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RSS2008 Vol. 20, No. 12
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2008,
20.
Abstract:
Shot reliability performance measures of laser facilities with more beam lines pertain to three categories: minimum-energy-on-target, power balance, and shot diagnostics. Accounting for symmetry of NIF beam line design and similarity of subset reliability in a same partition, a fault tree of meeting minimum-energy-on-target for the large laser facility shot of type K and a simplified method are presented, which are used to analyze hypothetic reliability of partition subsets in order to get trends of influences increasing number of beam lines and diverse shot types of large laser facilities on their shot reliability. Finally, it finds that improving component reliability is more crucial for laser facilities with more beam lines in comparison with those with beam lines and functional diversi
Shot reliability performance measures of laser facilities with more beam lines pertain to three categories: minimum-energy-on-target, power balance, and shot diagnostics. Accounting for symmetry of NIF beam line design and similarity of subset reliability in a same partition, a fault tree of meeting minimum-energy-on-target for the large laser facility shot of type K and a simplified method are presented, which are used to analyze hypothetic reliability of partition subsets in order to get trends of influences increasing number of beam lines and diverse shot types of large laser facilities on their shot reliability. Finally, it finds that improving component reliability is more crucial for laser facilities with more beam lines in comparison with those with beam lines and functional diversi
2008,
20.
Abstract:
The preparation techniques for poly 4-methyl-1-pentene(TPX) foams in binary solvent system applied in ICF experiments have been improved through controlling the thermal history in preparation process. Beta radiation detecting and X-ray photographic technology were introduced to analyze the foam density in this system. The results of the two methods, which are consistent with each other, revealed that the optimized condition is to keep the cooling velocity in gelatin at 1 ℃/min and then quench it quickly. However, the pore size of super low density TPX foams prepared with this preparation techniques are very big, and the diameters of very few pores even reach hundreds of micron, so a single solvent system was used and the foams of lowest density 3 mg/cm3 for Z-pinch had been made. These fo
The preparation techniques for poly 4-methyl-1-pentene(TPX) foams in binary solvent system applied in ICF experiments have been improved through controlling the thermal history in preparation process. Beta radiation detecting and X-ray photographic technology were introduced to analyze the foam density in this system. The results of the two methods, which are consistent with each other, revealed that the optimized condition is to keep the cooling velocity in gelatin at 1 ℃/min and then quench it quickly. However, the pore size of super low density TPX foams prepared with this preparation techniques are very big, and the diameters of very few pores even reach hundreds of micron, so a single solvent system was used and the foams of lowest density 3 mg/cm3 for Z-pinch had been made. These fo
2008,
20.
Abstract:
The broadband nanosecond shaped laser pulse obtained by chirped pulse stacking(CPS) method can make the output stacked pulse meet the requirement of the inertial confinement fusion(ICF). However, temporal pulse shape modulation will come forth due to the pulse coherence of stacked chirped pulses, so will spectrum modulation. Factors influencing stacked chirped pulse waveshape and characteristics of the amplification process of stacked chirped pulse were studied. Results show that the evolution law of stacked chirped pulses is consistent with that of narrow band pulses, and the time modulation structure does not change in the amplification process. However, the spectrum modulation changes, which could be preliminarily inferred from the nonlinear effect. The stacked chirped pulse has a gain
The broadband nanosecond shaped laser pulse obtained by chirped pulse stacking(CPS) method can make the output stacked pulse meet the requirement of the inertial confinement fusion(ICF). However, temporal pulse shape modulation will come forth due to the pulse coherence of stacked chirped pulses, so will spectrum modulation. Factors influencing stacked chirped pulse waveshape and characteristics of the amplification process of stacked chirped pulse were studied. Results show that the evolution law of stacked chirped pulses is consistent with that of narrow band pulses, and the time modulation structure does not change in the amplification process. However, the spectrum modulation changes, which could be preliminarily inferred from the nonlinear effect. The stacked chirped pulse has a gain
2008,
20.
Abstract:
Substrates with gold nanoparticles aggregates adsorbed on their surfaces were prepared after irradiation of silanized glass substrates attached with gold seeds smaller than 10 nm by a fluorescent lamp, with poly (vinylpyrrolidone) as reductant and HAuCl4 as precursor. The substrates were characterized by atomic force microscopy, scanning electron microscopy, X-ray diffraction, absorption and fluorescence spectroscopy. The results showed that the multi-crystalline gold nanoparticles which finally grew up to 140 nm after 20-hour irradiation took on irregular shape, and some of them stacked to form bilayer structure. A new broad band appeared in the absorption spectra of the substrates due to the interparticle dipole-dipole coupling of surface plasmon resonance response of the gold particles,
Substrates with gold nanoparticles aggregates adsorbed on their surfaces were prepared after irradiation of silanized glass substrates attached with gold seeds smaller than 10 nm by a fluorescent lamp, with poly (vinylpyrrolidone) as reductant and HAuCl4 as precursor. The substrates were characterized by atomic force microscopy, scanning electron microscopy, X-ray diffraction, absorption and fluorescence spectroscopy. The results showed that the multi-crystalline gold nanoparticles which finally grew up to 140 nm after 20-hour irradiation took on irregular shape, and some of them stacked to form bilayer structure. A new broad band appeared in the absorption spectra of the substrates due to the interparticle dipole-dipole coupling of surface plasmon resonance response of the gold particles,
2008,
20.
