Email alert
RSS2005 Vol. 17, No. 06
Recommend Articles
column
Display Method:
2005,
17.
Abstract:
By using the methods of matrix representation and complex Gaussian function expansion, the recurrence propagation formulae of a flattened Gaussian beam through multi-apertured optical ABCD systems are derived. Numerical examples are given to compare the two numerical simulation methods. It is shown that the form of matrix formulae is simple, and the matrix formulation is applicable to the Fraunhofer and Fresnel regions. However, this method is suited only to circularly symmetric optical beams and systems. On the other hand, the form of formulae derived by the method of complex Gaussian function expansion is complex, and its calculation errors become noticeable in the near Fresnel region closer to the aperture. But this method is suited to both circularly symmetric and circularly un-symmetr
By using the methods of matrix representation and complex Gaussian function expansion, the recurrence propagation formulae of a flattened Gaussian beam through multi-apertured optical ABCD systems are derived. Numerical examples are given to compare the two numerical simulation methods. It is shown that the form of matrix formulae is simple, and the matrix formulation is applicable to the Fraunhofer and Fresnel regions. However, this method is suited only to circularly symmetric optical beams and systems. On the other hand, the form of formulae derived by the method of complex Gaussian function expansion is complex, and its calculation errors become noticeable in the near Fresnel region closer to the aperture. But this method is suited to both circularly symmetric and circularly un-symmetr
2005,
17.
Abstract:
Different from a traditional double clad fiber laser, the front end of the double clad fiber is separated from the dichroic mirror which forms a Fabry-Perot filter. The efficiency of Fabry-Perot filter is analyzed theoretically. By adjusting the distance between the mirror and the end of the fiber, a novel Yb3+ doped double clad fiber laser with narrow line width and single mode is presented. In the experiment, the laser with an output power of 0.62 W and a slope efficiency of 20% is obtained. The line width at central wavelength of 1 082.79 nm is only 0.14 nm.
Different from a traditional double clad fiber laser, the front end of the double clad fiber is separated from the dichroic mirror which forms a Fabry-Perot filter. The efficiency of Fabry-Perot filter is analyzed theoretically. By adjusting the distance between the mirror and the end of the fiber, a novel Yb3+ doped double clad fiber laser with narrow line width and single mode is presented. In the experiment, the laser with an output power of 0.62 W and a slope efficiency of 20% is obtained. The line width at central wavelength of 1 082.79 nm is only 0.14 nm.
2005,
17.
Abstract:
In this paper, the modified 1-D time-dependent free electron laser (FEL) code is used to simulate the wavelength stabilization feedback system of a high average power FEL based on the parameters of Jefferson Lab's Demo-IR FEL facility. In the simulation, the distribution function of the electron is assumed to be Gaussian and there are 16 electrons in each longitude grid in the 1-D FEL code, the energy spread of the elctrons is ignored. The equivalent detuning caused by the electron energy changing has strong effects on the whole system of FEL. To some extent, it would destroy the interaction between the laser field and electrons, reduce the gain, even cause malfunction of the FEL. Therefore, this paper gives out a scheme to avoid the devastating influence, which shows it is feasible and ef
In this paper, the modified 1-D time-dependent free electron laser (FEL) code is used to simulate the wavelength stabilization feedback system of a high average power FEL based on the parameters of Jefferson Lab's Demo-IR FEL facility. In the simulation, the distribution function of the electron is assumed to be Gaussian and there are 16 electrons in each longitude grid in the 1-D FEL code, the energy spread of the elctrons is ignored. The equivalent detuning caused by the electron energy changing has strong effects on the whole system of FEL. To some extent, it would destroy the interaction between the laser field and electrons, reduce the gain, even cause malfunction of the FEL. Therefore, this paper gives out a scheme to avoid the devastating influence, which shows it is feasible and ef
2005,
17.
Abstract:
Improving illumination uniformity is one of the most important steps to restrain the influence of the atmospheric turbulence on free-space optical communication. Furthermore, partially coherent light source could be used to produce relative uniform illumination. In this paper an optical structure which takes advantage of the inter-mode dispersion of multimode fiber is proposed to produce a synthetic partly coherent light source. The principle is analyzed and a computer simulation is employed to demonstrate the feasibility. It is indicated that beam divergence angle is determined by fiber diameter and focus of lens. The simulated result shows that the spatial coherence of the synthetic light source decreases as the total optical path difference is increased and a synthetic source with 1mra
Improving illumination uniformity is one of the most important steps to restrain the influence of the atmospheric turbulence on free-space optical communication. Furthermore, partially coherent light source could be used to produce relative uniform illumination. In this paper an optical structure which takes advantage of the inter-mode dispersion of multimode fiber is proposed to produce a synthetic partly coherent light source. The principle is analyzed and a computer simulation is employed to demonstrate the feasibility. It is indicated that beam divergence angle is determined by fiber diameter and focus of lens. The simulated result shows that the spatial coherence of the synthetic light source decreases as the total optical path difference is increased and a synthetic source with 1mra
2005,
17.
