超短超强激光脉冲辐照超薄碳膜电离状态研究

为了进一步理解极端条件下物质的电离特性, 特别是超短超强激光脉冲辐照超薄靶时等离子体的形成与分布, 本文以超薄碳膜为例, 细致研究了超短超强激光脉冲辐照下原子的离化过程. 分析和比较了强激光场直接作用电离和靶内静电场电离等两种场致电离形式, 在碰撞电离可以忽略的情况下, 发现更多的电离份额是来自靶内静电场的电离方式. 研究了激光脉冲强度对电离的影响, 发现激光脉冲强度越强, 电离速度越快, 产生的高价态离子所占比例也越高.当激光强度为1×10²⁰ W/cm²时, 尽管该强度高于电离生成C⁺⁶所需要的激光强度阈值, 但该激光脉冲并不能将整个靶电离成C⁺⁶离子, 对此本文进行了详细的分析. 在研究激光脉冲宽度的影响时, 发现激光脉宽越小, 电离速度越快, 但越小的激光脉冲电离获得的高价态离子越少.     

Development of an intense pulsed metallic ion beam source

Intense pulse metallic ion beams (Al⁺, Cu⁺, and Pb⁺) were produced by a magnetically insulated ion diode having a metal anode. Metal ion plasmas on the anode could be generated through enhanced electron bombardment by using a radial cathode. The energy, current density, and duration time of the lead ion beam were 30~140 keV, ~7.5 A/cm² (total ion current ⩾0.5 kA), and 800 ns, respectively. The ion current density exceeded the space-charge-limited current by a factor of 50. The lead ions in the first-to-sixth states of ionization were detected by a Thomson-parabola ion-spectrometer together with light loss, such as C⁺ and O ⁺. The ratio of the ion current of heavy metals to the total ion current was measured using a magnetic mass analyzer with a charge collector. The ratio was about 90% for a lead ion beam and 20~50% for Al and Cu ion beams     

氦氢离子协同注入对锆膜形貌及物相结构的影响

 采用磁控溅射法制备了Zr-Mo膜，随后在低能静电加速器上分别采用剂量为2.80×10¹⁷~1.12 ×10¹⁸ions·cm^-2的He⁺、H⁺离子辐照Zr-Mo膜，利用光学透镜、扫描电镜、原子力显微镜和X射线衍射研究He⁺、H⁺离子协同注入效应对Zr-Mo膜微观结构的影响。实验结果表明：原始Zr-Mo膜表层晶粒清晰可见，尺寸约为200nm；辐照效应可导致Zr-Mo膜表层产生微观损伤区域，在注He⁺基础上注H⁺导致Zr-Mo膜出现更为严重的损伤现象；离子注入的表面溅射效应可使膜面晶粒边界逐渐刻蚀退让，导致膜面更加光滑、细致；He⁺、H⁺ 离子协同注入可使Zr-Mo膜晶格发生畸变，注入期间未使Zr-Mo膜发生吸H相变生成氢化物。     

Transmission of low-energy (< 10 eV) O ions through Au films on TiO2(110)

In an attempt to identify the fundamental processes that influence ion transport through metallic surface layers, we have studied the transmission of O⁺ ions through discontinuous Au films adsorbed on TiO₂(110). A low energy (< 10 eV) O⁺ ion beam is generated via electron stimulated desorption when an Au-dosed TiO₂(110) substrate is bombarded with a focused 250 eV electron beam. Low energy ion scattering data indicate that Au evaporated under ultrahigh vacuum conditions at 300 K forms three-dimensional clusters on TiO₂(110). As the Au coverage increases, the formation of Au clusters on TiO₂(110) blocks a fraction of the TiO₂ surface and the O⁺ yield is attenuated. However, for high coverages (≥30% Au covered substrate) the O⁺ signal decreases at a faster rate than the TiO₂ open area fraction. We attribute the attenuation of the O⁺ yield for high Au coverages mainly to blocking of O⁺ by Au clusters, to deflection of trajectories by the image force between ions and Au clusters, and to charge transfer between desorbing O⁺ and neighboring Au clusters.     

