A pulsed magnetic field generator was developed to study the effect of a magnetic field on the evolution of a laser-generated plasma. A 40 kV pulsed power system delivered a fast (-230 ns), 55 kA current pulse into ...A pulsed magnetic field generator was developed to study the effect of a magnetic field on the evolution of a laser-generated plasma. A 40 kV pulsed power system delivered a fast (-230 ns), 55 kA current pulse into a single-turn coil surrounding the laser target, using a capacitor bank of 200 nF, a laser-triggered switch and a low-impedance strip transmission line. A one-dimensional uniform 7 T pulsed magnetic field was created using a Helmholtz coil pair with a 6 mm diameter. The pulsed magnetic field was controlled to take effect synchronously with a nanosecond heating laser beam, a femtosecond probing laser beam and an optical Intensified Charge Coupled Device (ICCD) detector. The preliminary experiments demonstrate bifurcation and focusing of plasma expansion in a transverse magnetic field.展开更多
Generation of self-generated annular magnetic fields at the rear side of a solid target driven by relativistic laser pulse is investigated by using theoretical analysis and particle-in-cell simulations.The spatial str...Generation of self-generated annular magnetic fields at the rear side of a solid target driven by relativistic laser pulse is investigated by using theoretical analysis and particle-in-cell simulations.The spatial strength distribution of magnetic fields can be accurately predicted by calculating the net flow caused by the superposition of source flow and return flow of hot electrons.The theoretical model established shows good agreement with the simulation results,indicating that the magnetic-field strength scales positively to the temperature of hot electrons.This provides us a way to improve the magnetic-field generation by using a micro-structured plasma grating in front of the solid target.Compared with that for a common flat target,hot electrons can be effectively heated with the well-designed grating size,leading to a stronger magnetic field.The spatial distribution of magnetic fields can be modulated by optimizing the grating period and height as well as the incident angle of the laser pulse.展开更多
A pulsed transverse magnetic field with pulse width of 12 ms and magnitude of 2 T was used to modify the density distribution of a weakly-ionized plasma flow with strong collisions between the charged particles and ne...A pulsed transverse magnetic field with pulse width of 12 ms and magnitude of 2 T was used to modify the density distribution of a weakly-ionized plasma flow with strong collisions between the charged particles and neutrals.The morphology of the plasma is changed substantially,with the density increased upstream and decreased downstream.Meanwhile,the plasma toward the axis contracts laterally and gradually converges to a collimated flow.In addition,a drift wave is observed to be excited in the inhomogeneous plasma by the magnetic field.展开更多
A three-dimensional model is proposed in this paper to study the effect of the pulsed magnetic field on the density distribution of high flow velocity plasma sheath.Taking the typical parameters of plasma sheath at th...A three-dimensional model is proposed in this paper to study the effect of the pulsed magnetic field on the density distribution of high flow velocity plasma sheath.Taking the typical parameters of plasma sheath at the height of 71 km as an example,the distribution characteristics and time evolution characteristics of plasma density in the flow field under the action of pulsed magnetic field,as well as the effect of self-electric field on the distribution of plasma density,are studied.The simulation results show that pulsed magnetic field can effectively reduce the density of plasma sheath.Meanwhile,the simulation results of three-dimensional plasma density distribution show that the size of the density reduction area is large enough to meet the communication requirements of the Global Position System(GPS)signal.Besides,the location of density reduction area provides a reference for the appropriate location of antenna.The time evolution of plasma density shows that the effective density reduction time can reach 62%of the pulse duration,and the maximum reduction of plasma density can reach 55%.Based on the simulation results,the mechanism of the interaction between pulsed magnetic field and plasma flow field is physically analyzed.Furthermore,the simulation results indicate that the density distributions of electrons and ions are consistent under the action of plasma self-electric field.However,the quasi neutral assumption of plasma in the flow field is not appropriate,because the self-electric field of plasma will weaken the effect of the pulsed magnetic field on the reduction of electron density,which cannot be ignored.The calculation results could provide useful information for the mitigation of communication blackout in hypersonic vehicles.展开更多