Abstract:
From the flat-topped beam model proposed recently by Li and the Collins formula, an analytical propagation expression for the kurtosis parameter (K parameter) of flat-topped beams through a paraxial ABCD system is derived. The K parameter depends on the beam order, Rayleigh length and ratio A/B of transfer matrix elements. Based on the propagation equation of intensity moments, a closed-form propagation equation of the K parameter is deduced. The two expressions are shown to be numerically equivalent. The propagation properties of the K parameter of flat-topped beams are illustrated with the caculated results.
From the flat-topped beam model proposed recently by Li and the Collins formula, an analytical propagation expression for the kurtosis parameter (K parameter) of flat-topped beams through a paraxial ABCD system is derived. The K parameter depends on the beam order, Rayleigh length and ratio A/B of transfer matrix elements. Based on the propagation equation of intensity moments, a closed-form propagation equation of the K parameter is deduced. The two expressions are shown to be numerically equivalent. The propagation properties of the K parameter of flat-topped beams are illustrated with the caculated results.
2005,
17.
Abstract:
The threedimensional intensity distribution of the partially coherent beams focused by a lens is investigated. It is shown that the focused intensity distribution near the geometrical focus is dependent not only on the intensity distribution of the incident partially coherent beam, but also on the degree of coherence. Based on this point, a novel method is presented for achieving a quasi-ellipsoid light cage profile near the geometrical focus by modulating the spectral degree of coherence of the incident partially coherent beam. The modulation can obtain the desired three-dimensional intensity distribution and control the aperture of the ellipsoid light cage by choosing the appropriate parameters of spectral degree at the lens plane without changing the incident beam. The method is of th
The threedimensional intensity distribution of the partially coherent beams focused by a lens is investigated. It is shown that the focused intensity distribution near the geometrical focus is dependent not only on the intensity distribution of the incident partially coherent beam, but also on the degree of coherence. Based on this point, a novel method is presented for achieving a quasi-ellipsoid light cage profile near the geometrical focus by modulating the spectral degree of coherence of the incident partially coherent beam. The modulation can obtain the desired three-dimensional intensity distribution and control the aperture of the ellipsoid light cage by choosing the appropriate parameters of spectral degree at the lens plane without changing the incident beam. The method is of th
2005,
17.
Abstract:
The single-edge technique measuring Doppler shift of Rayleigh-scattering and Mie-scattering simultaneously is presented. The method is used to detect atmospheric wind velocity at low altitude（<12 km）. The error of the measurement caused by the atmospheric back-scattering ratio Rb can not be ignored. The measurement sensitivity and results are analyzed. The calibrated curve of wind velocity measurement is calculated under different value of Rb. The results show that the sensitivity tends to increase along with the increase of Rb and the error of measurement increases along with the deviation of Rb. At the same time, the measuremental error tends to increase with the augment of the radial wind velocity under the same deviation of Rb.
The single-edge technique measuring Doppler shift of Rayleigh-scattering and Mie-scattering simultaneously is presented. The method is used to detect atmospheric wind velocity at low altitude（<12 km）. The error of the measurement caused by the atmospheric back-scattering ratio Rb can not be ignored. The measurement sensitivity and results are analyzed. The calibrated curve of wind velocity measurement is calculated under different value of Rb. The results show that the sensitivity tends to increase along with the increase of Rb and the error of measurement increases along with the deviation of Rb. At the same time, the measuremental error tends to increase with the augment of the radial wind velocity under the same deviation of Rb.
2005,
17.
Abstract:
Accurate RKR potential functions and one of the best analytic potential functions � Murrell-Sorbie function have been combined with the best electric dipole moment functions to calculate the Einstein coefficients for HBr molecule. Calculations were done for the P-branch and R-branch fundamental transitions for vibration levels of no more than 7 for the X1Σ+ state of HBr.
Accurate RKR potential functions and one of the best analytic potential functions � Murrell-Sorbie function have been combined with the best electric dipole moment functions to calculate the Einstein coefficients for HBr molecule. Calculations were done for the P-branch and R-branch fundamental transitions for vibration levels of no more than 7 for the X1Σ+ state of HBr.
2005,
17.
Abstract:
An orthogonal subspace projection approach is introduced. Using the method, the background radiance can be eliminated from the received mixture signal. Using the matching pursuit algorithm, optimum wavelength bands can be picked out. The aim to detect target can be achieved by choosing the bands. Applying this method to target detection out of the atmosphere, the result has been obtained. It can be approved the method is effective to choose optimum wavelength bands for target detection.
An orthogonal subspace projection approach is introduced. Using the method, the background radiance can be eliminated from the received mixture signal. Using the matching pursuit algorithm, optimum wavelength bands can be picked out. The aim to detect target can be achieved by choosing the bands. Applying this method to target detection out of the atmosphere, the result has been obtained. It can be approved the method is effective to choose optimum wavelength bands for target detection.
2005,
17.
