2013 Vol. 37, No. 11
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2013, 37(11): 113101. doi: 10.1088/1674-1137/37/11/113101
Abstract:
In this work the mass spectra for some of the baryon resonances of the particle data group with three and four star status are obtained,and a unified description of the ground states and excitation spectra of baryons are provided in the framework of a non-relativistic potential model. For this goal we have analytically solved the radial Schrödinger equation for three identical interacting particles with the anharmonic potential by using the Ansatz method and then we have calculated the baryon resonances spectrum by using the Gürsey Radicati mass formula (GR) and with generalized Gürsey Radicati mass formula (GGR). The results of our model show that the calculated masses of baryon resonances by using the generalized Gürsey Radicati mass formula are found to be in good agreement with the tabulations of the Particle Data Group. The overall good description of the spectrum which we obtain shows that our model can also be used to give a fair description of the energies of the excited multiples up to 3 GeV mass and negative-parity resonance. Moreover,we have shown that our model reproduces the position of the Roper resonance of the nucleon.
In this work the mass spectra for some of the baryon resonances of the particle data group with three and four star status are obtained,and a unified description of the ground states and excitation spectra of baryons are provided in the framework of a non-relativistic potential model. For this goal we have analytically solved the radial Schrödinger equation for three identical interacting particles with the anharmonic potential by using the Ansatz method and then we have calculated the baryon resonances spectrum by using the Gürsey Radicati mass formula (GR) and with generalized Gürsey Radicati mass formula (GGR). The results of our model show that the calculated masses of baryon resonances by using the generalized Gürsey Radicati mass formula are found to be in good agreement with the tabulations of the Particle Data Group. The overall good description of the spectrum which we obtain shows that our model can also be used to give a fair description of the energies of the excited multiples up to 3 GeV mass and negative-parity resonance. Moreover,we have shown that our model reproduces the position of the Roper resonance of the nucleon.
2013, 37(11): 113102. doi: 10.1088/1674-1137/37/11/113102
Abstract:
In this paper we calculate the thermal entanglement and teleportation in a two-qubit Heisenberg XYZ chain with the different Dzyaloshinskii-Moriya interaction and inhomogeneous magnetic fields. The analytical expressions of the concurrence and the average fidelity are obtained for this model. We have shown that the quantum phase transition occurs in the system and the quantum phase transition point depends on the inhomogeneity of magnetic fields. We compare the x-component Dzyaloshinskii-Moriya interaction with the z-component Dzyaloshinskii-Moriya interaction on the effects of quantum teleportation. It is found that we can take Dzyaloshinskii-Moriya interaction as one of the effective control parameters for the teleportation manipulation.
In this paper we calculate the thermal entanglement and teleportation in a two-qubit Heisenberg XYZ chain with the different Dzyaloshinskii-Moriya interaction and inhomogeneous magnetic fields. The analytical expressions of the concurrence and the average fidelity are obtained for this model. We have shown that the quantum phase transition occurs in the system and the quantum phase transition point depends on the inhomogeneity of magnetic fields. We compare the x-component Dzyaloshinskii-Moriya interaction with the z-component Dzyaloshinskii-Moriya interaction on the effects of quantum teleportation. It is found that we can take Dzyaloshinskii-Moriya interaction as one of the effective control parameters for the teleportation manipulation.
2013, 37(11): 113103. doi: 10.1088/1674-1137/37/11/113103
Abstract:
In this paper we first introduce the famous Klein paradox. Afterwards by proposing the Krein quantization approach and taking the negative modes into account,we will show that the expected and exact current densities could be achieved without confronting any paradox.
In this paper we first introduce the famous Klein paradox. Afterwards by proposing the Krein quantization approach and taking the negative modes into account,we will show that the expected and exact current densities could be achieved without confronting any paradox.
2013, 37(11): 113104. doi: 10.1088/1674-1137/37/11/113104
Abstract:
An approximate analytical solution of the Dirac equation is obtained for the ring-shaped Woods-Saxon potential within the framework of an exponential approximation to the centrifugal term. The radial and angular parts of the equation are solved by the Nikiforov-Uvarov method. The general results obtained in this work can be reduced to the standard forms already present in the literature.
