Injection-seeded single frequency 2.05 μm output by ring cavity optical parametric oscillator

An injection-seeded single-resonant optical parametric oscillator(SROPO) with single frequency nanosecond pulsed 2.05 μm wavelength output is presented. Based on two potassium titanyl phosphate crystals and pumped by a 1064 nm single frequency laser pulse, injection seeding is performed successfully by using the ramp-hold-fire technique in a ring cavity with a bow-tie configuration. The SROPO provides 2.65 m J single frequency signal pulse output with a 17.6 ns pulse duration at a 20 Hz repetition rate. A near-diffraction-limited beam is achieved with a beam quality factor M~2 of about 1.2. The spectrum linewidth of the signal pulse is around 26.4 MHz,which is almost the Fourier-transform-limited value.     

Conceptional design of a heavy ion linac injector for HIRFL-CSRm

A room temperature heavy ion linac has been proposed as a new injector of the main Cooler Storage Ring(CSRm) at the Heavy Ion Research Facility in Lanzhou(HIRFL), which is expected to improve the performance of HIRFL. The linac injector can supply heavy ions with a maximum mass to charge ratio of 7 and an injection kinetic energy of 7.272 MeV/u for CSRm; the pulsed beam intensity is 3 emA with the duty factor of 3%. Compared with the present cyclotron injector, the Sector Focusing Cyclotron(SFC), the beam current from linac can be improved by 10–100 times. As the pre-accelerator of the linac, the 108.48 MHz 4-rod Radio Frequency Quadrupole(RFQ) accelerates the ion beam from 4 keV/u to 300 keV/u, which achieves the transmission efficiency of 95.3% with a 3.07 m long vane.The phase advance has been taken into account in the analysis of the error tolerance, and parametric resonances have been carefully avoided by adjusting the structure parameters. Kombinierte Null Grad Struktur Interdigital H-mode Drift Tube Linacs(KONUS IH-DTLs), which follow the RFQ, accelerate ions up to the energy of 7.272 MeV/u for CSRm. The resonance frequency is 108.48 MHz for the first two cavities and 216.96 MHz for the last 5 Drift Tube Linacs(DTLs). The maximum accelerating gradient can reach 4.95 MV/m in a DTL section with the length of17.066 m, and the total pulsed RF power is 2.8 MW. A new strategy, for the determination of resonance frequency,RFQ vane voltage and DTL effective accelerating voltage, is described in detail. The beam dynamics design of the linac will be presented in this paper.     

Physics design for the C-ADS main linac based on two dif f erent injector design schemes

The China ADS（C-ADS） project proposes to build a 1000 MW Accelerator Driven sub-critical System around 2032. The accelerator will work in CW mode with 10 mA in beam current and 1.5 GeV in final beam energy. The linac is composed of two major sections： the injector section and the main linac section. There are two diferent schemes for the injector section. The Injector-scheme is based on a 325 MHz RFQ and superconducting spoke cavities of the same RF frequency and the Injector-scheme is based on a 162.5 MHz RFQ and superconducting HWR cavities of the same frequency. The main linac design will be diferent for diferent injector choices. The two diferent designs for the main linac have been studied according to the beam characteristics from the diferent injector schemes.     

Simulation and measurement of the resonant Schottky pickup

A resonant Schottky pickup with high sensitivity, built by GSI, will be used for nuclear mass and lifetime measurement at CSRe. The basic concepts of Schottky noise signals, a brief introduction of the geometry of the detector, the transient response of the detector, and MAFIA simulated and perturbation measured results of characteristics are presented in this paper. The resonant frequency of the pickup is about 243 MHz and can be slightly changed at a range of 3 MHz. The unloaded quality factor is about 1072 and the shunt impedance is 76 kΩ. The measured results of the characteristics are in agreement with the MAFIA simulations.     

