混合式电极结构X-pinch的研究

X-pinch作为X射线源进行背光照相,具有较高的空间分辨率和时间分辨率,可用于拍摄快速变化的过程,如丝阵负载的内爆过程。为了得到同一组丝阵负载内爆过程的多幅背光成像图片,需多个X射线源对其进行背光成像,在天光Ⅱ-B(~250kA,50ns)脉冲功率装置的驱动下,通过实验选择了一种混合式电极结构X-pinch。实验结果表明:此种混合式电极结构X-pinch可箍缩产生X射线,所辐射出的X射线光子能量主要在2~4keV之间,因其固有的空间对称性及出光电流较小,可完成多路背光照相。     

兆安级电流下Al丝阵的芯晕结构抑制研究

为了抑制丝阵Z箍缩中金属丝在电流早期电爆炸形成的芯晕结构,基于强光一号加速器,利用二级丝阵负载开展了Al丝阵早期物理状态的调控研究。通过陡化预脉冲和调整二级丝阵的参数,实现了负载Al丝的全部汽化,抑制了芯晕结构的产生,气态Al丝芯的平均直径约为1.80 mm,且沿轴向均匀分布,降低了丝阵消融引起的初始不稳定性。若丝长度和直径保持不变,反转型丝阵的关断时间主要取决于Al丝的丝数;反转型丝阵关断后,气态丝芯在主电流脉冲作用下迅速电离并开始内爆,磁瑞丽泰勒不稳定性迅速发展,内爆等离子体流沿轴向呈周期性调制分布,调制波长约为650 μm。Al丝阵初始状态的改变,有效抑制了丝的消融过程,消除了先驱等离子体,在内爆后期降低了拖尾质量,提高了箍缩品质。     

百千安电流下的单丝Z箍缩实验研究

为更深层次理解Z箍缩基本物理过程,认识单丝早期演化对丝阵后续内爆过程产生的影响,基于百千安直线脉冲变压器（FLTD）平台开展了不同材料（钨丝、镀膜钨丝和铝丝）单丝Z箍缩实验研究,实验获得了单丝演化过程的双分幅激光阴影和干涉图像。实验发现：初始直径相同（15 μm）的条件下,铝丝核的膨胀速度比钨丝核的快,在电流开始一段时间内,铝丝核沿轴向呈均匀膨胀,而钨丝核因电极效应沿轴向膨胀不均;镀膜钨丝（15 μm W+2 μm Polyimide）核的膨胀速度远大于钨丝核的,甚至高于铝丝核的,同时镀膜还降低了消融等离子体不稳定性的发展速度。     

A concept of very high ratio gas compression device

A very high ratio gas compression device based on liquid metal conical implosion is described in this paper, which can reach a compression ratio up to 10^9–12. This device can produce extremely high density, high pressure, and high temperature, thermally equilibrated states by rapid but continuous compression of gaseous materials. The changes in the state parameters (temperature, pressure, density, radiation, line emission, Doppler broadening, dissociation, ionization) of the compressed material can be monitored over a very wide temperature range up to a million Kelvin. Potential applications of the device include many research fields such as chemical molecule property analyses, high density plasma production, high pressure physics, molecular and atomic physics, intermediate density nuclear fusion, sonoluminescence, etc.     

基于X-pinch丝负载的背光照相研究

以天光Ⅱ-B装置（250 kA/50 ns）作为实验平台,在装置负载的阴阳极和回流盘上同时安装X-pinch丝负载,利用天光Ⅱ-B驱动X-pinch丝负载,通过背光照相实验获得箍缩发展不同时刻的序列图像。在序列图像中可观察到箍缩叉点处等离子体的内爆及外爆消散。实验结果有助于进一步理解丝负载箍缩等离子体发展的物理机制。     

Hydrophilicity and morphological investigation of polycarbonate irradiated by ArF excimer laser

Lasers are used to modify polymeric materials. In this work, a number of polycarbonate (PC) pieces were exposed by ArF excimer laser, 193 nm, at various UV doses from 10 to 100 J/cm² with 50-500 mJ/pulse at 10 Hz pulse repetition rate. Morphology of PC has been investigated by scanning electron microscope (SEM) at three regimes pre-ablation, slow and fast ablation. SEM identifies that the conical defects are created on the polymer surface to grow opposite to the direction of laser irradiation. It increases the superficial absorptivity of the material dependent on the ArF laser induced conical microstructure geometry. The contact angle measurement was performed here, in order to determine the hydrophilicity of the irradiated polymer at various coherent doses. It is shown that the contact angle of PC samples which are exposed to the ArF laser significantly alters with UV dose below 7 J/cm².     