Abstract:
To reduce the reflection efficiency of the grating is the basic task during the design and fabricating process. Due to the speciality of the Brewster angle, the polarization light which propagates at Brewster angle can reduce the reflection efficiency. In this paper, the physical model of this kind of scheme is introduced, and the strict coupling wave method is used to calculate the optical character of the transmission grating under the Brewster angle. The results show that if the angle of incidence is chose to Brewster angle when the grating period is 2.80μm(wavelength is 0.35 μm), the reflection efficiency of the grating is restrained. For the short cycle grating(period is 0.21 μm), the highest 1 order diffraction efficiency of the transmission beam can be at depth of 3.50 μm, and t
To reduce the reflection efficiency of the grating is the basic task during the design and fabricating process. Due to the speciality of the Brewster angle, the polarization light which propagates at Brewster angle can reduce the reflection efficiency. In this paper, the physical model of this kind of scheme is introduced, and the strict coupling wave method is used to calculate the optical character of the transmission grating under the Brewster angle. The results show that if the angle of incidence is chose to Brewster angle when the grating period is 2.80μm(wavelength is 0.35 μm), the reflection efficiency of the grating is restrained. For the short cycle grating(period is 0.21 μm), the highest 1 order diffraction efficiency of the transmission beam can be at depth of 3.50 μm, and t
2005,
17.
Abstract:
Wavefront rms gradient is a very improtant optical parameter used in ICF system. Critical technique involved in numerical computation of wavefront gradient are space processing, frequency filtering and computing algorithm of gradient et al. The simplest difference and central algorithm, least-square method and "five-point" algorithm are applied to compute rms gradient of tested wavefront. The analysis result shows that Quad-flip technique is a good choice for space processing and the filtering validty is more important for frequency filter. For original wavefront, the difference of rms gradient value of four methods is less than 0.01 λ/cm; while for 33 mm low-pass filtered wavefront , the difference is less than 0.001 λ/cm which is neglectable.
Wavefront rms gradient is a very improtant optical parameter used in ICF system. Critical technique involved in numerical computation of wavefront gradient are space processing, frequency filtering and computing algorithm of gradient et al. The simplest difference and central algorithm, least-square method and "five-point" algorithm are applied to compute rms gradient of tested wavefront. The analysis result shows that Quad-flip technique is a good choice for space processing and the filtering validty is more important for frequency filter. For original wavefront, the difference of rms gradient value of four methods is less than 0.01 λ/cm; while for 33 mm low-pass filtered wavefront , the difference is less than 0.001 λ/cm which is neglectable.
2005,
17.
Abstract:
Under the conditions of the quick-charging to energy storage net with constant current and the pre-igniting of the Xe lamp, by controlling the voltage value and the repetitive frequency of the spark switch, the laser output in the heat capacity mode using a Nd:Glass laser pumped by the Xe lamp was obtained. Its output parameters were as follows: the repetition frequency was 4 Hz, the single-pulse energy 40 J, the lasting time 25 s, the output energy 4 kJ, and the operating interval 10 min. In addition, when the lasing on target each time, the laser could penetrate an aluminum plate with thickness of 1.5 cm. The output power of the laser could be scaled up to the order of kW, therefore many experiments related with the heat capacity mode can be made completely.
Under the conditions of the quick-charging to energy storage net with constant current and the pre-igniting of the Xe lamp, by controlling the voltage value and the repetitive frequency of the spark switch, the laser output in the heat capacity mode using a Nd:Glass laser pumped by the Xe lamp was obtained. Its output parameters were as follows: the repetition frequency was 4 Hz, the single-pulse energy 40 J, the lasting time 25 s, the output energy 4 kJ, and the operating interval 10 min. In addition, when the lasing on target each time, the laser could penetrate an aluminum plate with thickness of 1.5 cm. The output power of the laser could be scaled up to the order of kW, therefore many experiments related with the heat capacity mode can be made completely.
2005,
17.
Abstract:
A novel method of beam shaping by liquid crystal light valve (LCOS) is introduced in this paper. The incident phase modulation and spatial transmission properties of a shaped beam are studied, as well as the modulation characteristics of the liquid crystal light valve. There is no any additional phase modulation on the shaped beam when a LCOS is used as the beam shaper. A Gaussian beam has successfully been converted to a square flattop super-Gaussian beam by use of a LCOS. The results show that the LCOS of a liquid crystal projector working as a programmable spatial light amplitude modulation is feasible. An efficiency of 42% can be achieved.
A novel method of beam shaping by liquid crystal light valve (LCOS) is introduced in this paper. The incident phase modulation and spatial transmission properties of a shaped beam are studied, as well as the modulation characteristics of the liquid crystal light valve. There is no any additional phase modulation on the shaped beam when a LCOS is used as the beam shaper. A Gaussian beam has successfully been converted to a square flattop super-Gaussian beam by use of a LCOS. The results show that the LCOS of a liquid crystal projector working as a programmable spatial light amplitude modulation is feasible. An efficiency of 42% can be achieved.
Spectral gain narrowing compensation modulation function in high-power ultrashort-pulse laser system
2005,
17.
Abstract:
A modulation function related to the total gain of amplifier chains was established to compensate the spectral gain narrowing in high-power ultrashort-pulse laser systems. The modulation function to be used for a system could be given by putting in all data of the system, including the spectrum of the total gain, bandwidths of the gain medium and laser pulse, and central wavelength. For different laser systems, the form of the modulation function could remain the same. Spectral compensation simulations for the SILEX-I Ti:sapphire laser system were conducted by modulating the seeding pulse with a designed function at different parameters of bandwidth of gain medium, laser spectral width and laser central wavelength etc. The simulation results indicate that this modulated function is very go
A modulation function related to the total gain of amplifier chains was established to compensate the spectral gain narrowing in high-power ultrashort-pulse laser systems. The modulation function to be used for a system could be given by putting in all data of the system, including the spectrum of the total gain, bandwidths of the gain medium and laser pulse, and central wavelength. For different laser systems, the form of the modulation function could remain the same. Spectral compensation simulations for the SILEX-I Ti:sapphire laser system were conducted by modulating the seeding pulse with a designed function at different parameters of bandwidth of gain medium, laser spectral width and laser central wavelength etc. The simulation results indicate that this modulated function is very go
2005,
17.