An approximate analytical solution of the Dirac equation is obtained for the ring-shaped Woods-Saxon potential within the framework of an exponential approximation to the centrifugal term. The radial and angular parts of the equation are solved by the Nikiforov-Uvarov method. The general results obtained in this work can be reduced to the standard forms already present in the literature.
2013, 37(11): 114101. doi: 10.1088/1674-1137/37/11/114101
Abstract:
The nucleon-nucleon interaction is investigated by using the improved quantum molecular dynamic (ImQMD) model with three sets of parameters IQ1,IQ2 and IQ3,in which the corresponding incompressibility coefficients of nuclear matter are different. The charge distributions of fragments are calculated for various reaction systems at different incident energies. The parameters strongly affect the charge distributions and the fragment multiplicity spectrum below the threshold energy of nuclear multifragmentation. The fragment multiplicity spectrum for 238U+197Au at 15 A MeV and the charge distributions for 129Xe+120Sn at 32 and 45 A MeV,and 197Au+197Au at 35 A MeV are reproduced by the ImQMD model with the set of parameter IQ3. It is found that: 1) The charge distribution of the fragments and the fragment multiplicity spectrum are good observables for testing the model and the parameters. 2) The Fermi energy region is a sensitive energy region for studying nucleon-nucleon interaction.
The nucleon-nucleon interaction is investigated by using the improved quantum molecular dynamic (ImQMD) model with three sets of parameters IQ1,IQ2 and IQ3,in which the corresponding incompressibility coefficients of nuclear matter are different. The charge distributions of fragments are calculated for various reaction systems at different incident energies. The parameters strongly affect the charge distributions and the fragment multiplicity spectrum below the threshold energy of nuclear multifragmentation. The fragment multiplicity spectrum for 238U+197Au at 15 A MeV and the charge distributions for 129Xe+120Sn at 32 and 45 A MeV,and 197Au+197Au at 35 A MeV are reproduced by the ImQMD model with the set of parameter IQ3. It is found that: 1) The charge distribution of the fragments and the fragment multiplicity spectrum are good observables for testing the model and the parameters. 2) The Fermi energy region is a sensitive energy region for studying nucleon-nucleon interaction.
2013, 37(11): 114102. doi: 10.1088/1674-1137/37/11/114102
Abstract:
We investigate the alpha-decay half-lives of non-spherical nuclei with the Yukawa potential as the proximity potential and an angle-dependent term that accounts for the deformation effects and apply the results to Ho,Tb,Lu,Tm,Ta,Hf,Yb,Re,Ir,Pt,Au,Po,etc. as examples. The comparison with the existing data is encouraging.
We investigate the alpha-decay half-lives of non-spherical nuclei with the Yukawa potential as the proximity potential and an angle-dependent term that accounts for the deformation effects and apply the results to Ho,Tb,Lu,Tm,Ta,Hf,Yb,Re,Ir,Pt,Au,Po,etc. as examples. The comparison with the existing data is encouraging.
2013, 37(11): 116001. doi: 10.1088/1674-1137/37/11/116001
Abstract:
GPM based on THGEM has shown its competitive strength compared to the conventional PMT,especially in the low background research such as dark matter detection. A kind of THGEM made from PTFE,named PTFE-THGEM,is developed for the GPM to be used in CDEX. The PTFE has a lot of advantages especially its low level radioactivity. The PTFE-THGEM was tested at room and cryogenic temperature. It has a high gain in different gases and shows good stability at room temperature. The gain of a single PTFE-THGEM reached 112 at 117 K. The penning effect is also discussed in this paper to explain the “abnormal” phenomena of the gain in different gases.
GPM based on THGEM has shown its competitive strength compared to the conventional PMT,especially in the low background research such as dark matter detection. A kind of THGEM made from PTFE,named PTFE-THGEM,is developed for the GPM to be used in CDEX. The PTFE has a lot of advantages especially its low level radioactivity. The PTFE-THGEM was tested at room and cryogenic temperature. It has a high gain in different gases and shows good stability at room temperature. The gain of a single PTFE-THGEM reached 112 at 117 K. The penning effect is also discussed in this paper to explain the “abnormal” phenomena of the gain in different gases.
