the recent 10 topics studied intensively in laboratory experiments.A brief review is given by citing recent papers.Then,modeling cosmic-ray acceleration with lasers is reviewed in a following session as a special topic to be the future main topic in laboratory astrophysics research.
文摘X-band accelerators for multi-bunches are a new way to produce high luminosity and energy efficiency bunches. The smaller the size and the more bunches, the more severe is the wakefield in the X-band accelerators, unless some means of strongly suppressing the transverse wakefield is adopted in the design of the accelerating structure. Here, the derivation of the wakefield function of the double circuit model and its application to the designed accelerator structure have been demonstrated.
基金supported in part by NSFC (Grant Nos. 11105217, 11121504, and 10925421)National Basic Research Program of China (Grant No. 2009GB105002)
文摘It is found that there is an upper-limit critical power for self-guided propagation of intense lasers in plasma in addition to the well-known lower-limit critical power set by the relativistic effect.Above this upper-limit critical power,the laser pulse experiences defocusing due to expulsion of local plasma electrons by the transverse ponderomotive force.Associated with the upper-limit power,a lower-limit critical plasma density is also found for a given laser spot size,below which self-focusing does not occur for any laser power.Both the upper-limit power and the lower-limit density are derived theoretically and verified by two-dimensional particle-in-cell simulations.The present study provides new guidance for experimental designs,where self-guided propagation of lasers is essential.
基金supported by the National Natural Science Foundation of China (Project No. 51175324)supported by IZEST, Ecole Polytechnique, France,Shanghai Jiao Tong University, Institute of Physics, CAS, Chinathe Center for Relativistic Laser Science, Institute for Basic Science (IBS), Korea
文摘Recently, intense research into laser plasma accelerators has achieved great progress in the production of high-energy,high-quality electron beams with Ge V-level energies in a cm-scale plasma. These electron beams open the door for broad applications in fundamental, medical, and industrial sciences. Here we present conceptual designs of an extreme ultraviolet radiation source for next-generation lithography and a laser Compton Gamma-beam source for nuclear physics research on a table-top scale.
基金supported in part by National Natural Science Foundation of China(Nos.10734130,10925421,11075105)the National Basic Research Program of China(Nos.2007CB310406,2009GB105002)
文摘A wakefield driven by a short intense laser pulse in a perpendicularly magnetized underdense plasma is studied analytically and numerically for both weakly relativistic and highly relativistic situations. Owing to the DC magnetic field, a transverse component of the electric fields associated with the wakefield appears, while the longitudinal wave is not greatly affected by the magnetic field up to 22 Tesla. Moreover, the scaling law of the transverse field versus the longitudinal field is derived. One-dimensional particle-in-cell simulation results confirm the analytical results. Wakefield transmission through the plasma-vacuum boundary, where electromagnetic emission into vacuum occurs, is also investigated numerically. These results are useful for the generation of terahertz radiation and the diagnosis of laser wakefields.
基金supported by the National ‘973’ Program of China under Grant No.2013CBA01504supported by Shanghai Supercomputer Center and the center for high performance computing at Shanghai Jiao Tong University
文摘Ionization-induced electron injection in laser wakefield accelerators, which was recently proposed to lower the laser intensity threshold for electron trapping into the wake wave, has the drawback of generating electron beams with large and continuous energy spreads, severely limiting their future applications. Complex target designs based on separating the electron trapping and acceleration stages were proposed as the only way for getting small energy-spread electron beams. Here, based on the self-truncated ionization-injection concept which requires the use of unmatched laser–plasma parameters and by using tens of TW laser pulses focused onto a gas jet of helium mixed with low concentrations of nitrogen, we demonstrate single-stage laser wakefield acceleration of multi-hundred MeV electron bunches with energy spreads of a few percent. The experimental results are verified by PIC simulations.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11127901,11425418,and 61221064)the National Basic Research Program of China(Grant No.2011CB808100)the Science and Technology Talent Project of Shanghai City,China(Grant Nos.12XD1405200 and 12ZR1451700)
文摘Laser wakefield accelerators（LWFAs） are compact accelerators which can produce femtosecond high-energy electron beams on a much smaller scale than the conventional radiofrequency accelerators. It is attributed to their high acceleration gradient which is about 3 orders of magnitude larger than the traditional ones. The past decade has witnessed the major breakthroughs and progress in developing the laser wakfield accelerators. To achieve the LWFAs suitable for applications,more and more attention has been paid to optimize the LWFAs for high-quality electron beams. A single-staged LWFA does not favor generating controllable electron beams beyond 1 Ge V since electron injection and acceleration are coupled and cannot be independently controlled. Staged LWFAs provide a promising route to overcome this disadvantage by decoupling injection from acceleration and thus the electron-beam quality as well as the stability can be greatly improved.This paper provides an overview of the physical conceptions of the LWFA, as well as the major breakthroughs and progress in developing LWFAs from single-stage to two-stage LWFAs.
