Field ion source development for neutron generators

An ion source based on the principles of electrostatic field desorption is being developed to improve the performance of existing compact neutron generators. The ion source is an array of gated metal tips derived from field electron emitter array microfabrication technology. A comprehensive summary of development and experimental activities is presented. Many structural modifications to the arrays have been incorporated to achieve higher tip operating fields, while lowering fields at the gate electrode to prevent gate field electron emission which initiates electrical breakdown in the array. The latest focus of fabrication activities has been on rounding the gate electrode edge and surrounding the gate electrode with dielectric material. Array testing results have indicated a steady progression of increased array tip operating fields with each new design tested. The latest arrays have consistently achieved fields beyond those required for the onset of deuterium desorption (∼20 V/nm), and have demonstrated the desorption of deuterium at fields up to 36 V/nm. The number of ions desorbed from an array has been quantified, and field desorption of metal tip substrate material from array tips has been observed for the first time. Gas-phase field ionization studies with ∼10,000 tip arrays have achieved deuterium ion currents of ∼50 nA. Neutron production by field ionization has yielded ∼10² n/s from ∼1 mm² of array area using the deuterium-deuterium fusion reaction at 90 kV.     

Hydrogen isotope permeation through yttria coatings on Eurofer in the diffusion limited regime

In fusion power plants a tritium permeation barrier is required in order to prevent the loss of the fuel. Moreover, the tritium permeation barrier is necessary to avoid that the radioactive tritium accumulates in the first wall, the cooling system, and other parts of the power plant. Oxide thin films, e.g. Al₂O₃, Er₂O₃ and Y₂O₃, are promising candidates as tritium permeation barrier layers. With regard to the application, this is especially true for yttrium due to its favorably short decay time after neutron activation compared to the other candidates. The Y₂O₃ layers with thicknesses from 100 nm to 500 nm are deposited on both sides of Eurofer substrates by RF magnetron sputter deposition. Some of the samples are additionally deposited with palladium thin films to analyse the limited regime. During the annealing in the experiments the palladium layers do not show any crack formation or delamination, verified by scanning electron microscopy. After annealing the cubic crystal structure of the Y₂O₃ layers is verified by X-ray diffraction. The cubic phase contains a small amount of a monoclinic phase, which is eliminated after the permeation measurements. The permeation reduction factors of the samples are determined in gas-driven deuterium permeation experiments. A permeation reduction of 5000 of the yttria thin film is verified. The diffusion limited regime is identified by the pressure dependence of the permeation measurement and by permeation experiments with the palladium top layers on the Y₂O₃ thin films. Furthermore, the activation energy of the permeation through the yttria thin films is determined. Pre-annealing times for more than 70 h of the Y₂O₃ thin films and permeation measurements with temperature cycles for 20 days are performed to show the stability of the permeation flux and hence the microstructure of the barrier layers. Measurement times at each constant temperature level of more than 25 h are required for the stabilization of each permeation flux to a constant value. The permeation measurement setup is enhanced to enable a continuously running equipment for these measurement times.     

Deuterium retention and surface morphology modification in oxidized tungsten exposed to D plasma

Tungsten (W) is the most promising plasma facing material in future fusion reactor. However, oxidation occurs readily on W and might influence the hydrogen isotopes retention behavior in W. To explore the mechanism of oxidation on the hydrogen isotopes retention behavior in W, oxidized W samples have been exposed to D plasma (32.3 eV, 2 × 10²⁰ Dm⁻²s⁻¹) in a linear plasma device. Surface morphology and deuterium (D) retention behavior in W have been characterized after exposure to D plasma with fluence of 10²³ D/m². After D plasma exposure, a porous layer has been found on the surface of oxidized W. The main chemical content of the porous layer is pure W. The existence of pre-oxide layer contributes the increase of retention amount of D in the form of D₂O and may contribute to the decrease of the retention amount of D in the form of HD/D₂.     

Characteristics of hydrogen and oxygen stable isotopes in precipitation and the environmental controls in tropical monsoon climatic zone

The characteristics of hydrogen and oxygen stable isotopes and their environmental controls were investigated in five regions which were influenced by tropical monsoon climate from January 2015 to December 2016. The result showed that the local meteoric water line (LMWL) for each region deviated from the global meteorological water line (GMWL) in varying degrees and difference existed between wet and dry seasons. The isotopic composition and d-excess on temporal and spatial scales varied considerably among stations, showing the difference of the controlling air masses and the distance of water transport. Generally, the heavy isotopes depleted along the direction of monsoon flow. The influences of temperature and precipitation amount were studied by monadic regression analysis and bivariate regression analysis, the coefficients for both meteorological parameters were calculated. The “precipitation amount effect” was obvious in the whole area, while both positive and negative correlations were observed between temperature and isotopes, which showed the synergy of temperature and precipitation to stable isotopes.     

