Deuterium permeation in tungsten by mixed ion irradiation

Deuterium ion driven permeation was studied for mixed ion irradiation conditions with He and C. Addition of He greatly reduced permeation, while addition of C enhanced permeation. These phenomena are strongly temperature dependent, but both are significant around surface temperature of blankets (～800 K). Permeation flux has very weak dependence on microstructure. These results are important for evaluation of T behavior in blanket first walls.     

As离子注入形成硅化钨的研究

大规模集成电路的发展使集成度不断提高,器件尺寸减小,线条变窄。现常用的多晶硅栅和互连,由于电阻率高,限制了集成电路的速度。近年发展起来的硅化物材料,因其电阻率低、稳定性好、自对准性能好而常被用作大规模集成电路中的欧姆接触,互连和肖特基势垒。     

Deuterium Retention and Physical Sputtering of Low Activation Ferritic Steel

Low activation materials have to be developed toward fusion demonstration reactors. Ferritic steel, vanadium alloy and SiC/SiC composite are candidate materials of the first wall, vacuum vessel and blanket components, respectively. Although changes of mechanical-thermal properties owing to neutron irradiation have been investigated so far, there is little data for the plasma material interactions, such as fuel hydrogen retention and erosion. In the present study, deuterium retention and physical sputtering of low activation ferritic steel, F82H, were investigated by using deuterium ion irradiation apparatus. After a ferritic steel sample was irradiated by 1.7 keV D^ ions, the weight loss was measured to obtain the physical sputtering yield. The sputtering yield was 0.04, comparable to that of stainless steel. In order to obtain the retained amount of deuterium, technique of thermal desorption spectroscopy (TDS) was employed to the irradiated sample. The retained deuterium desorbed at temperature ranging from 450 K to 700 K, in the forms of DHO, D2, D2O and hydrocarbons. Hence, the deuterium retained can be reduced by baking with a relatively low temperature. The fiuence dependence of retained amount of deuterium was measured by changing the ion fiuence. In the ferritic steel without mechanical polish, the retained amount was large even when the fluence was low. In such a case, a large amount of deuterium was trapped in the surface oxide layer containing O and C. When the fluence was large, the thickness of surface oxide layer was reduced by the ion sputtering, and then the retained amount in the oxide layer decreased. In the case of a high fluence, the retained amount of deuterium became comparable to that of ferritic steel with mechanical polish or SS 316 L, and one order of magnitude smaller than that of graphite. When the ferritic steel is used, it is required to remove the surface oxide layer for reduction of fuel hydrogen retention. Ferritic steel sample was exposed to the environment of JFT-2M tokamak in JAERI and after that the deuterium retention was examined. The result was roughly the same as the case of deuterium ion irradiation experiment.     

Study of the tungsten sputtering source suppression by wall conditionings in the EAST tokamak

The steady fusion plasma operation is constrained by tungsten(W) material sputtering issue in the EAST tokamak. In this work, the suppression of W sputtering source has been studied by advanced wall conditionings. It is also concluded that the W sputtering yield becomes more with increasing carbon(C) content in the main deuterium(D) plasma. In EAST, the integrated use of discharge cleanings and lithium(Li) coating has positive effects on the suppression of W sputtering source. In the plasma recovery experiments, it is suggested that the W intensity is reduced by approximately 60% with the help of ～35 h Ion Cyclotron Radio Frequency Discharge Cleaning(ICRF-DC) and ～40 g Li coating after vacuum failure. The first wall covered by Li film could be relieved from the bombardment of energetic particles, and the impurity in the vessel would be removed through the particle induced desorption and isotope exchange during the discharge cleanings. In general, the sputtering yield of W would decrease from the source, on the bias of the improvement of wall condition and the mitigation of plasmawall interaction process. It lays important base of the achievement of high-parameter and longpulse plasma operation in EAST. The experiences also would be constructive for us to promote the understanding of relevant physics and basis towards the ITER-like condition.     