Atomic collision processes relevant for heavy ion beam probes

Atomic collision processes of fast Tl and Cs ions with particles in a high temperature fusion plasma are investigated. At low beam energies (<5 MeV), ion impact collisions and charge exchange processes can be neglected compared to electron ionization processes. At beam energies above 5 MeV and high plasma ion temperatures, collisions with ions start to contribute significantly to signal generation and attenuation. Also, collisions with the neutral background gas in the beamlines can attenuate the ion beam significantly and lower the signal level, if the vacuum pressure is above 10^-4 Torr. For the heavy ion beam probes operating today, only electron impact ionization processes are important and accurate predictions of the secondary signal level and electron density profile measurements are possible because of the good knowledge of electron impact ionization cross sections for Cs ⁺ and Tl⁺ ions     

Pulse intense metal-ion diode with a vacuum arc plasma anode

An intense pulsed ion beam of metal was extracted from a magnetically insulated ion diode operated in a mode of plasma prefill generated from a vacuum arc discharge, anode plasma source. With this ion diode, an intense metal-ion beam of a high melting-point metal (Ta) was obtained. A variety of operational modes appeared, depending on the amount of plasma in the diode gap at the initiation of the high-voltage pulse. The energy, current, and duration time of the ion beam were 20~100 keV, ~1 kA, and 1 μs, respectively. Measurements of ions were performed with an ion energy analyzer or a biased ion collector located at the end of a long drift tube and a Thomson parabola ion spectrometer. The Ta ions in the first to fifth states of ionization were detected accompanied by C⁺, O⁺, F⁺, and H⁺ . A Ta ion beam current of about half the total ion flux was obtained in this experiment     

Statistics of secondary electrons from W induced by He ions and atoms at 0° –90° incidence

Secondary electrons from a W target, induced by 2 KeV He⁰ and He⁺ projectiles at 0° -90° angles of incidence have been measured for the first time using the statistics of secondary electron emission. The statistics were determined from the analysis of measured pulse height distribution spectra for 8–32 KeV He⁺ ions. The pulse height response of the detector is found to be sensitive to the applied bias to the detector. Its consequences in the interpretation of data are investigated. It was established that the number of electrons emitted per incident ion satisfy a Poisson distribution. Some new suggestions are made on the possible use of these results, in particular, on the role of the zeroth and the first Poisson coefficients, for surface studies.     

超强激光与固体气体复合靶作用产生高能氦离子

激光氦离子源产生的MeV能量的氦离子因有望用于聚变反应堆材料辐照损伤的模拟研究而得到关注.目前激光驱动氦离子源的主要方案是采用相对论激光与氦气射流作用加速高能氦离子,但这种方案在实验上难以产生具有前向性和准单能性、数MeV能量、高产额的氦离子束,而这些氦离子束特性是材料辐照损伤研究中十分关注的.不同于上述激光氦离子产生方法,我们提出了一种利用超强激光与固体-气体复合靶作用产生氦离子的新方法.利用这种方法,在实验上,采用功率密度5×10~(18)W/cm~2的皮秒脉宽的激光脉冲与铜-氦气复合靶作用,产生了前向发射的2.7 MeV的准单能氦离子束,能量超过0.5 MeV的氦离子产额约为10~(13)/sr.二维粒子模拟显示,氦离子在靶背鞘场加速和类无碰撞冲击波加速两种加速机理共同作用下得到加速.同时粒子模拟还显示氦离子截止能量与超热电子温度成正比.     

中等光强纳秒激光电离苯团簇产生多价碳离子的数值模拟和实验研究

飞秒强激光与团簇相互作用产生多价离子的现象已被广泛报道,然而近期多个研究小组发现当功率密度低至1010W/cm2的纳秒激光照射团簇时,同样也观察到了多价离子的存在.虽然可以用"多光子电离引发-逆韧致吸收加热-电子碰撞电离"电离机理对这种现象进行解释,但是缺乏相应的数值模拟.建立了一个简化的数值模型,根据有质动力势Up计算团簇内电子能量,再由Lotz公式计算出相应的电离截面,最后由动力学反应速率方程计算出团簇内多价碳离子随时间的演变.详细分析了团簇尺寸、电子密度等关键参数对多价离子产生的影响.数值模拟结果表明:团簇电离在小于0.7 ns时间尺度内完成,C2+,C3+和C4+多价离子强度达到平衡后,离子相对强度由大到小依次为C2+,C3+,C4+,这与实验结果相一致;多价离子的价态随着团簇尺寸的增加而升高,半径为5.6 nm的苯团簇比半径为3 nm的苯团簇更容易产生高价态的离子,这也与实验结果相一致.     

