高能光源束流位置探测器支撑架结构优化设计

从热稳定性和振动稳定性两个角度出发,优化设计得到了超高稳定的刚性支撑架结构;通过ANSYS有限元模态分析,验证了结构的热膨胀变化量和特征频率;采用混凝土二次灌浆方法对支撑架进行地面固定和特征频率测试,结果表明,支撑架结构的特征频率达到61.9 Hz、振动幅值小于30 nm,均满足设计要求。最后采用动态刚度测试方法,得到混凝土二次灌浆层的主要刚度值,进一步验证支撑架结构优化结果的准确性。     

双极性固态直线变压器驱动器的研制

在针对脉冲电磁场肿瘤消融的应用场合,双极性脉冲比单极性脉冲效果更均匀,而要产生ns级前沿的双极性高压纳秒或亚微秒脉冲难度大,电磁干扰强,控制要求更高。设计了一台双极性全固态直线型变压器驱动源(SSLTD),双极性SSLTD由结构完全相同的LTD模块经过副边绕组反向串联构成,在负载上实现双极性窄脉冲。双极性SSLTD输出波形稳定的脉冲的关键在于磁芯复位,通过电阻负载实验,重点对比分析了复位电流的形式对复位效果的影响,以及采用直流复位时幅值、脉宽、正负脉冲时间间隔、单级模块中开关管并联数量、复位电流大小对双极性SSLTD输出的影响。实验结果表明,所设计的双极性SSLTD能够在500 Ω负载上稳定产生重频双极性纳秒脉冲,输出电压0～±5 kV可调,脉宽200～400 ns可调,正负脉冲时间间隔0～1 ms可调,上升沿和下降沿20～50 ns;反向串联的直流复位电路结构简单、复位效果好。该脉冲源使用模块化设计,结构紧凑,电气绝缘要求较低,可灵活输出双极性、正极性与负极性高压亚微秒脉冲。     

变压器寄生参数和负载特性对高压脉冲波形的影响

构建了输出电压幅值为0～20 kV、脉冲重复频率为0.25～20 kHz的双极性高压脉冲电源实验平台,研究了变压器寄生参数与负载特性对输出脉冲波形的影响。采用等效电路复频域解析方法,分析了变压器寄生参数对输出脉冲波形的上升沿、平顶及下降沿的影响规律,并通过改变变压器绕线方案间接验证。发现变压器分布电容和漏感越大,输出脉冲波形上升沿与下降沿越平缓,过冲电压幅值越大,并采用脉冲变压器二次侧均匀密绕、一次侧均匀疏绕、高匝数的方案进行优化。进一步分析了纯阻性、阻容性或阻感性负载特性对输出高压脉冲波形的影响规律,发现电阻值增大（5～50 kΩ）,过冲电压幅值增大,脉冲上升沿和下降沿变陡;当负载电阻回路串联小电容时,过冲电压幅值显著增大,而电容值高于一定值时输出脉冲波形恢复至与纯电阻波形一样;当负载电阻回路串联电感时,输出脉冲波形下降沿变平缓。     

基于双平行马赫-曾德尔调制器和平衡光电探测器的四倍频可调对称三角形函数波形信号发生器

提出并研究了一种基于双平行马赫-曾德尔调制和平衡光探测的四倍频可调对称三角形函数波形信号发生器.将调制非线性和多参量调控应用到可调对称三角形波形信号的产生中,可实现四倍频信号输出.通过调整调制系数β和时延量τ,可实现光电流表达式向目标函数波形微波信号傅里叶展开式前三项的近似表征,最后得到四倍于射频调制频率的周期性三角形...     

Coherent Control of High Harmonic Generation Driven by Metal Nanotip Photoemission

Steering ultrafast electron dynamics with well-controlled laser fields is very important for generation of intense supercontinuum radiation. It can be achieved through coherent control of the symmetry of the interaction between strong-field laser fields and a metal nanotip. We employ a scheme of two-color laser pulses combined with a weak static field to realize the control of a single quantum path to generate high harmonic generation from a single solid-state nanoemitter. Moreover, a smooth and ultrabroad supercontinuum in the extreme ultraviolet region is obtained, which can produce a single attosecond pulse. Our findings are beneficial for efficient generation of isolated sub-100 as XUV pulses from solid-state sources.     

