An injection-seeded high-repetition rate Ti:Sapphire laser for high-resolution spectroscopy and trace analysis of rare isotopes

An injection-seeded high-repetition rate (～10 kHz) Ti:sapphire laser with a spectral bandwidth of ～20 MHz and an average output power of above 1.5 W has been developed. We report on its demonstration and characteristics with respect to the spectral, temporal, and spatial properties as well as the output energy. In crossed-beam resonance ionization on a well-collimated thermal atomic beam, the ～200 MHz hyperfine structure of the D₂ transition at 308 nm of ²⁷Al has been well resolved. Applications of the system in the field of insource laser spectroscopy for on-line produced short-lived radioactive isotopes as well as for selective-trace isotope determination are discussed.     

An experimentally validated electromagnetic energy harvester

A relatively simple method for determining the electromechanical parameters of electromagnetic energy harvesters are presented in this paper. The optimal power generated through a load resistor at both off-resonance and resonance is derived analytically. The experimentally measured performance of a rudimentary electromechanical energy harvester using a rare-earth magnet shows good agreement with the results from the model. The parasitic generator coil resistance can have a profound effect on the overall performance of an electromagnetic generator by essentially acting to degrade the effective coupling coefficient. Data from the setup electromagnetic generator shows normalized power densities of 1.7 μW/[(m/s²)² cm³] operating at a resonance frequency of 112.25 Hz. This power density is comparable with other electromagnetic devices of the same volume operating at these frequencies. The power output of the presented electromagnetic generator is comparable to equivalent piezoelectric generators.     

HL-2A装置辅助加热高压电源控制系统的设计与实现

研制了HL-2A装置LHCD和ECRH系统使用的高压电源,其电源拓扑分别为晶闸管交流调压型和星点控制型高压电源,通过高压脉冲调制器给LHCD和ECRH系统供电,采用了波头补偿、前馈和反馈相结合的控制方法,弥补了电源拓扑本身固有的瞬态特性不足和发电机输出的不稳定性,使电源输出电压输出平顶的稳定度优于1%。介绍了高压电源的主回路结构,对高压电源的控制进行了论述,同时给出了实验结果。     

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研制了HL-2A装置LHCD和ECRH系统使用的高压电源,其电源拓扑分别为晶闸管交流调压型和星点控制型高压电源,通过高压脉冲调制器给LHCD和ECRH系统供电,采用了波头补偿、前馈和反馈相结合的控制方法,弥补了电源拓扑本身固有的瞬态特性不足和发电机输出的不稳定性,使电源输出电压输出平顶的稳定度优于1%。介绍了高压电源的主回路结构,对高压电源的控制进行了论述,同时给出了实验结果。     

高效转换的大功率皮秒脉冲激光器

本文描述我们设计的带抗共振环(ARR)的对撞脉冲锁模(CPM)非稳腔Nd:YAP和Nd:YAG激光器,该激光腔结合了CPM腔脉宽窄、工作稳定和非稳腔输出能量高的特点,是一理想的高功率激光器同时选择了KTP、BBO和LBO等优良非线性晶体作为腔内倍频元件,实现高效倍频转换获得×10mJ和5GW/cm²的高能量和高功率绿光皮秒脉冲输出,倍频转换效率高达(50～70)%.     

紧凑型Marx发生器高功率微波源研究进展

紧凑型Marx发生器不但体积小,重量轻,而且能量效率高,能以一定的重复频率运行,在窄带、宽带和超宽带高功率微波源中获得了广泛的应用。这种类型的高功率微波源是近几年来国内外的研究热点和重要发展方向。对国内外基于紧凑型Marx发生器的高功率微波源的研究进展进行了系统介绍,评述其输出参数和结构特点,并探讨其发展趋势,为正确把握基于紧凑型Marx发生器的高功率微波源的发展动态、科学探索其技术路线提供参考和依据。     