Experimental Study on Influence of Atmospheric Turbulence on Coherence of Dual-Frequency Laser

The influence of atmospheric turbulence on the coherence of a dual-frequency laser beam is studied experimentally. An atmospheric turbulence simulator is inserted in one arm of a Mach-Zehnder interferometer. A single frequency laser beam and a dual-frequency laser beam with a frequency difference of 100 MHz travel through the interferometer, respectively. The visibilities of the interference fringes of the single and dual-frequency laser beams under different turbulent forces are compared. When the turbulence becomes stronger, the visibilities of the interference pattern of the single frequency interferometer decrease more rapidly. This shows that the atmospheric turbulence has less influence on the coherence of the dual-frequency laser beam. The linewidths broadened by the turbulence are calculated with the Wiener-Khintchine theory.     

Physics design for the C-ADS main linac based on two different injector design schemes

The China ADS (C-ADS) project proposes to build a 1000 MW Accelerator Driven sub-critical System around 2032. The accelerator will work in CW mode with 10 mA in beam current and 1.5 GeV in final beam energy. The linac is composed of two major sections: the injector section and the main linac section. There are two different schemes for the injector section. The Injector-Ⅰ scheme is based on a 325 MHz RFQ and superconducting spoke cavities of the same RF frequency and the Injector-Ⅱ scheme is based on a 162.5 MHz RFQ and superconducting HWR cavities of the same frequency. The main linac design will be different for different injector choices. The two different designs for the main linac have been studied according to the beam characteristics from the different injector schemes.     

Soft magnetic properties of amorphous Fe52Co34Hf7B6Cu1 alloy treated by pulsed magnetic field and annealing

<正>The crystallization,microstructure,and soft magnetic properties of Fe₅₂Co₃₄Hf₇B₆Cu₁ alloy are studied.Amorphous Fe₅₂Co₃₄Hf₇B₆Cu₁ alloys are first treated by a pulsed magnetic field with a medium frequency,and then annealed at 100℃-400℃for 30 min in a vacuum.The rise in temperature during the treatment by a pulsed magnetic field is measured by a non-contact infrared thermometer.The soft magnetic properties of specimens are measured by a vibrating sample magnetometer（VSM）.The microstructure changes of specimens are observed by a Mossbauer spectroscopy and transmission electron microscope（TEM）.The results show the medium-frequency pulsating magnetic field will promote nanocrystallization of the amorphous alloy with a lower temperature rise.The nanocrystalline phase isα-Fe（Co） with bcc crystal structure,and the grain size is about 10 nm.After vacuum annealing at 100℃for 30 min,scattering nanocrystalline phases become more uniform,the coercive force and the saturation magnetization of the specimens are 41.98 A/m and 185.15 emu/g.     

Continuous-wave green laser of 34 W by intracavity frequency doubling in diode-side-pumped Nd:YAG/KTP

Continuous-wave green laser with a maximum power of 34 W has been obtained by intracavity frequency doubling with KTP in diode-side-pumped Nd：YAG. The Nd：YAG/KTP green laser has a simple three- mirror V-fold cavity structure. The optical-to-optical conversion efficiency is 9.5%. The instability of the laser is measured when the output powers are near 16, 21, 30, and 34 W after the beam is filtered. At the maximum output power, the M^2 factor is measured to be 8.     

Frequency Stabilization of Pulsed Injection-Seeded OPO Based on Optical Heterodyne Technique

A frequency stabilizing system for a pulsed injection seeded 1550 nm optical parametric oscillator(OPO) at 20 Hz repetition rate is demonstrated.The optical heterodyne method is used to measure the frequency difference between the seed laser and the OPO output.Using the frequency difference as the error signal,a proportionalintegral controller in combination with a scanner is applied to stably match the OPO cavity length to the seed laser frequency.The root-mean-square(rms) error of the frequency discrimination method is 0.07 MHz according to a ‘frequency shifting-chopping-beat' evaluation.The frequency fluctuation of the frequency-stabilized OPO is0.29 MHz(rms),and the Allan deviation is less than 20 k Hz for averaging time of more than 3 s.     

