Cryogenic hydrogen fuel for controlled inertial confinement fusion (formation of reactor-scale cryogenic targets)

In inertial fusion energy research, considerable attention has recently been focused on low-cost fabrication of a large number of targets by developing a specialized layering module of repeatable operation. The targets must be free-standing, or unmounted. Therefore, the development of a target factory for inertial confinement fusion (ICF) is based on methods that can ensure a cost-effective target production with high repeatability. Minimization of the amount of tritium (i.e., minimization of time and space at all production stages) is a necessary condition as well. Additionally, the cryogenic hydrogen fuel inside the targets must have a structure (ultrafine layers—the grain size should be scaled back to the nanometer range) that supports the fuel layer survivability under target injection and transport through the reactor chamber. To meet the above requirements, significant progress has been made at the Lebedev Physical Institute (LPI) in the technology developed on the basis of rapid fuel layering inside moving free-standing targets (FST), also referred to as the FST layering method. Owing to the research carried out at LPI, unique experience has been gained in the development of the FST-layering module for target fabrication with an ultrafine fuel layer, including a reactor- scale target design. This experience can be used for the development of the next-generation FST-layering module for construction of a prototype of a target factory for power laser facilities and inertial fusion power plants.     

Development of Hybrid Transport Systems for Delivering Cryogenic Fusion Targets Into Focus of High-Power Laser System or ICF Reactor

We present our results on utilization of the quantum levitation effect for HTSC samples (superconducting ceramics based on YBa₂Cu₃O_7?x and SuperOx J-PI-12-20Ag-20Cu superconducting tapes) in magnetic fields of different configurations with respect to developing special carriers for hybrid systems of noncontact transport of cryogenic targets in ICF experiments. We implement the obtained results for developing and engineering of “HTSC-MAGLEV” delivery system to minimize the risk for damage of the fuel layer at the target acceleration and during target injection into the center of the ICF reaction chamber.     

Multilevel System for Protecting the Cryogenic Target during Its Delivery to the Focus of High-Power Laser Facility at High Repetition Rate

An urgent issue in research of inertial confinement fusion (ICF) is the development of the scientific, engineering, and technological base to settle the problem of quality protection of the fuel layer during the high repetition rate delivery of a cryogenic fuel target (CFT) to the focus of a high-power laser facility or ICF reactor. A concept of the multilevel system of CFT protection developed at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The concept includes possible ways of integration of the latest developments in the area of formation of the stable ultrafine fuel structure and also the application of external methods of CFT protection such as the (cryogenic and/or metallic) CFT external coatings, the profiling of a target nest inside the sabot (CFT carrier), and the noncontact CFT delivery using a hybrid accelerator based on the effect of quantum levitation of high-temperature superconductors in a magnetic field. The results obtained during the theoretical and experimental simulation made it possible to transfer from the stage of conceptualization to the stage of engineering implementation of the problem.     

D-3He先进燃料靶惯性约束聚变的燃耗和增益

计算了球形均匀D-3He先进燃料靶惯性约束聚变(ICF)的燃耗和增益。讨论了这种堆系统的能量平 衡。设计了一种新型的由毛细管阵列组成具有抗辐射损伤、可自动更新的液态金属锂自由表面多孔湿壁,用它取 出聚变能。同时与D-T热核燃料靶系统的燃耗和增益及它们不同的堆工程特性作了比较。     

基于温度梯度的ICF冷冻靶均化技术研究

惯性约束聚变(ICF)冷冻靶中氘氘(D2)、氘氚(DT)等燃料冰层在靶丸中的分布由靶丸所处的温度场决定。在氘氘冷冻靶中,垂直温度梯度引起的气-液界面张力梯度可以抵消重力作用,使氘氘液体在靶丸内均匀分布;然后在氘氘的三相点附近缓慢降温,可以实现燃料冰层的均化。在氘氘冷冻靶均化实验系统上,采用温度梯度结合制冷速率与制冷过程控制的方法,实现了1mm直径、30μm壁厚的辉光放电聚合物(GDP)靶丸中氘氘冰层的均化,对背光阴影图像中亮环位置进行分析表明:氘氘冰层的平均厚度为185.56μm,均匀度为80.2%,模数-功率谱曲线中模数2~100对应的内表面粗糙度为2.26μm。     