In this work,laser induced tungsten plasma has been investigated in the absence and presence of 0.6 T static transverse magnetic field at atmospheric pressure in air.The spectroscopic characterization of laser induced...In this work,laser induced tungsten plasma has been investigated in the absence and presence of 0.6 T static transverse magnetic field at atmospheric pressure in air.The spectroscopic characterization of laser induced tungsten plasma was experimentally studied using space-resolved emission spectroscopy.The atomic emission lines of tungsten showed a significant enhancement in the presence of a magnetic field,while the ionic emission lines of tungsten presented little change.Temporal variation of the optical emission lines of tungsten indicated that the atomic emission time in the presence of a magnetic field was longer than that in the absence of a magnetic field,while no significant changes occurred for the ionic emission time.The spatial resolution of optical emission lines of tungsten demonstrated that the spatial distribution of atoms and ions were separated.The influence of a magnetic field on the spatial distribution of atoms was remarkable,whereas the spatial distribution of ions was little influenced by the magnetic field.The different behaviors between ions and atoms with and without magnetic field in air were related to the various atomic processes especially the electrons and ions recombination process during the plasma expansion and cooling process.展开更多
Quasistatic magnetic fields generated by nonrelativistic intense linearly polarized (LP) and circularly polarized (CP) laser pulses in an initially uniform underdense plasma in the collision-dominated limit are in...Quasistatic magnetic fields generated by nonrelativistic intense linearly polarized (LP) and circularly polarized (CP) laser pulses in an initially uniform underdense plasma in the collision-dominated limit are investigated analytically. Using a selfconsistent analytical model, we perform a detailed derivation of quasistatic magnetic fields in the laser pulse envelope in the collision-dominated limit to obtain exact analytical expressions for magnetic fields and discuss the dependence of magnetic fields on laser and plasma parameters. Equations for quasistatic magnetic fields including both axial componentBz and the azimuthal one Be are derived simultaneously from such a selfconsistent model. The dependence of quasistatic magnetic field on incident laser intensity, transverse focused radius of laser pulse, electron density and electron temperature is discussed.展开更多
We consider the radiation from the beam electrons traveling in a strong uniform axial magnetic field and an axial alternating electric field of wavelength Aw generated by a voltage-supplied pill-box cavity. The beam e...We consider the radiation from the beam electrons traveling in a strong uniform axial magnetic field and an axial alternating electric field of wavelength Aw generated by a voltage-supplied pill-box cavity. The beam electrons emit genuine laser radiation that propagates only in the axial direction through free-electron two- quantum Stark radiation. We find that laser radiation takes place only at the expense of the axial kinetic energy when Aw 〈〈 c/(ωc/γ), where ωc/γ is the relativistic electron--cyclotron frequency. We formulate the laser power based on quantum-wiggler electrodynamics, and envision a laser of length lore with estimated power 0.1 GW/(kA) in the 10-4 cm wavelength range.展开更多
As a hybrid approach to realizing fusion energy,Magnetized Target Fusion(MTF)based on the Field Reversed Configuration(FRC),which has the plasma density and confinement time in the range between magnetic and inertial ...As a hybrid approach to realizing fusion energy,Magnetized Target Fusion(MTF)based on the Field Reversed Configuration(FRC),which has the plasma density and confinement time in the range between magnetic and inertial confinement fusion,has been recently widely pursued around the world.To investigate the formation and confinement of the FRC plasma injector for MTF,the Yingguang-I,which is an FRC test device and contains a multi-bank program-discharged pulsed power sub-system,was constructed at the Institute of Fluid Physics(IFP),China.This paper presents the pulsed power components and their parameters of the device in detail,then gives a brief description of progress in experiments of FRC formation.Experimental results of the pulsed power sub-system show that the peak current/magnetic field of 110 kA/0.3 T,10 kA/1.2 Tand 1.7 MA/3.4 Twere achieved in the bias,mirror and q-pinch circuits with quarter cycle of 80 ms,700 ms and 3.8 ms respectively.The induced electric field in the neutral gas was greater than 0.25 kV/cm when the ionization bank was charged to 70 kV.With H_(2) gas of 8 Pa,the plasma target of density 10^(16) cm^(-3),separatrix radius 4 cm,half-length 17 cm,equilibrium temperature 200 eV and lifetime 3 ms(approximately the half pulse width of the reversed field)have been obtained through the q-pinch method when the bias,mirror,ionization and θ-pinch banks were charged to 5 kV,5 kV,55 kV and ±45 kV respectively.The images from the high-speed end-on framing camera demonstrate the formation processes of FRC and some features agree well with the results with the two-dimension magneto hydrodynamics code(2D-MHD).展开更多