Abstract:
Nomarski interferometer is an effective measurement to diagnose the electron density of laser-produced plasma. Using Raman compression cascade system with 1 054 nm incident light, a probe beam that has a 308 nm wavelength, 28 ps pulse duration and 1 mJ energy was obtained. The probe beam was applied in the polarization interferometry to measure the electron density of Au plasmas produced by 527 nm main beam at Xingguang-Ⅱ facility. The measured interferograms were analyzed to and a two-dimension profile of electron density was obtained. The result shows that with the aid of the probe beam, the electron density can be probed with a much higher temporal resolution and the disturbance of harmonic can be effectively avoided.
Nomarski interferometer is an effective measurement to diagnose the electron density of laser-produced plasma. Using Raman compression cascade system with 1 054 nm incident light, a probe beam that has a 308 nm wavelength, 28 ps pulse duration and 1 mJ energy was obtained. The probe beam was applied in the polarization interferometry to measure the electron density of Au plasmas produced by 527 nm main beam at Xingguang-Ⅱ facility. The measured interferograms were analyzed to and a two-dimension profile of electron density was obtained. The result shows that with the aid of the probe beam, the electron density can be probed with a much higher temporal resolution and the disturbance of harmonic can be effectively avoided.
2005,
17.
Abstract:
Concentration distribution expression of hydrogen diffusion process in multilayer polymer shells, that is the relationship among hydrogen concentration diffusion, time and diffusion distance was derived based on the second Fick's law. In each layer, in a certain diffusion time, the relationship between hydrogen concentration and diffusion depth is parabolic for a certain quality gas, which indicates in the direction of penetrant diffusion the polymer systems are swelled and the penetrant diffuses along the direction of polymer swelling. In different diffusion time, the concentration of ration hydrogen was increased with time delay at the same place. Because polymer free volumn was largened owing to polymer systems being swelled, and the hydrogen's diffusion path was increassed and the diff
Concentration distribution expression of hydrogen diffusion process in multilayer polymer shells, that is the relationship among hydrogen concentration diffusion, time and diffusion distance was derived based on the second Fick's law. In each layer, in a certain diffusion time, the relationship between hydrogen concentration and diffusion depth is parabolic for a certain quality gas, which indicates in the direction of penetrant diffusion the polymer systems are swelled and the penetrant diffuses along the direction of polymer swelling. In different diffusion time, the concentration of ration hydrogen was increased with time delay at the same place. Because polymer free volumn was largened owing to polymer systems being swelled, and the hydrogen's diffusion path was increassed and the diff
2005,
17.
Abstract:
The optical properties of inhomogeneous coatings which were prepared by double-source linear co-evaporation, were discussed and compared with that of homogeneous coatings. The influences of the refractive index distributions, maximum index-departure and coating thickness-deviation on the optical characteristics of coatings were discussed respectively. Analysis results show that the refractive-index distribution regularity error has an important influence on the wavelength application range of the coatings, and the thickness error or index-departure has a vital influence on the optical properties of inhomogeneous coatings．
The optical properties of inhomogeneous coatings which were prepared by double-source linear co-evaporation, were discussed and compared with that of homogeneous coatings. The influences of the refractive index distributions, maximum index-departure and coating thickness-deviation on the optical characteristics of coatings were discussed respectively. Analysis results show that the refractive-index distribution regularity error has an important influence on the wavelength application range of the coatings, and the thickness error or index-departure has a vital influence on the optical properties of inhomogeneous coatings．
2005,
17.
Abstract:
For rearching the acceleration mechanism of hot electron, the integrated image pattern and spectrum of optical transition radiation (OTR) were measured at the normal direction from the rear side of targets employing optical CCD camera and OMA optical multi-channel spectrometer. The experiment was carried out on the 100 TW laser. The measured integrated image pattern presents a ring-shape of about 225 μm in diameter. In the near edge of the ring-shape there is a bright localized signal, which indicates a filament effect exists during hot electron transportation. The spectrum presents a series of nonperiodic sharp peaks between 300～500 nm, which is attributed to the coherent transition radiation (CTR) of hot electron generated by v×B acceleration mechanism near 400 nm(2ω0).
For rearching the acceleration mechanism of hot electron, the integrated image pattern and spectrum of optical transition radiation (OTR) were measured at the normal direction from the rear side of targets employing optical CCD camera and OMA optical multi-channel spectrometer. The experiment was carried out on the 100 TW laser. The measured integrated image pattern presents a ring-shape of about 225 μm in diameter. In the near edge of the ring-shape there is a bright localized signal, which indicates a filament effect exists during hot electron transportation. The spectrum presents a series of nonperiodic sharp peaks between 300～500 nm, which is attributed to the coherent transition radiation (CTR) of hot electron generated by v×B acceleration mechanism near 400 nm(2ω0).
2005,
17.