Numerical comparison between the ICF and the ICF-spherical pinch

The spherical pinch concept is an outgrowth of the inertial confinement model. The salient feature of the spherical pinch concept is the creation of a hot plasma in the center of a sphere.^(1,2) This plasma is then compressed by a strong shock wave launched from the periphery of the vessel by an imploded plasma acting as a driver. This scheme, reveals that convergence of the shock, which is the main feature of all inertial confinement schemes, is a component of the spherical pinch model. The reasons for classifying the spherical pinch as a particular ICF model and designating it as a ICF-SP are given here. The fluid mechanics and high-temperature hydrodynamics of the spherical pinch can be briefly described as an explosion within an implosion. The structure of the shock wave for such explosion within an implosion and for, an implosion alone is determined by solving numerically the governing equations of the phenomena. We present here a detailed computational comparison of the inertial confinement model and the spherical pinch in terms of density, pressure, temperature, confinement time, total accumulated number of neutrons, and time-resolved neutron flux from reactions in deuterium-tritium mixture. It is shown that temperature, confinement time, and total number of neutrons for the ICF-Spherical Pinch improve upon the classical ICF.     

Pressure Drop Performance of Fuel Pin Bundle with Spiral Wire Spacer

The pressure drop characteristics of a JEFR type fuel pin bundle were obtained from hydraulic tests. The coefficient of drag attributable to the spiral wire spacer wound round each fuel pin, as defined by de Stordeur, was found to be approximately 0.30 for the hexagonal lattice arrangement adopted. The coefficient is independent of spiral wire pitch, which ranged from 90 to 260 mm.

The pressure drop to be expected in a fuel pin bundle with spiral wire spacer, such as used in current fast breeder applications, can be satisfactorily estimated by using the coefficients reported.     

Expansion of Plasma of Electrically Exploding Single Copper Wire Under 4.5kA～9.5kA/Wire

Abstract The experimental system for electrically exploding single metal wire has been de-signed and manufactured. Expansion of the dense plasma column formed from an electricallyexploding Cu wire of diameter 30 μm has been studied with a high-speed photographer to obtainthe time-dependent radius (R-t) curve. The experimental results demonstrate that the mean ex-pansion rate of the dense plasma column is 1.94 μm/ns, 2.6 μm/ns and 3.75 μm/ns according tothe peak pulse current 4.5 kA, 7 kA and 9.5 kA respectively. The results can be beneficial to givinga profound understanding of the early stage of wire-array Z-pinch physics and to improvement ontheir design.     

Criteria for neutron fusion

The reaction ⁶Li(n, α) T is studied as a possible mechanism for driving a fuel pellet of ⁶LiD to fusion temperatures through bombardment with low energy neutrons. The criterion Jt 10²³ for fusion by this scheme is derived where J is incident neutron current (cm⁻² · s⁻¹) and t is time (s). The possibility of fusion through implosion is also examined. Ablation pressure exerted by products of the Li(n, α) T reaction is found to be independent of the cross section of this reaction. The index of refraction of neutrons in the neV to eV range indicates total absorption on a sample of ⁶Li.     

定位绕丝结构对棒束通道热工水力特性影响数值分析

定位绕丝设计广泛应用于金属快堆堆芯设计及气冷快堆堆芯设计中,本文基于三维精细化绕丝定位棒束通道网格模型模拟分析了定位绕丝螺距、定位绕丝数量及定位绕丝形状对超临界二氧化碳在棒束通道中流动换热的影响。模拟结果表明定位绕丝螺距比定位绕丝数量及定位绕丝形状对温场流场的影响更大,定位绕丝螺距小于200 mm时,进出口压降大幅增加,表面换热系数增加,温度不均匀度大幅降低;随着定位绕丝数量增加,进出口压降线性增加,表面换热系数变化不大;圆形定位绕丝可以以较小截面积达到与方形定位绕丝相似的效果,梯形定位绕丝对流场影响不如矩形定位绕丝。     

Development of Merged Compact Toroids for Use as a Magnetized Target Fusion Plasma

We report on the development of compact toroid (CT) accelerators to create the target plasma for magnetized target fusion (MTF) devices. Due to the requirements of high initial density of ~10¹⁷ cm⁻³, strong internal fields of 5–10 T, and base temperatures of >100 eV, a design based on conical compression electrodes is an effective avenue to pursue. Progress is being made at General Fusion Inc, (Vancouver, Canada) to develop a pair of large CT accelerators for generating an MTF target plasma. In this design, tungsten coated conical electrodes (with a formation diameter of 1.9 m, a radial compression factor of 4, and overall accelerator length of 5 m) will be used to achieve ohmic heating and acceleration of the CT, yet with low wall sputtering rates. A pair of these accelerators can be synchronized and shot at one another, producing a collision and reconnection of the two CTs within the center of an MTF chamber. Depending on the choice of relative helicities, the two CTs will merge to form either a spheromak-like or an FRC-like plasma. ICC 2008 Reno NV, June 25th, IP: 021.     