Abstract:
Large deuterium clusters were produced in a supersonic expansion of high pressure gases into vacuum through a 0.5 mm nozzle. The average size clusters (with 3×103 atoms) was verified by measuring the Rayleigh scattered signal using a He-Ne laser beam. Neutrons (2.45 MeV) from deuterium clusters fusion induced by the intense femtosecond (30 fs) laser pulse is experimentally demonstrated. The average neutron yield of 1×103 per shot was obtained. The yield grew slightly with the increasing of the laser spot size. No neutron was observed when the laser spot was larger than 470 micron. The fusion events mainly happened in the hot plasma region radiated by the intense laser.
Large deuterium clusters were produced in a supersonic expansion of high pressure gases into vacuum through a 0.5 mm nozzle. The average size clusters (with 3×103 atoms) was verified by measuring the Rayleigh scattered signal using a He-Ne laser beam. Neutrons (2.45 MeV) from deuterium clusters fusion induced by the intense femtosecond (30 fs) laser pulse is experimentally demonstrated. The average neutron yield of 1×103 per shot was obtained. The yield grew slightly with the increasing of the laser spot size. No neutron was observed when the laser spot was larger than 470 micron. The fusion events mainly happened in the hot plasma region radiated by the intense laser.
2008,
20.
Abstract:
The nonlinear dispersion relation of a linearly polarized laser beam in magnetized plasma was derived using the Lorentz transform, in which the nonlinearity of the relativistic factor was taken into account. In terms of Karpman method, the nonlinear governing equation for the amplitude of the linearly polarized laser field was obtained theoretically. Thus, the modulational instability of this intense laser beam in magnetized plasma was analyzed and the temporal growth rate for the finite amplitude of the perturbed field was found analytically. It is shown that the growth rate of magnetic modulation instability increases significantly in the corona region near the critical surface in laser-produced plasma.
The nonlinear dispersion relation of a linearly polarized laser beam in magnetized plasma was derived using the Lorentz transform, in which the nonlinearity of the relativistic factor was taken into account. In terms of Karpman method, the nonlinear governing equation for the amplitude of the linearly polarized laser field was obtained theoretically. Thus, the modulational instability of this intense laser beam in magnetized plasma was analyzed and the temporal growth rate for the finite amplitude of the perturbed field was found analytically. It is shown that the growth rate of magnetic modulation instability increases significantly in the corona region near the critical surface in laser-produced plasma.
2008,
20.
Abstract:
Fe-embedding diamond-like carbon(Fe: DLC) films with different Fe content were deposited by using a pulsed laser deposition(PLD) technique. An X-ray photoelectron spectroscopy(XPS) was used to probe the composition of deposited Fe: DLC films. The effects of Fe-embedding on the microstructure and electrical properties of diamond-like carbon films were investigated by means of transmission electron microscopy(TEM), Raman spectroscopy and current-voltage characteristics. The XPS, TEM and Raman spectra analyses indicate that the Fe nano-particles periodically embed in the amorphous carbon matrix and their embedding promote aromatic bond formation, and accordingly, the degree of order of the films increase gradually as the Fe content increase. The current-voltage characteristics show Fe-embeddi
Fe-embedding diamond-like carbon(Fe: DLC) films with different Fe content were deposited by using a pulsed laser deposition(PLD) technique. An X-ray photoelectron spectroscopy(XPS) was used to probe the composition of deposited Fe: DLC films. The effects of Fe-embedding on the microstructure and electrical properties of diamond-like carbon films were investigated by means of transmission electron microscopy(TEM), Raman spectroscopy and current-voltage characteristics. The XPS, TEM and Raman spectra analyses indicate that the Fe nano-particles periodically embed in the amorphous carbon matrix and their embedding promote aromatic bond formation, and accordingly, the degree of order of the films increase gradually as the Fe content increase. The current-voltage characteristics show Fe-embeddi
2008,
20.
Abstract:
Transporting in solenoid magnetic fields, sheet electron beams tend to manifest Diocotron instability, which could lead to collapse of beam propagation. Wiggler-field can be used to focus sheet electron beam and prevent Diocotron instability. The theory of the Wiggler-field focusing sheet electron beams was analyzed, and the corresponding beam envelope was gotten. Using 3D PIC program, the formation of Diocotron instability a Wiggler-field focusing sheet electron beam was simulated. Results show that Wiggler-field design, such as increasing the inagnitude and reducing the period properly, would restrain Diocotron instability. This might make the sheat-electron-beam travelling wave tube possible.
Transporting in solenoid magnetic fields, sheet electron beams tend to manifest Diocotron instability, which could lead to collapse of beam propagation. Wiggler-field can be used to focus sheet electron beam and prevent Diocotron instability. The theory of the Wiggler-field focusing sheet electron beams was analyzed, and the corresponding beam envelope was gotten. Using 3D PIC program, the formation of Diocotron instability a Wiggler-field focusing sheet electron beam was simulated. Results show that Wiggler-field design, such as increasing the inagnitude and reducing the period properly, would restrain Diocotron instability. This might make the sheat-electron-beam travelling wave tube possible.
2008,
20.
