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RSS2005 Vol. 17, No. 12
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2005,
17.
Abstract:
A self-adapting FBG (Fiber Bragg grating) dynamic sensor system based on the temperature controlled filter FBG is investigated. Using the semiconductor cooling device the temperature of the FBG filter was controlled, so that the wavelength of the narrowband filter FBG could be controlled to suit the environment temperature variation, and the self adaptation of the temperature variation be realized. Using the reference channel and wiping off the system noise, the measurement precision was improved. The system dynamic strain resolution is 9.745×10-10 (Hz)-1/2.
A self-adapting FBG (Fiber Bragg grating) dynamic sensor system based on the temperature controlled filter FBG is investigated. Using the semiconductor cooling device the temperature of the FBG filter was controlled, so that the wavelength of the narrowband filter FBG could be controlled to suit the environment temperature variation, and the self adaptation of the temperature variation be realized. Using the reference channel and wiping off the system noise, the measurement precision was improved. The system dynamic strain resolution is 9.745×10-10 (Hz)-1/2.
2005,
17.
Abstract:
The AMK-02 ultrasonic measurement meter can measure meteorological and turbulent parameters of the atmosphere. The temperature pulsation sensitivity of the AMK-02 is too low to calculate the refractive-index-structure parameter C2n accurately at the time of sunrise and sunset. The calibrated meteorological parameters are used to calculate the refractive-index-structure parameter C2n accurately, and the calculated results accord well with that of the hot wire anemometer.
The AMK-02 ultrasonic measurement meter can measure meteorological and turbulent parameters of the atmosphere. The temperature pulsation sensitivity of the AMK-02 is too low to calculate the refractive-index-structure parameter C2n accurately at the time of sunrise and sunset. The calibrated meteorological parameters are used to calculate the refractive-index-structure parameter C2n accurately, and the calculated results accord well with that of the hot wire anemometer.
2005,
17.
Abstract:
By using the Wigner distribution function(WDF) method, the transformation properties of a Cosine-Gaussian beam in the fractional Fourier transform plane are studied. Closed-form expressions for the intensity distribution and beam widths of Cosine-Gaussian beams in the FRFT's plane are derived and changes in the intensity distribution of Cosine-Gaussian beams with the order of the FRFT are illustrated with numerical examples. It is shown that the intensity in the FRFT plane depends on the fractional order, the variation of the on-axis intensity and beam width with fractional order are periodic, and the period is 2. A flat-topped beam can be achieved by a suitable choice of the transform order for the Cosine-Gaussian beams with the modulation parameter.
By using the Wigner distribution function(WDF) method, the transformation properties of a Cosine-Gaussian beam in the fractional Fourier transform plane are studied. Closed-form expressions for the intensity distribution and beam widths of Cosine-Gaussian beams in the FRFT's plane are derived and changes in the intensity distribution of Cosine-Gaussian beams with the order of the FRFT are illustrated with numerical examples. It is shown that the intensity in the FRFT plane depends on the fractional order, the variation of the on-axis intensity and beam width with fractional order are periodic, and the period is 2. A flat-topped beam can be achieved by a suitable choice of the transform order for the Cosine-Gaussian beams with the modulation parameter.
2005,
17.
Abstract:
The lidar technique based on stimulated Raman scattering (SRS) process has been extensively used in monitoring trace gas concentrations in the atmosphere. To monitor the atmospheric CO2 concentration, a nonlinear Raman lidar based on the SRS process was devised. A third harmonic Nd:YAG laser wave (354.7 nm) was injected into the Raman cells filled with high-pressure gases, CO2 and N2. The first order Stokes lights 371.66 nm(CO2) and 386.7 nm(N2) were generated by the stimulated Raman scattering process. The energy of the first order Stokes lights was measured by changing the gas pressure in the Raman cell and the Nd:YAG laser system output energy. The optimum pressures of CO2 and N2 in the Raman cell were achieved, which were 0.8 MPa and 3.5 MPa respectively. The principles of this physics
The lidar technique based on stimulated Raman scattering (SRS) process has been extensively used in monitoring trace gas concentrations in the atmosphere. To monitor the atmospheric CO2 concentration, a nonlinear Raman lidar based on the SRS process was devised. A third harmonic Nd:YAG laser wave (354.7 nm) was injected into the Raman cells filled with high-pressure gases, CO2 and N2. The first order Stokes lights 371.66 nm(CO2) and 386.7 nm(N2) were generated by the stimulated Raman scattering process. The energy of the first order Stokes lights was measured by changing the gas pressure in the Raman cell and the Nd:YAG laser system output energy. The optimum pressures of CO2 and N2 in the Raman cell were achieved, which were 0.8 MPa and 3.5 MPa respectively. The principles of this physics
2005,
17.
Abstract:
As a novel pumping scheme, the line focus system applied in the grazing incidence is the on-axis parabola. Using 2D ray-tracing program, the line focus effects with different incidence angle of a Gaussian laser pulse were calculated. As the incidence angle increases from 5° to 7°, the length of the line focus is improved from 6 mm to 12 mm, and the widthes are varied from 150 μm to 40 μm. The results show that the 6.5°~7° incidence is capable of realizing a well line focus with 10 mm×20 μm to satisfy our experiment.