Performance evaluation of a resonance ionization mass spectrometer developed for the FFDL system of fast reactors

To prevent a fuel failure event from becoming a serious radiation accident, sodium-cooled fast reactors are equipped with a system for failed fuel detection and location (FFDL). The FFDL instrument employed in the prototype fast breeder reactor Monju is based on the gas tagging method, in which precise and accurate measurements of krypton and xenon isotope ratios (⁷⁸Kr/⁸⁰Kr, ⁸²Kr/⁸⁰Kr and ¹²⁶Xe/¹²⁹Xe) must be performed in a short time. Burnup measurements also contribute to accurate determination of ⁸²Kr/⁸⁰Kr. We have developed a highly sensitive resonance ionization mass spectrometer for the isotopic analyses, which uses resonance ionization of Kr and Xe atoms by a pulsed laser at wavelengths of 216.7 and 249.6 nm, respectively. In evaluating the performance of our spectrometer, we find that systematic errors caused by isotope shifts can be reduced to negligible levels, and that statistical errors of 3% at a nuclide concentration of 7 ppt can be achieved with a single measurement time of about 40 minutes for each Kr and Xe isotope ratio. This means that, within one hour, about 200 fuel assemblies can be individually identified with a probability of 99%, verifying the applicability of our spectrometer to the FFDL system of fast reactors.     

Application of X-Ray Computer Tomography for Observing the Deflection and Displacement of Fuel Pins in an Assembly Irradiated in FBR

A nondestructive method making use of X-ray computer tomography (X-ray CT) has been applied to post irradiation examination of fast breeder reactor (FBR) fuel assemblies. In the study, an examination is made of the deflection and displacement of fuel pin in a fuel assembly irradiated to 74.2GWd/t peak burnup in the fast reactor “JOYO.”

In the examination, X-ray CT images of transverse cross sections of fuel pin were obtained at different heights of fuel pin along its axis. Analysis of the resulting images indicated that:

1. The hexagonal wrapper tube had its lateral wall faces slightly bulged outward;

2. The fuel pins loaded in the outermost array were markedly displaced in the direction of wrapper tube, particularly in portions of fuel pin intermediate between positions constrained by wrapping wire.

The latter behavior of fuel pins was substantiated by the contours of fuel pin along its axis, which were derived from cross section images obtained at different levels along axis.

Such fuel pin displacement is surmised to have been caused by thermal stressing of the affected fuel assembly cladding.     

Compression, Heating and Fusion of Colliding Plasmoids by a Z-theta Driven Plasma Liner

A potentially promising approach to fusion employs a plasma shell to radially compress two colliding plasmoids. The presence of the magnetic field in the target plasma suppresses the thermal transport to the confining shell, thus lowering the imploding power needed to compress the target to fusion conditions. With the momentum flux being delivered by an imploding plasma shell, many of the difficulties encountered in imploding a solid metal liner are eliminated or minimized. The best plasma for the target in this approach is the FRC. It has demonstrated both high β, and robustness in translation and compression that is demanded for the target plasma. A high density compressed plasmoid is formed by a staged axial and radial compression of two colliding/merging FRCs where the energy that is required for the implosion compression and heating of the magnetized target plasmoid is stored in the kinetic energy of the plasmas used to compress it. An experimental apparatus is being constructed for the demonstration of both the target plasmoid formation as well as the compression of the plasmoid by a plasma liner. It is believed that with the confinement properties and the high β nature of the FRC, combined with the unique approach to be taken, that an nτ_E T _i triple product ∼5 × 10¹⁷ m⁻³ s keV can be achieved.     

Preparation of ultrafine tungsten wire via electrochemical method in an ionic liquid

Ultrafine tungsten wire less than 10 μm in diameter is often used as wire array load applied in Inertial Confinement Fusion (ICF) physical experiments. In order to obtain a higher yield of X-ray, both initial radius and line quality of metal wire were required to be of high quality simultaneously. This paper has studied the electrochemical method to corrode tungsten wires uniformly in an ionic liquid electrolyte containing 1 wt% sodium hydroxide. A three electrode system composed of a tungsten anode electrode, a stainless steel cathode and a saturated calomel electrode as a reference electrode, was used in the electrochemical experiments. Liner sweep voltammetry (LSV) and Tafel experiments were used to investigate the electrochemical behaviors of tungsten wires in ionic liquid and aqueous solution. Based on scanning electron microscope (SEM) observation, the morphologies of tungsten wire surface with uniform corrosion under different applied voltages have been demonstrated. X-ray diffraction (XRD) methods were employed to track the evolution of the crystal structure before and after corrosions, and there is an obvious difference in peak intensities. The ultrafine tungsten wire with a uniform diameter of 8.5 μm was obtained under the optimized electric potential (2.5 V) applied for decreasing diameter at 30 °C.     

