Plasma-surface interaction in ITER

The decreasing availability of energy and the concern about climate change necessitate the development of novel sustainable energy sources. Fusion energy is such a source. The ultimate potential of fusion energy is very high and badly needed. A major step forward in the development of fusion energy is the decision to construct the experimental test reactor ITER.ITER will stimulate research in many areas of science. This article discusses research opportunities in the context of plasma-surface interaction. The fusion plasma with a typical temperature of 10 keV has to be brought into contact with a physical wall in order to remove the helium produced and drain the excess energy in the fusion plasma. The fusion plasma is far too hot to be brought into direct contact with a physical wall. It would degrade the wall and the debris from the wall would extinguish the plasma. Therefore, schemes are developed to cool down the plasma. The resulting plasma-surface interaction concerned in ITER is facing several challenges including surface erosion, material redeposition and tritium retention. In this article we introduce how plasma-surface interaction relevant for ITER can be studied in a smaller scale experiment: Magnum-PSI.     

Electrode Regions of a Continuous Optical Discharge in a Thermionic Converter of Laser Radiation Energy to Electric Energy

A mathematical model is developed of nonequilibrium electrode regions of a continuous optical discharge burning in the interelectrode gap of a thermionic converter of laser radiation energy to electric energy, which is free of a number of limitations of the previously suggested analytical theory. The structure of the electrode regions is investigated. The singularities of the distribution of plasma parameters at different electron temperatures are revealed. The boundary conditions on the electrode boundaries of the equilibrium core of continuous optical discharge are obtained for equations which describe the distribution of the plasma temperature and in the discharge core.     

Thermal regime of an electric ARC

The burning stability of an arc in a stream of gas is estimated on the basis of the energy balance. It is shown that instability and the presence of a drooping branch on the current-voltage characteristic may be attributed to nonlinearity of the conductivity of a weakly ionized plasma. Critical values of the voltage for arc quenching and striking are indicated.     

Influence of energy contributions to a high-voltage atmospheric-pressure discharge on the efficiency of conversion of ethanol

The results of experimental investigations of the conversion of ethanol in a high-voltage atmospheric-pressure discharge have been presented. The influence of the energy parameters of the discharge on the yield and energy cost of conversion products has been investigated. It has been established that the minimum energy cost of hydrogen is possible in regimes of discharge burning with a maximum degree of nonequilibrium of the plasma. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 6, pp. 3–6, November–December, 2006.     

聚变堆中面向等离子体材料的研究进展

受控热核聚变能是公认的可以有效解决人类未来能源需求的主要途径之一,经过多年的努力,其研究已经取得很大进展,进入了从物理可行性向工程可行性的验证阶段.决定核聚变能未来发展的一个关键问题是相关的材料问题,尤其是面向等离子体材料的发展.评述了国内外目前核聚变实验装置中面向等离子体材料的研究进展.     

Development of a deterred propellant for a large caliber weapon system

There is a continuing need to increase the velocity and associated terminal performance of kinetic energy ammunition as tougher armor targets are encountered. Application of a deterrent, or burning rate reducer, into the surface of standard propellants, together with appropriate changes in geometry and loading density, has been suggested as a means of increasing velocity by as much as ten percent. The attainment of such a desirable performance gain is critically dependent on the deterrent's satisfying certain requirements: (1) chemical compatability with the base propellant, (2) sufficient penetration of the base propellant, (3) diffusion stability of the deterred region over an extended time, (4) ignitability of the deterred layer, (5) sufficient decrease in burning rate. Unfortunately, there exists only a minuscule data base on the way deterrents behave when applied to various base propellants. The deterred propellants used in small arms and anti-aircraft guns were developed by a cut-and-try technique, and the sort of data required for rational design of large caliber weapons systems, e.g. burning rates in the deterred region, is extremely scarce. Since we lack an appropriate data base we have used thermochemical calculations and burning rate estimates to identify promising deterrent/base propellant combinations. The burning rate estimates were based on empirical fits to available closed bomb and strand burner tests with small arms propellants. Several promising deterrent systems are presented, including five candidates which exhibit a decrease in burning rate with no decrease in propellant energy. On the basis of these theoretical predictions, an experimental deterrent coating and analysis study has been initiated at Radford Army Ammunition Plant.     

First-wall coatings for Tokamak fusion reactors

The coating of the first wall of a fusion reactor must withstand an intense neutron flux, the impact of energetic charged and neutral particles, and photons, all of which escape from the plasma. Penetration of material eroded from the first-wall coating into the plasma will have a detrimental effect on the plasma stability and energy balance. Therefore material selection for the first-wall coating of a fusion reactor represents one of the critical problem areas for the achievement of fusion power.Theoretical and experimental studies which have been conducted on the many facets of the problem are reviewed with special emphasis placed on the more critical aspects. Possible directions of future research in this area are outlined.     

