强流脉冲电子束作用下钽金属靶膨胀的轴向约束

研究了强流脉冲电子束与钽金属靶相互作用后靶材流体动力学膨胀的轴向约束问题。由于电子束在金属钛和钽内的能量沉积存在差异,未完全气化的钛箔对气化膨胀的钽材能够起到约束作用,并且可以通过吸收钽的能量来降低钽的膨胀速度。通过分析比较电子束在靶上形成孔洞的形貌以及高速相机拍摄得到的不同时刻靶材喷射的图像,证实了钛箔能够对钽金属靶的轴向膨胀起到一定的约束作用。尤其是电子束打靶过后1μs内的初始阶段,约束效果比较明显。     

高能通量脉冲电子束作用下钽靶破坏初步研究

 使用Monte-Carlo程序MCNP在2维情况下模拟得到了高能通量脉冲电子束在钽金属靶中的能量沉积。根据能量沉积的模拟结果以及实验后靶上穿孔的大小和形貌,提出了电子束对不同结构钽金属靶破坏的物理机制。由于能量沉积的差异,1 mm实心靶中的热激波在一定时间内沿径向和轴向持续对靶材进行压缩,而在叠靶中这种压缩效果并不明显,因此实验后1 mm实心靶上穿孔的大小几乎是叠靶上的两倍。根据理论模型分析得到的靶材熔融喷射和层裂现象与实验结果相吻合。     

强流脉冲电子束轰击下回喷靶材速度测量与数值模拟

 叙述了用高速摄影技术研究强流脉冲电子束与钽金属靶相互作用后靶材的回喷现象,得出了靶材回喷的速度。并且采用EGS4程序和Euler流体力学方程组分别模拟了电子束在靶内的能量沉积和束靶相互作用的动力学过程。实验表明,钽金属靶在强流脉冲电子束轰击下,回喷靶材的轴向速度大于2.9 mm/μs,而模拟结果表明理想情况下回喷靶材自由面的轴向速度可达9.7 mm/μs。实验和理论计算为阻挡回喷靶材的快门设计提供了必要的参数。     

用高速显微摄影技术测量神龙一号上回喷靶材速度

用高速显微摄影技术对强流脉冲电子束轰击钽金属靶的过程进行了研究,获得了“神龙一号”加速器上靶材回喷过程的实验图像.实验表明,钽金属靶在强流脉冲电子束的作用下,有强烈的热释光现象产生,靶材的回喷粒子的轴向速度可达4.7 mm/μs.     

不同入射角度下强流脉冲电子束能量沉积剖面和束流传输系数模拟计算

 强流脉冲电子束在材料中的能量沉积剖面、能量沉积系数和束流传输系数受其入射角的影响很大，理论计算了0.5~2.0MeV的电子束以不同的入射角在Al材料中的能量沉积剖面和能量沉积系数，并且还计算了0.4~1.4MeV电子束以不同入射角穿透不同厚度C靶的束流传输系数。计算结果表明，随着入射角的增大，靶材表面层单位质量中沉积的能量增大，电子在靶材料中穿透深度减小，能量沉积系数减小，相应的束流传输系数也减小；能量为0.5~2.0MeV的电子束当入射角在60°~70°时在材料表面层单位质量中沉积的能量较大。     

强流电子束加载下Ta,Al,Cu的温度测量

利用六波长瞬态光学高温计测量了"神龙一号"加速器发射的高能电子束与靶材作用后靶受作用区的温度变化过程。获得了厚度为0.1~0.25mm的Ta,Al和Cu片靶与强流电子束作用后的温度变化过程,最高温度接近9000K,达到了温密物质区域。实验结果表明,利用"神龙一号"加速器发射的强流电子束与特定靶材作用可以获得可供观测的温密物质,而多波长瞬态光学高温计是测量这种温密物质的温度变化的有效手段。     

强流相对论电子束与靶物质相互作用

本文用经典理论、双流不稳定性理论及磁增强效应,计算了强流相对论电子束在靶物质中的射程及沉积功率。认为反常吸收是靶物质对强流相对论电子束的主要能量吸收机制,考虑双流不稳定性效应及磁增强效应就可以比较好地解释实验结果。     

电子束在材料中的能量沉积和热激波特性

采用解析法、矩方法和Monte Carlo法等方法,计算了电子束在硬铝靶材中的能量沉积.计算表明,3个结果基本符合.根据得出的能量沉积结果和一维应变弹塑性流体动力学模型,计算了电子束热激波在硬铝靶材中的传播,并将其应力峰值的计算值与实测值进行了比较.     