Abstract:
The field distribuition in the high frequency structure of the radial three-cavity transmit time oscillator was solved approximately. Frequencies and field distribution characteristics of the models are obtained. When the ratio of the cavity radial length to the average radius is 0.34, the solution of the analytical theory is conformed with the simulative one. The error of the solution compared with the simulative results was analyzed comparing the results of the two. The results indicates that the relative error of the field swing decreases with the reducing of the ratio of the cavity radial length to the average radius. When the ratio is less than 0.3, the relative error is less than 5.4%.
The field distribuition in the high frequency structure of the radial three-cavity transmit time oscillator was solved approximately. Frequencies and field distribution characteristics of the models are obtained. When the ratio of the cavity radial length to the average radius is 0.34, the solution of the analytical theory is conformed with the simulative one. The error of the solution compared with the simulative results was analyzed comparing the results of the two. The results indicates that the relative error of the field swing decreases with the reducing of the ratio of the cavity radial length to the average radius. When the ratio is less than 0.3, the relative error is less than 5.4%.
2008,
20.
Abstract:
Based on the CST software, numerical simulations are carried out for the frequency response in a coaxial Bragg structure with tapered ripples. The bandwidth of the coaxial Bragg structure with positive taper can be narrowed by increasing the tapering angle, whereas the bandwidth of the coaxial Bragg structure with negative taper can be expanded by increasing the tapering angle. The residual side-lobes of the frequency response can be effectively suppressed by employing the window function technique, using Hanning, Hamming and Blackman window functions. These characteristics of a tapered coaxial Bragg structure are favorable to improvement of its performance as a reflector or a filter.
Based on the CST software, numerical simulations are carried out for the frequency response in a coaxial Bragg structure with tapered ripples. The bandwidth of the coaxial Bragg structure with positive taper can be narrowed by increasing the tapering angle, whereas the bandwidth of the coaxial Bragg structure with negative taper can be expanded by increasing the tapering angle. The residual side-lobes of the frequency response can be effectively suppressed by employing the window function technique, using Hanning, Hamming and Blackman window functions. These characteristics of a tapered coaxial Bragg structure are favorable to improvement of its performance as a reflector or a filter.
2008,
20.
Abstract:
A novel foilless S-band low-impedance transit-time oscillator was designed. The impedance of this oscillator is about 20 Ω. Such an oscillator with coaxial structure has the advantages of low guide magnetic field and quick saturation time, expectantly operating repetitively and in a long-pulse state. As indicated by PIC simulations, the average power of output microwave is about 4.0 GW at the main frequency of 3.175 GHz with the input-diode voltage of 550 kV, the input-diode current of 27.6 kA, and the extra magnetic field of 0.8 Ｔ. Based on the simulation results, the power efficiency of microwave is about 26.4%, much better than that of a high-impedance transit-time radiation oscillator at the same input voltage．
A novel foilless S-band low-impedance transit-time oscillator was designed. The impedance of this oscillator is about 20 Ω. Such an oscillator with coaxial structure has the advantages of low guide magnetic field and quick saturation time, expectantly operating repetitively and in a long-pulse state. As indicated by PIC simulations, the average power of output microwave is about 4.0 GW at the main frequency of 3.175 GHz with the input-diode voltage of 550 kV, the input-diode current of 27.6 kA, and the extra magnetic field of 0.8 Ｔ. Based on the simulation results, the power efficiency of microwave is about 26.4%, much better than that of a high-impedance transit-time radiation oscillator at the same input voltage．
2008,
20.
Abstract:
Two key techniques are presented to treat the initial-value problem of the partial mode and to monitor the calculation error in the nonlinear simulation of a gyro-TWT amplifier with helical interaction waveguide. Based on these techniques, a code is programmed and simulation results are in good agreement with the experimental data recorded by Denisov G G, et al. Influences of the electron-beam velocity spread, the period and depth of the helical corrugations on the efficiency are studied. The results show that the beam-wave efficiency is not sensitive to the velocity spread, but is dependent on the period and depth of the helical corrugations, and that the efficiency in the present experiment may achieve 25.6% by optimizing the helical corrugation parameters.
Two key techniques are presented to treat the initial-value problem of the partial mode and to monitor the calculation error in the nonlinear simulation of a gyro-TWT amplifier with helical interaction waveguide. Based on these techniques, a code is programmed and simulation results are in good agreement with the experimental data recorded by Denisov G G, et al. Influences of the electron-beam velocity spread, the period and depth of the helical corrugations on the efficiency are studied. The results show that the beam-wave efficiency is not sensitive to the velocity spread, but is dependent on the period and depth of the helical corrugations, and that the efficiency in the present experiment may achieve 25.6% by optimizing the helical corrugation parameters.
2008,
20.
Abstract:
This paper describes the basic theory of radio frequency feedback, and then presents a digital algorithm which adopts the rotation matrix to adjust the gain and phase of the radio frequency feedback loop in the field programmable gate array. Experimental results show the loop delay is 1.2 μs, and the band width of the superconductivity cavity changes from 3.3 kHz to 4.8 kHz after adding the radio frequency feedback. And the quality factor of the superconductivity cavity changes from 150 550 to 104 130．
This paper describes the basic theory of radio frequency feedback, and then presents a digital algorithm which adopts the rotation matrix to adjust the gain and phase of the radio frequency feedback loop in the field programmable gate array. Experimental results show the loop delay is 1.2 μs, and the band width of the superconductivity cavity changes from 3.3 kHz to 4.8 kHz after adding the radio frequency feedback. And the quality factor of the superconductivity cavity changes from 150 550 to 104 130．
2008,
20.