Gas sources in fusion devices

Fusion plasmas are routinely produced from pure gas injected into the vacuum vessel of fusion devices at pressures in the range of millitorr. The large surface to volume ratio, characteristic of these fully instrumented devices, makes plasma density and impurity control a difficult task. The problem is further aggravated due to the large fluxes of energetic species produced by the imperfect confinement of particles and energy into the plasma and, additionally, due to the large efficiency of the plasma in pumping the gas released by the interaction of such particles with the vessel walls. Many of these processes have a direct impact in the control of the tritium inventory, of high relevance in the operation of future fusion reactors, and they are presently the focus of very active research.In the present work, the problems associated to the control of gas sources in fusion devices are addressed. First, the impact of the gas release on the particle and impurity control of the fusion plasmas is discussed. Secondly, the different types of sources that are present either before or during plasma formation are identified and finally, the techniques oriented to control the interchange of particles between the plasma and its surroundings are described.     

磁约束核聚变托卡马克等离子体与壁相互作用研究进展

核聚变能是潜在的清洁安全能源,其最终的实现对中国能源问题的解决尤其重要。磁约束托卡马克是目前最有可能实现受控热核聚变的方法。磁约束聚变能的实现面临两大瓶颈问题:高参数稳态等离子体物理问题和托卡马克装置及未来反应堆关键材料问题。其中关键材料问题的解决在很大程度上取决于我们对等离子体与壁材料相互作用(Plasma-Wall Interactions,PWI)过程和机理的深入理解。PWI现象主要发生在托卡马克磁场最外封闭磁面以外的边界等离子体(又称为刮削层,Scrapped-Off Layer,SOL)和直接接触SOL的面对等离子体材料(Plasma-Facing Materials,PFM)区域内。因此,PWI问题直接决定了聚变的装置运行安全性、壁材料部件研发进程和未来壁的使用寿命。弄清PWI的各种物理过程和机理并施以有效的控制,是未来核聚变能实现的重要环节之一。对PWI国内外研究现状进行了详细的总结评述,并阐述了PWI的未来发展趋势和亟待解决的问题。     

高燃速功能材料对高能发射药性能的影响

为了研究一种具有高能、高燃速特性的新型发射药,在高能发射药的配方体系中添加了两种高燃速功能材料乙二胺-三乙烯二胺高氯酸盐(SY)和硝酸肼镍(NHN)。利用密闭爆发器试验研究高燃速功能材料对高能发射药燃速特性的影响规律,并考察其对高能、高燃速发射药综合性能的影响。采用中止燃烧试验和SEM探索了燃速提高的机理。结果表明,添加质量分数3%的SY或NHN可以有效地提高发射药的燃速,使燃速分别提高了31.8%、17.8%,SY对燃速的提高效果更为显著;高能、高燃速发射药的火药力为1 200 J/g左右,具有较高的能量特性;在20 ℃和－40 ℃下,NDCS-02(含SY)的抗冲强度分别为73.89 kJ/m²和7.12 kJ/m²,NDCN-02(含NHN)的抗冲击强度分别为未断和6.60 kJ/m²,力学性能优良;NDCS-02和NDCN-02的撞击感度分别为19.0、22.4 cm,摩擦感度分别为84%、90%,都可以满足应用要求;NDCS-02和NDCN-02化学安定性测试的放气量分别为1.15、1.79 mL/g,安定性较好。中止燃烧试验和SEM的测试结果表明,高燃速功能材料先于发射药基体燃烧,使燃烧过程中燃面增加,从而提高燃速。     

Superconducting magnetic energy storage

After a brief review of the reasons for and forms of secondary energy storage and of the elements and history of inductive or magnetic storage, we discuss the four distinct areas in which superconducting magnetic energy storage can be applied. Differences in energy transfer times place different requirements on the storage coil, on the switch or transfer element, and on the energy losses in the superconductor. We report on designs and experiments in one of these areas with 2 to 300 kJ units, and on the analysis and plans for an installation that is to provide 250 MJ of plasma compression energy for the theta-pinch controlled thermonuclear fusion test reactor. We point out those elements of inductive storage that need further development before a theta-pinch fusion reactor can become economically competitive. Finally, we compare the size and costs of the energy storage components of these systems with similar and with larger inductive storage systems that are to interact reversibly with electric utility networks.     

Energy Deposition of Heavy Ions in Matter

The energy loss of heavy ions in matter is completely different from the case of laser beams. Whereas laser radiation produces a plasma on the surface of the target and heats the volume mostly by shock waves, heavy ions penetrate deep into the target with an almost-constant energy loss in the beginning and a very high energy loss at the end of the range, the so called Bragg peak. This special behavior offers excellent possibilities for the examination of critical points of different materials, the measurement of benchmarks for equations of state, production and detection of X-rays and XUV radiation, investigations in physics of overdense plasma, and many more topics. In particular, heavy ion beams are considered to be a very efficient driver for an inertial confinement fusion power plant. Thus, research on the elementary processes of the energy deposition of heavy ions in matter with respect to inertial fusion energy is of primary interest.     