Low energy ion beams by laser interaction

We developed an ion accelerator with a double accelerating gap system supplied by two power generators of different polarity. The ions were generated by laser ion source technique. The laser plasma induced by an excimer KrF laser, freely expanded before the action of accelerating fields. After the first gap action, the ions were again accelerated by a second gap. The total acceleration can imprint a maximum ion energy up to 160 keV per charge state. We analysed the extracted charge from a Cu target as a function of the accelerating voltage at laser energy of 9, 11 and 17 mJ deposited on a spot of 0.005 cm². The peak of current density was 3.9 and 5.3 mA for the lower and medium laser energy at 60 kV. At the highest laser energy, the maximum output current was 11.7 mA with an accelerating voltage of 50 kV. The maximum ion dose was estimated to be 10¹² ions/cm². Under the condition of 60 kV accelerating voltage and 5.3 mA output current the normalized emittance of the beam measured by pepper pot method was 0.22 π mm mrad.     

100 kV重复频率高压脉冲电源

为研究气体间隙的放电特性,设计了输出幅度在30～100 kV、重复频率1～5 kHz可调的高压脉冲电源。利用谐振充电的原理,将10 kV的初级电源的能量转移到中储电容,中储电容的电压升高到至少18 kV。在光触发信号的作用下,氢闸流管导通,中储电容上的能量通过脉冲变压器放电,在脉冲变压器的副边得到最大幅度为100 kV的负脉冲,其脉宽大于200 ns,前沿时间小于90 ns。整个装置在不加散热系统的情况下,可连续工作1 min以上。     

Q-switched operation of an in-band-pumped Ho:LuAG laser with kilohertz pulse repetition frequency

We report continuous-wave (CW) and repetitively Q-switched operation of an in-band-pumped Ho:LuAG laser at room temperature. End-pumped by a Tm:YLF solid-state laser with emission wavelength of 1.91 μm, the CW Ho:LuAG laser generated 5.4-W output at 2100.7 nm with beam quality factor of M ²～1.03 for an incident pump power of 14.1 W, corresponding to slope efficiency of 67% with respect to absorbed pump power. Up to 1.5-mJ energy per pulse at pulse repetition frequency (PRF) of 3 kHz and 4.5-W average power with FWHM pulse width of 28 ns at 5 kHz were demonstrated in repetitively Q-switched operation.     

High efficient Tm3+ doped double cladding silica fiber laser with an intracavity biconical taper

A high efficient LD (laser diode) pumped Tm³⁺ doped double clad silica fiber laser with an intravacity biconical taper was reported. A biconical taper located ～3 cm from the output end of the fiber laser was fabricated by heating and stretching method with a length 1.5 cm and waist diameter ～20 µm. The slope efficiency was 49.8% with respected to the launched pump power, and the maximum output power was 1.97 W. Pre and post output laser power ratio was ～10. This fiber laser was compared with other three biconical tapered fiber lasers (the same fiber with different tapers) and a uniform geometry fiber laser. With intracavity biconical tapers, fiber lasers’ thresholds were ～1 W higher than the fiber laser without the taper (1.97 W). The pump end’s slope efficiencies of fiber lasers with tapers were 3–5% in contrast with 37.6% of the uniform one. After tapered, the pre and post laser power ratios were much higher than the un-tapered one’s, but not changed much with the launched pump power.     

Modeling a novel energy harvester working in Lame mode

A new square shaped piezoelectric bimorph structure for energy scavenging purposes has been proposed and simulated. It is derived from theoretical analysis that the output power of the structure is proportional to the value of the resonant frequency. The device working in Lame mode has a much higher resonant frequency of 2.39 MHz than devices working in ordinary bending modes, which is expected to significantly increase the energy output of radioisotope power generators (RPGs). The results of static analysis and dynamic response show that output voltage is linear with the applied load; the output power is quadratic with the applied load.     