2013, 37(11): 116101. doi: 10.1088/1674-1137/37/11/116101
Abstract:
An all-transistor active-inductor shunt-peaking structure has been used in a prototype of 8 Gbps high-speed VCSEL driver which is designed for the optical link in ATLAS liquid Argon calorimeter upgrade. The VCSEL driver is fabricated in a commercial 0.25 u m Silicon-on-Sapphire (SoS) CMOS process for radiation tolerant purpose. The all-transistor active-inductor shunt-peaking is used to overcome the bandwidth limitation from the CMOS process. The peaking structure has the same peaking effect as the passive one,but takes a small area,does not need linear resistors and can overcome the process variation by adjust the peaking strength via an external control. The design has been taped out,and the prototype has been proven by the preliminary electrical test results and bit error ratio test results. The driver achieves 8 Gbps data rate as simulated with the peaking. We present the all-transistor active-inductor shunt-peaking structure,simulation and test results in this paper.
An all-transistor active-inductor shunt-peaking structure has been used in a prototype of 8 Gbps high-speed VCSEL driver which is designed for the optical link in ATLAS liquid Argon calorimeter upgrade. The VCSEL driver is fabricated in a commercial 0.25 u m Silicon-on-Sapphire (SoS) CMOS process for radiation tolerant purpose. The all-transistor active-inductor shunt-peaking is used to overcome the bandwidth limitation from the CMOS process. The peaking structure has the same peaking effect as the passive one,but takes a small area,does not need linear resistors and can overcome the process variation by adjust the peaking strength via an external control. The design has been taped out,and the prototype has been proven by the preliminary electrical test results and bit error ratio test results. The driver achieves 8 Gbps data rate as simulated with the peaking. We present the all-transistor active-inductor shunt-peaking structure,simulation and test results in this paper.
2013, 37(11): 116102. doi: 10.1088/1674-1137/37/11/116102
Abstract:
Time interleaved analog-to-digital conversion (TIADC) based on parallelism is an effective way to meet the requirement of the ultra-fast waveform digitizer beyond Gsps. Different methods to correct the mismatch errors among different analog-to-digital conversion channels have been developed previously. To overcome the speed limitation in hardware design and to implement the mismatch correction algorithm in real time,this paper proposes a fully parallel correction algorithm. A 12-bit 1-Gsps waveform digitizer with ENOB around 10.5 bit from 5 MHz to 200 MHz is implemented based on the real-time correction algorithm.
Time interleaved analog-to-digital conversion (TIADC) based on parallelism is an effective way to meet the requirement of the ultra-fast waveform digitizer beyond Gsps. Different methods to correct the mismatch errors among different analog-to-digital conversion channels have been developed previously. To overcome the speed limitation in hardware design and to implement the mismatch correction algorithm in real time,this paper proposes a fully parallel correction algorithm. A 12-bit 1-Gsps waveform digitizer with ENOB around 10.5 bit from 5 MHz to 200 MHz is implemented based on the real-time correction algorithm.
2013, 37(11): 116201. doi: 10.1088/1674-1137/37/11/116201
Abstract:
Online fuel pebble burnup measurement in a future high temperature gas cooling reactor is proposed for implementation through a high purity germanium (HPGe) gamma spectrometer. By using KORIGEN software and MCNP Monte Carlo simulations,the single pebble gamma radiations to be recorded in the detector are simulated under different irradiation histories. A specially developed algorithm is applied to analyze the generated spectra to reconstruct the gamma activity of the 137Cs monitoring nuclide. It is demonstrated that by taking into account the intense interfering peaks,the 137Cs activity in the spent pebbles can be derived with a standard deviation of 3.0%(1σ). The results support the feasibility of utilizing the HPGe spectrometry in the online determination of the pebble burnup in future modular pebble bed reactors.