Abstract:
High-quality metal films with theoretical density are important to measurement of equation of state under high temperature and high pressure. Mo films with thickness more than 20 μm, surface roughness(rms) less than 100 nm and thickness uniformity more than 99% have been prepared by lapping in the paper. Influences of process parameters on appearance, thickness uniformity, surface roughness of the films, etc. have been investigated.
High-quality metal films with theoretical density are important to measurement of equation of state under high temperature and high pressure. Mo films with thickness more than 20 μm, surface roughness(rms) less than 100 nm and thickness uniformity more than 99% have been prepared by lapping in the paper. Influences of process parameters on appearance, thickness uniformity, surface roughness of the films, etc. have been investigated.
2005,
17.
Abstract:
Pinhole imaging of the neutron production in laser-driven inertial confinement fusion experiments can provide important information about performance of various capsule designs. In order to get good results in experiments, it is needed to judge performance of various pinhole designs qualitatively or quantitatively before experiment. Calculation of imaging can be simply separated into pinhole imaging and image spectral analysis. In this paper, pinhole imaging is discussed, codes for neutron pinhole imaging and image showing are programed. The codes can be used to provide theoretical foundation for pinhole designing and simulating data for image analysing.
Pinhole imaging of the neutron production in laser-driven inertial confinement fusion experiments can provide important information about performance of various capsule designs. In order to get good results in experiments, it is needed to judge performance of various pinhole designs qualitatively or quantitatively before experiment. Calculation of imaging can be simply separated into pinhole imaging and image spectral analysis. In this paper, pinhole imaging is discussed, codes for neutron pinhole imaging and image showing are programed. The codes can be used to provide theoretical foundation for pinhole designing and simulating data for image analysing.
2005,
17.
Abstract:
Using a relatively strict method, the formulas of the harmonic current of the modulated electron beam in the klystron and Cherenkov devices were derived in the relativistic regime,in which the effect of the space charge wave was taken into account. The role of the space charge wave is that it makes bunching reduce at small signal, but it makes bunching enhance at large signal.
Using a relatively strict method, the formulas of the harmonic current of the modulated electron beam in the klystron and Cherenkov devices were derived in the relativistic regime,in which the effect of the space charge wave was taken into account. The role of the space charge wave is that it makes bunching reduce at small signal, but it makes bunching enhance at large signal.
2005,
17.
Abstract:
In order to solve the problem in calculating the klystron output circuit characteristic, based on field analysis and post-processing of 3D electromagnetic field simulation software ISFEL3D, a field analysis method is proposed. The theory analysis shows that the characteristic parameters, such as resonance frequency, real part of gap-impedance, external quality factor in all kinds of klystron output circuits including single-beam single-gap, multi-beam single-gap, single-beam multi-gap, multi-beam multi-gap klystron output circuit, can be calculated by the field analysis method. The calculated result of the single-beam single-gap klystron output circuit shows that the calculated result by field analysis method coincides with that by the reflectance phase method and that by the equivalent ga
In order to solve the problem in calculating the klystron output circuit characteristic, based on field analysis and post-processing of 3D electromagnetic field simulation software ISFEL3D, a field analysis method is proposed. The theory analysis shows that the characteristic parameters, such as resonance frequency, real part of gap-impedance, external quality factor in all kinds of klystron output circuits including single-beam single-gap, multi-beam single-gap, single-beam multi-gap, multi-beam multi-gap klystron output circuit, can be calculated by the field analysis method. The calculated result of the single-beam single-gap klystron output circuit shows that the calculated result by field analysis method coincides with that by the reflectance phase method and that by the equivalent ga
2005,
17.
Abstract:
Boundary element method(BEM) is presented as a new approach for the analysis and design of various transmission lines filled with piecewise homogeneous dielectric. The solution of the boundary-value problem associated with transmission lines filled with piecewise homogeneous dielectric is transformed into a matrix formula of BEM. The procedure to obtain the capacitance is described. Two representative computational examples, eccentric coaxial cable partially filled with dielectric and transmission line of parallel dielectric-coated cylinders, are given to validate the theory, and to demonstrate the accuracy and flexibility of BEM.
Boundary element method(BEM) is presented as a new approach for the analysis and design of various transmission lines filled with piecewise homogeneous dielectric. The solution of the boundary-value problem associated with transmission lines filled with piecewise homogeneous dielectric is transformed into a matrix formula of BEM. The procedure to obtain the capacitance is described. Two representative computational examples, eccentric coaxial cable partially filled with dielectric and transmission line of parallel dielectric-coated cylinders, are given to validate the theory, and to demonstrate the accuracy and flexibility of BEM.
2005,
17.
Abstract:
The design and the measurements of the coaxial fin-inserted mode converter are presented. It is shown that with four metal fins inserted in the coaxial waveguide, the TEM mode is converted to coaxial TE11 mode and outputted with different phases, and finally, it forms a TE11 conventional circular waveguide mode. Moreover, four matching metal poles were designed to compensate for the reflection from inserted fins. The measured radiation patterns of the mode coveter agree well with the calculated results, which indicates that the out-put modes of the mode converter are the same as the simulated results. The experiment demonstrates the feasibility of the coaxial fin-inserted mode converter.