As a promising new way to generate a controllable strong magnetic field, laser-driven magnetic coils have attracted interest in many research fields. In 2013, a kilotesla level magnetic field was achieved at the Gekk...As a promising new way to generate a controllable strong magnetic field, laser-driven magnetic coils have attracted interest in many research fields. In 2013, a kilotesla level magnetic field was achieved at the Gekko XⅡ laser facility with a capacitor–coil target. A similar approach has been adopted in a number of laboratories, with a variety of targets of different shapes. The peak strength of the magnetic field varies from a few tesla to kilotesla, with different spatiotemporal ranges. The differences are determined by the target geometry and the parameters of the incident laser. Here we present a review of the results of recent experimental studies of laser-driven magnetic field generation, as well as a discussion of the diagnostic techniques required for such rapidly changing magnetic fields. As an extension of the magnetic field generation, some applications are discussed.展开更多
The quasistatic axial magnetic fields in plasmas produced by ultrashort laser pulses were measured by measuring the Faraday rotation angle of the backscattered emission. The spatial distribution of the axial magnetic ...The quasistatic axial magnetic fields in plasmas produced by ultrashort laser pulses were measured by measuring the Faraday rotation angle of the backscattered emission. The spatial distribution of the axial magnetic field was obtained with a peak value as high as 170 Tesla. Theory suggests that the axial magnetic field is generated by dynamo effect in laser-plasma interaction.展开更多
In this paper, the recent studies of laboratory astrophysics with strong magnetic fields in China have been reviewed.On the Shenguang-II laser facility of the National Laboratory on High-Power Lasers and Physics, a la...In this paper, the recent studies of laboratory astrophysics with strong magnetic fields in China have been reviewed.On the Shenguang-II laser facility of the National Laboratory on High-Power Lasers and Physics, a laser-driven strong magnetic field up to 200 T has been achieved. The experiment was performed to model the interaction of solar wind with dayside magnetosphere. Also the low beta plasma magnetic reconnection(MR) has been studied. Theoretically, the model has been developed to deal with the atomic structures and processes in strong magnetic field. Also the study of shock wave generation in the magnetized counter-streaming plasmas is introduced.展开更多
In this paper, the nonlinear interaction of ultra-high power laser beam with fusion plasma at relativistic regime in the presence of obliquely external magnetic field has been studied. Imposing an external magnetic fi...In this paper, the nonlinear interaction of ultra-high power laser beam with fusion plasma at relativistic regime in the presence of obliquely external magnetic field has been studied. Imposing an external magnetic field on plasma can modify the density profile of the plasma so that the thermal conductivity of electrons reduces which is considered to be the decrease of the threshold energy for ignition. To achieve the fusion of Hydrogen–Boron(HB) fuel,the block acceleration model of plasma is employed. Energy production by HB isotopes can be of interest, since its reaction does not generate radioactive tritium. By using the inhibit factor in the block model acceleration of plasma and Maxwell's as well as the momentum transfer equations, the electron density distribution and dielectric permittivity of the plasma medium are obtained. Numerical results indicate that with increasing the intensity of the external magnetic field, the oscillation of the laser magnetic field decreases, while the dielectric permittivity increases. Moreover, the amplitude of the electron density becomes highly peaked and the plasma electrons are strongly bunched with increasing the intensity of external magnetic field. Therefore, the magnetized plasma can act as a positive focusing lens to enhance the fusion process. Besides, we find that with increasing θ-angle(from oblique external magnetic field) between 0 and 90°, the dielectric permittivity increases, while for θ between 90° and 180°, the dielectric permittivity decreases with increasing θ.展开更多
基金supported by National Natural Science Foundation of China(Nos.11105147,11375197 and 11175179)the Ministry of Education of China(No.IRT1190)
文摘A pulsed magnetic field generator was developed to study the effect of a magnetic field on the evolution of a laser-generated plasma. A 40 kV pulsed power system delivered a fast (-230 ns), 55 kA current pulse into a single-turn coil surrounding the laser target, using a capacitor bank of 200 nF, a laser-triggered switch and a low-impedance strip transmission line. A one-dimensional uniform 7 T pulsed magnetic field was created using a Helmholtz coil pair with a 6 mm diameter. The pulsed magnetic field was controlled to take effect synchronously with a nanosecond heating laser beam, a femtosecond probing laser beam and an optical Intensified Charge Coupled Device (ICCD) detector. The preliminary experiments demonstrate bifurcation and focusing of plasma expansion in a transverse magnetic field.