As a novel pumping scheme, the line focus system applied in the grazing incidence is the on-axis parabola. Using 2D ray-tracing program, the line focus effects with different incidence angle of a Gaussian laser pulse were calculated. As the incidence angle increases from 5° to 7°, the length of the line focus is improved from 6 mm to 12 mm, and the widthes are varied from 150 μm to 40 μm. The results show that the 6.5°~7° incidence is capable of realizing a well line focus with 10 mm×20 μm to satisfy our experiment.
2005,
17.
Abstract:
The self-focusing properties of the femtosecond pulse were analyzed through numerical calculation using modified Schr-dinger equation. On the basis of the analysis, the self-focusing properties of the chirped Gaussian pulse in the chirped pulse amplification (CPA) system were analyzed and discussed, and the numerical calculations were performed. The results showed that the effect of group velocity dispersion(GVD) on the pulse with large chip was slight and the effect of spectral width on the self-focusing properties could be ignored. Consequently, the self-focusing properties of the pulse with large chirp in the nonlinear medium with normal dispersion were different from those of femtosecond pulse, but similar to those of nanosecond pulse.
The self-focusing properties of the femtosecond pulse were analyzed through numerical calculation using modified Schr-dinger equation. On the basis of the analysis, the self-focusing properties of the chirped Gaussian pulse in the chirped pulse amplification (CPA) system were analyzed and discussed, and the numerical calculations were performed. The results showed that the effect of group velocity dispersion(GVD) on the pulse with large chip was slight and the effect of spectral width on the self-focusing properties could be ignored. Consequently, the self-focusing properties of the pulse with large chirp in the nonlinear medium with normal dispersion were different from those of femtosecond pulse, but similar to those of nanosecond pulse.
2005,
17.
Abstract:
A method of measuring the atmospheric turbulence based on the arrival angle fluctuation of a focused laser beam backscattering was numerically simulated. Based on the paraxial scalar wave equation and a fractal phase-screen algorithm a simu-lation model for the focused laser beam propagating along a fold path was proposed. With a constant Fried length, the arrival angle fluctuation variance was analyzed between the focused laser beam backscattering and the fixed point-source as reference beacon. A relatively high correlation between them was obtained. The simulation results were verified by experimental data.
A method of measuring the atmospheric turbulence based on the arrival angle fluctuation of a focused laser beam backscattering was numerically simulated. Based on the paraxial scalar wave equation and a fractal phase-screen algorithm a simu-lation model for the focused laser beam propagating along a fold path was proposed. With a constant Fried length, the arrival angle fluctuation variance was analyzed between the focused laser beam backscattering and the fixed point-source as reference beacon. A relatively high correlation between them was obtained. The simulation results were verified by experimental data.
2005,
17.
Abstract:
The effect of third-order nonlinearity on the second harmonic generation of ultrashort pulses in KDP crystal is analyzed theoretically. It is found that the influence of third-order nonlinearity on conversion efficiency becomes dominant when the incident intensity is above 100 GW/cm2. A novel approach in which an initial phase-mismatch is introduced to compensate for third-order nonlinearity effect is proposed. The calculated results show that for a 50 fs pulse and a 250 GW/cm2 input intensity, the conversion efficiency is increased by a factor of 1.1 at the condition of 0.9 mrad initial phase-mismatching angle. At the same time, the fluence modulation of the fundamental and second harmonic pulses due to third-order nonlinearity is suppressed effectively and the temporal profiles are impro
The effect of third-order nonlinearity on the second harmonic generation of ultrashort pulses in KDP crystal is analyzed theoretically. It is found that the influence of third-order nonlinearity on conversion efficiency becomes dominant when the incident intensity is above 100 GW/cm2. A novel approach in which an initial phase-mismatch is introduced to compensate for third-order nonlinearity effect is proposed. The calculated results show that for a 50 fs pulse and a 250 GW/cm2 input intensity, the conversion efficiency is increased by a factor of 1.1 at the condition of 0.9 mrad initial phase-mismatching angle. At the same time, the fluence modulation of the fundamental and second harmonic pulses due to third-order nonlinearity is suppressed effectively and the temporal profiles are impro
2005,
17.
Abstract:
A secondary-throat diffuser and an 8°diffuser are used respectively on COIL. The performance parameters of the two diffusers are measured and compared. The result indicates that the secondary-throat diffuser may effectively insulate the flow disarrangement from the diffuser, avoid the down-stream flow disarrangement into the optical resonator, improve the stability of static-pressure in resonator, and enhance the stability of the output power of COIL. The secondary-throat diffuser is propitious to COIL at high back-pressure.
A secondary-throat diffuser and an 8°diffuser are used respectively on COIL. The performance parameters of the two diffusers are measured and compared. The result indicates that the secondary-throat diffuser may effectively insulate the flow disarrangement from the diffuser, avoid the down-stream flow disarrangement into the optical resonator, improve the stability of static-pressure in resonator, and enhance the stability of the output power of COIL. The secondary-throat diffuser is propitious to COIL at high back-pressure.
2005,
17.