Broadband Sheet Parametric Oscillator for x~((2)) Optical Frequency Comb Generation via Cavity Phase Matching

We demonstrate a broadband optical parametric oscillation, using a sheet cavity, via cavity phase-matching. A21.2 THz broad comb-like spectrum is achieved, with a uniform line spacing of 133.0 GHz, despite a relatively large dispersion of 275.4 fs~2/mm around 1064 nm. With 22.6% high slope efficiency, and 14.9 kW peak power handling, this sheet optical parametric oscillator can be further developed for x~((2)) comb.     

Two-proton radioactivity within Coulomb and proximity potential model

Considering the preformation probability of the two emitted protons in the parent nucleus, we extend the Coulomb and proximity potential model (CPPM) to systematically study two-proton (2p) radioactivity half-lives of the nuclei close to proton drip line. The proximity potential chosen is Prox. 81 proposed by Blocki et al. in 1981. Furthermore, we apply this model to predict the half-lives of possible 2p radioactive candidates whose 2p radioactivity is energetically allowed or observed but not yet quantified in the evaluated nuclear properties table NUBASE2016. The predicted results are in good agreement with those from other theoretical models and empirical formulas, namely the effective liquid drop model (ELDM), generalized liquid drop model (GLDM), Gamow-like model, Sreeja formula and Liu formula.     

A general framework for describing photofission observables of actinides at an average excitation energy below 30 MeV

A reasonable prediction of photofission observables plays a paramount role in understanding the photofission process and guiding various photofission-induced applications, such as short-lived isotope production, nuclear waste disposal, and nuclear safeguards. However, the available experimental data for photofission observables are limited, and the existing models and programs have mainly been developed for neutron-induced fission processes. In this study, a general framework is proposed for characterizing the photofission observables of actinides, including the mass yield distributions (MYD) and isobaric charge distributions (ICD) of fission fragments and the multiplicity and energy distributions of prompt neutrons (n_p) and prompt γ rays (γ_p). The framework encompasses various systematic neutron models and empirical models considering the Bohr hypothesis and does not rely on the experimental data as input. These models are then validated individually against experimental data at an average excitation energy below 30 MeV, which shows the reliability and robustness of the general framework. Finally, we employ this framework to predict the characteristics of photofission fragments and the emissions of prompt particles for typical actinides including ²³²Th, ^{235, 238}U and ²⁴⁰Pu. It is found that the ²³⁸U(γ, f) reaction is more suitable for producing neutron-rich nuclei compared to the ²³²Th(γ, f) reaction. In addition, the average multiplicity number of both n_p and γ_p increases with the average excitation energy.     

Systematic study on α-decay half-lives of uranium isotopes with a screened electrostatic barrier

In the present work, we systematically study the α-decay half-lives of uranium (Z=92) isotopes based on the Gamow model with a screened electrostatic barrier. There are only two adjustable parameters in our model i.e. the parameter g and the screening parameter t in the Hulthen potential for considering the screened electrostatic effect of the Coulomb potential. The calculated results are in good agreement with experimental data, and the corresponding root-mean-square (rms) deviations of uranium isotopes with α transition orbital angular momentum l=0 and l=2 are 0.141 and 0.340, respectively. Moreover, we extend this model to predict α-decay half-lives of uranium isotopes whose α decay is energetically allowed or observed but not yet quantified in NUBASE2020. For comparison, the modified Hatsukawa formula (XLZ), the unified Royer formula (DZR), the universal decay law (UDL) and the Viola–Seaborg–Sobiczewski formula (VSS) are also used. The predictions are basically consistent with each other. Meanwhile, the results also indicate that N=126 shell closure is still robust at Z=92 and the spectroscopic factor \begin{document}$ S_{\alpha} $\end{document} is almost the same for uranium isotopes with the same l.     

Entropic destruction of heavy quarkonium in a rotating hot and dense medium from holography

Previous studies have indicated that the peak of the quarkonium entropy at the deconfinement transition can be related to the entropic force, which would induce the dissociation of heavy quarkonium. In this study, we investigated the entropic force in a rotating hot and dense medium using AdS/CFT correspondence. It was found that the inclusion of angular velocity increases the entropic force, thus enhancing quarkonium dissociation, while chemical potential has the same effect. The results imply that the quarkonium dissociates easier in rotating medium compared with the static case.