Showing papers in "High Power Laser and Particle Beams in 2004"

Fitting method of the simulated HEMP waveform by the double-exponential function

Abstract: An important nature of the double-exponential function, which is used to describe the typical high-altitude electromagnetic pulse (HEMP) waveform in many standards and publications, is studied by the numerical method. Based on the function nature it is discussed in details the relation of the physical parameters of the simulated HEMP waveform and the character parameters of the double-exponential function. Here the physical parameters of HEMP include peak value, rise time, fall time and full-width at half-maximum amplitude (FWHM). A simple and effective method is proposed to evaluate the character parameters of the function from the physical parameters. And it's effectivity and reliability is validated by evaluating the HEMP parameters defined by IEC and by the numerical fitting of a measured simulated data. The method can be applied to fit the simulated HEMP waveforms of various peak values, rise times and FWHM.

Investigation of deformation experiment for active polishing lap

Abstract: In optics polishing process, the active lap can reshape the profile for fitting the surface of large aspheric optical component with different local position and rotating angle in real time. In this way, the high order residual error by traditional polishing technique can be overcome. In this paper, the working process of active lap is modeled. The deforming capability of the active lap matching a parabolic mirror, diameter 1.3m and F/2, is simulated and verified by experiment. The results show the active 1ap can reshape the quadratic curved figure, both symmetrically and dissymmetrically with high precision. The residual errors of deflection are analyzed.

Self-integrating Rogowski coil for nanosecond current measurement

Abstract: This paper introduces the advantage, purpose, principle and design of self-integral Rogowski coil for ns-level current measurement. The response and distribute of Rogowski coil are discussed. The coil with a shield is treated as a distributed circuit, so that the toroidally wound coil acts as a delay line. The coil is calibrated. This coil could get the signal with rise time less than 2ns, value 10A～40kA, sensitivities about 1.4mV/A, pulsed width less than 200ns. The coil can be used in pulsed power technology for ns-level high current measurement.

Analysis and design of series resonant charging power supply

Abstract: This paper firstly derives expressions of current and voltage at various work modes for the series resonant charging power supply, gives recursion formulas calculating the value of current and voltage at various periods; secondly, utilizing recursion formulas, it makes out that the power supply characterizes pulse constant current charging; thirdly, this paper calculates the parameters of the power supply when capacitor-load incompletely discharge, the power supply provides half the maximum output when capacitor-load completely discharge, and provides maximum output to maintain the voltage of capacitor-load; at last, describes a 100Hz steady operation power supply for accelerator utilizing Tesla transformer, measured results and calculated results are well consistent.

Analysis on shielding effectiveness of aperture arrays with different shapes

Abstract: It is important to study the shielding effectiveness to reduce the electromagnetic interference and to protect electronic components. In this paper the shielding effectiveness of aperture arrays on different shapes is calculated and analyzed. The effects of the spaces between the adjacent apertures are analyzed. The results show that the penetration coefficient (PC) of a circle aperture array is the smallest, the one of a square aperture array is medium, and the one of a honey aperture array is the biggest, but their spectrums are almost the same. While for a dumbbell aperture array, because the contour shape is very different with the former aperture arrays, its magnetic current distribution is very different with the other’s. Thus the PC of a dumbbell aperture array is bigger than the ones of the former three others, and the PC’s spectrum at high frequency is also changed a lot. In addition, when the space between the apertures adds, the mutual coupling between the apertures becomes week, and the field coupled into the shielding enclosure also becomes small.

Inter-comparison of models for radiative transfer in the atmosphere

Abstract: The characteristics and limits of the general three models of radiative transfer in the atmosphere are discussed. Numerical tests were carried out by means of both the radiative transfer's law and the transmittances measurements in the real atmosphere. The results show that there are very good agreements between the transmittance measured in the fields and calculated by the model for COIL and HF overtone 20P4 lines, but big error for HF overtone 20P5. Moreover, the significant influence of aerosol types on transmittance of the laser beam through the atmosphere is studied.

Reconstruction of electromagnetic pulse waveform based on the amplitude spectrum data

Abstract: Measured CW amplitude spectrum data are often obtained in EMP research, especially in effects experiments and probe calibration. This paper investigates the minimum phase reconstruction of the transient waveform from amplitude spectrum data. This technique involves the use of Hilbert transform, an assumption of minimum phase and cepstrum. The reconstruction of minimum phase signal, such as the HEMP waveform, cosine or sine exponentially damped waveform etc, shows good agreement with the original. For non-minimum phase signal, the total energy, the approximate amplitude and shape of the waveform can be indicated although the rise (fall) time and peak value are different from the original.