Abstract:
The characteristics of spectral distribution of harmonic emission are analyzed with a single electron model in the cases of circularly polarized femtosecond laser pulses. It is discovered that the oscillation of electrons will generate harmonic emission due to their relativistic motion,and broadening and redshift in the spectrum of harmonic emission occur with the increase of laser intensity. The effects discussed in this paper can explain qualitatively the broadening and redshift of harmonic emission from plasma irradiated by femtosecond intense laser pulses．
The characteristics of spectral distribution of harmonic emission are analyzed with a single electron model in the cases of circularly polarized femtosecond laser pulses. It is discovered that the oscillation of electrons will generate harmonic emission due to their relativistic motion,and broadening and redshift in the spectrum of harmonic emission occur with the increase of laser intensity. The effects discussed in this paper can explain qualitatively the broadening and redshift of harmonic emission from plasma irradiated by femtosecond intense laser pulses．
2005,
17.
Abstract:
The technology of XeF(C-A) laser pumped by two counter optical sources is discussed and the photographes of the XeF2 photodissociation waves propagating from two directions are given. The output energy of XeF(C-A) laser is enhanced under two pump sources condition, which is 3.3 J with the laser pulse duration of 1 100 ns. The output properties of XeF(C-A) laser are obviously affected by the initial XeF2 concentration. The laser formation time increases with the increase of the initial XeF2 concentration and the near-field pattern of the laser beams has different profiles under different XeF2 concentration.
The technology of XeF(C-A) laser pumped by two counter optical sources is discussed and the photographes of the XeF2 photodissociation waves propagating from two directions are given. The output energy of XeF(C-A) laser is enhanced under two pump sources condition, which is 3.3 J with the laser pulse duration of 1 100 ns. The output properties of XeF(C-A) laser are obviously affected by the initial XeF2 concentration. The laser formation time increases with the increase of the initial XeF2 concentration and the near-field pattern of the laser beams has different profiles under different XeF2 concentration.
2005,
17.
Abstract:
Using a complex analytical signal representation, the free-space propagation properties of ultrashort pulsed Bessel-Gauss beams whose waist width is independent of frequency are studied. It is found that within the diffraction-free range the transversal intensity distribution of ultrashort pulsed Bessel-Gauss beams remains nearly unchanged, and the on-axis temporal pulse forms broaden along the propagation. Beyond this range, there is a remarkable spreading of the transversal intensity. With the increase of the propagation distance, the on-axis blue shift increases firstly, then gradually decreases after reaching its maximum, and finally approaches an asymptotic value. For example, for a single-cycle ultrashort pulsed Bessel-Gauss beam, the on-axis blue shift increases and reaches a maximu
Using a complex analytical signal representation, the free-space propagation properties of ultrashort pulsed Bessel-Gauss beams whose waist width is independent of frequency are studied. It is found that within the diffraction-free range the transversal intensity distribution of ultrashort pulsed Bessel-Gauss beams remains nearly unchanged, and the on-axis temporal pulse forms broaden along the propagation. Beyond this range, there is a remarkable spreading of the transversal intensity. With the increase of the propagation distance, the on-axis blue shift increases firstly, then gradually decreases after reaching its maximum, and finally approaches an asymptotic value. For example, for a single-cycle ultrashort pulsed Bessel-Gauss beam, the on-axis blue shift increases and reaches a maximu
2005,
17.
Abstract:
HfO2 films were prepared by electron beam evaporation. The residual stress was measured by ZYGO interferometer. The results showed that the residual stresses of HfO2 films were tensile and increased with the increase of deposition temperature firstly, then decreased. The microstructure of the HfO2 films was inspected with X-ray diffraction (XRD). The microstructure of the films transmitted from amorphous to polycrystalline, which corresponded to the variation of the residual stress. The microstructure of HfO2 film changed as the deposition temperature increased and the residual stress evolved as the changing of the microstructure.
HfO2 films were prepared by electron beam evaporation. The residual stress was measured by ZYGO interferometer. The results showed that the residual stresses of HfO2 films were tensile and increased with the increase of deposition temperature firstly, then decreased. The microstructure of the HfO2 films was inspected with X-ray diffraction (XRD). The microstructure of the films transmitted from amorphous to polycrystalline, which corresponded to the variation of the residual stress. The microstructure of HfO2 film changed as the deposition temperature increased and the residual stress evolved as the changing of the microstructure.
2005,
17.
Abstract:
Using our series codes, quasi-stable Ni-like Ag collisional excitation scheme driven by laser with grazing incidence was studied. Comparing with that with normal incidence, at low drive intensity of 1.2×1013 W·cm-2, the laser energy is mainly deposited around gain region, and the electronic temperature on the gain region can be dramatically increased, as well as gain coefficients. The delay time and the grazing incidence angle were optimized. If the delay time of 10.5 ns and grazing incidence angle of 16 degree are adopted, the effective gain of grazing incident scheme reaches 23.8 cm-1, which is 84% higher than that of normal incidence. Using driving laser energy of only 13 J, deeply saturated gain with gain length product being 23.8 can be obtained.
Using our series codes, quasi-stable Ni-like Ag collisional excitation scheme driven by laser with grazing incidence was studied. Comparing with that with normal incidence, at low drive intensity of 1.2×1013 W·cm-2, the laser energy is mainly deposited around gain region, and the electronic temperature on the gain region can be dramatically increased, as well as gain coefficients. The delay time and the grazing incidence angle were optimized. If the delay time of 10.5 ns and grazing incidence angle of 16 degree are adopted, the effective gain of grazing incident scheme reaches 23.8 cm-1, which is 84% higher than that of normal incidence. Using driving laser energy of only 13 J, deeply saturated gain with gain length product being 23.8 can be obtained.