The design and the measurements of the coaxial fin-inserted mode converter are presented. It is shown that with four metal fins inserted in the coaxial waveguide, the TEM mode is converted to coaxial TE11 mode and outputted with different phases, and finally, it forms a TE11 conventional circular waveguide mode. Moreover, four matching metal poles were designed to compensate for the reflection from inserted fins. The measured radiation patterns of the mode coveter agree well with the calculated results, which indicates that the out-put modes of the mode converter are the same as the simulated results. The experiment demonstrates the feasibility of the coaxial fin-inserted mode converter.
2005,
17.
Abstract:
The dynamics of radiation spectra of fast Z-pinch plasmas is studied on the S-300 machine. By means of the polychromator APCH—10, X-ray spectra of imploding wire arrays are measured in the range of 50~1 500 eV. The main part of the radiation power falls at the spectral interval 60~220 eV. The radiation spectrum is described by the Planckian -spectrum with the “black-body” temperature of 40~50 eV. For the part of radiation with more than 500 eV energy of quanta, remarkable deviation from the Planckian-spectrum is observed. The deviation seems to be the result of the appearance of hot plasma spots, existence of characteristic spectral lines in the range of 1.5~2 keV, and bremsstrahlung losses of the accelerated electrons.
The dynamics of radiation spectra of fast Z-pinch plasmas is studied on the S-300 machine. By means of the polychromator APCH—10, X-ray spectra of imploding wire arrays are measured in the range of 50~1 500 eV. The main part of the radiation power falls at the spectral interval 60~220 eV. The radiation spectrum is described by the Planckian -spectrum with the “black-body” temperature of 40~50 eV. For the part of radiation with more than 500 eV energy of quanta, remarkable deviation from the Planckian-spectrum is observed. The deviation seems to be the result of the appearance of hot plasma spots, existence of characteristic spectral lines in the range of 1.5~2 keV, and bremsstrahlung losses of the accelerated electrons.
2005,
17.
Abstract:
Experimental researches on operating characteristics of three-electrode repetitive gas switch were performed on the accelerator CHP01, and experimental results were analyzed. The results show that the switch operates more steadily at trigger mode than at self-breakdown mode and its operating voltage range is related to such factors as the position of the trigger pin and gas pressure. It's also revealed that the switch has excellent operating characteristics, expecially low jitter and low misfire rate, when it operates at about eighty percent of self-breakdown voltage.
Experimental researches on operating characteristics of three-electrode repetitive gas switch were performed on the accelerator CHP01, and experimental results were analyzed. The results show that the switch operates more steadily at trigger mode than at self-breakdown mode and its operating voltage range is related to such factors as the position of the trigger pin and gas pressure. It's also revealed that the switch has excellent operating characteristics, expecially low jitter and low misfire rate, when it operates at about eighty percent of self-breakdown voltage.
2005,
17.
Abstract:
Two-dimensional (2-D) geometry effect on space-charge-limited(SCL) current of an axially symmetrical planar diode was studied with 2.5 D particle-in-cell(PIC) simulation. A volume-weighting cloud-in-cell model was used to improve the accuracy of the PIC method in z-r coordinates system. The simulations with various emitter radii were carried out on the same diode with the applied voltages being 100 kV and 1 MV respectively. The simulation results show that the 2-D geometry effect on SCL current monotonically diminishes with the dimensionless ratio of emitter radius to gap separation, whether in relativistic or non-relativistic regime. When the ratio is more than 0.5, the first-order analytical theory well predicts the limiting current. But when the ratio is no more than 0.5, the second-ord
Two-dimensional (2-D) geometry effect on space-charge-limited(SCL) current of an axially symmetrical planar diode was studied with 2.5 D particle-in-cell(PIC) simulation. A volume-weighting cloud-in-cell model was used to improve the accuracy of the PIC method in z-r coordinates system. The simulations with various emitter radii were carried out on the same diode with the applied voltages being 100 kV and 1 MV respectively. The simulation results show that the 2-D geometry effect on SCL current monotonically diminishes with the dimensionless ratio of emitter radius to gap separation, whether in relativistic or non-relativistic regime. When the ratio is more than 0.5, the first-order analytical theory well predicts the limiting current. But when the ratio is no more than 0.5, the second-ord
2005,
17.
Abstract:
A diode- type electron gun is used to investigate the DC emitting characteristics of a single crystal LaB6 thermionic cathode. The emitting area is a planar 2 mm- diameter, achieving transmitted currents up to 175 mA and a current density of 5.6 A/cm2. Comparing the measured current with fit result by Longo equation, Longo equation fitting is more accurate than the other methods, and applicable for practical operation. The circumstance has an effect on the emitting ability of cathode, when the vacuum is below 7×10-4 Pa, the current density apparently decreases. The C and O in the surface of the emitter can increase the work function. Aggredation and diffusion of LaB6 to pyrolytic graphite make the resistance of heater lower. Experimental results show that DC emitting current density is lo
A diode- type electron gun is used to investigate the DC emitting characteristics of a single crystal LaB6 thermionic cathode. The emitting area is a planar 2 mm- diameter, achieving transmitted currents up to 175 mA and a current density of 5.6 A/cm2. Comparing the measured current with fit result by Longo equation, Longo equation fitting is more accurate than the other methods, and applicable for practical operation. The circumstance has an effect on the emitting ability of cathode, when the vacuum is below 7×10-4 Pa, the current density apparently decreases. The C and O in the surface of the emitter can increase the work function. Aggredation and diffusion of LaB6 to pyrolytic graphite make the resistance of heater lower. Experimental results show that DC emitting current density is lo
2005,
17.
