Model of a disk-shaped explosive magnetic generator with a submicrosecond current pulse magnetodynamic shaper in a liner load

A model of a disk-shaped explosive magnetic generator 400 mm in diameter with an initial energy storage capacity of about 40 MJ is considered. The generator is integrated with a cumulative current pulse shaper and is also equipped with a remote magnetodynamic interrupter. Calculations show that this generator is capable of forming current pulses with an amplitude of up to 20 MA and a rise time of about 130 ns in finiteinductance (～10 nH) dynamic loads. This allows rapid (for about 60 ns) compression of light (20–30 mg) liners to generate intense beams of soft X rays. Results obtained using a computational model of the magnetodynamic interrupter, which is the key component of the generator, are verified experimentally.     

Brunel-dominated proton acceleration with a few-cycle laser pulse

Experimental measurements of backward accelerated protons are presented. The beam is produced when an ultrashort (5 fs) laser pulse, delivered by a kHz laser system, with a high temporal contrast (10(8)), interacts with a thick solid target. Under these conditions, proton cutoff energy dependence with laser parameters, such as pulse energy, polarization (from p to s), and pulse duration (from 5 to 500 fs), is studied. Theoretical model and two-dimensional particle-in-cell simulations, in good agreement with a large set of experimental results, indicate that proton acceleration is directly driven by Brunel electrons, in contrast to conventional target normal sheath acceleration that relies on electron thermal pressure.     

磁脉冲压缩器在卤化铜激光器上的应用

在卤化铜激光器脉冲放电电源系统中，为减轻闸流管的工作负担并同时保证电路的快放电激励，采用了单级磁脉冲压缩器.分析了磁脉冲压缩器的工作机理，介绍了所采用磁脉冲压缩器的设计考虑及参数选用. 关键词： 磁脉冲压缩器 闸流管 CuBr激光器     

Design and simulation of a C-band pulse compressor

The design and optimization procedure of a pulse compressor is presented. A C-band (5712 MHz) pulse compressor using a TE_0;1;15 mode cylindrical cavity with dual side-wall coupling irises has been designed. Also the coupling coeffcient, position of the short plane and size of the bottom groove have been optimized by using HFSS.     

Analysis and simulation of a coupled-cavity pulse compressor

An equivalent circuit model is built for a coupled-resonator pulse compressor. Based on the circuit, the general second order differential equation is derived and converted into the first order equation to save computing time. In order to analyze the transient response and optimize parameters for the pulse compressor, we have developed a simulation code. In addition, we have also designed a three-cavity pulse compressor to get the maximum energy multiplication factor. The size of the cavities and coupling apertures is determined by HFSS.     

Ponderomotive acceleration of electrons by a whistler pulse

A Gaussian whistler pulse is shown to cause ponderomotive acceleration of electrons in a plasma when the peak whistler amplitude exceeds a threshold value and the whistler frequency is greater than half the cyclotron frequency, ω>ω _c /2. The threshold amplitude decreases with the ratio of plasma frequency to electron cyclotron frequency, ω _p /ω _c . However, above the threshold amplitude, the acceleration energy decreases with ω _p /ω _c . The electrons gain velocities about twice the group velocity of the whistler.     

On the resonance and operational behavior of an oscillating electrodynamic compressor

A mathematical model of a single piston oscillating compressor is presented. The compressor is of the electrodynamic type. The model results in a set of non-linear equations in terms of piston displacement and current amplitude. The equations are solved by an iterative algorithm. Measurements on an existing compressor verified some of the results of the mathematical model. The mathematical model explains certain perculiarities of behavior of this type of compressor, observed directly or reported elsewhere in the literature.     

The electrodynamic response of heavy-electron materials with magnetic phase transitions

We have investigated the electrodynamic response of the heavy-electron compounds U₂Zn₁₇, UPd₂Al₃, UCu₅ and URu₂Si₂. Particular emphasis has been devoted to the optical evidence of the antiferromagnetic phase transitions at T_N = 9.7 K, 14 K, 15 K and 17 K for U₂Zn₁₇, UPd₂Al₃, UCu₅ and URu₂Si₂, respectively. In the excitation spectrum of UCu₅ and URu₂Si₂, we found an absorption in the far-infrared, which develops below T_N and is ascribed to the excitation across a spin-density-wave type gap, suggesting that the antiferromagnetic phase transition might be itinerant in nature, and invokes a Fermi surface instability. Since this gap-like feature is absent in U₂Zn₁₇ and UPd₂Al₃, we argue that these latter compounds belong to a characteristically different class of antiferromagnets, representative of the heavy-electron compounds with an ordering of essentially localized magnetic moments. The antiferromagnetic ordering then leads to a suppression of the spin-flip mechanism below T_N. At low temperatures, we observe for all compounds the formation of a narrow Drude-like resonance in the optical conductivity, which is ascribed to the electrodynamic response of the heavy-quasiparticles, and is indicative of the progressive development of the manybody coherent Kondo state, coexisting with both types of magnetic ordering. In this review, we also present the evolution of the optical properties due to Ni- and Redoping in UCu₅ and URu₂Si₂, respectively. The optical evidence of the itinerant antiferromagnetic ordering is suppressed in both compounds upon doping and particularly for the URu₂Si₂ compound this is consistent with a crossover to a ferromagnetic ground state upon Re-doping.     