Abstract:
The characteristics of stimulated Smith-Purcell radiation in THz region are simulated and numerically calculated. The experimental device is designed to be compact. The notion of the design for the experiment device is originated from the prototype of the Shanghai Electron Beam Ion Trap. Strong axial magnetic field is necessary to achieve high current and low emittance of electron beam. The simulation results of dynamic characteristics for the electron beam show that an average beam current can be as high as 0.2 A with an RMS beam radius of 75 μm, which is the precondition to work as free electron laser(FEL) while passing over the grating surface. Based on the theory of Andrews and Brau, we have optimized the parameters of grating to ensure the emission angle is near 60°. And the calcula
The characteristics of stimulated Smith-Purcell radiation in THz region are simulated and numerically calculated. The experimental device is designed to be compact. The notion of the design for the experiment device is originated from the prototype of the Shanghai Electron Beam Ion Trap. Strong axial magnetic field is necessary to achieve high current and low emittance of electron beam. The simulation results of dynamic characteristics for the electron beam show that an average beam current can be as high as 0.2 A with an RMS beam radius of 75 μm, which is the precondition to work as free electron laser(FEL) while passing over the grating surface. Based on the theory of Andrews and Brau, we have optimized the parameters of grating to ensure the emission angle is near 60°. And the calcula
2008,
20.
Abstract:
Methods to determine the transverse impedance of a linear induction accelerator(LIA) cavity both in calculation and experiment were introduced. To minimize transverse impedance is very important in designing induction cavities for an LIA，since for a new designed cavity to investigate its RF fields related to the shape of the accelerating gap is in very high priority. Three different cavities were chosen as models, accelerating cavities of a 10 MeV LIA and “Dragon-I”, and a non-accelerating cavity of “Dragon-I” designed for vacuum pump and beam diagnosis. Both coaxial line method and η factor method were employed in experimental tests. The main parts of the device used in both methods were identical, which was a coaxial line with two off center inner conductors formed by one under tes
Methods to determine the transverse impedance of a linear induction accelerator(LIA) cavity both in calculation and experiment were introduced. To minimize transverse impedance is very important in designing induction cavities for an LIA，since for a new designed cavity to investigate its RF fields related to the shape of the accelerating gap is in very high priority. Three different cavities were chosen as models, accelerating cavities of a 10 MeV LIA and “Dragon-I”, and a non-accelerating cavity of “Dragon-I” designed for vacuum pump and beam diagnosis. Both coaxial line method and η factor method were employed in experimental tests. The main parts of the device used in both methods were identical, which was a coaxial line with two off center inner conductors formed by one under tes
2008,
20.
Abstract:
A new highly sensitive radiochromic film is developed by using poly(vinyl butyral) as the base and using acetylene-type compounds as organic dye material. It becomes blue after irradiation by an electron beam. The absorbance spectrum is analyzed and the peak in visual region locates at about 675 nm.There is a linear relationship between absorbency and e-flux when irradiated by the same electron energy. The response of absorbency is affected by the sequence radiation. A linear fitting relationship is also discovered between the sensitive layer thickness and absorbency. The sensitivety of the response can be changed when different inverse proportion of halides are added into the radiochromic system. Good stability is proved from environment analysis.
A new highly sensitive radiochromic film is developed by using poly(vinyl butyral) as the base and using acetylene-type compounds as organic dye material. It becomes blue after irradiation by an electron beam. The absorbance spectrum is analyzed and the peak in visual region locates at about 675 nm.There is a linear relationship between absorbency and e-flux when irradiated by the same electron energy. The response of absorbency is affected by the sequence radiation. A linear fitting relationship is also discovered between the sensitive layer thickness and absorbency. The sensitivety of the response can be changed when different inverse proportion of halides are added into the radiochromic system. Good stability is proved from environment analysis.
2008,
20.
Abstract:
The analytic theory of the energy deposition of electron beam on the conversion target and the design approach for the composite target are presented. The high temperature plasma formed in the simple target would eject along positive and negative axial directions and make the target perforated. In the same beam energy, the beam with larger focal spot makes smaller ablated cavities with curl edge in the target, but the beam with smaller spot makes larger ones with relativly smooth edge. The composite target and the modified composite target can bear continuous strikes of 2~3 beam pulses. The Monte Carlo simulation shows that the spot size of bremsstrahlung sources are the same as the electron beam spot size on the target, thus the composite target can be used in the multi-pulse radiograph
The analytic theory of the energy deposition of electron beam on the conversion target and the design approach for the composite target are presented. The high temperature plasma formed in the simple target would eject along positive and negative axial directions and make the target perforated. In the same beam energy, the beam with larger focal spot makes smaller ablated cavities with curl edge in the target, but the beam with smaller spot makes larger ones with relativly smooth edge. The composite target and the modified composite target can bear continuous strikes of 2~3 beam pulses. The Monte Carlo simulation shows that the spot size of bremsstrahlung sources are the same as the electron beam spot size on the target, thus the composite target can be used in the multi-pulse radiograph
2008,
20.