2005,
17.
Abstract:
The high-order harmonic generation spectrums of He+ irradiated by the two-color coherent laser field are researched by numerically solving the 1-D time-dependent Schr dinger equation using symplectic algorithm. The computational results show that great changes have already taken place at the emission of the high-order harmonics and the efficiency of the harmonic generation increases greatly and it averagely increases 103 times in the plateau, despite the fact that the intensity of the higher frequency laser is only 10% of the initial field in the two-color coherent field. The efficiency of the high-order harmonics is enhanced by nearly four orders of magnitude relative to the monomer field; moreover, the corresponding order of the higher frequency field is enhanced by about five ord
The high-order harmonic generation spectrums of He+ irradiated by the two-color coherent laser field are researched by numerically solving the 1-D time-dependent Schr dinger equation using symplectic algorithm. The computational results show that great changes have already taken place at the emission of the high-order harmonics and the efficiency of the harmonic generation increases greatly and it averagely increases 103 times in the plateau, despite the fact that the intensity of the higher frequency laser is only 10% of the initial field in the two-color coherent field. The efficiency of the high-order harmonics is enhanced by nearly four orders of magnitude relative to the monomer field; moreover, the corresponding order of the higher frequency field is enhanced by about five ord
2005,
17.
Abstract:
Copper nano-particles were prepared by flow-levitation method and compacted for 40 min under pressure of 1.5 GPa by cold pressing method . The pressing process was studied well under 25 ℃ and inert gas protection. The relative density and the microhardess of a specimen were 97% and 1.85 GPa, respectivity. XRD analysis showed that the average grain size of the specimens was 20 nm. The positron annihilation spectroscopy (PAS) results showed that the size and amount of the vacancies and microvoids were similar to those of the nanocrystalline Cu prepaered by inert gas condensation method (IGC) but more large voids. The simulation experiment of inertial confinement fusion indicated that the efficiency of Kα-ray conversed from laser with nanocrystalline Cu was 5 times higher than that of coars
Copper nano-particles were prepared by flow-levitation method and compacted for 40 min under pressure of 1.5 GPa by cold pressing method . The pressing process was studied well under 25 ℃ and inert gas protection. The relative density and the microhardess of a specimen were 97% and 1.85 GPa, respectivity. XRD analysis showed that the average grain size of the specimens was 20 nm. The positron annihilation spectroscopy (PAS) results showed that the size and amount of the vacancies and microvoids were similar to those of the nanocrystalline Cu prepaered by inert gas condensation method (IGC) but more large voids. The simulation experiment of inertial confinement fusion indicated that the efficiency of Kα-ray conversed from laser with nanocrystalline Cu was 5 times higher than that of coars
2005,
17.
Abstract:
Big error would be introduced in numerical computation of power spectrum density(PSD) because of the use of the weighted window function. Using simulated single-frequency wavefront, PSD values before and after applying Hanning window were computed and a modification factor was deduced using theory of Fourier transform. Relationship between wavefront frequency and modification factor was analyzed by theoretical computation. It shows that under certain measurement errors and certain frequency scope, a constant, 8/3 or 64/9 is effective to modify one-dimensional or two-dimensional PSD value after applying Hanning window.
Big error would be introduced in numerical computation of power spectrum density(PSD) because of the use of the weighted window function. Using simulated single-frequency wavefront, PSD values before and after applying Hanning window were computed and a modification factor was deduced using theory of Fourier transform. Relationship between wavefront frequency and modification factor was analyzed by theoretical computation. It shows that under certain measurement errors and certain frequency scope, a constant, 8/3 or 64/9 is effective to modify one-dimensional or two-dimensional PSD value after applying Hanning window.
2005,
17.
Abstract:
Thermal stability of nanocrystalline intermetallic compound Cu4Al obtained from flow-levitation method is studied by means of DTA (Differential Thermal Analysis) and XRD (X-Ray Diffraction). By DTA experiments on Cu4Al nanopowder, three endothermal peaks at 258 ℃, 423 ℃ and 537 ℃ on DTA curve were found. By XRD experiments on original sample and its heat-treating samples, the results show that the endothermal peak at 537 ℃ is related to the structure phase transition from nanostructure Cu4Al to Cu3Al, accompanying growing up of Cu3Al crystalline grain. The test results are compared and it can be seen that Cu4Al nanopowder possess a nice thermal stability below 440 ℃，and it will bring about phase transition above 537 ℃.
Thermal stability of nanocrystalline intermetallic compound Cu4Al obtained from flow-levitation method is studied by means of DTA (Differential Thermal Analysis) and XRD (X-Ray Diffraction). By DTA experiments on Cu4Al nanopowder, three endothermal peaks at 258 ℃, 423 ℃ and 537 ℃ on DTA curve were found. By XRD experiments on original sample and its heat-treating samples, the results show that the endothermal peak at 537 ℃ is related to the structure phase transition from nanostructure Cu4Al to Cu3Al, accompanying growing up of Cu3Al crystalline grain. The test results are compared and it can be seen that Cu4Al nanopowder possess a nice thermal stability below 440 ℃，and it will bring about phase transition above 537 ℃.