Study of average time and source data differentiation in measuring atmospheric optical turbulence

Abstract: To measure the atmospheric optical turbulence, the micro-temperature sensor is often used. But statistic average time can affect the measuring results of temperature structure constants. From analyzing the source data the average time can be set as 5～15 seconds. In the measuring period of micro-temperature, the results will be erroneous when the environmental influence exists or the instrument state is not proper. Most of these situations can be found out from the source data analysis. One method of data differentiation was presented and discussed. First, error data was removed according to the experiment records. Second, if some data was abnormally large or small, the spectrum of source data of temperature difference was used to determine the facticity of data. These two steps could ensure the reliability and authenticity of the data.

Faint targets detection based on gray morphological filtering and neighborhood entropy method

Abstract: A new method of faint-target detection is put forward. To improve the practicality of the method, especially it is used to deal with those images that involves the complex background and a lot of noise, the method of neighborhood entropy was brought forward. Furthermore, to increase the validity of it, this method was combined with gray morphological filtering. First ,the image is processed with morphological filtering. Second, the neigborhood entropy is calculated. And then, the target is detected according to the maximum value and minimum value of entropy. The experiment results indicated the new method can detect small target stably and guickly.

Effect on air refraction index by effective electric-field intensity in high power microwave propagation

Abstract: The intense field of high power microwave causes ionization of neutral particle in atmosphere and the plasma comes into being The ionization frequency of neutral particle relates to electric field intensity and atmospheric pressure This paper presents the interaction between electron and air neutral molecules in comparatively wide region When an impulse of high power microwave is propagated, the variation of electron concentration and refractive index accompanying with that of effective electric-field also intensity is also introduced

Study of beams automatic alignment in four-pass amplifiers

Abstract: Laser beam automatic alignment systems are used to align the SG-Ⅲ prototype facility laser. Considering the facility qequirement, combining the key technique of automatic alignment, according to the image relay of the pinhole, utilizing the optical position and the spatial location of the four pinholes of the main spatial filter in the four-pass beam in the SG-Ⅲ, this paper presents a reasonable scheme for automatic aligning in the four-pass amplifier, which has been fully checked on the multi-pass amplifier experiment system.The centering sensitivities of the system are less than 0.5% of the beam diameter. The pointing sensitivities of the system are less than 10μm.

Nonlinear hot holographic image in high power solid-state laser systems

Abstract: A theoretical analysis and results of numerical calculations for the hot image formation in high power solid-state laser system are presented. According to holographic imaging theory, an approximately functional expression for the hot image intensity from opaque scatterer is derived, showing an intensity several times as much as the background light intensity. The hot image appears in a plane located downstream from the nonlinear medium at a distance equal to that from the scatterer to the medium. It is found that the hot image intensity and location are accurately predicted by theory and numerical calculations.

Development and experimental research on the fast rise time EMP generator

Abstract: A novel high voltage pulse generator is developed for the simulation of HEMP according to the standard of IEC61000-2-9 and MIL-STD-461E. The generator can produce both single and repeated pulse. Its double-exponential output has a rise time less than 3ns, with the pulse width around 58ns and amplitude up to 4kV. It can also generate square wave with rise time less than 2ns and amplitude up to 4kV. The circuit design and experimental test of the pulse generator are introduced in this paper. The test result is also presented to show the difference of the interference effect produced by the new generator and the original HEMP defined in MIL-STD-461D.

Image matching based on multi-features fusion

Abstract: The conventional methods of image matching are based on gray and shape of image. These two features can't describe image data well especially in tracking the faint and small targets. It's difficult to track the target with high-precision and steady. In this paper, a new algorithm of image matching was proposed. It extracts characters including gray and shape from image data and gains an integrated character using the information fusion algorithm with simplicity and effect. Then calculates the position coordinate of target using integrated characteristics by correlation degree. Simulation shows that the method is feasible and effective.

Study on mechanism of electrode erosion of high-power gas spark gap switch

Abstract: From thermodynamics, the electrode erosion process of high-power gas spark gap switch is analysed in theory. The simplified mathematical model is built and solved numerically, the relations between electrode erosion depth and some characteristics of electrode materials such as density, specific heat, melting point, boiling point, thermal conductivity, and so on, are studied. The capabilities of three common electrodes (made of Cu, W, and Al) to resist erosion are compared, which indicates that a ranking of the erosion rate for three materials, from least to greatest, is W, Cu, Al.