Online fuel pebble burnup measurement in a future high temperature gas cooling reactor is proposed for implementation through a high purity germanium (HPGe) gamma spectrometer. By using KORIGEN software and MCNP Monte Carlo simulations,the single pebble gamma radiations to be recorded in the detector are simulated under different irradiation histories. A specially developed algorithm is applied to analyze the generated spectra to reconstruct the gamma activity of the 137Cs monitoring nuclide. It is demonstrated that by taking into account the intense interfering peaks,the 137Cs activity in the spent pebbles can be derived with a standard deviation of 3.0%(1σ). The results support the feasibility of utilizing the HPGe spectrometry in the online determination of the pebble burnup in future modular pebble bed reactors.
2013, 37(11): 116202. doi: 10.1088/1674-1137/37/11/116202
Abstract:
The model of three-body Borromean halo nuclei breakup was described by using standard phase space distributions and the Monte Carlo simulation method was established to resolve the detection problem of two neutrons produced from breakup reaction on the neutron wall detector. For 6He case,overall resolution σEk for the Gaussian part of the detector response and the detection efficiency including solid angle acceptance with regard to the excitation energy Ek are obtained by the simulation of two neutrons from 6He breakup into the neutron wall. The effects of the algorithm on the angular and energy correlations of the fragments are briefly discussed.
The model of three-body Borromean halo nuclei breakup was described by using standard phase space distributions and the Monte Carlo simulation method was established to resolve the detection problem of two neutrons produced from breakup reaction on the neutron wall detector. For 6He case,overall resolution σEk for the Gaussian part of the detector response and the detection efficiency including solid angle acceptance with regard to the excitation energy Ek are obtained by the simulation of two neutrons from 6He breakup into the neutron wall. The effects of the algorithm on the angular and energy correlations of the fragments are briefly discussed.
2013, 37(11): 117001. doi: 10.1088/1674-1137/37/11/117001
Abstract:
Generally,a standard bunching system is composed by an SW pre-buncher,a TW buncher and a standard accelerating section. However,there is one way to simplify the whole system to some extent by using the hybrid buncher,which is a combined structure of the SW pre-buncher and the TW buncher. Here the beam dynamics studies on an S-band bunching system with the hybrid buncher is presented,and simulation results show that similar beam performance can be obtained at the linac exit by using this kind of bunching system rather than the standard one. In the meantime,the structure design of the hybrid buncher is also described. Furthermore,the standard accelerating section can also be integrated with the hybrid buncher,which can further simplify the usual bunching system and lower the construction cost.
Generally,a standard bunching system is composed by an SW pre-buncher,a TW buncher and a standard accelerating section. However,there is one way to simplify the whole system to some extent by using the hybrid buncher,which is a combined structure of the SW pre-buncher and the TW buncher. Here the beam dynamics studies on an S-band bunching system with the hybrid buncher is presented,and simulation results show that similar beam performance can be obtained at the linac exit by using this kind of bunching system rather than the standard one. In the meantime,the structure design of the hybrid buncher is also described. Furthermore,the standard accelerating section can also be integrated with the hybrid buncher,which can further simplify the usual bunching system and lower the construction cost.
2013, 37(11): 117002. doi: 10.1088/1674-1137/37/11/117002
Abstract:
The back-streaming neutrons from the spallation target at CSNS are very intense,and can pose serious damage problems for the devices in the accelerator-target interface region. To tackle the problems,a possible scheme for this region was studied,namely a specially designed optics for the proton beam line produces two beam waists,and two collimators are placed at the two waist positions to maximize the collimation effect of the back-streaming neutrons. Detailed Monte Carlo simulations with the beams in the two different CSNS phases show the effectiveness of the collimation system,and the radiation dose rate decreases largely in the interface section. This can ensure the use of epoxy coils for the last magnets and other devices in the beam transport line with reasonable lifetimes,e.g.,thirty years. The design philosophy for such an accelerator-target interface region can also be applicable to other high-power proton beam applications.