16μm tunable source using parametric processes in non-linear crystals

A reliable continuously tunable source of 16μm radiation with ～$\text{1}\text{2}$ kW peak power and repetition rates up to 20 pps is described. This consists of an Nd : YAG driven lithium niobate return pump parametric oscillator, with non-linear mixing of the signal and idler wavelengths in cadmium selenide. Pulse energies of 5 μJ and linewidths of 2.6 cm^-1 at 16 μm have been observed with the grating tuned OPO. Potential improvements in output energy and bandwidth (spectrum narrowing) are discussed.     

Direct‐current nanogenerator based on ZnO nanotube arrays

Due to the special structure of a nanotube (NT), the different potential from piezoelectricity can be naturally divided by the hollow of the tube when the NT is bent or deformed. Furthermore, both the bent/deformed inner and outer wall can form a steady voltage/current, which might enhance the output voltage/current. We demonstrate a direct‐current nanogenerator (NG) based on zinc oxide (ZnO) NT arrays driven by an ultrasonic wave. The average output voltage is ca. 0.10 mV and the current density is ca. 0.069 μA/mm². Our study shows that the maximum power output of the ZnO NT array NG is 0.112 nW and the power density is 1.4 nW/cm². The success of energy harvesting from ZnO NTs reveals the potential of using nanogenerators for tubular piezoelectric materials. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Problems and prospects for microsecond pulsed power above tenmegamperes

Systems, such as Shiva Star, Atlas, and magnetic-flux compression generators (MCGs), that can deliver several megajoules at currents above 10 MA offer the opportunity for many interesting experiments in controlled fusion technology and basic material dynamics. Typical current rise-times of a few microseconds result, even with low inductance (<20 nH) circuitry, because several megajoules are delivered at less than 200 kV. This means that conductor surfaces can move significantly relative to the skin-layer thickness, and surface plasmas can interfere with power flow. Success with such multimegampere technology, therefore, requires considerable attention to the detailed design of joints and conductor surfaces. This paper discusses these and other design considerations. It also describes opportunities enabled by operation above 10 MA     

Ionization spectrum transformation and compression of powerful femtosecond laser pulses in experiments on the propagation in gas-filled dielectric capillaries

The propagation of an intense (I≤10⁶ W/cm²) femtosecond laser radiation with a duration of ～100 fs through gas-filled dielectric capillaries was studied. The radiation with a power up to 0.2 TW propagates along the paths up to 20 cm with a transmission efficiency of ～45%. The beam transverse structure at the output is close to the capillary fundamental mode under gas-ionization conditions. The transformation of pulse spectrum was studied as a function of input intensity. It is demonstrated experimentally that the pulse is compressed to a duration of ～30 fs due to the compensation of ionization-induced self-phase modulation in a linear dispersive element at the capillary output.     

Characteristics of high-power radiating imploding discharge with cold start

A qualitative model of the dynamics of a multiterawatt radiating Z-pinch with cold start and high rate of current rise is proposed. The model is used to analyze discharges with currents I ～ 2–5 MA (with dI/dt > 10¹³ A/s) through uniform or structured plasma-producing loads, including wire arrays. The most important consequence of cold start is that spatially nonuniform plasma production is prolonged to almost the entire current rise time. Under these conditions, the Ampére force begins to play a dominant role in the plasma dynamics before the plasma-producing load is completely transformed into an accelerated plasma. The results of computations of wire-array vaporization are presented. A formula is proposed for estimating the highest attainable velocity of plasma flow into a heterogeneous liner driven by the Ampére force. It is shown that local imbalance between radial motion of the produced plasma and supply of the plasma-producing substance to be ionized leads to axially nonuniform breakthrough of magnetic flux into the liner, which precedes plasma collapse. The magnetic-flux breakthrough gives rise to a chaotic azimuthal-axial plasma structure consisting of radial plasma jets of relatively small diameter, which is called a radial plasma rainstorm. The breaking-through azimuthal magnetic flux obstructs further current flow in the breakthrough region. Analyses of Z-pinch implosion based on the theory of Rayleigh-Taylor instability or the snowplow model are incorrect under the plasma-rainstorm conditions. The processes taking place in a stagnant Z-pinch include conversion of the energy carried by the current-generated magnetic field into turbulent MHD flow of the ion component of the plasma, its convective mixing with magnetic field, heating, energy transfer from ions to electrons, and emission from the plasma. Under typical experimental conditions, emission plays a key role in the energy balance in an imploding pinch. Z-pinch is modeled by an electric-circuit component that has a time-dependent nonlinear impedance and consumes the magnetic energy supplied by a generator through a magnetically insulated transmission line (MITL). The peak power reached in the circuit is comparable to the peak soft X-ray power output emitted by the pinch in terms of magnitude and timing. Optimum matching conditions are formulated for the generator-MITL-pinch circuit.     