Stable isotope mass balance of the Laurentian Great Lakes

    We investigate the physical limnology of the Laurentian Great Lakes of North America using a new dataset of ¹⁸O/¹⁶O and ²H/¹H ratios from over 500 water samples collected at multiple depths from 75 stations during spring and summer of 2007. δ¹⁸O and δ²H values of each lake plot in distinct clusters along a trend parallel to, but offset from, the Global Meteoric Water Line, reflecting the combined effects of evaporative enrichment and the addition of precipitation and runoff along the chain lake system. We apply our new dataset to a stable-isotope-based evaporation model that explicitly incorporates downwind lake effects, including humidity build-up and changes to the isotope composition of atmospheric vapor. Our evaporation estimates are consistent with previous mass transfer results for Michigan, Huron, Ontario and Erie, but not for Superior, which has a much longer residence time. Calculated evaporation from Superior is ~300 mm per year, less than previous estimates of ~500 mm per year, likely arising from integration of the ‘isotopic memory' of lower evaporation rates under cooler climatic conditions with greater ice-cover than the present. Uncertainties in the estimates from the stable-isotope-based model are comparable to mass transfer results, offering an independent technique for evaluating evaporation fluxes.     

UV—240型自动记录紫外分光光度计故障排除实例

本文简要介绍了几例UV—240型紫外分光光度计的安装调试及UV—240自检无法通过和氘灯控制电路的故障排除方法和元件代换。     

Recovery of deuterium from water–isotope mixture by thermal diffusion in inclined Frazier scheme

A separation theory for the recovery of deuterium from water–isotope mixture in flat-plate thermal diffusion columns of the Frazier scheme inclined for improved performance has been developed. Equations for the optimal angles of inclination and the corresponding maximum recovery, maximum production rate and minimum column length have been derived. Considerable improvements in performance are obtainable if the columns are inclined at the best angles, so that the convective strength can be properly reduced and controlled, resulting in suppression of the undesirable remixing effect while still reserving the desirable cascading effect.     

放射性同位素示踪剂技术研究油水井间高渗透层

研究油水井间的高渗透带及大孔道对油田开发具有重要意义。现场常用的普通示踪剂只能定性监测井间高渗透带或大孔道，放射笥同位素示踪剂技术主要是水井中注入一种氚放射性同位素示踪剂，通过不同部位油井放射笥示踪剂产出计算及峰值征分析，利用解释软件处理推导出多种地层参数，在此基础上计算出油水井之间存在的高渗透层及大孔道参数，为下步注采调整方案及封堵大孔道控水稳油等工作提供了可靠的依据。该技术在2个断块开展了现场试验，均取得成功。     

Li dust injection experiments into T-10 tokamak

An improved 0D transport model has been applied to model the deuterium, lithium and carbon densities of T-10 plasmas during Li dust injection. The deuterium recycling coefficient is found to drop from 0.92 to 0.80 during Li dust injection at the expense of higher Z_eff values. The dust injection results are compared with the alternative techniques, Li pellet injection and Li evaporation. Dust injection provides the best recycling conditions at the lowest levels of Li consumption.     

Mechanistic investigation of the hydrodechlorination of 1,1,1,2-tetrafluorodichloroethane on metal fluoride-supported Pt and Pd

The hydrodechlorination of CF₃CCl₂F over Pd and Pt supported on β-AlF₃ and MgF₂ with D₂ gas has been investigated employing temperature programmed isotope exchange (TPIE) under static conditions. The isotope exchange observed between the H-loaded metal catalyst and the D₂ gas phase demonstrates the significantly higher hydrogen uptake capability of Pd-based catalysts. Both Pd and Pt on β-AlF₃, show significantly higher hydrogen/deuterium uptake and isotope exchange activity as compared with the MgF₂ support, probably due to the presence of hexagonal channels in β-AlF₃ and its higher Lewis acidity. The combination of these properties make Pd/β-AlF₃ a superior catalyst for selective hydrodechlorination of CF₃CCl₂F. Based on the results of the hydrodechlorination of CF₃CCl₂F with D₂, a competitive rather than a consecutive mechanism is proposed. The data from H/D-TPIE are best interpreted by the formation of surface carbene species as intermediates.