Radiation-Burst Propagation in Air

A position sensitive proportional counter of a charge division type with a single resistive anode wire was constructed for the measurement of the movement of ³H labelled gas which is flowing or diffusing in a pipe. The introduction of resistors between the anode wire and pre-amplifiers brought a uniform detection efficiency for ³H β-rays throughout the counter. The position resolution was 3.1mm FWHM. Detection efficiency was almost 100% uniformly over about 700 mm in the total anode length of 740 mm. The movement of ³H labelled gas. could be measured effectively.     

Aspects of 238Pu production in the experimental fast reactor JOYO

Experimental determination of ²³⁸Pu in ²³⁷Np samples irradiated in the experimental fast reactor JOYO was done as part of the demonstration of ²³⁸Pu production from ²³⁷Np in fast reactors within the framework of the protected Pu production project, which aims at reinforcement of proliferation resistance of Pu by increasing the ²³⁸Pu isotopic ratio. ²³⁸Pu production amount in the irradiated ²³⁷Np samples was determined by a radioanalytical technique. Aspects of ²³⁸Pu production were examined on the basis of the present radioanalysis. The ²³⁸Pu production amount depends on the neutron spectrum which can range from that of a typical fast reactor to a nearly epi-thermal spectrum. It is concluded that the fast reactor has not only high potential for use in protected Pu production, but also as an incinerator for excess Pu.     

Condensed Atomic Hydrogen as a Possible Target in Inertial Confinement Fusion (ICF)

H atom Rydberg matter (RM) in excitation state n = 1 is concluded to be a form of metallic hydrogen [Badiei S, Holmlid L (2004) J Phys Condens Matter 16:7017]. This material can be produced at low pressure. This condensed form of hydrogen may be very useful as a dense hydrogen inertial confinement fusion (ICF) target, being almost metallic and ten times denser than solid (frozen) diatomic hydrogen used at present. Coulomb explosions and plasma formation are initiated in condensed atomic hydrogen even by relatively weak nanosecond pulsed lasers. The protons emitted with high directivity in these explosions are energetic, corresponding to T = 10⁵ K, and they may be utilized to give strong compression of the material. The fastest protons observed at up to 1 keV indicate a compression considerably higher than that required for “fast ignition” fusion.     

Study on the LLFPs transmutation in a super-critical water-cooled fast reactor

The performance of the super-critical water-cooled fast reactor (Super FR) for the transmutation treatment of long-lived fission products (LLFPs) was evaluated. Two regions with the soft neutron spectrum, which is of great benefit to the LLFPs transmutation, can be utilized in the Super FR. First region is in the blanket assembly due to the ZrH_1.7 layer which was utilized to slow down the fast neutrons to achieve a negative void reactivity. Second region is in the reflector region of core like other metal-cooled fast reactors. The LLFPs selected in the transmutation analysis include ⁹⁹Tc, ¹²⁹I and ¹³⁵Cs discharged from LWR or fast reactor. Their isotopes, such as ¹²⁷I, ¹³³Cs, ¹³⁴Cs and ¹³⁷Cs were also considered to avoid the separation. By loading the isotopes (⁹⁹Tc or ¹²⁷I and ¹²⁹I) in the blanket assembly and the reflector region simultaneously, the transmutation rates of 5.36%/GWe year and 2.79%/GWe year can be obtained for ⁹⁹Tc and ¹²⁹I, respectively. The transmuted amounts of ⁹⁹Tc and ¹²⁹I are equal to the yields from 11.8 and 6.2 1000 MWe-class PWRs. Because of the very low capture cross section of ¹³⁵Cs and the effect of other cesium isotopes, ¹³⁵Cs was loaded with three rings of assemblies in the reflector region to make the transmuted amount be larger than the yields of two 1000 MWe-class PWRs.Based on these results, ⁹⁹Tc and ¹²⁹I can be transmuted conveniently and higher transmutation performance can be obtained in the Super FR. However, the transmutation of ¹³⁵Cs is very difficult and the transmuted amount is less than that produced by the Super FR. It turns out that the transmutation of ¹³⁵Cs is a challenge not only for the Super FR but also for other commercial fast reactors.