4 MeV闪光X光机轫致辐射靶设计

对4 MeV闪光X光机的轫致辐射靶参数进行了设计和模拟计算。利用蒙特卡罗程序,计算得到当轫致辐射靶的有效钽靶材厚度约为0.6 mm时,靶正前方1 m处产生的单脉冲X光的照射量值最大,可以达到约2.86×10－3 C/kg,满足4 MeV闪光X光机对其单脉冲X光的设计要求。对不同能量下的单脉冲电子束加载在轫致辐射靶上的能量沉积密度进行了计算和比较,分析研究了不同结构下的靶破坏,结果表明:轫致辐射靶采用叠靶结构的钽靶能够满足4 MeV闪光机的实验需求。     

12MeV直线感应加速器轫致辐射靶靶面回流离子测量

强流直线感应加速器（LIA）能够产生2—3kA、10-20MeV、约80ns（FWHM）的强流高功率的脉冲电子束，经过数十米的传输、聚焦成毫米量级的束斑后打击到轫致辐射靶上，来产生高剂量的X光。同时电子束打靶使靶面沉积大量的能量导致靶面的温度骤然升高，引起靶表面物质或杂质（如碳、氢、水蒸气与靶材料等）被汽化电离而产生等离子体。强流电子束在靶前附近产生的强空间电荷电场（场强可达MV／cm）把离子从靶面拉出，以逆着电子束的方向前进，被称为回流离子。人们提出回流离子与电子束发生作用，会导致电子束被提前聚焦，在预定的靶面形成散焦。     

12MeV直线感应加速器X光能谱的实验测量

12MeV直线感应加速器能够产生能量～12MeV、流强2.2kA的电子束, 被传输、聚焦后形成～4mm的束斑, 与轫致辐射靶靶作用来产生高剂量的X光. 首先设计了X光探测器, 并利用多层吸收拟合法来对X光能谱进行了测量, 得到了X光的轫致辐射能谱, X光峰值大约在2MeV,最后对实验结果进行了分析.     

“闪光二号”电子束辐照平板靶产生热击波的实验研究

 热击波是电子束辐照靶材料时在其内产生材料响应的一个重要力学现象。论述了近两年来我们在“闪光二号”装置上进行电子束辐照平板靶产生热击波的实验研究。使用的靶厚为2.8~6.5 nm,靶材为LY-12铝,靶上能通量为87~152 J/cm²。实验结果表明,实测热击波应力峰值为0.35~2.0 GPa,热击波平均作用时间约为0.29 μs,均半高宽约为0.14 μs,平均上升时间约为0.10 μs。     

Optimization studies of photo-neutron production in high-<Emphasis Type="Italic">Z</Emphasis> metallic targets using high energy electron beam for ADS and transmutation

Monte Carlo calculations have been performed using MCNP code to study the optimization of photo-neutron yield for different electron beam energies impinging on Pb, W and Ta cylindrical targets of varying thickness. It is noticed that photo-neutron yield can be increased for electron beam energies ≥100 MeV for appropriate thickness of the target. It is also noticed that it can be maximized by further increasing the thickness of the target. Further, at higher electron beam energy heat gradient in the target decreases, which facilitates easier heat removal from the target. This can help in developing a photoneutron source based on electron LINAC by choosing appropriate electron beam energy and target thickness to optimize the neutron flux for ADS, transmutation studies and as high energy neutron source etc. Photo-neutron yield for different targets, optimum target thickness and photo-neutron energy spectrum and heat deposition by electron beam for different incident energy is presented.      