Analysis of surface morphological change in PET films induced by tungsten ion implantation

Surface morphological changes and metal nanograin formation of polyethylene terephthalate films with tungsten ion implantation were studied. Tungsten ions were accelerated with a voltage of 40 kV and implanted at fluences from 5 × 10¹⁶ to 2 × 10¹⁷ cm^?2 using a metal vapor vacuum arc implanter. Scanning electron micrographs at the highest fluence show semi-spherical hills, indicating formation of tungsten nanograins on the polymer. The tungsten nanograin formation in the polymer film is confirmed by cross-sectional observation using transmission electron microscopy. Depth profiles of tungsten atoms obtained from energy dispersive X-ray spectra indicate densification and sputtering of the polymer surface layer during implantation. These results indicate that surface morphological change is related with the effects of a critical fluence and tungsten nanograin formation.     

Swelling or erosion on the surface of patterned GaN damaged by heavy ion implantation

Wurtzite undoped GaN epilayers (0 0 0 1) was implanted with 500 keV Au⁺ ions at room temperature under different doses, respectively. Ion implantation was performed through photoresist masks on GaN to produce alternating strips. The experimental results showed that the step height of swelling and decomposition in implanted GaN depended on ion dose and annealing temperature, i.e., damage level and its evolution. This damage evolution is contributed to implantation-induced defect production, and defect migration/accumulation occurred at different levels of displacement per atom. The results suggest that the swelling is due to the formation of porous structures in the amorphous region of implanted GaN. The decomposition of implanted area can be attributed to the disorder saturation and the diffusion of surface amorphous layer.     

Molecular Dynamics Study on the Diffusion Properties of Hydrogen Atoms in Bulk Tungsten

Molecular dynamics simulations were performed to study the diffusion behavior of hydrogen atoms in body-centered cubic(bcc) tungsten(W). The energy distribution of a single hydrogen atom in the (001) plane of tungsten lattice was computed. The values of diffusion barriers agree well with other theoretical and experimental results. The interaction between an H atom and a vacancy was simulated, which shows evidence of strong binding effect. The temperature effect on the diffusion behavior of hydrogen atoms was investigated. The critical temperature for an H atom to diffuse in bulk W with and without vacancies were calculated to be 950 K and 450 K, respectively, which is supported by several experimental results. In addition, the diffusion coefficient of hydrogen atoms in tungsten was evaluated and analyzed.     

Deuterium trapping by irradiation damage in tungsten induced by different displacement processes

The deuterium trapping behaviors in tungsten damaged by light ions with lower energy (10 keV C⁺ and 3 keV He⁺) or a heavy ion with higher energy (2.8 MeV Fe²⁺) were compared by means of TDS to understand the effects of cascade collisions on deuterium retention in tungsten. By light ion irradiation, most of deuterium was trapped by vacancies, whose retention was almost saturated at the damage level of 0.2 dpa. For the heavy ion irradiation, the deuterium trapping by voids was found, indicating that cascade collisions by the heavy ion irradiation would create the voids in tungsten. Most of deuterium trapped by the voids was desorbed in higher temperature region compared to that trapped by vacancies. It was also found that deuterium could accumulate in the voids, resulting in the formation of blisters in tungsten.     

Real-time in situ study of hydrogen diffusion in amorphous Si formed by ion implantation

The diffusion of hydrogen in amorphous silicon formed by ion implantation is studied using real-time elastic recoil detection analysis. An activation energy for H diffusion of 1.82 eV is determined in a single ramped anneal. This activation energy is consistent with diffusion studies in the high H concentration regime. The low beam current employed is found to have a negligible influence on the H diffusion within the sensitivity of the measurement. Further refinements for increased accuracy of this technique are discussed.     