Diffusion filling with fuel gas of high-gain direct-drive cryogenic targets

To provide continuous operation of a reactor based on inertial confinement fusion (ICF), the thermonuclear burn region should be refilled with fuel with a frequency of 1 million targets per day. The first stage in the target production is diffusion filling of polymeric (CH) shells with fuel gas which is deuterium (D₂) or deuterium–tritium (DT) mixture. The results of simulation of filling reactor-scale CH-shells (Ø ~ 4 mm) to a pressure of ~1100 atm at 300 K in the mode with a constant pressure gradient are presented. Simple and two-layer shells of compact and porous polymers are considered. The problems of constructing an optimum DT-filling scheme avoiding CH-shell fracture due to tritium beta decay are discussed.     

Fuel cycle for a fusion neutron source

The concept of a tokamak-based stationary fusion neutron source (FNS) for scientific research (neutron diffraction, etc.), tests of structural materials for future fusion reactors, nuclear waste transmutation, fission reactor fuel production, and control of subcritical nuclear systems (fusion–fission hybrid reactor) is being developed in Russia. The fuel cycle system is one of the most important systems of FNS that provides circulation and reprocessing of the deuterium–tritium fuel mixture in all fusion reactor systems: the vacuum chamber, neutral injection system, cryogenic pumps, tritium purification system, separation system, storage system, and tritium-breeding blanket. The existing technologies need to be significantly upgraded since the engineering solutions adopted in the ITER project can be only partially used in the FNS (considering the capacity factor higher than 0.3, tritium flow up to 200 m³Pa/s, and temperature of reactor elements up to 650°C). The deuterium–tritium fuel cycle of the stationary FNS is considered. The TC-FNS computer code developed for estimating the tritium distribution in the systems of FNS is described. The code calculates tritium flows and inventory in tokamak systems (vacuum chamber, cryogenic pumps, neutral injection system, fuel mixture purification system, isotope separation system, tritium storage system) and takes into account tritium loss in the fuel cycle due to thermonuclear burnup and β decay. For the two facility versions considered, FNS-ST and DEMO-FNS, the amount of fuel mixture needed for uninterrupted operation of all fuel cycle systems is 0.9 and 1.4 kg, consequently, and the tritium consumption is 0.3 and 1.8 kg per year, including 35 and 55 g/yr, respectively, due to tritium decay.     

激光惯性约束聚变靶技术现状及其发展趋势北大核心CSCD

靶是激光惯性约束聚变(ICF)研究的物质基础,其质量的好坏对物理实验结果有极其重要的影响。靶本身的特点决定了制靶是一项极其复杂且特色鲜明的系统工程。主要介绍了国内ICF靶制备技术的现状,并对存在的问题及今后一段时期内的发展趋势作了简要说明。     

二元混合燃料在靶丸内壁形成均匀液体层的数学模型

 提出了一个数学模型，描述了二元混合燃料H-D和D-T在ICF低温靶丸内壁形成均匀液体层时，远端场的温度梯度和工作温度间的关系。在靶竖直方向施加一个温度梯度后，模型显示将在气液界面产生一个垂直向上的张力梯度，它将液体从靶丸底部拉到上部，适当的张力梯度抵消了重力对液层的作用，在靶丸的内壁形成了均匀的液体层。通过运用ANSYS软件对靶丸的导热情况进行了有限元分析，模型计算结果与Kim的实验数据吻合得较好，温度梯度的变化趋势也是相似的。     