Abstract:
In order to develop compact accelerators with small beam spot, a C-band 5.52 GHz 2 MeV SW accelerating tube is physically designed and studied, which operated in the π/2 mode. Not using any exterior focusing element，transverse emittance growth aroused from space charge effect is restrained efficiently by repeatedly bunching and utilizing dissymmetry field of first cavity. The accelerating tube consists of 3-cell buncher and 4-cell accelerating section with a total length of about 163 mm，excited with 1 MW magnetron. In final dynamics simulation, 2 MeV 150 mA beam pulse current is obtained, and the capture efficiency is more than 30%. By means of nolinear Gauss fit on electron transverse distribution, the diameter of beam spot (Full Width at Half Maximum of density distribution) is about
In order to develop compact accelerators with small beam spot, a C-band 5.52 GHz 2 MeV SW accelerating tube is physically designed and studied, which operated in the π/2 mode. Not using any exterior focusing element，transverse emittance growth aroused from space charge effect is restrained efficiently by repeatedly bunching and utilizing dissymmetry field of first cavity. The accelerating tube consists of 3-cell buncher and 4-cell accelerating section with a total length of about 163 mm，excited with 1 MW magnetron. In final dynamics simulation, 2 MeV 150 mA beam pulse current is obtained, and the capture efficiency is more than 30%. By means of nolinear Gauss fit on electron transverse distribution, the diameter of beam spot (Full Width at Half Maximum of density distribution) is about
2005,
17.
Abstract:
Conventional methods for electromagnetic compatibility (EMC) design of high power supplies are mostly based on experience. It can not insure the stability and reliability of the supply. A method was proposed to quantitatively analyse the electromagnetic interference (EMI) according to the main structure of the supply. The conductive interference of the supply was simulated and measured in a practical supply, and the ground potential difference is less than 10 V (corresponding to unit of the enclosure). The quasi- static magnetic field as well as shielding efficiency is calculated, and the magnetic field outside the supply is less than 0.16×10-4 T. The results of both calculation and measurement indicate that performance of EMC of the supply can measure up to the design criterion.
Conventional methods for electromagnetic compatibility (EMC) design of high power supplies are mostly based on experience. It can not insure the stability and reliability of the supply. A method was proposed to quantitatively analyse the electromagnetic interference (EMI) according to the main structure of the supply. The conductive interference of the supply was simulated and measured in a practical supply, and the ground potential difference is less than 10 V (corresponding to unit of the enclosure). The quasi- static magnetic field as well as shielding efficiency is calculated, and the magnetic field outside the supply is less than 0.16×10-4 T. The results of both calculation and measurement indicate that performance of EMC of the supply can measure up to the design criterion.
2005,
17.
Abstract:
In this paper the physical design and test of a new MITL for the Yang accelerator have been introduced. With reducing the total length of the MITL and width of the insulator, the common-vertex-coaxial-circular-cones-like MITL has been employed to displace the old one, resulting in the decrease of structural inductance from 70.9 nH of the old to 31.7 nH of the new, and electrical stress criterion for some special locations has also been satisfied by reiteration and modification, and minimum magnetic current has been kept below that of the old. The tests both with short load and wire array load have shown that the performance of the new MITL was improved.
In this paper the physical design and test of a new MITL for the Yang accelerator have been introduced. With reducing the total length of the MITL and width of the insulator, the common-vertex-coaxial-circular-cones-like MITL has been employed to displace the old one, resulting in the decrease of structural inductance from 70.9 nH of the old to 31.7 nH of the new, and electrical stress criterion for some special locations has also been satisfied by reiteration and modification, and minimum magnetic current has been kept below that of the old. The tests both with short load and wire array load have shown that the performance of the new MITL was improved.
2005,
17.
Abstract:
The mechanism of emission from ferroelectric cathode was introduced. With the purpose of obtaining the ferroelectric cathode material with large emission current density, the preparation conditions of PZT series ceramic were studied. By doping, modifying and some other methods of processing amelioration, the improvement of performance was observed in both ferroelectric and relaxor ferroelectric ceramic. In the preliminary experiment, with 5.4 kV external pulsed voltage, the electron emission density of PLZT8/65/35 reached up to 800 A/cm2, which was much greater than that calculated by C-L principle.
The mechanism of emission from ferroelectric cathode was introduced. With the purpose of obtaining the ferroelectric cathode material with large emission current density, the preparation conditions of PZT series ceramic were studied. By doping, modifying and some other methods of processing amelioration, the improvement of performance was observed in both ferroelectric and relaxor ferroelectric ceramic. In the preliminary experiment, with 5.4 kV external pulsed voltage, the electron emission density of PLZT8/65/35 reached up to 800 A/cm2, which was much greater than that calculated by C-L principle.
2005,
17.
Abstract:
Particles with low energy can not be accelerated only with harmonic number of 1 because of a restriction of the frequency range of the CSRm RF cavities with 0.25 to 1.7 MHz. This paper just simulated and studied the beam acceleration process of HIRFL-CSR. By means of changing harmonic, i.e. particles were captured and aecelerated to some energy with harmonic number of 2 first and then to the final energy with harmonic number of 1. The main RF parameters of CSRm and some beam parameters are given according to the simulation. In addition, the changing of particle distribution in longitudinal phase space during the accelerating process has been obtained.