Photoproduction of high-energy neutrons in thick targets by electrons in the energy range 150 to 270 MeV

Photoneutron spectra with energies greater than 12 MeV produced by electrons incident on a thick lead target have been measured for primary electron energies between 150 and 266 MeV and at a fixed angle of 90 ° to the beam axis. Measurements of the neutron yield have furthermore been performed at a primary energy of 234 MeV as a function of target depth for the same lead target and as a function of the mass number for C, Al, Cu, Cd and Pb targets. The results were obtained with three independent neutron detectors: two proton recoil counters and one time-of-flight set-up. The high-energy regions of the spectra are compared with the predictions of the phenomenological quasi-deuteron model and a satisfactory agreement in shape and scale of the spectra is found. Additional high-energy neutrons from pion reabsorption processes were observed at electron energies of 234 and 266 MeV.     

C波段加速器初步热测实验

为了开展加速器小型化技术研究,进行了C波段2 MeV驻波加速器研制工作。目前,该加速器研制取得了显著进展,完成了全密封加速管的焊接,建立了加速器热测实验平台。在重复频率50 Hz情况下,进行了初步热测出束实验,利用电离室剂量仪测试了加速器靶前1 m处的X射线剂量率,并利用钢吸收法测试了电子束的能量。初步实验结果表明:电子束能量约2.5 MeV,剂量率超过330 mGy/(minm)。     

BEPCⅡ Positron Source

BEPCⅡ— an upgrade project of the Beijing Electron Positron Collider (BEPC) is a factory type of e^＋e^－ collider. The fundamental requirements for its injector linac are the beam energy of 1.89GeV for on-energy injection and a 40mA positron beam current at the linac end with a low beam emittance of 1.6μm and a low energy spread of ±0.5% so as to guarantee a higher injection rate (≥50mA/min) to the storage ring. Since the positron flux is proportional to the primary electron beam power on the target, we will increase the electron gun current from 4A to 10A by using a new electron gun system and increase the primary electron energy from 120MeV to 240MeV. The positron source itself is an extremely important system for producing more positrons, including a positron converter target chamber, a 12kA flux modulator, the 7m focusing module with DC power supplies and the support. The new positron production linac from the electron gun to the positron source has been installed into the tunnel. In what follows, we will emphasize the positron source design, manufacture and tests.     

Laser Accelerated, High Quality Ion Beams

Intense beams of protons and heavy ions have been observed in ultra-intense laser-solid interaction experiments. Thereby, a considerable fraction of the laser energy is transferred to collimated beams of energetic ions (e.g. up to 50 MeV protons; 100 MeV fluorine), which makes these beams highly interesting for various applications. Experimental results indicate very short pulse duration and an excellent beam quality, leading to beam intensities in the TW range. To characterize the beam quality and its dependence on laser parameters and target conditions, we performed experiments at several high-power laser systems. We found a strong dependence on the target rear surface conditions allowing to tailor the ion beam by an appropriate target design. We also succeeded in the generation of heavy ion beams by suppressing the proton amount at the target surface. We will present recent experimental results demonstrating a transverse beam emittance far superior to accelerator-based ion beams. Finally, we will discuss the prospect of laser-accelerated ion beams as new diagnostics in laser-solid interaction experiements. Special fields of interest are proton radiography, electric field imaging, and relativistic electron transport inside the target.     

电子束放射照相的特性与参数优化

短脉冲强激光产生的电子束具有源尺寸小、脉宽窄、准单能谱等特点, 在放射照相诊断中具有独特作用. 本文通过分析电子在材料中散射并采用蒙特卡罗方法数值模拟, 研究了100 keV到几百MeV能量电子束对有厚度起伏或存在界面的靶的透视, 并与质子、X射线束透视结果比较, 给出了电子束放射照相的特性与参数优化: 基于电子在材料中非弹性散射或能量损失, 选用能量使其射程与靶厚度接近的电子束来诊断靶厚度不均匀性; 基于电子在材料中的弹性散射, 选用射程超过靶厚度的电子束来诊断靶界面.