Abstract:
This paper introduces the time response of a new type ZnO:Ga crystal to a fast rep-rate pulse hard X-ray. The hard X-ray energy spectrum (from 10 keV to 100 keV ) was measured by X-ray fluorescence analysis apparatus. The results show that the rise time is 316 ps, the FWHM is 440 ps, and the energy response to hard X-ray is flat when the X-ray energy greater than 40 keV. The ZnO:Ga crystal could be used as a component for hard X-ray detection.
This paper introduces the time response of a new type ZnO:Ga crystal to a fast rep-rate pulse hard X-ray. The hard X-ray energy spectrum (from 10 keV to 100 keV ) was measured by X-ray fluorescence analysis apparatus. The results show that the rise time is 316 ps, the FWHM is 440 ps, and the energy response to hard X-ray is flat when the X-ray energy greater than 40 keV. The ZnO:Ga crystal could be used as a component for hard X-ray detection.
2008,
20.
Abstract:
Various partial discharge of an organic and a polyethylene insulation materials in vacuum under impulse voltage (rise time of 50 ns, halfwidth of 350 ns and 3 μs) excitations were observed, and the characteristics of surface charge were investigated by an electrostatic probe, a current monitor system and a luminescence signal measurement system. The experimental results show that, a partial discharge current may be observed near the peak, the tail of pulse, or even close to zero voltage at pulse end. The partial discharge is the basic reason for the surface charge under nanosecond pulse excitations. Positive surface charge was measured after the partial discharge happen, and the charge density near cathode is alittle more than that near anode for the electron emission began from the catho
Various partial discharge of an organic and a polyethylene insulation materials in vacuum under impulse voltage (rise time of 50 ns, halfwidth of 350 ns and 3 μs) excitations were observed, and the characteristics of surface charge were investigated by an electrostatic probe, a current monitor system and a luminescence signal measurement system. The experimental results show that, a partial discharge current may be observed near the peak, the tail of pulse, or even close to zero voltage at pulse end. The partial discharge is the basic reason for the surface charge under nanosecond pulse excitations. Positive surface charge was measured after the partial discharge happen, and the charge density near cathode is alittle more than that near anode for the electron emission began from the catho
2008,
20.
Abstract:
For a pulsed power source which consists of multi-module and works in parallel, many gas spark switches in primary capacitor storage units and high voltage pulse-formed gas switches should be synchronized by triggering generator system. A multi-module and multi-output triggering generator system with high voltage, fast rise time, low jitter is developed. The system includes a multi-function synchronous signal generator DG535 and several step-by-step pulse amplifier units in series. The amplifier is based on hydrogen thyratron and spark gaps. Each amplifier unit can output multi-pulse at the same time, and when the output is 4-pulses or 8-pulses, the rise time is about 10 ns or 15 ns. The minimum delay time of the system is 305 ns and the jitter is about 2 ns. The maximum output voltage on
For a pulsed power source which consists of multi-module and works in parallel, many gas spark switches in primary capacitor storage units and high voltage pulse-formed gas switches should be synchronized by triggering generator system. A multi-module and multi-output triggering generator system with high voltage, fast rise time, low jitter is developed. The system includes a multi-function synchronous signal generator DG535 and several step-by-step pulse amplifier units in series. The amplifier is based on hydrogen thyratron and spark gaps. Each amplifier unit can output multi-pulse at the same time, and when the output is 4-pulses or 8-pulses, the rise time is about 10 ns or 15 ns. The minimum delay time of the system is 305 ns and the jitter is about 2 ns. The maximum output voltage on
2008,
20.
Abstract:
Synchronization of laser pulse and voltage pulse is important in laser-triggered surface flashover experiments. Of the laser-triggered surface flashover facilities, a high precision laser trigger system was built. A single/double harmonic, with wavelengths of 1 064/532 nm, Q-switched Nd:YAG laser was used to trigger the surface flashover. The delay time and jitter of Marx generator’s trigger input and output, Marx generator input and output, laser input and output were respectively measured. A self-made digital delay and pulse generator was used in the trigger system. The digital delay/pulse generator controls Marx generator’s trigger and the Xe lamp of laser. The Q-switch of laser was controlled by the Marx gneerator’s output. Based on the result of the delay time and the time sequence
Synchronization of laser pulse and voltage pulse is important in laser-triggered surface flashover experiments. Of the laser-triggered surface flashover facilities, a high precision laser trigger system was built. A single/double harmonic, with wavelengths of 1 064/532 nm, Q-switched Nd:YAG laser was used to trigger the surface flashover. The delay time and jitter of Marx generator’s trigger input and output, Marx generator input and output, laser input and output were respectively measured. A self-made digital delay and pulse generator was used in the trigger system. The digital delay/pulse generator controls Marx generator’s trigger and the Xe lamp of laser. The Q-switch of laser was controlled by the Marx gneerator’s output. Based on the result of the delay time and the time sequence
2008,
20.