Particles with low energy can not be accelerated only with harmonic number of 1 because of a restriction of the frequency range of the CSRm RF cavities with 0.25 to 1.7 MHz. This paper just simulated and studied the beam acceleration process of HIRFL-CSR. By means of changing harmonic, i.e. particles were captured and aecelerated to some energy with harmonic number of 2 first and then to the final energy with harmonic number of 1. The main RF parameters of CSRm and some beam parameters are given according to the simulation. In addition, the changing of particle distribution in longitudinal phase space during the accelerating process has been obtained.
2005,
17.
Abstract:
Some important effects of gas switch on power gain in the pulse compressed system of high power microwave are analyzed, including the absorbed energy of gas switch in the progress of opening, the descending resonance inhere quality factor because of plasma instant power wastage, and the result because of plasma not being an ideal conductor. Modified coefficients are used to show these effects and the formula of power gain deduced by microwave equivalent circuit theory can be amended and the precision can be improved from 60% to about 85%.
Some important effects of gas switch on power gain in the pulse compressed system of high power microwave are analyzed, including the absorbed energy of gas switch in the progress of opening, the descending resonance inhere quality factor because of plasma instant power wastage, and the result because of plasma not being an ideal conductor. Modified coefficients are used to show these effects and the formula of power gain deduced by microwave equivalent circuit theory can be amended and the precision can be improved from 60% to about 85%.
2005,
17.
Abstract:
Amorphous hydrogenated silicon carbide(a-SiC:H) films were prepared by the reactive sputtering method, which were irradiated by high energy (average value is 1.25 MeV) γ rays. The absorbed dose of five samples were 0, 2×104, 4×104, 6×104, and 8×104 Gy respectively. Resistivity, Raman scattering and infrared transimissing spectroscopy were used to investigate the effects of γ rays irradiation on the structure and properties of a-SiC:H films. It is found that the increase of absorbed doses results in light crystallization in a-SiC:H films and the decrease in resistivity (the level is 105 Ω·cm). The main reason may be that Si which comes from the breakdown of Si�O�Si bonds takes the place of C of C�C bonds in the films, and brings out the increase of crystal SiC. The infrared
Amorphous hydrogenated silicon carbide(a-SiC:H) films were prepared by the reactive sputtering method, which were irradiated by high energy (average value is 1.25 MeV) γ rays. The absorbed dose of five samples were 0, 2×104, 4×104, 6×104, and 8×104 Gy respectively. Resistivity, Raman scattering and infrared transimissing spectroscopy were used to investigate the effects of γ rays irradiation on the structure and properties of a-SiC:H films. It is found that the increase of absorbed doses results in light crystallization in a-SiC:H films and the decrease in resistivity (the level is 105 Ω·cm). The main reason may be that Si which comes from the breakdown of Si�O�Si bonds takes the place of C of C�C bonds in the films, and brings out the increase of crystal SiC. The infrared
2005,
17.
Abstract:
The signal detection system is an important part for BEPCII transverse feedback system. A commercial front-end RFTF (radio frequency front-end for transverse feedback system) was bought for this system. Two working modes and the remote control are its advantages. To test the performance and master the use of it, experiments on the BEPC with the bunch-by-bunch mode were carried out. The experiment results indicate that using this facility can acquire ideal wave for BEPCII while it doesn't work when the longitudinal instability emerges, the longitudinal instability must be suppressed.
The signal detection system is an important part for BEPCII transverse feedback system. A commercial front-end RFTF (radio frequency front-end for transverse feedback system) was bought for this system. Two working modes and the remote control are its advantages. To test the performance and master the use of it, experiments on the BEPC with the bunch-by-bunch mode were carried out. The experiment results indicate that using this facility can acquire ideal wave for BEPCII while it doesn't work when the longitudinal instability emerges, the longitudinal instability must be suppressed.
2005,
17.
Abstract:
The technology using optical transition radiation(OTR) is a measurement method for the electron beam of high energy and high current and it has been applied in the on-line beam diagnostic system with ultra-fast response, high special resolution. It measures the beam parameters such as beam energy, divergence and emmittance. The effect of structure parameters of the measurement system, such as the focus length of the lens, the location of image, the pixel size of CCD, upon the measurement accuracy of the beam energy resolution was analyzed. The influence of beam divergence angle on energy resolution in OTR measurement was simulated. The effect was applied to correct the measuring data of beam energy resolution. The effect of OTR data noise on the precision of beam energy resolution was also
The technology using optical transition radiation(OTR) is a measurement method for the electron beam of high energy and high current and it has been applied in the on-line beam diagnostic system with ultra-fast response, high special resolution. It measures the beam parameters such as beam energy, divergence and emmittance. The effect of structure parameters of the measurement system, such as the focus length of the lens, the location of image, the pixel size of CCD, upon the measurement accuracy of the beam energy resolution was analyzed. The influence of beam divergence angle on energy resolution in OTR measurement was simulated. The effect was applied to correct the measuring data of beam energy resolution. The effect of OTR data noise on the precision of beam energy resolution was also
