超短激光与薄膜靶作用加速产生质子初步研究

物理学家利用高能粒子加速器进行了多方面的研究，但高能粒子加速器庞大且耗资巨大。随着超短超强激光的发展，现在的激光的功率密度可达到10^22W／cm^2。许多实验室利用不同功率密度的激光与固体靶、薄膜靶及气体等相互作用，进行加速产生高能粒子的研究。其中，利用超短超强激光与薄膜薄相互作用加速产生质子是一重要的研究课题，利用超热电子加速产生超热电子，     

强激光与固体靶相互作用所致硬X射线剂量和能谱的实验测量

为了研究强激光与固体靶相互作用产生的电离辐射危害,本文在星光Ⅲ300TW强激光装置上开展了一系列激光打靶实验。实验使用的激光功率密度为5×10~(18)~4×10~(19)W/cm~2,激光脉冲能量为60~153J,靶为直径1mm、厚度1mm的Ta圆柱,本文分别对X射线剂量、X射线能谱和超热电子能谱进行了测量。实验结果表明,测量到的单发最大X射线剂量约为16.8mSv,靠近激光传播方向(0°),距靶50cm处;激光0°方向的X射线剂量随激光功率密度的增加而显著增加,激光90°方向的X射线剂量随激光功率密度的变化相对较小;测量到的X射线能谱可大致用含有两个X射线温度的指数分布函数描述,其中0°方向测量到的X射线温度为0.4~1.15 MeV,90°方向测量到的X射线温度为0.25~0.54 MeV;实测超热电子温度与Wilks定标率符合较好。     

超短脉冲激光辐照固体靶产生超热电子研究

实验研究了超短脉冲激光辐照固体靶产生的超热电子温度 ,所用方法是测量超热电子在固体中韧致辐射产生的硬X射线 ( >30keV)能量连续谱。中等强度 ( 1 0 16W /cm2 )、无预脉冲、红外超短脉冲( 74 4nm ,1 30fs,6mJ)、P极化激光 4 5°照射 5mm铜靶 ,产生了能量为 4 0 0keV的X射线信号 ,利用Maxwellian分布拟合能谱得到的超热电子温度为 85keV ,产生高能电子的主导吸收机制为真空加热。     

超短脉冲激光与固体靶相互作用的硬X射线能谱

本实验使用高纯锗探测器，运用单光子法，对超短脉冲激光与固体铜靶相互作用产生的硬X射线能谱进行测量。实验结果表明：在激光强度I≈8×10¹⁶W/cm²的P极化光以45°入射角照射5 mm铜靶、探测立体角为4.5×10^－6的实验条件下，产生的硬X射线的能量主要集中在低于100keV能量范围内，超热电子温度分别为(7.4±0.7)keV和(19.5±1.6)keV。     

超热电子能谱测量

采用180电子磁谱仪方法测量了超短(120 fs)红外(744 nm)脉冲激光与固体等离子体相互作用产生的超热电子能谱。激光参数为无预脉冲、45斜入射的P激化光,靶为5 mm的铜,靶表面经机械抛光,靶上功率密度为1016 W/cm2。谱仪设置在入射激光的正反射方向,测量到的能谱采用 Maxwellian(e     

强激光与固体靶相互作用所致硬X射线的辐射安全初步研究

激光技术的迅速发展使得国际国内涌现出一批强激光装置,而这些装置中强激光与固体靶相互作用所致硬X射线产生的辐射危害也逐渐被人们发现和重视.通过广泛的调研,对强激光与固体靶产生硬X射线的物理过程及其源项特点进行了分析和讨论,包括激光到电子的能量转换效率,热电子能谱和电子温度,以及热电子所产生硬X射线的能谱等,并且得到了激光强度在1014到1020 W/cm2之间的激光与靶相互作用后,产生的X射线剂量的初步评估结果.最后以斯坦福直线加速器中心(SLAC)的一个强激光装置为例,介绍了其辐射安全系统的初步设计.研究结果为强激光装置的辐射安全评估及其安全系统设计提供了相关参考.     