The back-streaming neutrons from the spallation target at CSNS are very intense,and can pose serious damage problems for the devices in the accelerator-target interface region. To tackle the problems,a possible scheme for this region was studied,namely a specially designed optics for the proton beam line produces two beam waists,and two collimators are placed at the two waist positions to maximize the collimation effect of the back-streaming neutrons. Detailed Monte Carlo simulations with the beams in the two different CSNS phases show the effectiveness of the collimation system,and the radiation dose rate decreases largely in the interface section. This can ensure the use of epoxy coils for the last magnets and other devices in the beam transport line with reasonable lifetimes,e.g.,thirty years. The design philosophy for such an accelerator-target interface region can also be applicable to other high-power proton beam applications.
2013, 37(11): 117003. doi: 10.1088/1674-1137/37/11/117003
Abstract:
Precise measurement of betatron tune is required for good operating condition of CSNS RCS. The fractional part of betatron tune is important and it can be measured by analyzing the signals of beam position from the appointed BPM. Usually these signals are contaminated during the acquisition process,therefore several power spectrum methods are used to improve the frequency resolution. In this article classical and modern power spectrum methods are used. In order to compare their performance,the results of simulation data and IQT data from J-PARC RCS are discussed. It is shown that modern power spectrum estimation has better performance than the classical ones,though the calculation is more complex.
Precise measurement of betatron tune is required for good operating condition of CSNS RCS. The fractional part of betatron tune is important and it can be measured by analyzing the signals of beam position from the appointed BPM. Usually these signals are contaminated during the acquisition process,therefore several power spectrum methods are used to improve the frequency resolution. In this article classical and modern power spectrum methods are used. In order to compare their performance,the results of simulation data and IQT data from J-PARC RCS are discussed. It is shown that modern power spectrum estimation has better performance than the classical ones,though the calculation is more complex.
2013, 37(11): 117004. doi: 10.1088/1674-1137/37/11/117004
Abstract:
Modeling multipacting to steady state saturation is of interest in determining the performance of the micro-pulse electron gun. In this paper,a novel method is proposed to calculate the multipacting resonance parameters for the gun. This method works well,and the 2-D simulation results suggest that steady state saturation can be achieved in the gun. After saturation the transition from two-surface multipacting to single-surface multipacting occurred,and an extensive range of electron emission time is a suggested way to avoid this kind of transition.
Modeling multipacting to steady state saturation is of interest in determining the performance of the micro-pulse electron gun. In this paper,a novel method is proposed to calculate the multipacting resonance parameters for the gun. This method works well,and the 2-D simulation results suggest that steady state saturation can be achieved in the gun. After saturation the transition from two-surface multipacting to single-surface multipacting occurred,and an extensive range of electron emission time is a suggested way to avoid this kind of transition.
2013, 37(11): 117005. doi: 10.1088/1674-1137/37/11/117005
Abstract:
In this paper we present the physical design of the pulsed sextupole injection system for Beijing Advanced Photon Source (BAPS) with an ultralow emittance. The BAPS ring lattice is designed in such a way that two options of pulsed sextupole injection are allowed,i.e.,with septum and pulsed sextupole in different drift spaces or in the same drift space. We give the magnetic parameters of the injection system and the optimal condition of the optical functions for both options. In addition,we find that the pulsed sextupole induces position-dependent dispersive effect and causes a non-ignorable effect on the injection efficiency in a storage ring with a relatively small acceptance,which should be well considered.
In this paper we present the physical design of the pulsed sextupole injection system for Beijing Advanced Photon Source (BAPS) with an ultralow emittance. The BAPS ring lattice is designed in such a way that two options of pulsed sextupole injection are allowed,i.e.,with septum and pulsed sextupole in different drift spaces or in the same drift space. We give the magnetic parameters of the injection system and the optimal condition of the optical functions for both options. In addition,we find that the pulsed sextupole induces position-dependent dispersive effect and causes a non-ignorable effect on the injection efficiency in a storage ring with a relatively small acceptance,which should be well considered.
2013, 37(11): 117006. doi: 10.1088/1674-1137/37/11/117006
Abstract:
A prototype laser ion source that could demonstrate the possibility of producing intense pulsed high charge state ion beams has been established with a commercial Nd:YAG laser (Emax=3 J,1064 nm,8-10 ns) to produce laser plasma for the research of Laser Ion Source (LIS). At the laser ion source test bench,high purity (99.998%) aluminum and lead targets have been tested for laser plasma experiment. An Electrostatic Ion Analyzer (EIA) and Electron Multiply Tube (EMT) detector were used to analyze the charge state and energy distribution of the ions produced by the laser ion source. The maximum charge states of Al12+ and Pb7+ were achieved. The results will be presented and discussed in this paper.