基金supported by the National Natural Science Foundation of China(Grant Nos.12175310,12305268,and U2241281)the Natural Science Foundation of Hunan Province(Grant Nos.2024JJ6184,2022JJ20042,and 2021JJ40653)the Scientific Research Foundation of Hunan Provincial Education Department(Grant Nos.22B0655 and 22A0435)。
文摘Generation of self-generated annular magnetic fields at the rear side of a solid target driven by relativistic laser pulse is investigated by using theoretical analysis and particle-in-cell simulations.The spatial strength distribution of magnetic fields can be accurately predicted by calculating the net flow caused by the superposition of source flow and return flow of hot electrons.The theoretical model established shows good agreement with the simulation results,indicating that the magnetic-field strength scales positively to the temperature of hot electrons.This provides us a way to improve the magnetic-field generation by using a micro-structured plasma grating in front of the solid target.Compared with that for a common flat target,hot electrons can be effectively heated with the well-designed grating size,leading to a stronger magnetic field.The spatial distribution of magnetic fields can be modulated by optimizing the grating period and height as well as the incident angle of the laser pulse.
基金supported by National Natural Science Foundation of China (Nos. 11975086, 51577043)
文摘A pulsed transverse magnetic field with pulse width of 12 ms and magnitude of 2 T was used to modify the density distribution of a weakly-ionized plasma flow with strong collisions between the charged particles and neutrals.The morphology of the plasma is changed substantially,with the density increased upstream and decreased downstream.Meanwhile,the plasma toward the axis contracts laterally and gradually converges to a collimated flow.In addition,a drift wave is observed to be excited in the inhomogeneous plasma by the magnetic field.
基金supported by the Innovation Fund for TT&C and Measurement of Near Space Vehicles(No.20180102).
文摘A three-dimensional model is proposed in this paper to study the effect of the pulsed magnetic field on the density distribution of high flow velocity plasma sheath.Taking the typical parameters of plasma sheath at the height of 71 km as an example,the distribution characteristics and time evolution characteristics of plasma density in the flow field under the action of pulsed magnetic field,as well as the effect of self-electric field on the distribution of plasma density,are studied.The simulation results show that pulsed magnetic field can effectively reduce the density of plasma sheath.Meanwhile,the simulation results of three-dimensional plasma density distribution show that the size of the density reduction area is large enough to meet the communication requirements of the Global Position System(GPS)signal.Besides,the location of density reduction area provides a reference for the appropriate location of antenna.The time evolution of plasma density shows that the effective density reduction time can reach 62%of the pulse duration,and the maximum reduction of plasma density can reach 55%.Based on the simulation results,the mechanism of the interaction between pulsed magnetic field and plasma flow field is physically analyzed.Furthermore,the simulation results indicate that the density distributions of electrons and ions are consistent under the action of plasma self-electric field.However,the quasi neutral assumption of plasma in the flow field is not appropriate,because the self-electric field of plasma will weaken the effect of the pulsed magnetic field on the reduction of electron density,which cannot be ignored.The calculation results could provide useful information for the mitigation of communication blackout in hypersonic vehicles.