Abstract:
A 10-stage wave erection Marx generator is designed and set up by using 50 kV non-inductive capacitors and solid resistors, which realizes the miniaturization of pulse power modulator with capacitance energy storage. The impedance characteristic of the generator is experimentally studied by utilizing water resistor loads with different resistance, and further estimated to be about 45 Ω by utilizing a metal film resistor load of 90 Ω which makes the discharging circuit critically damped. For 40 kV charge, an output high voltage pulse with amplitude of about 210 kV, full width half maximum (FWHM) of about 40 ns, and rise time of 5 ns is obtained on the metal film resistor load. This voltage pulse generator is applied to drive a fieldemission diode successfully. For a cathode-anode gap of
A 10-stage wave erection Marx generator is designed and set up by using 50 kV non-inductive capacitors and solid resistors, which realizes the miniaturization of pulse power modulator with capacitance energy storage. The impedance characteristic of the generator is experimentally studied by utilizing water resistor loads with different resistance, and further estimated to be about 45 Ω by utilizing a metal film resistor load of 90 Ω which makes the discharging circuit critically damped. For 40 kV charge, an output high voltage pulse with amplitude of about 210 kV, full width half maximum (FWHM) of about 40 ns, and rise time of 5 ns is obtained on the metal film resistor load. This voltage pulse generator is applied to drive a fieldemission diode successfully. For a cathode-anode gap of
2008,
20.
Abstract:
Based on high-speed MOSFET switches, the dual ultrafast high voltage pulses are generated with the inductive adder circuit topology. The pulses’ half-width is 300 ns, the rise time is about 60 ns and the time interval between two pulses is 600 ns. The peak pulse current could be 365 A for a load of 11.5 Ω and the corresponding output peak pulse power is 1.5 MW.
Based on high-speed MOSFET switches, the dual ultrafast high voltage pulses are generated with the inductive adder circuit topology. The pulses’ half-width is 300 ns, the rise time is about 60 ns and the time interval between two pulses is 600 ns. The peak pulse current could be 365 A for a load of 11.5 Ω and the corresponding output peak pulse power is 1.5 MW.
2008,
20.
Abstract:
Z-pinch and flash X-ray radiography have an important application in inertial confine fusion (ICF) and nuclear radiation effects simulation and high performance hydrodynamic test, etc. Z-pinch ICF and multi-pulse multi-axis high energy X-ray radiography put forward a huge challenge for pulsed power driver, so the direct-driven-load fast pulsed power driver are developed actively in home and abroard. The paper summarized the recent advances and developing trends of the fast pulsed power driver based on fast Marx(FMG) and fast linear transformer driver(LTD), and analysized the advantages and disadvantages and restricting factors about FMG and FLTD and their key technologies, then introduced the state-of-arts on the investigation in Northwest Institute of Nuclear Technology. In the end, the p
Z-pinch and flash X-ray radiography have an important application in inertial confine fusion (ICF) and nuclear radiation effects simulation and high performance hydrodynamic test, etc. Z-pinch ICF and multi-pulse multi-axis high energy X-ray radiography put forward a huge challenge for pulsed power driver, so the direct-driven-load fast pulsed power driver are developed actively in home and abroard. The paper summarized the recent advances and developing trends of the fast pulsed power driver based on fast Marx(FMG) and fast linear transformer driver(LTD), and analysized the advantages and disadvantages and restricting factors about FMG and FLTD and their key technologies, then introduced the state-of-arts on the investigation in Northwest Institute of Nuclear Technology. In the end, the p
2008,
20.
Abstract:
Working principle of fast linear transformer driver(LTD) is a new pulsed power technology developed recently. Status of LTD technology research is summarized. Application of LTD in such fields as Z-pinch and flash X-ray radiography are reviewed. Developments in key technologies of LTD including switch and trigger system are analyzed. The crucial technique problems that should be investigated in the future and some research approaches are presented.
Working principle of fast linear transformer driver(LTD) is a new pulsed power technology developed recently. Status of LTD technology research is summarized. Application of LTD in such fields as Z-pinch and flash X-ray radiography are reviewed. Developments in key technologies of LTD including switch and trigger system are analyzed. The crucial technique problems that should be investigated in the future and some research approaches are presented.
2008,
20.
Abstract:
A three-mirror compound configuration formed by two overlapping collinear cavities was used to achieve both 1 064 nm and 1 342 nm emission of an LD pumped Nd:YVO4 laser. According to the condition that the dual-wavelength laser oscillations possess the same threshold, the relations of cavity length and transmissivity at the output coupler of 1 064 nm cavity branch with that of 1 342 nm cavity branch was numerically calculated. The dual-wavelength lasers with 1.59 W output power at 1 064 nm and 1.17 W output power at 1 342 nm was obtained at the pump power of 13 W when the two cavity branches were optimized. The parameters of the compound resonator Nd:YVO4 laser with the intracavity sum-frequency mixing was calculated under the condition that the photon number densities of 1 064 nm and 1 34
A three-mirror compound configuration formed by two overlapping collinear cavities was used to achieve both 1 064 nm and 1 342 nm emission of an LD pumped Nd:YVO4 laser. According to the condition that the dual-wavelength laser oscillations possess the same threshold, the relations of cavity length and transmissivity at the output coupler of 1 064 nm cavity branch with that of 1 342 nm cavity branch was numerically calculated. The dual-wavelength lasers with 1.59 W output power at 1 064 nm and 1.17 W output power at 1 342 nm was obtained at the pump power of 13 W when the two cavity branches were optimized. The parameters of the compound resonator Nd:YVO4 laser with the intracavity sum-frequency mixing was calculated under the condition that the photon number densities of 1 064 nm and 1 34
2008,
20.