Pseudospark produced pulsed electron beam for material processing

An intense pulsed electron beam produced by a pseudospark discharge is used for material processing. The electron beam propagates in a self-focused manner in the background gas. Hardly 12 ns after the beginning of the discharge the fraction of space charge neutralization is about 96%. To sustain the neutralization effect high energy electrons (E <500 keV) are accelerated in radial direction at the beam head, due to strong electric field gradients. At current maximum the beam pinches due to its own magnetic field. At peak current of 400 A and charging voltage up to 16 kV power density reaches 10⁹ W/cm ² on the target surface. Some results of copper thin films are presented. Due to the high expansion velocity of 10⁴ m/s of the ablated target material a copper-matrix has been masked     

Photoluminescence of green nanophosphors Sr2MgSi2O7 doped with Tb3+ under 374-nm excitation

A series of Sr₂MgSi₂O₇:Tb³⁺ nanophosphors is prepared using a high-temperature solid-state reaction. The x-ray diffraction patterns show that the crystal structure of the sample is not significantly affected by Tb³⁺ ions. However, the images of the scanning electron microscope illustrate that the average size of nanoparticles becomes larger with the increase of Tb³⁺ concentration. Unlike earlier investigations on down-conversion emission of Tb³⁺ ion excited by deep ultraviolet light, in this work, the photoluminescence characteristics of Sr₂MgSi₂O₇ nanophosphors doped with different Tb³⁺ concentrations are analyzed under 374-nm excitations. The intense green emission at 545 nm is observed at an optimal doping concentration of 1.6 mol%. The main reason for the concentration quenching is due to the electric dipole-electric dipole interaction among Tb³⁺ ions.     

Energy distributions of ions produced by electron-stimulated desorption

We have measured the initial kinetic energy distributions of ions produced by electron bombardment of various oxides and halides. The instrument used allows ions directly ejected from the sample surface to be distinguished from ions formed by electron impact in the gas phase. Singly and multiply charged positive ions of species present in the matrix as anions and cations were desorbed by high energy ( 11 keV) electron impact. Directly desorbed positive halogen ions show a narrow, low energy peak, consistent with conventional models of electron stimulated desorption (ESD). In addition, some of the cation species exhibited similar narrow energy spectra. Charge states up to +6 were observed for the halides; with the exception of F²⁺ and Cl²⁺, multiple charge states were due to electron impact ionization of desorbed neutrals. Charge states up to +4 were seen for silicon from electron-bombarded SiO₂; energy distributions of Si⁺, Si²⁺ and Si³⁺ showed that these species were desorbed directly from the surface. The energy distributions of O⁺ and O²⁺ ions ejected from SiO₂ are relatively wide, compared to the energy distribution of Si⁺ ions. In contrast, O⁺ ions ejected from TiO₂ have a much narrower energy distribution, like those observed for the halogen ions.     

A two-component model for the electron distribution function in ahigh-current pseudospark or back-lighted thyratron

Temperature, energy, and densities of two electron distribution function components, including an isotropic bulk part and an anisotropic beam, are analyzed for a hydrogen pseudospark and/or back-lighted thyratron switch plasma with a peak electron density of 1-3×10¹⁵ cm^-3 and peak current density of ≈10⁴ A/cm². Estimates of a very small cathode-fall width during the conduction phase and high electric field strengths lead to the injection of an electron beam with energies ⩾100 eV and density of 10¹³-10¹⁴ cm^-3 into a Maxwellian bulk plasma. Collisional and radiative processes of monoenergetic beam electrons, bulk plasma electrons and ions, and atomic hydrogen are modeled by a set of rate equations, and line intensity ratios are compared with measurements. Under these high-current conditions, for an initial density n_H2=10¹⁶ cm^-3 and electron temperature of 0.8-1 eV, the estimated beam density is ≈10¹³ -10¹⁴ cm^-3. These results suggest the possibility of producing in a simple way a very high-density electron beam     

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实验研究了超强激光与平面薄膜Cu靶的相互作用中,在靶背法线方向产生的离子能量分布.实验中采用固体核径迹探测器CR39和Thomson谱仪相结合测量离子能谱.实验中同时测量到了质子和C4+、C3+、C2+和C1+离子.实验结果表明:离子沿着靶背法线方向发射,离子在一定能量处出现截断;在固体核径迹探测器CR39上可以看出碳离子信号比质子信号弱,质子的产额远高于碳离子,质子对碳离子有屏蔽作用;在相同发次中C4+、C3+、C2+和C1+离子随着荷质比的增大,相应离子的截止能增加.     