Finite element analysis of thermal distortion of infrared CW laser reflectors

Abstract: Based on the thermal conduction equations and thermal-elastic equations, while the laser speckle radius on the reflectors are much larger than or almost approximate to the thermal diffusion lengths of the substrate materials, and while the reflectors boundaries are constrained or unconstrained, the maximum temperature rise, thermal distortion and thermal stress of silicon- or silica-based multi-layered infrared CW laser reflectors are calculated by a finite element analysis method. And the dependences of these parameters on the laser speckle radius is discussed. The results indicate that the ultimate axial displacements on the surfaces of the reflectors are approximately linear with the incidence beams radius while the reflectors have unconstrained boundarties, but the ultimate thermal stress in the reflectors are approximately linear with the radius for constrained boundaries. The influences of the reflector tackling states on these two parameters increase while the beam radius increases. Irradiated by the same laser sources and under the same boundary conditions, the silicon reflectors have lower temperature rise or higher thermal damage threshold but higher thermal distortion ratio than the silica ones.

Experimental investigation of a compact L-band magnetically insulated transmission line oscillator

Abstract: A compact L-band magnetically insulated transmission line oscillator(MILO),which has a new-type mode converter and a vew-type beam dump which increases a beam dump disk,a noe-cavity RF choke and a carefully designed impedance discontinuity between the choke-vane section and the SWS-vane section, is experimentally investigated The compact MILO is driven by a self-built 600kV, 8Ω, 100ns pulser:SPARK-01When the input voltage is 515～538kV, and the diode current is 58～61kA, high power microwaves of the TM_(01) mode are generated from the device with a frequency of 176～178GHz, an output power of 22～25GW, and the power conversion efficiency of 73%～79% in experiments In this case, the duration of the effective voltage (above the threshold voltage, 500kV) is 30ns, and the duration of the radiated microwave is 15ns (FWHM) The experimental results agree well with that of simulation

Precise measurement of the effective area of laser spot

Abstract: The system for effective area measurement of laser spot on target plane was designed based on the definition of effective area. A 12-bit CCD camera is used for the effecive area measurement. A bmp image of the beam profile is stored. This image is processing by software to evaluate the ratio of total energy and peak fluence (effective area). Some test results were given using effective area measurement system. The system was employed in the laser induced damage threshold test and it is helpful to improving the precision of laser induced damage threshold test.

Simulation of different electromagnetic pulse couplingto the finite cable near ground

Abstract: In this paper, the induced current in the finite cable near ground is calculated by FDTD method when exposed to HEMP,HPM and UWB pulse respectively. The numerical results indicate that the induced current varies with the length of cable, incident angle and the conductivity of ground. With the same electric field intensity, the HEMP induced current is the largest one among the three induced currents. There's almost no comparable difference between the induced currents in the 5m and 20m cable when exposed to HPM and UWB pulse. The larger the conductivity of ground is, the more quickly the induced current attenuates. When the cable is grounded at one end the current at the grounded end will increase.

Deduction of formulas for electrical parameters of common-vertex-coaxial-circular-cones-like and disk-like ideal transmission lines

Abstract: The paper has derived the formulas from Ampere's Law and Gauss law, which are used to evaluate the electrical parameters of common-vertex-coaxial-circular-cones-like and disk-like ideal transmission lines, such as capacitance, inductance and impedance. However, some of these formulas are analytical expressions while the others are only some method to get numeric solution. The expressions or method has been validated by a practical example and sequentially used to evaluate a new design.

Degradation failure model of self-healing metallized film pulse capacitor

Abstract: The high energy density self-healing metallized film pulse capacitor has been applied to all kinds of laser facilities for their power conditioning systems, whose reliability and expense are straightforwardly affected by the reliability level of the capacitors. Based on the related research in literature, this paper analyses the degradation mechanism of the capacitor, and presents a new degradation failure modelthe Gauss-Poisson model.The Guass-Poisson model divides degradation of capacitor into naturalness degradation and outburst one.Compared with traditional weibull failure model, the new model is more precise in evaluating the lifetime of the capacitor, and the life tests for this model are simple in design, and lower in the cost of time or expense.The Gauss-Poisson model will be a fine and widely used degradation disable model.

Analysis on thermal effect and stress-birefringence of laser window

Abstract: The phaseshifts induced by thermal effect and pressure difference between outer-surface and inner-surface of plane laser window are analysed. The phaseshifts caused by stress-birefringence are discussed in detail. Distributions of temperature increment, stress, phaseshifts, Strehl-ratio and depolarization are calculated.It is indicated that window deformation and refractive index changing with temperature are primary factors of phaseshifts and result from non-uniformity of temperature increment, making beam quality declining. Stress-birefringence is related with Miller indices of laser window surface, which results in depolarization and also affect beam quality.