不同黑腔的X光辐射和散射光特性实验研究

在神光Ⅱ三倍频实验中，设计了多种半腔靶构型，研究不同黑腔构型的X光辐射和散射光特性。采用多种探测设备对多角度辐射温度、软X光谱、M带角分布、X光总量、超热电子、散射光、漏激光和受激拉曼散射（SRS）等物理量进行了综合测量，并比较了不同靶型的相关物理量。     

电子磁谱仪法测量超热电子温度

利用超热电子磁谱仪测量了紫外超短脉冲激光与固体等离子体相互作用产生超热电子的能谱,在无预脉冲、激光强度为1017 W/cm2 条件下,紫外超短脉冲激光与固体(Cu)等离子体相互作用产生超热电子的能谱呈双温麦克斯韦分布,超热电子温度为81 keV,激光吸收的主导机制为真空吸收。     

短波长激光超热电子产生和抑制机理的研究

介绍了在“神光Ⅰ”和“星光Ⅱ”上分别进行的二倍频、三倍频激光照射金盘靶、腔靶、碳氢有机膜平面靶的实验。通过测量硬X光谱推断超热电子特性,结合受激Raman散射光(SRS)和双等离子体衰变(TPD)产生的3/2ω_0谐波的观测,分析各种靶超热电子产生和抑制的机理,并探讨了抑制超热电子的有效途径。     

超短脉冲激光与固体等离子体相互作用实验研究

实验研究了超短脉冲激光（744nm/120fs/12mJ）与固体（Cu）等离子体相互作用产生超热电子的能谱与角分布,利用电子磁谱仪与成像板（IP）探测器测量能谱,采用IP在入射平面内测量角分布。在无预脉冲、P极化激光45°斜入射下,采用Maxwellian分布拟合得到的超热电子温度为46keV,超热电子主要沿靶法线方向发射。产生超热电子的主导机制为真空加热,等离子体的电荷分离势约为70keV。     

Effect of Foil Target Thickness in Proton Acceleration Driven by an Ultra-Short Laser

Proton acceleration experiments were carried out by a 1.2 x 101s W/cm2 ultra-short laser interaction with solid foil targets.The peak proton energy observed from an optimum target thickness of 7μm in our experiments was 2.1 MeV.Peak proton energy and proton yield were investigated for different foil target thicknesses.It was shown that proton energy and conversion efficiency increased as the target became thinner,on one condition that the preplasma generated by the laser prepulse did not have enough shock energy and time to influence or destroy the target rear-surface.The existence of optimum foil thickness is due to the effect of the prepulse and hot electron transportation behavior on the foil target.     

吸收法在强激光与固体靶所致脉冲X射线能谱测量中的研究进展北大核心CSCD

脉冲X射线能谱测量,对于强激光装置中的物理诊断以及辐射防护具有重要意义。脉冲X射线具有脉冲时间短、注量大、能谱范围宽等特点,常规脉冲测量技术往往受到探测器死时间、堆积效应的限制而无法适用。目前多个国家都建立了强激光装置的研究平台,并开展X射线能谱测量相关研究。本文首先介绍了基于吸收法原理且适用于中低能脉冲X射线的测量方法:Ross Pair法和衰减法。然后针对这两种方法从5个方面(探测器结构、滤片材料、探测介质选择、散射控制以及解谱方法)综述了脉冲X射线吸收谱仪的研究进展,并分析了各自的适用性。目前激光装置中脉冲X射线能谱的测量还面临着能量分辨率不理想、结果不确定度无法量化和被动式能谱测量操作不便等问题。随着激光装置的不断升级,脉冲X射线注量以及打靶频次将不断增加,对探测器的耐辐照性能以及响应速度提出了更高的要求。     

硅材料和二极管的单粒子位移损伤的多尺度模拟研究

基于二体碰撞近似理论（BCA）,应用分子动力学（MD）和动力学蒙特卡罗（KMC）方法相结合的多尺度模拟方法,研究了单粒子位移损伤（SPDD）缺陷及电流的演化过程。研究结果表明,SPDD事件中引起的缺陷在106 s内分为3个阶段：阶段Ⅰ(1×10-11 s≤t<2×10-3 s)以点缺陷成团为主;阶段Ⅱ(2×10-3 s ≤t<2×102 s)中以缺陷团内部的间隙原子和空位复合反应为主;阶段Ⅲ(t≥2×102 s)中以小缺陷团发射间隙原子和空位为主。提出一种计算粒子在硅二极管中引起的SPDD电流的方法,推导了多种缺陷存在时引起的二极管反向电流增加的计算公式。基于KMC模拟的位移损伤缺陷演化结果,计算了光电二极管的SPDD电流密度及归一化退火因子。结果表明,KMC模拟计算的退火因子与文献实验测量结果相一致,建立的多尺度模拟方法可预估硅器件的SPDD电流。     