稀土离子(Eu3+,Tb3+,Ce3+)掺杂ZnAl2O4/SiO2微晶玻璃的制备与发光性能

采用凝胶法分别制备出4.5ZnO-5.5Al₂O₃-90SiO₂(ZAS)以及ZAS[DK]:RE³⁺ (RE=Eu,Tb,Ce) 透明微晶玻璃。利用X射线衍射仪(XRD)、透射电子显微镜(TEM)和荧光光谱仪(PL)等测试手段,研究了稀土离子掺杂浓度对ZAS微晶玻璃的结构和发光性能的影响。XRD结果表明,ZAS[DK]:RE³⁺ (RE=Eu,Tb,Ce)微晶玻璃包含ZnAl₂O₄晶相和SiO₂非晶相,ZnAl₂O₄平均晶粒尺寸约为30 nm,稀土离子的掺杂没有显著改变原来的ZnAl₂O₄晶体结构。TEM结果表明,900 ℃时ZnAl₂O₄从ZAS体系中析出。PL光谱显示,Eu³⁺ 存在 ⁵D₀→⁷F₂跃迁,ZAS[DK]:Eu³⁺在611 nm 处发出强烈的红色光;由于Tb³⁺ 的⁵D₄→⁷F₅ 跃迁,ZAS[DK]:Tb³⁺在541 nm 处发出明亮的绿色光;ZAS[DK]:Ce³⁺ 在381 nm处显示了蓝光发射,对应于Ce³⁺ 的5d→4f 轨道跃迁。ZAS[DK]:RE³⁺ (RE=Eu, Tb, Ce)的PL发射光谱存在着浓度猝灭现象,Eu³⁺、Tb³⁺ 和Ce³⁺的最佳单掺杂摩尔分数分别为20%、20%和3%。CIE色度图表明,ZAS[DK]: RE³⁺ (RE=Eu,Tb,Ce)的色坐标分别位于红光、绿光和蓝光区域。实验结果表明,ZAS:RE³⁺ (RE=Eu,Tb,Ce) 微晶玻璃是一种良好的可用于全色显示的白光LED材料。     

Eu掺杂的高Gd玻璃荧光及闪烁发光性能研究

分别在空气和还原气氛下,采用高温熔融法制备了Eu 掺杂(1 wt%) 的15SiO₂-25B₂O₃-30Al₂O₃-30Gd₂O₃ 氧化物玻璃,对二者的光致发光和闪烁发光性能进行测试. 结果显示：还原气氛下制得的玻璃在395 nm 紫光和X 射线激发下,均可以得到450–550 nm 的Eu²⁺ 蓝绿发光和615 nm 的Eu³⁺ 红光;然而在不同的激发光源下,Eu²⁺ 和Eu³⁺发光强度比存在明显不同,395 nm 紫光激发下,Eu³⁺ 发光强度仅为Eu²⁺ 的0.02 倍,X 射线激发下,Eu³⁺ 发光强度变为Eu²⁺ 强度的1.37 倍. 通过声子边带谱分析,还原后玻璃中Si 形成体附近的Eu³⁺ 全部被还原为Eu²⁺,B 和Al形成体周围的Eu³⁺ 部分被还原为Eu²⁺. 进一步分析闪烁发光的机理表明：Gd 的敏化剂作用以及B 和Al 形成体周围Eu²⁺→Eu³⁺ 的能量传递都增强了还原玻璃中Eu³⁺ 的闪烁发光性能. 关键词： 高Gd玻璃 2+')" href="#">Eu²⁺ 闪烁发光 声子边带谱     