2005,
17.
Abstract:
By analyzing the optical design in the off-axis and multi-pass amplification system, and combining the application in the three high power solid laser facilities, it is indicated that avoiding the ghost image damage and controlling the system aberration are important in the optical design of similar facilities. The key for the optical design is confirming the F number of lens, and making the system aberration least by transforming the curvature of lens and the degree of lens tilt in the case of no ghost image damager. This work could provide guidance for the optical design in similar systems.
By analyzing the optical design in the off-axis and multi-pass amplification system, and combining the application in the three high power solid laser facilities, it is indicated that avoiding the ghost image damage and controlling the system aberration are important in the optical design of similar facilities. The key for the optical design is confirming the F number of lens, and making the system aberration least by transforming the curvature of lens and the degree of lens tilt in the case of no ghost image damager. This work could provide guidance for the optical design in similar systems.
2005,
17.
Abstract:
A measurement apparatus which composes of a reformed atomic force microscope (AFM), a precision rotating air-bearing and a auxiliary transform rotary is developed. The spindle error is approximately 0.049 μm. This apparatus can measure the inertial confinement fusion(ICF) target's circles in three orthogonal orientations. With the measured data of given targets, the sphericity, surface roughness and power spectrum were analyzed. The results showed that the sphericity was approximately 0.42 μm, and the average surface roughnesses were 105.7, 12.2, 6.2 and 18.25 nm corresponding to the mode number in the range of 2~10, 11~50, 51~100, and 101~1000, respectively. The average one-dimensional spectrum as a function of the mode number was also calculated.
A measurement apparatus which composes of a reformed atomic force microscope (AFM), a precision rotating air-bearing and a auxiliary transform rotary is developed. The spindle error is approximately 0.049 μm. This apparatus can measure the inertial confinement fusion(ICF) target's circles in three orthogonal orientations. With the measured data of given targets, the sphericity, surface roughness and power spectrum were analyzed. The results showed that the sphericity was approximately 0.42 μm, and the average surface roughnesses were 105.7, 12.2, 6.2 and 18.25 nm corresponding to the mode number in the range of 2~10, 11~50, 51~100, and 101~1000, respectively. The average one-dimensional spectrum as a function of the mode number was also calculated.
2005,
17.
Abstract:
A simplified two-dimension calculation model for helical magnetic flux compression generator with explosive initiated axially(AMFCG) was built by Maxwell equation. By the theoretic model the calculation formula of magnetic flux was simplified, which combined the equivalent circuit equation with magnetic flux expression. The expanding process of the explosive tube radius, the evolution process of AMFCG initial inductance and output current were simulated with three groups of parameters. The competition process between the detonation pressure and magnetic pressure was calculated and the magnetic field distribution was presented.
A simplified two-dimension calculation model for helical magnetic flux compression generator with explosive initiated axially(AMFCG) was built by Maxwell equation. By the theoretic model the calculation formula of magnetic flux was simplified, which combined the equivalent circuit equation with magnetic flux expression. The expanding process of the explosive tube radius, the evolution process of AMFCG initial inductance and output current were simulated with three groups of parameters. The competition process between the detonation pressure and magnetic pressure was calculated and the magnetic field distribution was presented.
2005,
17.
Abstract:
By using the finite-difference time-domain method in two-dimension, the transient response of BJT (bipolar junction transistor) under the high power electromagnetic pulse was simulated. The distribution and variation of the electronic field, current density, and the temperature in the transistor during the burnout of the device were obtained and analyzed. The formations of hot spots during the process under the pulse with low and high magnitude were observed. That how the time and energy needed for burnout depended on the magnitude of the pulse was also obtained. When the magnitude of the pulse is relatively low, the hot spot locates near the collector in the breakdown tunnel. When the magnitude of the pulse is sufficiently high, the voltage between the base and the emitter will become ver
By using the finite-difference time-domain method in two-dimension, the transient response of BJT (bipolar junction transistor) under the high power electromagnetic pulse was simulated. The distribution and variation of the electronic field, current density, and the temperature in the transistor during the burnout of the device were obtained and analyzed. The formations of hot spots during the process under the pulse with low and high magnitude were observed. That how the time and energy needed for burnout depended on the magnitude of the pulse was also obtained. When the magnitude of the pulse is relatively low, the hot spot locates near the collector in the breakdown tunnel. When the magnitude of the pulse is sufficiently high, the voltage between the base and the emitter will become ver
2005,
17.
Abstract:
Considering the ponderomotive force, the high-power microwave propagation in waveguide filled with plasma is analyzed and simulated. The propagation characteristics of the high-power microwave and the relationship between the power of the microwave and the distribution of the plasma density are researched. The results show that the ponderomotive force of high-power microwave would affect the dispersion, make the distribution of microwave different from Bessel distribution, and drive the plasma to the region where the microwave field is lower. When the microwave filed is sufficiently large, the low plasma density channel would form in the axial region.