A prototype laser ion source that could demonstrate the possibility of producing intense pulsed high charge state ion beams has been established with a commercial Nd:YAG laser (Emax=3 J,1064 nm,8-10 ns) to produce laser plasma for the research of Laser Ion Source (LIS). At the laser ion source test bench,high purity (99.998%) aluminum and lead targets have been tested for laser plasma experiment. An Electrostatic Ion Analyzer (EIA) and Electron Multiply Tube (EMT) detector were used to analyze the charge state and energy distribution of the ions produced by the laser ion source. The maximum charge states of Al12+ and Pb7+ were achieved. The results will be presented and discussed in this paper.
2013, 37(11): 118001. doi: 10.1088/1674-1137/37/11/118001
Abstract:
This paper reports the design and cold test of the cavity beam position monitor (CBPM) for SX-FEL to fulfill the requirement of beam position measurement resolution of less than 1 u m,even 0.1 u m. The CBPM was optimized by using a coupling slot to damp the TM010 mode in the output signal. The isolation of TM010 mode is about 117 dB,and the shunt impedance is about 200Ω@4.65 GHz with the quality factor 80 from MAFIA simulation and test result. A special antenna was designed to load power for reducing excitation of other modes in the cavity. The resulting output power of TM110 mode was about 90 mV/mm when the source was 6 dBm,and the accomplishable minimum voltage was about 200 uV. The resolution of the CBPM was about 0.1u m from the linear fitting result based on the cold test.
This paper reports the design and cold test of the cavity beam position monitor (CBPM) for SX-FEL to fulfill the requirement of beam position measurement resolution of less than 1 u m,even 0.1 u m. The CBPM was optimized by using a coupling slot to damp the TM010 mode in the output signal. The isolation of TM010 mode is about 117 dB,and the shunt impedance is about 200Ω@4.65 GHz with the quality factor 80 from MAFIA simulation and test result. A special antenna was designed to load power for reducing excitation of other modes in the cavity. The resulting output power of TM110 mode was about 90 mV/mm when the source was 6 dBm,and the accomplishable minimum voltage was about 200 uV. The resolution of the CBPM was about 0.1u m from the linear fitting result based on the cold test.
2013, 37(11): 118002. doi: 10.1088/1674-1137/37/11/118002
Abstract:
The photoelectron spectroscopy beamline at National Synchrotron Radiation Laboratory (NSRL) is equipped with a spherical grating monochromator with the included angle of 174°. Three gratings with line density of 200,700 and 1200 lines/mm are used to cover the energy region from 60 eV to 1000 eV. After several years' operation,the spectral resolution and flux throughput were deteriorated,and realignment was necessary to improve the performance. First,the wavelength scanning mechanism,the optical components position and the exit slit guide direction are aligned according to the design value. Second,the gratings are checked by Atomic Force Microscopy (AFM) and then the gas absorption spectrum is measured to optimize the focusing condition of the monochromator. The spectral resolving power E/ΔE is recovered to the designed value of 1000@244 eV. The flux at the end station for the 200 lines/mm grating is about 1010 photons/sec/200 mA,which is in accordance with the design. The photon flux for the 700 lines/mm grating is about 5×108 photons/sec/200mA,which is lower than expected. This poor flux throughput may be caused by carbon contamination on the optical components. The 1200 lines/mm grating has roughness much higher than expected so the diffraction efficiency is too low to detect any signal. A new grating would be ordered. After the alignment,the beamline has significant performance improvements in both the resolving power and the flux throughput for 200 and 700 lines/mm gratings and is provided to users.