Determinations of plasma density and decay time in the hollow cathode discharge by microwave transmission

The microwave （MW） transmission method is employed to measure both the plasma density and the plasma decay time in the hollow cathode discharge （HCD） in argon at low pressure. The plasma density in DC-driven or pulsed HCD is on the order of 1012 cm-3, which can block the X-band MW effectively. In the case of pulsed HCD, the MW transmittance shows the same waveform as the pulsed current during the rising edge if the driving frequency is low, but with a longer delay during the falling edge. The MW transmittance reaches a constant low level when the driving frequency is high enough. The plasma decay time in the HCD system is measured to be about 100 μs around a pressure of 120 Pa. The ambipolar diffusion is considered to be the major mechanism in the decay process.     

脉冲X光与其他模拟源的结构响应等效性分析

 分析了脉冲X光与电子束和化爆模拟引起的结构响应的冲量等效性原则。并以脉冲X光与柔爆索化爆作用硬铝圆柱壳的结构响应测量结果为实例，对其进行了定量的等效性分析，得出了较好的等效性结果。     

Reduced critical rotation for resistive-wall mode stabilization in a near-axisymmetric configuration

Recent DIII-D experiments with reduced neutral beam torque and minimum nonaxisymmetric perturbations of the magnetic field show a significant reduction of the toroidal plasma rotation required for the stabilization of the resistive-wall mode (RWM) below the threshold values observed in experiments that apply nonaxisymmetric magnetic fields to slow the plasma rotation. A toroidal rotation frequency of less than 10 krad/s at the q=2 surface (measured with charge exchange recombination spectroscopy using C VI) corresponding to 0.3% of the inverse of the toroidal Alfvén time is sufficient to sustain the plasma pressure above the ideal MHD no-wall stability limit. The low-rotation threshold is found to be consistent with predictions by a kinetic model of RWM damping.     

脉冲Nd:YAG激光熔覆修复塑料模具工艺参数的优化

 激光器的电压、电流、脉冲宽度、脉冲频率与激光的扫描速度、光斑直径等工艺参数直接影响着脉冲Nd:YAG激光熔覆质量。为了简化工艺调整过程，提出了重叠率的概念，并进行了理论推导，建立了重叠率与脉冲频率、激光扫描速度、激光光斑直径相互关系的方程式。利用预置法在低碳钢基体上熔覆Ni基合金粉末,获得了2组最佳工艺参数，即单脉冲能量、重叠率分别为6.7 J,97.4%和21 J,69.4%。研究表明：在单脉冲能量和重叠率一定的条件下，改变电流、脉宽、脉冲频率及熔覆速度不会影响熔覆质量。     

Influence of hydrogen on the properties of Zr-1%Nb alloy modified by a pulsed electron beam

The influence of hydrogen and a pulsed electron beam on the properties of Zr-1%Nb alloy is studied. It is shown that electron beam processing results in the formation of martensite with an intricate morphology in the subsurface layer of the alloy. It is found that the amount of hydrogen penetrating into the modified alloy is twice as low as in the as-prepared material. In addition, the modified alloy is more stable against the hydrogen action.     

基于超导储能脉冲变压器的多模块脉冲电源设计

为了探索一种更加紧凑的导轨型电磁推进基础实验用脉冲电源,以实验室现有高温超导储能脉冲变压器为单元模型,在单谐振电路脉冲成形方案的基础上,设计了环形结构的多模块脉冲电源,分析了环形结构中考虑互感的多模脉冲电源电路的充放电过程。通过对八模块环形结构脉冲电源进行仿真分析,得到了接近150kA的电流脉冲,原边电压限制13kV左右。可以得出,利用单谐振电路的多模块超导储能脉冲变压器并联放电方式,可以实现大电流脉冲的输出的要求,而且环形结构中各线圈存在的互感更有利于多模块脉冲电源。     

Effect of subsonic toroidal flows on plasma poloidal rotation and ion heat conductivity. In collisional plasmas of elongated tokamaks

The ion poloidal rotation and heat conductivity in collisional plasmas of axially-symmetric tokamaks with elongated cross-sections and with subsonic toroidal plasma flows are considered. It is shown that subsonic toroidal plasma flows, induced by neutral beam injection or radio frequency waves, can strongly affect the poloidal plasma velocity and ion heat conductivity in collisional plasmas of tokamaks. The transport coefficients also depend on the tokamak ellipticity parameter which, in combination with the Mach number, allows to operate transport processes at smaller values of the toroidal Mach number. The importance of taking into account the ion-electron heat exchange and electron temperature toroidal perturbations to find ion temperature toroidal perturbations is demonstrated. This work was partially supported by the State University of Rio de Janeiro (UERJ) and the Rio de Janeiro Research Foundation (FAPERJ).     