Considering the ponderomotive force, the high-power microwave propagation in waveguide filled with plasma is analyzed and simulated. The propagation characteristics of the high-power microwave and the relationship between the power of the microwave and the distribution of the plasma density are researched. The results show that the ponderomotive force of high-power microwave would affect the dispersion, make the distribution of microwave different from Bessel distribution, and drive the plasma to the region where the microwave field is lower. When the microwave filed is sufficiently large, the low plasma density channel would form in the axial region.
2005,
17.
Abstract:
Absolute instability is a major physics limitation in the realization of the ultimate capability of gyro-traveling-wave tube. The physical interpretations ,character and suppressing methods of absolute instability were analyzed and verified by a W-band TE01 experiment. A threshold current which brings about the transition to absolute instability was investigated. PIC results show that the occurrence of absolute instability is determined by the operating current. The interaction circuit with distributed loss is proved effective for stabilizing amplification by increasing the threshold current.
Absolute instability is a major physics limitation in the realization of the ultimate capability of gyro-traveling-wave tube. The physical interpretations ,character and suppressing methods of absolute instability were analyzed and verified by a W-band TE01 experiment. A threshold current which brings about the transition to absolute instability was investigated. PIC results show that the occurrence of absolute instability is determined by the operating current. The interaction circuit with distributed loss is proved effective for stabilizing amplification by increasing the threshold current.
2005,
17.
Abstract:
The bunching cavity with dielectric absorber for gyroklystron is studied by using the mode-matching technique to build scattering matrix. By the theoretical analysis and the numerical simulation, the effect of loss dielectric absorber on Q factor and resonance characteristic of bunching cavity, and the effect of side apertures on resonance characteristic are presented. The numerical simulation shows that the bunching cavity with loss dielectric absorber can bate parasitical EH212 mode and EH311 mode effectively, but profit H01 mode at 8 mm band. When the thickness of loss dielectric absorber increases, the quality factor Q will decrease. Cold-test shows that the simulation results are in good agreement with experimental results.
The bunching cavity with dielectric absorber for gyroklystron is studied by using the mode-matching technique to build scattering matrix. By the theoretical analysis and the numerical simulation, the effect of loss dielectric absorber on Q factor and resonance characteristic of bunching cavity, and the effect of side apertures on resonance characteristic are presented. The numerical simulation shows that the bunching cavity with loss dielectric absorber can bate parasitical EH212 mode and EH311 mode effectively, but profit H01 mode at 8 mm band. When the thickness of loss dielectric absorber increases, the quality factor Q will decrease. Cold-test shows that the simulation results are in good agreement with experimental results.
2005,
17.
Abstract:
The injection power of a diagnostic neutral beam (DNB) can be obtained with the thermocouple probe measurement system on the Hefei superconducting Tokamak-7 (HT-7). With the 49 kV, 6 A, 100 ms pulse charge of an acceleration electrode, a thermocouple probe measurement system with 13 thermocouples crossly distributed on a coppery heat target was used to measure the temperature rise of the target, and the maximum measured temperature rise was 14 ℃. And the neutral beam power of 160 kW and beam profile distribution were obtained by calculation. The total neutral beam power of 130 kW was also obtained by integral calculation with the temperature rise on the heat section board. The difference between the two means was analyzed. The experiment result shows that the method of heat section board
The injection power of a diagnostic neutral beam (DNB) can be obtained with the thermocouple probe measurement system on the Hefei superconducting Tokamak-7 (HT-7). With the 49 kV, 6 A, 100 ms pulse charge of an acceleration electrode, a thermocouple probe measurement system with 13 thermocouples crossly distributed on a coppery heat target was used to measure the temperature rise of the target, and the maximum measured temperature rise was 14 ℃. And the neutral beam power of 160 kW and beam profile distribution were obtained by calculation. The total neutral beam power of 130 kW was also obtained by integral calculation with the temperature rise on the heat section board. The difference between the two means was analyzed. The experiment result shows that the method of heat section board
2005,
17.
Abstract:
In order to reduce the amplitude of corkscrew motion to obtain a high current pulsed electron beam with good quality, both simulation and experimental work were done based on the beam transport system of “Dragon-I”, which is a pulsed high current electron LIA. The beam centroid motion was controlled by adjusting the current fed into two pairs of steering coils located inside the accelerator cavities. The two pairs of steering coils are perpendicular to each other. The principle of the adjustments, simulations and experiments are introduced in this paper. Corkscrew amplitude of the output electron beam with 50 ns pulse flattop is reduced from 4 mm to less than 1 mm.
In order to reduce the amplitude of corkscrew motion to obtain a high current pulsed electron beam with good quality, both simulation and experimental work were done based on the beam transport system of “Dragon-I”, which is a pulsed high current electron LIA. The beam centroid motion was controlled by adjusting the current fed into two pairs of steering coils located inside the accelerator cavities. The two pairs of steering coils are perpendicular to each other. The principle of the adjustments, simulations and experiments are introduced in this paper. Corkscrew amplitude of the output electron beam with 50 ns pulse flattop is reduced from 4 mm to less than 1 mm.
2005,
17.
Abstract:
A current-controlled model of semiconductor opening switch(SOS) was developed to study the current opening effect and the physical process of SOS in pulsed power system. The p+-p-n-n+ type SOS was analyzed on the basis of the model. The distributions of carriers and field in SOS were simulated during forward and reverse current pumping, and the current opening effect was obtained. The results show that the opening process starts first at the p-type region.