带有质量分析系统的强流质子束低能传输线研究

强流质子源与低能传输线（LEBT）是作为CIADS注入器的超导强流质子直线加速器的关键前端系统。目前LEBT采用双螺线管匹配结构设计,并安装有限制锥,但仍然不能避免少量H₂+和H₃+进入后端加速装置,这对直线加速器长期运行稳定性与可靠性会产生一定影响。为此,在LEBT加入分析磁铁对混合束（H+,H+2,H₃+）进行分离再注入后端加速器腔体,将是一个有效的方案。本研究对经过带有30度分析磁铁的LEBT的强流质子束的束流品质进行了模拟与实验测量。结果表明,分析磁铁高阶磁场的影响使经过分析磁铁的强流质子束束流品质变差,并且该影响随着束流包络的增大而增大。这些结果为CIADS注入器的低能传输线设计提供了参考依据。High current proton source and the low energy beam transport(LEBT) are the key front-end systems for CIADS injector:high current proton linac accelerator. CIADS injector's LEBT adopts double solenoid matching structure, using a limit cone which can partially avoid H₂+ and H₃+ which injecting into the back-end linac accelerator may impact the long-term stability and reliability of the whole system. It will be an effective method to separate the hybrid ions (H+, H₂+, H₃+) by adding a dipole magnet at LEBT. In this article, we simulated and mesasured the high current proton beam quality behind the LEBT with a 30 degree dipole. The results show that the the proton beam quality is significantly effected by high-order magnetic fields of the dipole magnet, and the effect increases with the increase of the beam envelope. The achieved result is useful for the LEBT design of CIADS injector.     

Secondary ion emission from clean and K-covered Ni surfaces near threshold impact energies

Clean and K-covered Ni surfaces are bombarded with low energy (10–500 eV) beams of He⁺, Ne⁺, Ar²⁺, and Kr⁺ ions, and the emitted ion yield is measured as a function of beam energy. The apparent threshold energies for K⁺ and Ni⁺ emission are proportional to the ionic binding energies of K⁺ and Ni⁺ to the Ni surface. From comparison of the ion and neutral yield curves, it is suggested that these ions are emitted via momentum transfer collisions similar to neutral sputtering.     

Study of the electron damage of the MgO(100)-D2O system by ESD

An electron-stimulated desorption (ESD) study of electron damage of a D₂O layer adsorbed on the MgO(100) surface at room temperature is presented. After exposing the surface to D₂O, the surface spectrum shows the main ESD component to be D⁺ ions, with lower intensity signals corresponding to O⁺ and OD⁺ ions. When the surface is simultaneously exposed to heavy water and electron bombardment, there is a rapid initial increase of the D⁺ intensity accompanied by a decrease of the intensity of the O⁺ ions. Electron damage of the surface after exposing to D₂O produces a significant decrease of the D⁺ intensity, while the O⁺ and OD⁺ intensities decrease more slowly. Heavy water adsorption does not change the form of the ion kinetic energy distribution of the O⁺ ions with electron dose, except for a decrease in intensity. Electron damage increases the intensity of the ion kinetic energy distribution of D⁺ again without changing its shape. These experiments show that heavy water adsorption under electron bombardment does not induce any chemistry of the adsorbed species, but enhances the fragmentation rate of the OD species which, in turn, increases the yield of D⁺ ions. Values of total desorption cross-sections for the three ions species are reported.     

高低温条件下氟化锂材料的离子激发发光光谱分析

在北京师范大学GIC4117串列加速器原有离子激发发光(ion beam induced luminescence,IBIL)分析靶室基础上,安装了可实现80—900 K温度范围内精确控温的冷热样品台,实现高低温条件下IBIL光谱的测量.添加金硅面垒探测器,在离子辐照材料样品过程中同步采集背散射离子的计数,实现束流的在线监测.在不同温度下,利用2 MeV H~+束轰击氟化锂样品,获得的IBIL光谱中可明显观察到温度对不同发光中心发光效果的影响:激子峰和杂质峰发光在低温条件下更为清晰;高温时各类型F色心的发光强度在较小的注量下即可达到饱和值或开始衰减.辐照初期受扰激子峰(296 nm)发光强度的上升过程表明不能排除受扰激子峰与点缺陷发光中心相关的可能性,激子峰强度的上升源自低注量时核弹性碰撞产生的应变键;温度对空位迁徙速率及非辐射复合的影响是造成发光强度随注量演变差异的重要原因.