Magnetic Acceleration of the Levitating Sabot Made of Type-II Superconductors

Creation of a delivery system based on noncontact positioning and transport of the cryogenic fuel targets represents one of the major tasks in a general program of inertial fusion energy (IFE) research. The purpose is to maintain the fuel layer quality during acceleration and injection of IFE targets at the focus of a powerful laser facility or IFE reactor. The program of the Lebedev Physical Institute (LPI) includes much development work on creation of different designs of the hybrid accelerators for IFE target transport with levitation. One of the main directions is an electromagnetic accelerator (EM-AC) + PMG system, where PMG is the permanent magnet guideway. The operational principle is based on quantum levitation of type-II high-temperature superconductors (HTSC) in the magnetic field. At the current stage, conceptual development of “EM-AC + PMG” hybrid accelerator is complete, and proof-of-principle experiments in mutually normal magnetic fields are made. This accelerator is a combination of the acceleration system (field coils generating the traveling magnetic waves) and the levitation system (PMG including a magnetic rail or magnetic track). The results obtained show that the HTSCs can be successfully used to maintain friction-free motion of HTSC sabots over the PMG, and also provide the required stability of the levitation height over the whole acceleration length due to the pinning effect. Additionally, using the driving body from MgB₂ superconducting coils as a sabot component (critical current 5,000 A at magnetic induction 0.25 T) allows one to reach injection velocities of 200 m/s under 400 g at 5 m acceleration length.     

背光阴影成像表征降温速率对ICF冷冻冰层均化的影响

利用背光阴影成像技术研究了降温速率对惯性约束聚变(ICF)球形氘氘冷冻靶中燃料冰层均化的影响.实验中,首先对ICF冷冻靶温度场进行标定以确定靶丸处的温度,然后利用背光阴影成像系统对降温过程中靶丸内燃料冰层的空间变化进行实时原位测量,得到了不同降温条件下冷冻靶背光阴影成像图像中亮环的功率谱.实验结果表明:相比快速降温,台阶式缓慢降温有利于形成均匀的燃料冰层;同时验证了背光阴影成像技术表征ICF冷冻靶内冷冻冰层均化的有效性.     

玻璃微球内氘结晶行为研究

为研制出满足惯性约束聚变(ICF)实验的氘氚(DT)冷冻靶, 需要控制DT结晶生长过程, 实现DT单晶生长, 由此减少影响冰层均匀化及聚变实验的晶体缺陷. 本文运用晶体生长形态动力学理论建立了密排六方晶体(hcp)单晶生长模型, 实验中通过对靶室进行± 3 mK精确控温, 采用可见光背光成像技术在线表征了低温下玻璃微球内氘(D₂)的结晶生长过程, 结果表明: 在20–100 Pa低温氦气导热环境下, 通过缓慢降温可显著降低氘晶体生长过程中形成的缺陷; 当降温速率达到2 mK/min时, 观测到了氘燃料的两种单晶生长过程, 实验具有可重复性; 建立的hcp单晶生长理论模型与实验结果符合, 并与美国利弗莫尔国家实验室(LLNL)的DT单晶生长过程进行了对比, 提出了冷冻靶内D₂/DT燃料的单晶生长方法.     

ICF冷冻靶燃料冰层原位表征技术

背光阴影成像是表征ICF冷冻靶燃料冰层的有效方法。基于背光阴影成像技术,冷冻靶燃料冰层原位表征技术能原位实时监测靶丸内燃料气体相变与冰层均化过程,得到打靶零前时刻燃料冰层厚度和粗糙度信息,为物理实验提供准确参数。在冷冻靶制备实验中,根据背光阴影成像的光线追迹模型和实验测得的阴影图像中的亮环位置,计算得到了均化后冷冻靶中燃料冰层的厚度以及内表面粗糙度。     

Contribution of different mechanisms of energy transfer in the development of the thermonuclear combustion wave upon fast ignition of ICF-targets

Temporal characteristics of the thermonuclear combustion wave, critical parameters of the igniter, and the total energy yield were computed using numerical modeling of the fast ignition of the spherically symmetric inertial confinement fusion (ICF) target of the reactor type taking into account different mechanisms of energy transfer from the central igniter to the main mass of fusionable fuel of the target. The program TERA was used for mathematical modeling. Along with complete calculations (including all known mechanisms of energy transfer), model computations with consecutive disengagement of energy transfer by thermonuclear charged particles (local energy deposition approximation) and by neutrons were also carried out. Our computations showed that the main effect consists in variation of the temporal characteristics of the combustion wave. Unlike the diagnostic-type targets, in the case of the reactor targets, energy transfer by neutrons exerts the main influence, and the second in importance is nonlocality of the energy deposition by charged thermonuclear particles.     