A current-controlled model of semiconductor opening switch(SOS) was developed to study the current opening effect and the physical process of SOS in pulsed power system. The p+-p-n-n+ type SOS was analyzed on the basis of the model. The distributions of carriers and field in SOS were simulated during forward and reverse current pumping, and the current opening effect was obtained. The results show that the opening process starts first at the p-type region.
2005,
17.
Abstract:
Conventional analog I/Q demodulator suffers from phase and amplitude imbalance and DC offset, which cause big error into the measurement. A digital PAD is designed. Based on I/Q demodulation principle, using digital algorithms, such as digital filter and Hilbert transform, the conventional measurement error can basically be removed. Measuremental results show that the digital PAD has a maximum phase error of ±0.5° and a resolution of 0.2°. Its temperature coefficient is -0.1°/℃. Its dynamic ranges for phase-measurement and amplitude-measurement are -18~5 dBm and -20~0 dBm, respectively. The digital PAD can meet the need of the BEPCⅡ phasing system.
Conventional analog I/Q demodulator suffers from phase and amplitude imbalance and DC offset, which cause big error into the measurement. A digital PAD is designed. Based on I/Q demodulation principle, using digital algorithms, such as digital filter and Hilbert transform, the conventional measurement error can basically be removed. Measuremental results show that the digital PAD has a maximum phase error of ±0.5° and a resolution of 0.2°. Its temperature coefficient is -0.1°/℃. Its dynamic ranges for phase-measurement and amplitude-measurement are -18~5 dBm and -20~0 dBm, respectively. The digital PAD can meet the need of the BEPCⅡ phasing system.
2005,
17.
Abstract:
The paper introduces the calculation and measurement method of Q factor which describes the performance of cyclotron's RF D circuit. It mainly introduces the formula and principle for calculating the Q factor. The calculation data are compared with the measurement data of the capacitor coupling method, which shows good accordance with small errors. Analysis suggests that errors are mainly caused by approximate computation and the value of contacted resistance adopted. As contacted resistance is an important factor, more attention should be paid on it in designing cavities.
The paper introduces the calculation and measurement method of Q factor which describes the performance of cyclotron's RF D circuit. It mainly introduces the formula and principle for calculating the Q factor. The calculation data are compared with the measurement data of the capacitor coupling method, which shows good accordance with small errors. Analysis suggests that errors are mainly caused by approximate computation and the value of contacted resistance adopted. As contacted resistance is an important factor, more attention should be paid on it in designing cavities.
2005,
17.
Abstract:
The control of the electron beam in an intense current linear induction accelerator(LIA)is very important. The center position of the electron beam and the beam profile are two important parameters which should be measured accurately. The setup of a time-resolved measurement system and a data processing method for determining the beam center position are introduced for the purpose of obtaining Dragon-Ⅰ electron beam trajectory including beam profile.The actual results show that the centroid position error can be controlled in one to two pixels. The time-resolved beam centroid trajectory of Dragon-Ⅰ(18.5 MeV, 2 kA, 90 ns) is obtained recently in 10 ns interval, 3 ns exposure time with a multi-frame gated camera. The results show that the screw movement of the electron beam is mainly limit
The control of the electron beam in an intense current linear induction accelerator(LIA)is very important. The center position of the electron beam and the beam profile are two important parameters which should be measured accurately. The setup of a time-resolved measurement system and a data processing method for determining the beam center position are introduced for the purpose of obtaining Dragon-Ⅰ electron beam trajectory including beam profile.The actual results show that the centroid position error can be controlled in one to two pixels. The time-resolved beam centroid trajectory of Dragon-Ⅰ(18.5 MeV, 2 kA, 90 ns) is obtained recently in 10 ns interval, 3 ns exposure time with a multi-frame gated camera. The results show that the screw movement of the electron beam is mainly limit
2005,
17.
Abstract:
Velvet as a cathode has the ability to emit intense multi-pulsed beams. The characteristics of the double-pulsed relativistic electron beams generated by velvet cathode were studied. The integral emittance and brightness of the double-pulsed beams were presented. The time-resolved envelope radii of the beams were measured. The double-pulsed beams integral brightness reached up to about 108 A·(m·rad)-2 in the experiment. It was the difference of the influence of the cathode plasma generated in the process of emitting beams on the vacuum diode and the recovery velocity of the cathode plasma that resulted in the different envelope radii of the two beams.
Velvet as a cathode has the ability to emit intense multi-pulsed beams. The characteristics of the double-pulsed relativistic electron beams generated by velvet cathode were studied. The integral emittance and brightness of the double-pulsed beams were presented. The time-resolved envelope radii of the beams were measured. The double-pulsed beams integral brightness reached up to about 108 A·(m·rad)-2 in the experiment. It was the difference of the influence of the cathode plasma generated in the process of emitting beams on the vacuum diode and the recovery velocity of the cathode plasma that resulted in the different envelope radii of the two beams.
2005,
17.