Lifetime testing of high power diode laser

Abstract: This paper introduces a failure mechanism of defferent modes and lifetime test methods for high power diode laser.The diode laser lifetime is tested.According to the experimental result and degradation rate to calculate,out power of QCW diode laser reach 91W and 1.16W/A of slope efficiency,the average lifetime is 2.19×10~9 shots at room temperature,when the operating current is 90A,10% duty-cycle(500Hz,200μs). But the average lifetime of DL reduce to 1.65×10~9 when the actual temperature is 35℃.Experimental results and analysis show that the environment temperature,deposit solder and multiple layers welding in the package technology are the key point to the reliability of diode laser.\;

Computer simulation of electron beam characteristics focused by periodic permanent magnets

Abstract: A fully three-dimensional (3-D) of an electron beam optical model focused by a periodic permanent magnet (PPM) stack has been developed using 3-D particle-in-cell (PIC) code of MAFIA, the static magnetic field and electron beam transmission characteristics were simulated using static solver and PIC module. The characteristics of the electron beam confined by the PPM stack are analyzed and the effects of the peak magnetic flux density, magnetic tapering, initial transversal velocity distribution are mainly discussed. Some useful data are obtained for the PPM stack engineering design and optimization.

Study on 3-D MAFIA PIC simulation for microwave tube electron gun

Abstract: After analyzing the design process with previous electron beam optics simulation and modeling tools and their shortcomings, this paper presents that MAFIA PIC simulation is a more accurate method as it can wholly support space-charge-limited (Child's law) and temperature-limited emission, cathode thermal initial velocity and non-laminar flow. The 3-dimensional time-dependent PIC code is also desired for studying the beam transient and noise character. Using MAFIA PIC code to simulate an electron gun, some useful data are obtained, which show that the simulation results are close to the experimental data within acceptable error range. It can be used to instruct the engineering design of microwave tube electron optics.

Influence of laser window's thermal lensing effect on beam quality

Abstract: This paper concerns the thermal lensing effect that occurs as laser going through an optical window, and its influence on beam quality. By the method of impetus theorem, 2D solution of the thermal conduction equation is derived, in the form of generalized Fourier series. Then, the finite element method is applied to simulate the thermal deformation as a plane-stress problem. Combined with the thermal deformation and the shift of the refractive index with the temperature, the wavefront distortion is calculated without considering the optic-stress effect. Furthermore, the beam quality on far field is discussed. Temperature rise, thermal deformation, wavefront distortion and beam quality of fused quartz(SiO_2) window and white bijou(Al_2O_3) window irradiated by the annulus beam are simulated as examples. The influence of cooling window, the laser output duration and spatial gradient of the beam energy intensity, and material parameters on the beam quality is analyzed.

Simulation of non-linear winding with magnetic core by PSpice

Abstract: The cavity around magnetic cores in linear induction cell act as a non-linear winding when the pulses come. This paper explains how to create PSpice model by its normal parts to simulate a non-linear winding with magnetic core, with a flux switch, the model take into account factors such as saturation, hysteresis and the power losses caused by frequency. By change some pellucid parameters, this model can work in different frequency. This paper also gives some practive examples.

Study on the PFM and PWM driver circuit of LD for laser fuze

Abstract: Because of the needs of variable pulse width, variable frequency and variable power of LD in the laser fuze communication systems, a model of the driver circuit is brought out for the system based on the circuits's principle. Using retriggerable monostable multivibrators to provide the trigger signal and double MOS driver to drive the LD, with a lot of experiments, emulations and comparisons, the variable frequency, pulse width and power driver circuit is designed. And the pulse frequency and width can be changed easily for its situations. The dirver circuit has large range frefuency modulated from 10Hz to 2kHz and large range pulse width modulated from several nanoseconds to several hundreds nanoseconds. So the whole system capability and reliability can be improved greatly.

Generation of high power ulta wide-band bipolar pulse with chopping-peaking switch

Abstract: This paper presents the chopping-peaking type high power bipolar pulse former, and studies its operating principle.The bipolar pulses with different forms are gained through adjusting the conduction time. In ideal condition, the output bipolar high voltage pulses with the peak-peak voltage between the peaks of unlike polarity is twice the voltage of the injecting pulse. By tuning the gaps of chopping switch and peaking switch properly, the highest peak-peak voltage of 360kV is obtained with the injecting voltage of 205kV. The duration of the bipolar pulse can be changed,it's maximum is equal to the width of the injecting pulse.The steeper the injecting pulse,the higher the peak-peak voltage of the generated bipolar voltage pulse.