IRMS定量分析超轻水中氘同位素

超轻水氘同位素定量分析结果误差的主要来源是记忆效应和仪器的精确性等方面。为了探讨更准确快速的超轻水中氢同位素比值检测分析方法,采用疏水铂催化H2-H2O平衡法以及稳定同位素质谱仪来作为定量检测方法。分析标准水样、超轻水和蒸馏水样品的测试结果显示:多次分析标准水样,测量值均在推荐值的误差允许范围内;测试超轻水及蒸馏水相对标准偏差在1%以内(n≥5)。结果初步证明该分析方法减少了记忆效应和仪器精确性带来的误差,提高了超轻水检测的可靠性和稳定性。     

Deuterium retention in tungsten at fluences of up to 10 D/m using D ion beams

Deuterium retention in two types of polycrystalline tungsten (PCW) was studied as a function of incident ion fluence, ion energy, and specimen temperature. (i) D retention at 300 K, as a function of D⁺ fluence, demonstrated a trend to saturation in both the Rembar hot-rolled thin foil and Plansee tungsten plate. At 500 K, new D retention results for the Plansee PCW showed an increasing trend with increasing incident D⁺ fluence without any indication of saturation, in agreement with previous results for Rembar PCW [A.A. Haasz, J.W. Davis, M. Poon, R.G. Macaulay-Newcombe, J. Nucl. Mater. 258-263 (1998) 889-895]. Even when the incident D⁺ fluence was increased to 8 × 10²⁵ D⁺/m², which is in the fluence range of plasma devices, there was still no sign of saturation. (ii) The temperature dependence results for the Plansee PCW show a decreasing trend in D retention as the temperature is increased from 300 to 500 K. These results differ from previous studies of Rembar PCW [A.A. Haasz, J.W. Davis, M. Poon, R.G. Macaulay-Newcombe, J. Nucl. Mater. 258-263 (1998) 889-895], but are similar to those seen for single crystal tungsten [M. Poon, A.A. Haasz, J.W. Davis, R.G. Macaulay-Newcombe, J. Nucl. Mater. 313-316 (2003) 199]; an explanation for the different behaviour is suggested. (iii) Varying the D⁺ energy from 100 to 500 eV/D⁺ plays a minor role in the amount of D retained, suggesting that D retention in W depends more on the W structure, incident ion fluence and specimen temperature, rather than on the incident ion energy when the energy is below the threshold for damage formation (∼960 eV for D on W).     

Blister formation on tungsten damaged by high energy particle irradiation

In order to investigate the effect of radiation damage on hydrogen behavior in tungsten, tungsten samples with radiation damage of up to 3.5 dpa were irradiated by a mixed hydrogen-carbon ion beam. The radiation damage was produced with 700 keV negative hydrogen ion beam irradiation. The number density of blisters produced by the mixed ion beam irradiation decreased with increasing radiation damage. This was especially observed for blisters with diameters of 20 μm or less. This result showed that radiation damage produced by high-energy particle irradiation suppresses blister formation on tungsten surfaces.     

Investigating permeation and transport of H isotopes in tungsten by first-principles

We have investigated permeation and transport of hydrogen (H) isotopes in tungsten (W) single crystal employing first-principles calculations in junction with Fick’ law. Permeability was approximately evaluated according to the solubility and diffusion coefficient of H. The solubility for H in bulk W from present calculation is consistent with the experimental results measured by Frauenfelder. The permeation fluxes of H isotopes are examined at the different thickness of W wall. The permeation fluxes of deuterium with the W thickness of 21 μm at the temperature of 770 K and with the W thickness of 50 μm at the temperature of 893 K were 0.68 × 10¹³ atom/m²s and 0.34 × 10¹⁴ atom/m²s, respectively. The dissociation coefficients of H isotopes are also evaluated. We believe that the present first-principles combined with Fick’ law method can be also generalized to investigate permeation and transport of H isotopes in most metals since such H isotopes behaviors in most metals are similar to those of H isotopes in W.     