Abstract:
The principle of measuring the bunch length of the Beijing electron positron collider upgrade(BEPCⅡ) linac by harmonic bunch length monitor is presented. The measured bunch length ranging between 1.4 mm and 2.0 mm agrees well with the theoretic calculation of 1.5 mm. The electron beam current measured by the beam current monitor (BCT3) is almost in direct proportion to the induced voltage of the fundamental harmonic. When the parameters of the pre-buncher and buncher are adjusted greatly while the beam current being unchanged, the fifth harmonic signal has a great change, but the fundamental signal changes gently. The test results are all in good agreement with the theoretic analysis.
The principle of measuring the bunch length of the Beijing electron positron collider upgrade(BEPCⅡ) linac by harmonic bunch length monitor is presented. The measured bunch length ranging between 1.4 mm and 2.0 mm agrees well with the theoretic calculation of 1.5 mm. The electron beam current measured by the beam current monitor (BCT3) is almost in direct proportion to the induced voltage of the fundamental harmonic. When the parameters of the pre-buncher and buncher are adjusted greatly while the beam current being unchanged, the fifth harmonic signal has a great change, but the fundamental signal changes gently. The test results are all in good agreement with the theoretic analysis.
2005,
17.
Abstract:
Electron paramagnetic resonance(EPR) and cross-sectional transmission electron microscopy were used to study defect structure and radiated damage mechanism. Single crystal samples of cubic zirconia stabilized by 9.5 mol.% Y2O3 (YSZ) were implanted with 200 keV Xe ions and 400 keV Cs ions up to a dose of 5×1016 cm-2, respectively. EPR spectra show the trigonal signal with g‖=1.989 and g⊥=1.869, which exhibites axial symmetry with ［111］ direction as symmetry axis composed of sixfold-coordinated Zr3+ sites. Peak-to-peak intensity (per unit volume) of Cs-ion irradiated YSZ is as about 150 time as that of Xe-ion irradiated YSZ, which indicates that the concentration of sixfold-coordinated Zr3+ defects produced by Cs-ion irradiation is far more than that of Xe-ion irradiated. The cross-sect
Electron paramagnetic resonance(EPR) and cross-sectional transmission electron microscopy were used to study defect structure and radiated damage mechanism. Single crystal samples of cubic zirconia stabilized by 9.5 mol.% Y2O3 (YSZ) were implanted with 200 keV Xe ions and 400 keV Cs ions up to a dose of 5×1016 cm-2, respectively. EPR spectra show the trigonal signal with g‖=1.989 and g⊥=1.869, which exhibites axial symmetry with ［111］ direction as symmetry axis composed of sixfold-coordinated Zr3+ sites. Peak-to-peak intensity (per unit volume) of Cs-ion irradiated YSZ is as about 150 time as that of Xe-ion irradiated YSZ, which indicates that the concentration of sixfold-coordinated Zr3+ defects produced by Cs-ion irradiation is far more than that of Xe-ion irradiated. The cross-sect
2005,
17.
Abstract:
In this article, a non-laminar and non-collision numerical simulation model based on a third order trajectory equation is presented. In this model, the injection angles of beamlets are assumed as a random distribution. Simulation result shows that X-ray spot size is almost certainly convergent when the number of beamlets increases gradually, and the convergent size is about 1.03 mm. The calculated uncertainty is in range of ±0.05 mm with different numbers of beamlets. In the experiment, X-ray spot size being 1.3 mm and focusing length 23.2 mm are obtained, which indicates that the maximum absolute error of the X-ray spot size is 0.4 mm and that of focusing length is 3.5 cm.
In this article, a non-laminar and non-collision numerical simulation model based on a third order trajectory equation is presented. In this model, the injection angles of beamlets are assumed as a random distribution. Simulation result shows that X-ray spot size is almost certainly convergent when the number of beamlets increases gradually, and the convergent size is about 1.03 mm. The calculated uncertainty is in range of ±0.05 mm with different numbers of beamlets. In the experiment, X-ray spot size being 1.3 mm and focusing length 23.2 mm are obtained, which indicates that the maximum absolute error of the X-ray spot size is 0.4 mm and that of focusing length is 3.5 cm.
2005,
17.
Abstract:
The high beam current (0.9 A) and the large number of bunches (93 bunches) may cause coupled bunch instabilities (CBI) in BEPCII. Active feedback systems are required to suppress CBI. The BEPCII transverse feedback system mainly includes three parts that are the signal detection unit, the signal processing unit, and the kicker. The notch filter is an important part of the signal processing unit. In this paper a simple notch filter which is combined with two cables, a splitter and a combiner is introduced. And a -41 dB notch depth is achieved. Transverse feedback system with this notch filter succeeds in curing the instability of the beam. It is proved that the filter can satisfy the requirement of the BEPCII transverse feedback system.
The high beam current (0.9 A) and the large number of bunches (93 bunches) may cause coupled bunch instabilities (CBI) in BEPCII. Active feedback systems are required to suppress CBI. The BEPCII transverse feedback system mainly includes three parts that are the signal detection unit, the signal processing unit, and the kicker. The notch filter is an important part of the signal processing unit. In this paper a simple notch filter which is combined with two cables, a splitter and a combiner is introduced. And a -41 dB notch depth is achieved. Transverse feedback system with this notch filter succeeds in curing the instability of the beam. It is proved that the filter can satisfy the requirement of the BEPCII transverse feedback system.