Three-dimensional magnetic field enhancement in a liner implosionsystem

The magnetic field enhancement is calculated for a magnetically imploded liner system that has flux excluding radial vanes. For the thinnest vane tested the field is found to concentrate at the vanes to a maximum value of almost three times its ambient value with a corresponding temperature increase well above the melting point. These values are calculated using the three-dimensional magnetohydrodgnamic code, MACH3. Calculations are performed for three vane thicknesses, and the vane movement is estimated. A bound is established on the design specification of the vanes based the disruption of current delivery to the liner due to the movement of the vanes     

Nonlinear electrodynamic lag of electromagnetic signals in a magnetic dipole field

We investigate the propagation of electromagnetic waves in the magnetic dipole and gravitational fields of a neutron star, which follows the laws of nonlinear electrodynamics in a vacuum. Electromagnetic signals in these fields are shown to propagate along different rays and at different velocities, depending on their polarization. We found the law of motion for these signals along rays. We calculate the difference between the propagation times of electromagnetic signals with different polarizations from the same source to the detector. This difference is shown to reach a measurable value of 1 μs in some cases.     

Dispersion control of a pulse stretcher– compressor system with two-dimensional spectral interferometry

The frequency dependence of the group delay of both a pulse stretcher and a stretcher–compressor system of a chirped pulse amplification laser is determined with a two-dimensional extension of a spectral interferometric method called the stationary phase point method. The 800-nm, 15-fs probe pulse from a Ti:S oscillator propagates through the stretcher or the stretcher–compressor system. The reference pulse is one of the subsequent oscillator pulses but passes the system and interferes with the probe pulse; hence, a Mach–Zehnder-type interferometer is formed. The shape of the spectrally resolved interference fringes is peculiar to the amount and sign of the relative dispersion properties of the pulses. Group-delay dispersion is obtained from the observation of the position of the stationary phase point in spectrally resolved interferograms at different time delays. This simple method allows for an almost complete and fast alignment of the stretcher–compressor system from scratch until the final adjustments. PACS 42.65.Re     

RF study of a C-band barrel open cavity pulse compressor

This paper focuses on the RF study of a C-band barrel open cavity(BOC) pulse compressor. The operating principle of BOC is presented and the technical specifications are determined. The main parts of BOC such as the cavity, the matching waveguide, the coupling slots and the tuning rings were numerically simulated by 3-D codes software HFSS and CST Microwave Studio(MWS). The "whispering gallery" mode TM6,1,1 with an unload Q of 100000 was chosen to oscillate in the cavity. An energy multiplication factor of 1.99 and a peak power gain of6.34 was achieved theoretically.     

Formation of an external source by a hard radiation pulse in an electrodynamic problem

A method is proposed for calculating an external source that forms when hard radiation is absorbed by matter. The relevant electrodynamic problem is solved by numerical modeling. It is shown that the current density vector can be localized in space and time.     

Linear frequency-modulated pulse compressor based on a three-mirror ring cavity

A pulse compressor using a three-mirror cavity is tested at a frequency of 34.27 GHz and a low power level. The cavity is fed by a wave beam reflected from the corrugated mirror. The fourfold compression of a rectangular chirp is reached with an efficiency of ≈60%.     

Fine tuning of the higher-order dispersion of a prismatic pulse compressor

The wavelength-dependent thermal refractive index gives an extra degree of freedom for adjustment of higher-order dispersion of a prismatic pulse compressor. The effect allows of fine tuning of both intracavity and extracavity dispersion of ultra-fast oscillators. The calculations have been carried out using a new and rather handy formalism, which describes the operation of a prism pulse compressor as a linear function of the ratio of the total glass path in the prisms and the prism apex distance. The validity of theoretical calculations is supported by experimental evidence. Received: 16 April 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +36-62/544658, E-mail: osvay@physx.u-szeged.hu     

Steady state ion acceleration by a circularly polarized laser pulse

The steady state ion acceleration at the front of a cold solid target by a circularly polarized flat-top laser pulse is studied with one-dimensional particle-in-cell (PIC) simulation. A model that ions are reflected by a steady laser-driven piston is used by comparing with the electrostatic shock acceleration. A stable profile with a double-flat-top structure in phase space forms after ions enter the undisturbed region of the target with a constant velocity.     

一种耦合度可调节的微波脉冲压缩装置设计及实验

针对有源能量倍增器法(SLED)脉冲压缩实验中对储存能量阶段和释放能量阶段耦合度调节的需求,利用支臂短路波导H-T的调配功能,设计了一种耦合度可调节的SLED脉冲压缩装置。基于散射矩阵理论,分析了支臂短路波导H-T对SLED脉冲压缩装置耦合度的调节能力。利用大功率波导环形器代替3 dB耦合器,进行了基于单储能腔的无源SLED脉冲压缩实验,实验结果表明,支臂短路波导H-T对耦合度的调节能力与理论分析相吻合。