文摘In this work,laser induced tungsten plasma has been investigated in the absence and presence of 0.6 T static transverse magnetic field at atmospheric pressure in air.The spectroscopic characterization of laser induced tungsten plasma was experimentally studied using space-resolved emission spectroscopy.The atomic emission lines of tungsten showed a significant enhancement in the presence of a magnetic field,while the ionic emission lines of tungsten presented little change.Temporal variation of the optical emission lines of tungsten indicated that the atomic emission time in the presence of a magnetic field was longer than that in the absence of a magnetic field,while no significant changes occurred for the ionic emission time.The spatial resolution of optical emission lines of tungsten demonstrated that the spatial distribution of atoms and ions were separated.The influence of a magnetic field on the spatial distribution of atoms was remarkable,whereas the spatial distribution of ions was little influenced by the magnetic field.The different behaviors between ions and atoms with and without magnetic field in air were related to the various atomic processes especially the electrons and ions recombination process during the plasma expansion and cooling process.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60621063,60678007,and 10774184)the Chinese Academy of Sciences (Grant No. KJCX2-YW-T01)the National Basic Research Program of China (Grant No. 2007CB815101)
文摘Quasistatic magnetic fields generated by nonrelativistic intense linearly polarized (LP) and circularly polarized (CP) laser pulses in an initially uniform underdense plasma in the collision-dominated limit are investigated analytically. Using a selfconsistent analytical model, we perform a detailed derivation of quasistatic magnetic fields in the laser pulse envelope in the collision-dominated limit to obtain exact analytical expressions for magnetic fields and discuss the dependence of magnetic fields on laser and plasma parameters. Equations for quasistatic magnetic fields including both axial componentBz and the azimuthal one Be are derived simultaneously from such a selfconsistent model. The dependence of quasistatic magnetic field on incident laser intensity, transverse focused radius of laser pulse, electron density and electron temperature is discussed.
文摘We consider the radiation from the beam electrons traveling in a strong uniform axial magnetic field and an axial alternating electric field of wavelength Aw generated by a voltage-supplied pill-box cavity. The beam electrons emit genuine laser radiation that propagates only in the axial direction through free-electron two- quantum Stark radiation. We find that laser radiation takes place only at the expense of the axial kinetic energy when Aw 〈〈 c/(ωc/γ), where ωc/γ is the relativistic electron--cyclotron frequency. We formulate the laser power based on quantum-wiggler electrodynamics, and envision a laser of length lore with estimated power 0.1 GW/(kA) in the 10-4 cm wavelength range.
基金This work is supported by the National Natural Science Foundation of China(Grant Nos.11375163,11605182,11605183)the Development Foundation of China Academy of Engineering Physics(Grant No.2011B0402009)the Science Challenge Project No.2016212A505.
文摘As a hybrid approach to realizing fusion energy,Magnetized Target Fusion(MTF)based on the Field Reversed Configuration(FRC),which has the plasma density and confinement time in the range between magnetic and inertial confinement fusion,has been recently widely pursued around the world.To investigate the formation and confinement of the FRC plasma injector for MTF,the Yingguang-I,which is an FRC test device and contains a multi-bank program-discharged pulsed power sub-system,was constructed at the Institute of Fluid Physics(IFP),China.This paper presents the pulsed power components and their parameters of the device in detail,then gives a brief description of progress in experiments of FRC formation.Experimental results of the pulsed power sub-system show that the peak current/magnetic field of 110 kA/0.3 T,10 kA/1.2 Tand 1.7 MA/3.4 Twere achieved in the bias,mirror and q-pinch circuits with quarter cycle of 80 ms,700 ms and 3.8 ms respectively.The induced electric field in the neutral gas was greater than 0.25 kV/cm when the ionization bank was charged to 70 kV.With H_(2) gas of 8 Pa,the plasma target of density 10^(16) cm^(-3),separatrix radius 4 cm,half-length 17 cm,equilibrium temperature 200 eV and lifetime 3 ms(approximately the half pulse width of the reversed field)have been obtained through the q-pinch method when the bias,mirror,ionization and θ-pinch banks were charged to 5 kV,5 kV,55 kV and ±45 kV respectively.The images from the high-speed end-on framing camera demonstrate the formation processes of FRC and some features agree well with the results with the two-dimension magneto hydrodynamics code(2D-MHD).