无抖动ICF冷冻靶干涉图像的获取

提出一种克服由于冷冻靶制冷系统和真空系统工作时引起的振动所带来的干涉图像抖动的方法。通过两个完全相同的CCD同步捕获冷冻靶干涉图像和空间位置图像,以位置图像来标定冷冻靶的振动情况,从而获得冷冻靶在不同状态下的干涉图像。在标定冷冻靶位置的过程中,提出了频率估计、投影标定、特征匹配和全匹配这4种算法,并给出了对应的数字图像处理算法流程。     

薄壁玻璃靶丸低温保气性能研究

 对薄壁玻璃靶丸在液氮保存状态下保气性能进行了研究。实验结果表明：在－196℃环境中,薄壁靶丸的保气半寿命由常温的3~10d延长到100~500d左右,靶丸的表面粗糙度没有明显变化,能满足ICF打靶要求。     

Cryogenic reactor for the INS project

A feasible scheme of a cryogenic reactor based on muon catalyzed fusion for an intense 14 MeV neutron source (INS) is considered. This revised version was published online in August 2006 with corrections to the Cover Date.     

用于测量ICF靶丸内氚活度的电离室的设计

设计了一种可测量ICF靶内氚含量的圆柱电离室。密封部件的设计抛弃了传统的橡胶密封而采用全金属密封, 以消除橡胶、 塑料对氚的强吸附性产生的电离室污染。为防止氚扩散污染电离室的内壁, 内壁镀上一层2 μm的Au膜。在中心电极和外电极间引入保护电极以降低低水平放射性测量时的电极漏电流。保护电极和中心电极间的绝缘材料, 以及保护电极和外电极间的绝缘材料分别选择绝缘性好、 耐高温的蓝宝石和Al2O3陶瓷。另外, 基于对ICF靶参数测量的特殊要求, 在电离室中设计了一个压碎靶丸释放氚的装置。最后, 通过物理建模和复合损失计算, 得到了优化的电离室参数。A cylindrical ionization chamber was designed for the measurement of the tritium at the level enclosed in inertial confinement fusion(ICF) targets. In stead of the conventional rubber seals, the metallic seals was adopted to reduce the chamber contamination caused by the strong tritium absorption of rubber and plastics. A 2 μm thick Au layer was plated on the inner wall of the chamber to avoid the contamination due to tritium diffusion in the chamber. The protective electrode was introduced to reduce the leakage current when measuring the low level radioactivity. Sapphire was employed as an insulator between the protective electrode and central electrode, while Al2O3 ceramic was used in between the protective electrode and the external electrode. In addition, to meet the specific requirements on the measurement of ICF targets’ parameters, a component used to crash the target to release tritium was designed in the chamber. Finally, the optimal chamber parameters were obtained in terms of physics modeling and combination loss computation.     

燃料均化过程中红外光体加热率控制模拟

通过光线追迹程序对红外光在黑腔中的传播进行模拟,得到红外光聚焦位置不同时靶壳和燃料的体加热率。模拟结果表明:当燃料冰层实现均化时,相比靶壳,燃料吸收了少部分红外光能量。靶壳和燃料的体加热率随着红外光在黑腔上的聚焦位置而改变,聚焦位置偏移量的增加,靶壳的红外光加热率峰值对应的高度角逐渐变大,而燃料的红外光体加热率逐渐变小。因此,通过改变红外光的聚焦位置对靶丸以特定的体积热率加热,从而达到燃料均化所需的温度场。