Underwater explosive welding of tungsten to reduced-activation ferritic steel F82H

The present study reports the underwater explosive welding of commercially pure tungsten onto the surface of a reduced-activation ferritic steel F82H plate. Cross-sectional observation revealed the formation of a wave-like interface, consisting of a thin mixed layer of W and F82H. The results of nanoindentation hardness testing identified a gradual progressive change in the interface, with no hardened or brittle layer being observed. Small punch tests on the welded specimens resulted in cracking at the center of the tungsten, followed by crack propagation toward both the tungsten surface and the tungsten/steel interface.     

应用于离子注入的RFQ加速器

射频四极场(Radio frequency quodrupole,RFQ)加速器是一种非常适于用作MeV级能量离子注入的加速器.它具有束流强、体积小、使用方便、离子源处在地电位,还可同时加速正、负两种离子等优点.本文介绍了RFQ加速器在国际上的发展状况及其基本原理、北京大学研制的1 MeV RFQ加速器的具体结构、性能以及一种新型RFQ-SFRFQ组合加速器的特点.     

镧离子注入对纯锆耐蚀性的影响

为了研究镧离子注入对纯锆耐蚀性的影响,样品表面分别注入了1×10~(16)-1×10~(17)cm-2的镧离子,使用MEVVA源作为注入源,注入能量为40 kv。X光电子谱(XPS)分析了注入样品表面镧的价态,三电极动电位扫描测定了注入样品在0.5 mol/L H2SO4溶液中的极化曲线,通过与空白样(未注入样品)比较可知,镧离子注入后,纯锆样品的耐蚀性大大提高。最后,讨论了耐蚀性提高的机理。     

Separation Factor of Hydrogen and Deuterium by Suspension Electrolysis Using Mercury Cathode

The electrolytic separation factor between hydrogen and deuterium was examined using mercury or else platinum cathode immersed in IF NH₄Cl in 10v/oD₂O water containing cobalt sulfide powder in suspension. Several other kinds of powdered materials in suspension were also studied. In the case of mercury pool electrode, the materials added in suspension were effective in enhancing the hydrogen/deuterium separation factor, but powder suspension was ineffective on platinum plate electrode. The powdered material added in suspension served as catalyst on the hydrogen evolution reaction at the mercury cathode. The influence of the applied potential on the separation factor was studied over the temperature range of 15°~80°C. The results provided an indication of the rate-determining steps governing the electrolytic hydrogen evolution.

The experimental values obtained for the separation factor and activation energy gave an insight into the mechanism of the rate-determining step of the hydrogen evolution at the working electrode.     

Fabrication of hollow nanoclusters by ion implantation

Ag ions with four kinds of energies were implanted into silica to doses of 5 × 10¹⁶ and 1 × 10¹⁷ ions/cm², respectively. Hollow Ag nanoclusters were observed in the 1 × 10¹⁷ Ag⁺ ions/cm² implanted samples with energies of 150 and 200 keV. The evolution of hollow nanoclusters during annealing was carried out by in situ transmission electron microscopy observation. The energy dependence for the formation of hollow nanoclusters is studied. A potential mechanism for the formation of irradiation-induced nanovoids in nanoclusters is discussed.     

Ge nano-layer fabricated by high-fluence low-energy ion implantation

A Ge nano-layer embedded in the surface layer of an amorphous SiO₂ film was fabricated by high-fluence low-energy ion implantation. The component, phase, nano-structure and luminescence properties of the nano-layer were studied by means of Rutherford backscattering, glancing incident X-ray diffraction, laser Raman scattering, transmission electron microscopy and photoluminescence. The relation between nano-particle characteristics and ion fluence was also studied. The results indicate that nano-crystalline Ge and nano-amorphous Ge particles coexist in the nano-layer and the ratio of nano-crystalline Ge to nano-particle Ge increases with increasing ion fluence. The intensity of photoluminescence from the nano-layer increases with increasing ion fluence also. Prepared with certain ion fluences, high-density nano-layers composed of uniform-sized nano-particles can be observed.