Coatings for fusion reactor environments

The internal surfaces of a toroidal magnetically confined fusion reactor control the impurity injection and gas recycling into the fusion plasma. Coating of internal surfaces may provide a desirable and possibly necessary design flexibility for achieving the temperatures, ion densities and containment times necessary for net energy production from fusion reactions. In this paper the reactor environments experienced by various components are reviewed along with possible materials responses. Characteristics of coating-substrate systems that are important to fusion applications are delineated and the present status of coating development for fusion applications is reviewed. Coating development for fusion applications is just beginning and poses a unique and important challenge for materials development.     

Neutron-lean fusion reactor studies for thermal plasmas

The attractiveness of various advanced fusion fuel cycles for use in commercial fusion reactors is investigated. A plasma and reactor simulation code and a nuclear data library were developed for that porpose. Under the basic assumption of a two-component plasma (thermalized bulk plasma and suprathermal reaction products), lithium and boron were found not to qualify as fuel components because of their poor power performance. For (semi-)catalyzed D and for D-³He, a reasonably large window was identified in parameter space for which the overall energy balance is positive. Various “attractiveness indicators” (neutron load, tritium, etc.) are evaluated and compared to the corresponding values for D-T fueled reactors.     

快Z-箍缩——有前景的聚变能源新途径

简要介绍了快Z-箍缩的基本概念;综述了快Z-箍缩等离子体研究及其作为高能密度物理与惯性约束聚变(ICF),尤其作为低成本聚变能源研究的最新进展;探讨了快Z-箍缩驱动ICF作为聚变能源可能遇到的技术问题及应用前景.     

Fast ZPinch, A New Approach for Promising Fusion Energy

The basic concept of fast Zpinch, and late progress in fast Zpinch plasma research as HEDP and ICF research, especially as an approach for high yield lowcost fusion energy research, are summarized in this paper. The possible technical challenges of fast Zpinchdriven ICF as fusion energy and it application prospect are discussed.     

Phase-field modeling of thermomechanical damage in tungsten under severe plasma transients

Tungsten is now a primary candidate for plasma facing components in fusion energy systems because of its numerous superior thermophysical properties. International efforts are currently focused on the development of tungsten surfaces that can intercept ionized plasma and pulsed high heat flux in magnetic fusion confinement devices. Thermal shock under transient operating conditions, such as edge localized modes, have experimentally been shown to lead to severe surface and sub-surface damage. We present here a computational multiphysics model to determine the relationship between the thermomechanical loading conditions and the onset of damage and failure of tungsten surfaces. The model is based on thermo-elasto-plasticity constitutive relations, and is developed within the framework of the phase-field method. A coupled set of partial differential equations is solved for the temperature, displacement, and a damage phase fields under severe plasma transient loads. The results clearly show the initiation and propagation of surface and sub-surface cracks as a result of the transient high heat flux. The severity of surface cracking is found to correlate primarily with the magnitude of the near-surface temperature gradient.     

Global stochastic particles in a field-reversed configuration

This paper discusses the dynamics of the fusion products of the D-He³ reaction in a field-reversed configuration, with application to a reactor regime with a large value of the plasma β. It shows that, under the conditions in the Artemis-L design [H. Momota and Y. Tomita, J. Plasma Fusion Res. 69, 801 (1993)], the motion of protons with an initial energy of 14.1 MeV is strongly stochasticized. The confinement time of these particles and the energy transfer from the fusion products to the plasma are very small. Pis’ma Zh. Tekh. Fiz. 23, 37–39 (November 12, 1997)     

不同辐照粒子下钨及钨合金辐照损伤行为的研究进展

研究核聚变、准稳态等离子体下面向等离子体材料的辐照行为,发展适合于先进实验超导托卡马克(EAST)、国际热核聚变实验堆(ITER)和中国聚变工程实验堆(CFETR)长脉冲高参数运行乃至未来聚变反应堆稳态运行的高性能面向等离子体材料是当前核聚变研究一项艰巨而又紧迫的任务。钨因具有高熔点、高导热率、低溅射腐蚀速率、高自溅射阀值以及低蒸气压和低氚滞留等优异性能,被认为是聚变装置最具有前景的面向等离子体材料。综合评述了钨及钨合金在不同辐照粒子下损伤行为的最新研究进展。粒子辐照造成的微观缺陷在钨及钨合金内部累积,辐照造成缺陷的形成和数量与钨基材料颗粒微观结构、第二相成分等密切相关,辐照缺陷情况各异。同时,辐照粒子种类、能量、剂量和温度等辐照条件都会对钨材料辐照后的形貌特征和缺陷产生重要影响。     

非均匀磁场螺旋波等离子体研究进展

螺旋波等离子体具有高电离率、低工作气压、低外加磁场、无内电极、静态均匀性好等特点,广泛应用于聚变研究、等离子体推进、等离子体材料处理等领域。均匀磁场和非均匀磁场下螺旋波等离子体的耦合效率有所不同,在螺旋波等离子体源中应用非均匀磁场可显著改善等离子体参数和射频能量吸收,提高等离子体电离效率。本文主要对非均匀磁场下的螺旋波等离子体的磁场设计及分布、放电特性、应用进行综述,并展望了非均匀磁场螺旋波等离子体的发展方向。