预脉冲对超短激光与薄膜靶相互作用加速产生质子的影响

采用波长为744 nm、聚焦功率密度为6×10¹⁶W/cm²的超短激光分别与两种不同厚度的铝薄膜靶相互作用,根据鞘层加速机制在靶后法线方向测量质子束角分布和能谱随靶厚度的变化,研究了预脉冲对质子加速的影响。随着薄膜靶厚度的降低,质子计数迅速增加,但当薄膜靶厚度太薄时,激光预脉冲形成的预等离子体影响了薄膜靶的面型,导致质子横向发散角迅速增加,而薄膜靶面型的破坏减少了激光与等离子体相互作用过程中的电子回流,从而降低了超热电子的产生和鞘层加速电场的维持,影响了质子的加速能谱。因此,超短脉冲激光与薄膜靶相互作用加速产生质子束,应尽量降低预脉冲,不能采用太薄的薄膜靶,以避免预等离子体影响薄膜靶的面型,导致质子的能量降低、发散角增大。     

超短超强激光与薄膜铝靶作用加速产生质子的实验研究

实验研究了功率密度6×1016W/cm2、脉宽120fs的激光与5μm铝靶的相互作用,观测到了高能质子的产生。设计加工了用于测量质子能谱的Thomson质谱仪,用于快质子的测量。测得其能谱和产生的最高质子能量为180keV,同时测得质子发散全角为38°。     

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。     

电子能量损失谱仪用中高能电子枪的研制

研制了一台电子能量损失谱仪用的中高能电子枪。其产生的电子与原子、分子发生碰撞,通过谱仪收集、分析散射电子的动量和能量,可以获得靶的电子结构和碰撞动力学信息。该电子枪结构简单,由热阴极、栅极、阳极、聚焦极和偏转板组成;电子能量可调范围大(1-3 keV),操作简单。为了获得最优的束流条件,利用SIMION电子光学软件模拟了电子发射源大小和初始发散角对靶点处的束斑大小和束流发散角的影响。在电子能量为1.5 keV条件下,实验检验给出在离电子枪出口27 mm处可获得束径约为0.95 mm、束流发散角约0.93°和束流强度6.27mA的电子束,满足电子能量损失谱仪的使用要求。     

实验研究靶对超热电子行为的影响

研究了靶材料及靶厚度对超热电子产生机制及空间行为的影响。研究结果表明,在激光以45°角入射的条件下,靶材料对超热电子产生机制无明显影响,但靶材厚度对激光吸收效率有很大影响,而超热电子的空间行为并不随靶厚度变化,主要集中在靶前后表面的法线方向发射。     

超短超强激光与不同厚度的铝膜作用加速质子的实验研究

介绍了功率密度4×10¹⁶W/cm²,脉宽120 fs情况下超短超强激光分别与5和2.1 μm薄膜铝靶作用加速质子的实验。采用CR-39固体径迹探测器和Thomson谱仪结合测量得到质子能谱,并对实验结果进行分析。测得的5 μm铝靶的质子最大能量约为140 keV,2.1 μm铝靶的质子最大能量约为170 keV。2.1 μm铝靶的质子产额较5 μm铝靶的高1个量级。     

激光波长对超热电子产生影响的实验研究

实验研究了两种波长超短脉冲激光(744 nm/120 fs/12 mJ、248 nm/420 fs/35 mJ)与固体(Cu)等离子体的相互作用,利用电子磁谱仪与成像板探测器测量了激光入射平面内超热电子的能谱与角分布.在无预脉冲、P极化激光45°斜入射的条件下,采用Maxwellian分布拟合得到的超热电子温度分别为46和19.4 keV,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,实验验证了真空吸收定标率Th≈4.11×10-2(Iλ2)1/2.54(keV).等离子体的电荷分离势分别为70和45 keV.     

与ICF快点火相关的激光等离子体研究

高强度紫外飞秒激光作为ICF“快点火”的点火驱动器具有独特的优势。第一,紫外光具有更大的临界密度,产生超热电子区域更靠近燃料区,这就简化了所有与把能量输运到燃料区的物理过程;第二,按照超热电子温度Iλ2定标率,在“快点火”要求的强度下（1020w/cm2）,紫外光刚好能够产生可以与燃料区高效率耦合的超热电子温度（1MeV）;此外,紫外光具有更好的可聚焦性,在较低的能量下就可以达到要求的强度。目前,大多数关于紫外飞秒激光与固体靶相互作用的研究集中于吸收机制和软X射线方面,关于硬X射线和超热电子方面的研究非常缺乏。Teubner等利用K-α线谱方法研究了KrF激光在固体靶中的吸收和超热电子产生,Broughto和Fedosjevs等研究了脉冲宽度为1～100ps的KrF激光辐照固体靶产生     

快点火物理及其对数值模拟的要求

快点火(fast ignition)是一种新的惯性约束聚交点火方式。实验和理论研究表明其点火环节是非常复杂和困难的问题。研究快点火需要深入地进行数值模拟。报告主要从分析物理出发,探讨快点火对数值模拟的要求,同时结合实际情况进行讨论。快点火主要包括三个过程,即内爆预压缩、超强激光在次临界等离子体中和在超临界密度等离子体中的传播(成道和打洞)、超热电子的产生及其在介质,特别是稠密介质中的传输和高温点火区的形成。研究认为:研究预压缩不仅需要一维、二维,而且需要三维激光靶耦合总体程序;超热电子需要包括电磁场的Fokker-Planck方程描述;点火过程的等离子体流体力学则需要考虑电子、离子双流运动方程,而且应包括电磁场。PIC程序可用来研究局部的细节,并提供上述方程所需要的参数。此外,报告还简述了近两年来的快点火实验和一些国家的未来的计划。     