基金supported in part by the Science Challenge Project(No.TZ2016005)the CAS-JSPS Joint Research Program(External Cooperation Program of the BIC,Chinese Academy of Sciences,No.112111KYSB20160015)+1 种基金the National Natural Science Foundation of China(Nos.11520101003,11535001 and11861121001)the Strategic Priority Research Program of the Chinese Academy of Sciences(Nos.XDB16010200 and XDB07030300)
文摘As a promising new way to generate a controllable strong magnetic field, laser-driven magnetic coils have attracted interest in many research fields. In 2013, a kilotesla level magnetic field was achieved at the Gekko XⅡ laser facility with a capacitor–coil target. A similar approach has been adopted in a number of laboratories, with a variety of targets of different shapes. The peak strength of the magnetic field varies from a few tesla to kilotesla, with different spatiotemporal ranges. The differences are determined by the target geometry and the parameters of the incident laser. Here we present a review of the results of recent experimental studies of laser-driven magnetic field generation, as well as a discussion of the diagnostic techniques required for such rapidly changing magnetic fields. As an extension of the magnetic field generation, some applications are discussed.
文摘The quasistatic axial magnetic fields in plasmas produced by ultrashort laser pulses were measured by measuring the Faraday rotation angle of the backscattered emission. The spatial distribution of the axial magnetic field was obtained with a peak value as high as 170 Tesla. Theory suggests that the axial magnetic field is generated by dynamo effect in laser-plasma interaction.
基金supported by National Basic Research Program of China (973 Program) under grant No.2013CBA01503the National Natural Science Foundation of China under grant No.11573040, 11503041 and 11135012supported by the Science Challenge Program
文摘In this paper, the recent studies of laboratory astrophysics with strong magnetic fields in China have been reviewed.On the Shenguang-II laser facility of the National Laboratory on High-Power Lasers and Physics, a laser-driven strong magnetic field up to 200 T has been achieved. The experiment was performed to model the interaction of solar wind with dayside magnetosphere. Also the low beta plasma magnetic reconnection(MR) has been studied. Theoretically, the model has been developed to deal with the atomic structures and processes in strong magnetic field. Also the study of shock wave generation in the magnetized counter-streaming plasmas is introduced.
文摘In this paper, the nonlinear interaction of ultra-high power laser beam with fusion plasma at relativistic regime in the presence of obliquely external magnetic field has been studied. Imposing an external magnetic field on plasma can modify the density profile of the plasma so that the thermal conductivity of electrons reduces which is considered to be the decrease of the threshold energy for ignition. To achieve the fusion of Hydrogen–Boron(HB) fuel,the block acceleration model of plasma is employed. Energy production by HB isotopes can be of interest, since its reaction does not generate radioactive tritium. By using the inhibit factor in the block model acceleration of plasma and Maxwell's as well as the momentum transfer equations, the electron density distribution and dielectric permittivity of the plasma medium are obtained. Numerical results indicate that with increasing the intensity of the external magnetic field, the oscillation of the laser magnetic field decreases, while the dielectric permittivity increases. Moreover, the amplitude of the electron density becomes highly peaked and the plasma electrons are strongly bunched with increasing the intensity of external magnetic field. Therefore, the magnetized plasma can act as a positive focusing lens to enhance the fusion process. Besides, we find that with increasing θ-angle(from oblique external magnetic field) between 0 and 90°, the dielectric permittivity increases, while for θ between 90° and 180°, the dielectric permittivity decreases with increasing θ.