Abstract:
A transmitting antenna with tapered fiber is proposed to transform the divergence partially coherent light formed by multi-mode fiber to collimate light. This structure can produce a partially coherent light of low divergence and guarantee the output power of laser transfers completely. It is applicable to laser communication in atmosphere. Based on the ray tracing method, the divergence angle of random rays which incidents on the small section of tapered fiber in tapered fiber is analyzed. The propagation property of all the rays incidents on the small section and the angle of incidence less than numerical aperture angle are investigated. The result shows that the emission angle of these rays could be improved to less than the half of the taper angle in theory, if the length of the tapere
A transmitting antenna with tapered fiber is proposed to transform the divergence partially coherent light formed by multi-mode fiber to collimate light. This structure can produce a partially coherent light of low divergence and guarantee the output power of laser transfers completely. It is applicable to laser communication in atmosphere. Based on the ray tracing method, the divergence angle of random rays which incidents on the small section of tapered fiber in tapered fiber is analyzed. The propagation property of all the rays incidents on the small section and the angle of incidence less than numerical aperture angle are investigated. The result shows that the emission angle of these rays could be improved to less than the half of the taper angle in theory, if the length of the tapere
2008,
20.
Abstract:
The theoretical model of anomalous hollow beams proposed by Cai in the paraxial approximation is extended to the nonparaxial regime. The closed-form propagation expression for nonparaxial vectorial anomalous hollow beams in free space is derived and used to study their propagation properties in free space. It is found that anomalous hollow beams can not preserve their shape upon propagation, but the paraxial approximation condition for anomalous hollow beams additionally depends on the propagation distance, which is different from Gaussian beams. The far-field beam quality of nonparaxial vectorial anomalous hollow beams can be described by the power in the bucket(PIB), which decreases with increasing the f parameter (the ratio between wavelength and beam maist width).
The theoretical model of anomalous hollow beams proposed by Cai in the paraxial approximation is extended to the nonparaxial regime. The closed-form propagation expression for nonparaxial vectorial anomalous hollow beams in free space is derived and used to study their propagation properties in free space. It is found that anomalous hollow beams can not preserve their shape upon propagation, but the paraxial approximation condition for anomalous hollow beams additionally depends on the propagation distance, which is different from Gaussian beams. The far-field beam quality of nonparaxial vectorial anomalous hollow beams can be described by the power in the bucket(PIB), which decreases with increasing the f parameter (the ratio between wavelength and beam maist width).
2008,
20.
Abstract:
Experimental studies on the transmittance and reflectivity of COIL mirrors have been done using of the HITACHI U-4001 spectrophotometer and the high reflectivity meter based on cavity ring down spectroscopy, such as experiments of the effects of film uniformity, pollution, and so on. Experimental results show that the ion beam sputtered film is more stable than the electron gun evaporated film. The deposition time has no obvious effect on transmittance and reflectivity of films when the mirrors are put in the dry place.
Experimental studies on the transmittance and reflectivity of COIL mirrors have been done using of the HITACHI U-4001 spectrophotometer and the high reflectivity meter based on cavity ring down spectroscopy, such as experiments of the effects of film uniformity, pollution, and so on. Experimental results show that the ion beam sputtered film is more stable than the electron gun evaporated film. The deposition time has no obvious effect on transmittance and reflectivity of films when the mirrors are put in the dry place.
2008,
20.
Abstract:
The reflectivity of the fiber ends was estimated by studying the technology of fiber end polishing and lapping. Based on rate and propagation equations of the Ybdoped fiber amplifier, the effect of the fiberend reflectivity on the output characteristics induced by the error of the polishing angle was simulated numerically. The results show that both reducing the reflectivity of the fiber end and increasing the power of the input signal can reduce the amplified spontaneous emission and restrain the selfoscillations. The performance of the high power fiber amplifier can be improved by choosing the angle of the fiber end inclined-surface polished and the power of the input signal properly．
The reflectivity of the fiber ends was estimated by studying the technology of fiber end polishing and lapping. Based on rate and propagation equations of the Ybdoped fiber amplifier, the effect of the fiberend reflectivity on the output characteristics induced by the error of the polishing angle was simulated numerically. The results show that both reducing the reflectivity of the fiber end and increasing the power of the input signal can reduce the amplified spontaneous emission and restrain the selfoscillations. The performance of the high power fiber amplifier can be improved by choosing the angle of the fiber end inclined-surface polished and the power of the input signal properly．
2008,
20.
Abstract:
The far-field characteristics of a diode laser bar(DLB) (type JOLD-60-CPNN-1L) beam are studied both experimentally and theoretically. Experiments show that beams emitted from the 19 diodes, which compose the DLB, propagate nearly independently. The far-field intensity distribution of the DLB can be treated as the incoherent superposition of 19 individual beamlets and does not vary with time. The distances between the illumination zones are unequal. The theoretical model is improved in accordance with the experiments. The experimental results at low input current are compared with the numerical calculation results using the improved theoretical model and they are consistent with each other.
The far-field characteristics of a diode laser bar(DLB) (type JOLD-60-CPNN-1L) beam are studied both experimentally and theoretically. Experiments show that beams emitted from the 19 diodes, which compose the DLB, propagate nearly independently. The far-field intensity distribution of the DLB can be treated as the incoherent superposition of 19 individual beamlets and does not vary with time. The distances between the illumination zones are unequal. The theoretical model is improved in accordance with the experiments. The experimental results at low input current are compared with the numerical calculation results using the improved theoretical model and they are consistent with each other.
2008,
20.