2-MM WAVE VECTOR NETWORK ANALYZER UPON HIGH-ORDER IMPATT MULTIPLIERS

This paper shows the first results of development of the 2 millimeter-wave vector network analyzer (VNA) based on active high-order IMPATT multipliers — the new type of harmonic generators. The multipliers of this type can translate the spectra of highly stable centimeter-wave oscillators to any part of the millimeter range with the output power of 20÷13 dBm without additional amplification. Against Schottky-diode multipliers that are used in conventional VNAs, the active IMPATT multipliers generate more output power at large harmonic numbers that allows to lock the multipliers at their output frequencies. The phase noise of IMPATT multipliers is proportional to N against N² in the Schottky-diode multipliers (where N is the harmonic number). We have investigated the scheme of the VNA in which the PLL and receiving mixers operated at the fundamental frequency of the heterodyne.     

Miniature intra-cavity modulated solid state lasers and their use in optical communication systems

Based on a model for the calculation of the variance of relaxation noise we show that it is possible in principle to modulate aminiature solid state laser at data rates (random) of 50 Mbit s^?1 and higher by modulating the cavity loss, while keeping the relaxation oscillation noise small enough to permit a 10^?9 error rate. Because of the small transit time through the miniature cavity a large modulation index (M ～ 45) can be achieved, and although the laser power output suffers this can be compensated for in data transmission by the narrow output pulse shape that characterizes our intra-cavity modulation scheme. We discuss the design of a proposed miniature laser based on an acousto-optic intracavity modulator and compare its predicted performance with that of a modulated laser source based on an external modulator. Its major advantages are a somewhat lower electrical operating power and the simple construction which is based on an all-planar technology.     

高可靠性脉冲氙灯电源设计

对540 mm18 mm、极间距250 mm、充气压力26 kPa的脉冲氙灯进行分析计算,研制了一台具有手动和外触发功能、氙灯充电电压2.5～4.5 kV、输出脉冲电流幅度3～6 kA、脉冲宽度约230 s的脉冲氙灯电源,给出了单次触发情况下的实验结果。设计基于晶闸管移相调压方式,经由隔离模块、PLC控制构成的闭环反馈回路,控制调压模块对储能电容器线性充电;通过IGBT半导体开关器件产生脉冲信号,经脉冲变压器升压后触发氙灯,使氙灯导通发光。采用简单、可靠的绕丝触发方式和控制信号隔离、电容器一端接地等方法,有效抑制了地电位抬高,提高了氙灯电源的可靠性和抗干扰能力。通过百次的实验,脉冲氙灯电源能100%点亮负载氙灯,满足实际使用要求。     

Study of the radiation resistance of a carbon fiber based on viscose in carbon-carbon and carbon-ceramic composites

The results of the experimental study of the crystalline structure and morphology of carbon fibers based on viscose in a FEBUS carbon-ceramic composite and its preform as functions of temperature ranging from room values to ～400°C under irradiation with Ar⁺ ions with an energy of 10–30 keV are obtained. The average level of radiation damage corresponding to the initial fiber graphitization (〈ν_gr> ～ 80 dpa) is determined based on an analysis of the energy dependences of the ion-electron emission coefficient at different irradiation temperatures. It is shown that carbon fibers based on viscose are immune (in contrast to polyacrylonitrile fibers) to ion-induced destruction in the form of crimping. This is indicative of their enhanced radiation resistance.