基于衍射光学元件的激光相干合成研究进展

从衍射光学元件的基本原理出发,围绕连续波和脉冲波两大应用领域,综述了国内外基于衍射光学元件实现共孔径相干合成的研究进展。在国内,上海光学精密机械研究所分别实现了连续光和脉冲光的合成,连续光实现了206 W的输出功率,光束质量1.38,合束效率29.6%;脉冲光实现了峰值功率1.02 kW,重复频率2.2 MHz的ns级脉冲相干合成光束,合束效率61%。在国外,连续光方面实现了5 kW量级的合成光输出,合束效率82%;脉冲光方面实现了平均功率150 mW,重复频率100 MHz的fs级脉冲相干合成光束,合束效率83.4%。最后对基于衍射光学元件的激光相干合成技术的未来发展做出了展望,相信在不久的将来,基于衍射光学元件的相干合成技术会不断发展,逐渐突破技术瓶颈,从而为更多的应用领域奠定坚实基础。     

产生钠导引星星群的钠信标激光合/分束技术

研究了脉冲光束的偏振和时序非相干合成技术,通过偏振合束器将两路50 W级500 Hz的589 nm钠信标激光在空间上合为一束光线,成功突破了100 W级μs脉冲全固态钠信标激光输出;利用脉冲激光同步延时器控制两路激光脉冲的时序,使其按先后顺序合成一束脉冲激光,重复频率提升到1 kHz。合束后的激光光束质量M²约为1.41,与单光束的光束质量基本保持一致,光斑抖动性约为40μrad,可满足激光钠导引星自适应光学系统的应用需求。与传统的相干合成方法相比,该偏振和时序非相干合成方案具有结构简单、稳定、效率高的优点,且整个系统无需复杂的相位控制机制,为脉冲激光功率扩展提供了新途径。基于上述技术基础,结合自主提出的精密偏振分光专利技术,在丽江天文台通过一台发射望远镜将四束25 W/束的μs脉冲黄激光发射到钠层,成功产生了四颗钠导引星,这一结果将有助于推动大型地基光学望远镜中多层共轭自适应光学技术的发展。     

Electron-Beam Measurements of the Magnetic Surfaces in the Proto-Cleo Torsatron

The shape of the vacuum magnetic surfaces at a fixed toroidal angle in the Proto-Cleo torsatron was investigated by launching a beam of electrons along various magnetic-field lines. After completing a variable number of transits around the major axis, the beam was intercepted by a probe. The locations of the interception points for different numbers of toroidal transits trace out the minor cross section of the magnetic surfaces. A family of three experimentally measured magnetic surface cross sections are compared with computer magnetic surface cross sections. From interception-point location and corresponding time of flight data, the average rotational transform for each surface is calculated.     

The design and construction of a pulsed beam generation system based on high intensity cyclotron

In order to perform the studies on a pulsed beam generation system based on a high intensity cyclotron, a test beam line with a pulsed beam generation for a 10 MeV compact cyclotron (CYCIAE-10) has been designed and constructed at China Institute of Atomic Energy (CIAE). A 70 MHz continuous H-beam can be pulsed to the pulse length of less than 10 ns with a repetition rate of 4.4 MHz. The sine waveform with a frequency of 2.2 MHz is adopted for the chopper and a mesh structure with single drift and dual gaps is used for the 70 MHz buncher. A helical resonator is designed and constructed based on simulations and experiments on the RF matching for the chopper. A helical inductance loop that is exceptionally large of its kind and equipped with water cooling for the resonator has been successfully wound and a 500 W solid RF amplifier has been manufactured. A special measuring device has been designed, which can be used to measure both the DC beam and the pulsed beam. The required pulsed beam was obtained after pulsed beam tuning.