The photoelectron spectroscopy beamline at National Synchrotron Radiation Laboratory (NSRL) is equipped with a spherical grating monochromator with the included angle of 174°. Three gratings with line density of 200,700 and 1200 lines/mm are used to cover the energy region from 60 eV to 1000 eV. After several years' operation,the spectral resolution and flux throughput were deteriorated,and realignment was necessary to improve the performance. First,the wavelength scanning mechanism,the optical components position and the exit slit guide direction are aligned according to the design value. Second,the gratings are checked by Atomic Force Microscopy (AFM) and then the gas absorption spectrum is measured to optimize the focusing condition of the monochromator. The spectral resolving power E/ΔE is recovered to the designed value of 1000@244 eV. The flux at the end station for the 200 lines/mm grating is about 1010 photons/sec/200 mA,which is in accordance with the design. The photon flux for the 700 lines/mm grating is about 5×108 photons/sec/200mA,which is lower than expected. This poor flux throughput may be caused by carbon contamination on the optical components. The 1200 lines/mm grating has roughness much higher than expected so the diffraction efficiency is too low to detect any signal. A new grating would be ordered. After the alignment,the beamline has significant performance improvements in both the resolving power and the flux throughput for 200 and 700 lines/mm gratings and is provided to users.
2013, 37(11): 118101. doi: 10.1088/1674-1137/37/11/118101
Abstract:
The polarization switch of a free-electron laser (FEL) is of great importance to the user scientific community. In this paper,we investigate the generation of controllable polarization FEL from two well-known approaches for Dalian coherent light source,i.e.,crossed planar undulator and elliptical permanent undulator. In order to perform a fair comparative study,a one-dimensional time-dependent FEL code has been developed,in which the imperfection effects of an elliptical permanent undulator are taken into account. Comprehensive simulation results indicate that the residual beam energy chirp and the intrinsic FEL gain may contribute to the degradation of the polarization performance for the crossed planar undulator. The elliptical permanent undulator is not very sensitive to the undulator errors and beam imperfections. Meanwhile,with proper configurations of the main planar undulators and additional elliptical permanent undulator section,circular polarized FEL with pulse energy exceeding 100 uJ could be achieved at Dalian coherent light source.
The polarization switch of a free-electron laser (FEL) is of great importance to the user scientific community. In this paper,we investigate the generation of controllable polarization FEL from two well-known approaches for Dalian coherent light source,i.e.,crossed planar undulator and elliptical permanent undulator. In order to perform a fair comparative study,a one-dimensional time-dependent FEL code has been developed,in which the imperfection effects of an elliptical permanent undulator are taken into account. Comprehensive simulation results indicate that the residual beam energy chirp and the intrinsic FEL gain may contribute to the degradation of the polarization performance for the crossed planar undulator. The elliptical permanent undulator is not very sensitive to the undulator errors and beam imperfections. Meanwhile,with proper configurations of the main planar undulators and additional elliptical permanent undulator section,circular polarized FEL with pulse energy exceeding 100 uJ could be achieved at Dalian coherent light source.
2013, 37(11): 118201. doi: 10.1088/1674-1137/37/11/118201
Abstract:
Distortions caused by the neutron spectrum and scattered neutrons are major problems in fast neutron radiography and should be considered for improving the image quality. This paper puts emphasis on the removal of these image distortions and deviations for fast neutron radiography performed at the NECTAR facility of the research reactor FRM-Ⅱ in Technische Universität München (TUM),Germany. The NECTAR energy spectrum is analyzed and established to modify the influence caused by the neutron spectrum,and the Point Scattered Function (PScF) simulated by the Monte-Carlo program MCNPX is used to evaluate scattering effects from the object and improve image quality. Good analysis results prove the sound effects of the above two corrections.
Distortions caused by the neutron spectrum and scattered neutrons are major problems in fast neutron radiography and should be considered for improving the image quality. This paper puts emphasis on the removal of these image distortions and deviations for fast neutron radiography performed at the NECTAR facility of the research reactor FRM-Ⅱ in Technische Universität München (TUM),Germany. The NECTAR energy spectrum is analyzed and established to modify the influence caused by the neutron spectrum,and the Point Scattered Function (PScF) simulated by the Monte-Carlo program MCNPX is used to evaluate scattering effects from the object and improve image quality. Good analysis results prove the sound effects of the above two corrections.
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