高强度紫外激光驱动的质子加速

正超强脉冲激光驱动等离子体加速产生强流脉冲质子束,在高能量密度物理和惯性约束聚变等领域有着重要的研究意义。本文研究了超短脉冲激光加速质子的物理过程,研究了激光强度、激光波长、激光对比度、薄膜靶厚度等对超短脉冲激光驱动薄膜靶加速质子束的影响。研究了紫外超短脉冲激光在质子加速过程中的优势,高对比度的紫外激光有效抑制等离子体对质子加速的影响,波长短,具有高临界密度和更好的激光吸收效率,可产生具有超高密度梯度的高密度等离子体,有利于提高超热电子密度,提高质子加速的束流强度和能量转换效率。P极化激光以45°入射角入     

快电子对快离子损失诊断测量的影响

基于闪烁体原理的快离子损失探针(Fast Ion Loss Detector,FILD),可以同时测量损失快离子的能量和pitch-angle的值,是核聚变装置中对高能粒子诊断的重要方式。根据先进实验超导托卡马克(Experimental Advanced Superconducting Tokamak,EAST)的发展需求,为了更好地对损失快离子行为进行研究,设计并安装了快离子损失诊断,且探测到在中性束加热条件下产生的损失快离子。同时,探测到在放电中产生的逃逸电子,以及低杂波注入时快电子产生X射线对快离子损失背景信号的影响。并且在H-mode放电时边界扰动也对快离子损失信号产生影响,这些探测到的现象都为不断升级损失诊断系统提供依据。     

Calculations of reactivity-initiated transients in gas-cooled fast reactors using the code system fast

The FAST code system is a general tool for analyzing advanced reactors from the viewpoint of the static and dynamic behavior of the whole reactor system. It includes an integrated three-dimensional representation of the core neutronics, appropriate modeling of the core thermal-hydraulics and fuel pin behavior, coupled to models of the reactor primary and secondary systems. Use is made largely of well-established individual neutronic, thermal-hydraulic and fuel behavior modules. Clearly, it is important to verify the individual parts of the code, including the links between them. The paper is focused on this detailed verification procedure. Steady-state conditions, as well as the transient behavior of hypothetical reactivity-initiated accidents, are investigated for two specific gas-cooled fast reactors. While the first system, a CO₂-cooled CAPRA-CADRA core, is loaded with Superphénix-like MOX fuel, the second system being analyzed, a He-cooled Generation IV-like core, uses ceramic (U,Pu)C fuel dispersed in a silicon-carbide matrix. In the current study, the TRAC/PARCS elements of FAST are compared with the 3D-kinetics stand-alone ERANOS/KIN-3D code, which is considered state-of-the-art, using as far as possible equivalent options. A new methodology is proposed to improve a diffusion-theory, coarse-group PARCS-solution by scaling the original cross-section derivatives and input kinetic parameters.     

Commercialized fast reactor cycle systems and reactor core performance of the promising fast reactors

The Feasibility Study on Commercialized Fast Reactor (FR) Cycle Systems is under progress in order to propose prominent FR cycle systems that will respond to the diverse needs of society in the future. The design studies on various FR system concepts have been achieved and then the evaluations of potential to achieve the development targets have been also carried out. Crucial development issues have been found out for each FR system concept and their development plans for the key technologies are summarized as the roadmap. As a result, it has been confirmed that the sodium-cooled FR concept is highly suited to the development targets and R&D issues are related enhancing the economy with certain perspectives for realization. A flexible and robust development program for the FR cycle system will be proposed taking account of the characteristics for each FR concept until the end of the Phase II study.     

Safety of sodium-cooled fast reactors

Conclusions The accumulated experience in the operation of NPP, including those with fast reactors, shows that during normal operation, with due regard for possible operational difficulties and accidents, they ensure a significantly lower level of risk for personnel and the surrounding population than is present in industrial regions and those prone to natural disasters. Therefore, the dangers connected with the widespread development of nuclear power arise not so much from a real risk as from a risk which in principle can be realized in very improbable accidents. From this point of view sodium-cooled fast reactors have certain advantages. The probability of the maximum accident of the rupture of pipelines in high-pressure reactors must be considerably higher. Here a single event, and one difficult to detect, such as the failure to detect a flaw in manufacture, is enough to initiate the very dangerous first step of an accident. The rupture of equipment in the primary loop of a fast reactor at practically atmospheric pressure is considerably less probable, and the integral assembly is quite safe. All the other chains of development of maximum accidents in a fast reactor require the simultaneous realization of several events in systems and devices which are constantly being monitored (SS and power supply systems, etc.). The above considerations together with such important properties of sodium as the large reserve before the boiling point and the practically inertialess transport of heat from the reactor to structural elements and heat-transfer devices under natural circulation conditions gives one confidence that the level of risk for future industrial NPP with fast reactors will be at least no higher than that for NPP with thermal reactors.Translated from Atomnaya Énergiya, Vol. 43, No. 6, pp. 464–472, December, 1977.