Abstract:
Molecular filtered Rayleigh scattering(FRS) is an optical technique that utilizes the light scattering by atoms/molecules to allow the computation of thermodynamic properties and velocity in flow fields. The main components of diagnostics system are a narrow line-width laser, a molecular/atomic absorption filter and a collecting device such as ICCD, which can be used to suppress background surface/particle scattering and enhance flow visualization. In this paper, FRS working principle, the FRS diagnostic system and the iodine filter cell are described. On the basis of diagnosing FRS image and measuring iodine vapor absorption spectrum, methane/air premixed flame is diagnosed and the 2-dimension temperature and density fields are obtained. The temperature measured is compared with the resul
Molecular filtered Rayleigh scattering(FRS) is an optical technique that utilizes the light scattering by atoms/molecules to allow the computation of thermodynamic properties and velocity in flow fields. The main components of diagnostics system are a narrow line-width laser, a molecular/atomic absorption filter and a collecting device such as ICCD, which can be used to suppress background surface/particle scattering and enhance flow visualization. In this paper, FRS working principle, the FRS diagnostic system and the iodine filter cell are described. On the basis of diagnosing FRS image and measuring iodine vapor absorption spectrum, methane/air premixed flame is diagnosed and the 2-dimension temperature and density fields are obtained. The temperature measured is compared with the resul
2008,
20.
Abstract:
The gain characterization of photonic crystal fiber amplifier is theoretically and experimentally studied by using double-side pumped technique. The gain curves for different pumping power and different signal lights are obtained experimentally. When the power of the probe light is 6 W and the total pump power is 150.2 W, the output power, up to 72 W and the slope efficiency 60%, have been achieved eventually with double-side pumped. It is found in the experiment that when the total pump power is increased over a certain value, the parasitic oscillation and the self-pulsation are observed in the amplifier, because of the resonant cavity caused by the surface reflection of fiber and nonlinear effect, and in turn this degrades the system performance.
The gain characterization of photonic crystal fiber amplifier is theoretically and experimentally studied by using double-side pumped technique. The gain curves for different pumping power and different signal lights are obtained experimentally. When the power of the probe light is 6 W and the total pump power is 150.2 W, the output power, up to 72 W and the slope efficiency 60%, have been achieved eventually with double-side pumped. It is found in the experiment that when the total pump power is increased over a certain value, the parasitic oscillation and the self-pulsation are observed in the amplifier, because of the resonant cavity caused by the surface reflection of fiber and nonlinear effect, and in turn this degrades the system performance.
2008,
20.
Abstract:
Theoretical expressions for the key performance parameters(spatial resolution and imaging efficiency, et al) of a laser-driven-monochromatic X-ray backlighting system were deduced and the relationship beteween these parameters were analyzed when the optical parameters varied. An optimum design method for the system was then proposed based on the maxmum of the spatial resolution ability with the constraint of obtaining a well image(the exposure intensity is greater than the sensitivity of the detector). Two backlighting systems with photon energy of 5.07 keV and 5.41 keV were designed using this method and the ray tracing results show that both systems can achieve a spatial resolution smaller than 10 μm in about 1 cm2 field of view.
Theoretical expressions for the key performance parameters(spatial resolution and imaging efficiency, et al) of a laser-driven-monochromatic X-ray backlighting system were deduced and the relationship beteween these parameters were analyzed when the optical parameters varied. An optimum design method for the system was then proposed based on the maxmum of the spatial resolution ability with the constraint of obtaining a well image(the exposure intensity is greater than the sensitivity of the detector). Two backlighting systems with photon energy of 5.07 keV and 5.41 keV were designed using this method and the ray tracing results show that both systems can achieve a spatial resolution smaller than 10 μm in about 1 cm2 field of view.
2008,
20.
Abstract:
The damaged sites located on input and exit surface have been irradiated respectively with 355 nm pulse laser. After each shot, photograph of growth of the damaged site has been taken and the area of the damaged site has been measured. Experimental results show exponential growth in the lateral size of damage sites located on exit surface with shot number, whereas linear growth in the lateral site of damage sites located on input surface.
The damaged sites located on input and exit surface have been irradiated respectively with 355 nm pulse laser. After each shot, photograph of growth of the damaged site has been taken and the area of the damaged site has been measured. Experimental results show exponential growth in the lateral size of damage sites located on exit surface with shot number, whereas linear growth in the lateral site of damage sites located on input surface.
2008,
20.
Abstract:
The scattering of few-cycle laser pulse by single electron has been investigated through the classical theory of Thomson scattering using free electrons. The temporal and spatial characteristics of the radiation are presented for different laser intensity and initial phase. For low power-intensity laser pulses, the radiation pattern is the same as that from a dipole antenna. However the radiation pattern is three leafs for the high laser intensity. The influence of the initial phase on the temporal and spatial characteristics of the radiation is stronger for the high intense laser pulse than for the low intense case.
The scattering of few-cycle laser pulse by single electron has been investigated through the classical theory of Thomson scattering using free electrons. The temporal and spatial characteristics of the radiation are presented for different laser intensity and initial phase. For low power-intensity laser pulses, the radiation pattern is the same as that from a dipole antenna. However the radiation pattern is three leafs for the high laser intensity. The influence of the initial phase on the temporal and spatial characteristics of the radiation is stronger for the high intense laser pulse than for the low intense case.