激光与陡峭密度梯度等离子体相互作用电子加热机制研究

本文利用二维PIC模拟了超短超强激光与陡峭密度梯度等离子体相互作用过程中电子的加热机制。结果表明,在10²³ W/cm²的超短超强激光场与陡峭密度分布的μm级等离子体层相互作用的过程中有质动力加速、大幅度等离子体尾场及共振吸收共同决定了电子束的加速与加热。     

Simulation and Design of Biological Shield for the 115 kJ IR-MPF-100 Plasma Focus Device Using MCNP Code

The paper reports on the design of biological neutron shielding for IR-MPF100 plasma focus device which recently has been designed and constructed in plasma physics and nuclear fusion research institute. Plasma focus devices are known as pulsed intense sources of ionizing radiations such as hard X-ray and fast neutrons as a result of the formation of a hot dense plasma column then acceleration of energetic ions and electrons in the opposite directions. Therefore, taking into account a biological shield particularly for the operators of the PF device as radiation workers is crucial. Analytical calculations on the maximum permissible effective dose for radiation workers (for whole-body exposure) allow below 200 shots/year for IR-MPF100 operating at its nominal 115 kJ capacitor bank energy without any shielding wall. In order to decrease the personnel absorbed radiation dose and increase the maximum allowed shot per year the design considerations for a biological shield has been recognized using MCNP4C code. Our calculations was based on the effect of ordinary concrete, polyethylene mixed with 30 % natural boron and solid boric acid on the decrement of the absorbed dose. These calculations represent that using a double layer shield consists of 30 cm width of pure polyethylene as well as 10 cm lead, ends in appropriate decrement of the effective dose per shot from 0.1 mSv to 1.2 µSv, therefore increases the allowed usage of the device up to 15,600 annual shots.     

紫外超短激光驱动铜薄膜靶产生质子的实验研究

在中国原子能科学研究院的放电泵浦的紫外KrF超短脉冲激光放大装置上,开展了紫外超短脉冲激光与铜薄膜靶相互作用加速产生质子束的实验研究。紫外超短脉冲激光输出能量为30 mJ、波长为248 nm、脉冲宽度为500 fs,采用离轴抛物面镜聚焦获得激光聚焦功率密度为1.2×10¹⁷ W/cm²。激光以45°入射5 μm厚的铜薄膜靶,质子最大能量超过300 keV。紫外超短脉冲激光的高对比度和高吸收效率是紫外激光加速的优点。     

60Co辐照装置的辐射防护监测

对清华大学核能与新能源技术研究院的钻源辐照装置进行了辐射屏蔽分析和环境辐射监测。17年的安全运行表明：完善的安全联锁系统，主要工作人员相对固定，不断强化安全意识，制定严格的管理制度，定期进行个人和环境辐射监测是保证装置安全运行的必要条件。     

Numerical studies on pair production in ultra-intense laser interaction with a thin solid-foil

A theoretical and numerical model of photon and electron–positron pair production in strong-field quantum electrodynamics(QED) is described. Two processes are contained in our QED theoretical model, one is photon emission in the interaction of ultra-intense laser with relativistic electron(or positron), and the other is pair production by a gamma-ray photon interacting with the laser field.This model has been included in a PIC/MCC simulation code named BUMBLEBEE 1 D, which is used to simulate the laser plasma interaction. Using this code, the evolutions of electron–positron pair and gamma-ray photon production in ultra-intense laser interaction with aluminum foil target are simulated and analyzed. The simulation results revealed that more positrons are moved in the opposite direction to the incident direction of the laser under the charge separation field.     

Shielding study on iron and concrete assemblies of bremsstrahlung photons and photoneutrons from copper target bombarded by 18, 28 and 38 MeV electrons

Following the angular distribution measurements of bremsstrahlung photons and photoneutrons, we measured the distributions of photon and neutron dose rates in the iron and concrete assemblies using a copper target bombarded by 18, 28 and 38 MeV electrons at the electron linear accelerator (linac) of Hokkaido University. In this experiment, seven types of shielding assemblies of iron and concrete layers were used and the photon and neutron dosemeters were inserted into the assemblies to get the depth–dose distribution. The measured results were compared with the results calculated using the Monte Carlo code MCNP5 to verify the calculated results. The calculated results of the ambient dose equivalent rates were in agreement with the measured results within 30% accuracy. Since no work on the radiation behavior in the shielding wall of medical linac room has ever been reported, this work gives valuable benchmark data for the detailed shielding design with high accuracy.