Phonon excitation of quasiparticles in niobium and tantalum superconducting tunnel junction photon detectors

We report phonon pulse measurements of quasiparticle (qp) self-recombination and trapping by Abrikosov vortices in Nb and Ta superconducting tunnel junctions. The quasiparticle loss times, determined from the shape of the tunnel junction output pulse, were found to be strongly correlated with flux trapping. The measured results were compared with the model of Golubov and Houwman. It was found that qp self-recombination, as measured from the dependence of responsivity on absorbed phonon energy, was also modified by the presence of traps. A process of phonon-mediated de-trapping is proposed to explain the observed effects.     

The effect of quasiparticle self-generation on the performance of small gap multiple tunnelling STJs

Due to the slowness of the electron–phonon interaction in small gap STJs currently being developed as the latest generation of photon detectors, during the device operation a broad statistical distribution of interacting quasiparticles and phonons is established. This gives rise to new physical phenomena and also renders the traditional Rothwarf–Taylor model completely inadequate for the analysis of quasiparticle and phonon dynamics for all traditional superconductors except unproximised Nb. We have developed a new kinetic approach replacing the Rothwarf–Taylor scheme. We demonstrate the results of experimental and theoretical studies of the new physical phenomenon of quasiparticle self-generation in a heavily proximised multiple tunneling Ta/Al STJ and discuss the implications of the observed quasiparticle self-generation for photon detection.     

Non-equilibrium superconductivity and superconducting tunnel junction detectors

Superconducting tunnel junction (STJ) detectors can be characterized by ultra-high-energy resolution, high count rate capability, and stability against temperature fluctuation. This tutorial article briefly introduces some principles of STJ detectors and also reviews their recent developments.     

Quasiparticle loss rates in Ta-based superconducting tunnel junctions

The quasiparticle (QP) lifetime in superconducting tunnel junctions (STJs) at sufficiently low temperature is usually found to be governed by loss processes associated with edges, interfaces or contacts. Such losses are closely related to fabrication issues and difficult to control. In our Ta-based STJs we observe variations in pulse decay time up to a factor of 2–3 for nominally the same devices. Nevertheless, experiments with STJs in which the thickness of the Al layers adjacent to the barrier is progressively increased, show a clear trend of increasing QP lifetime. Alternatively, introducing Nb capping layers below and on top of the Ta STJs gives a significant reduction of QP lifetime.     

The role of epitaxy in superconducting tunnel junction detectors

We have experimentally analysed the use of epitaxial and polycrystalline tantalum trapping layers in tunnel junction detectors, using epitaxial niobium based double tunnel junction devices. We have shown that the trapping rate is enhanced by having a low mean-free-path in the Ta trap film and an epitaxial Nb absorber film. This effectively increases the proportion of time spent by a quasiparticle in the trap film. Phonon-quasiparticle scattering, which reduces the effective trapping rate, has been observed.     

Aluminum thickness dependence of spatial profile in niobium-based superconducting tunnel junctions

Spatial profiles of low-temperature detectors can be measured with Low-Temperature Scanning Synchrotron Microscopy directly. The dependence of the spatial profiles on the bias current, the magnetic field strength, and the size of junctions have been already studied in previous reports. In this study, we fabricated Nb-based junctions having Al layers of different thicknesses, which are located at the both sides of the tunneling barrier, by using a lift-off technique. It has been found that the spatial uniformity is improved by increasing the Al thickness. Therefore, it is demonstrated that the Al layers play a important role more than quasiparticle trapping.     

Measurement of the tunnel rate in SIS' tunnel junctions as function of bias voltage

Cryogenic detectors with superconducting tunnel junctions can provide an energy resolution improved by at least one order of magnitude compared with standard semiconductor detectors. While the detection principle was already demonstrated many years ago, the past years were dedicated to the transition from the laboratory sample to practical detectors. Our most favored detector design gives rise to tunnel junctions with electrodes of unequal energy gaps. In such hetero tunnel junctions bias conditions can be established which cause a negative signal current. We report the experimental verification of this effect, and we discuss the yield of charge signal of cryogenic detectors based upon superconducting tunnel junctions.     

Annular superconducting tunnel junction with injected current as a new configuration of radiation detector

We have experimentally demonstrated the capability of an annular superconducting tunnel junction with trapped flux quanta to detect X-ray without external magnetic field which is required in the conventional detection scheme. With this device, we have collected the pulse height spectrum with acceptable resolution.     

The role of quench back in quench protection of a superconducting solenoid

This report demonstrates the role of quench back in the quench protection of high current density superconducting solenoid magnets with well-coupled shorted secondary circuits. The phenomenon of ‘quench back’ can be used to greatly reduce the size of an external quench protection resistor or even to eliminate the need for an external quench protection system altogether. A comparison is made with conventional magnet quench protection systems with and without a closely coupled secondary circuit.     

Observation of subgap structures in high-quality Nb/Al-AlOx/Nb Josephson tunnel junctions

We have performedI-V measurements on high-quality Nb/Al-AlO_x/Nb Josephson junctions. All curves exhibit subgap structures. Some junctions exhibit in theI-V curves the (₁–₂)/e singularity, due to the presence of niobium films with different gaps. In these devices we observed sharply separated structures corresponding to the series 2₁/ne and 2₂/ne, with n3 corresponding to the tunneling of two and three electrons. The respective amplitudes of the two structures atn=2 allow one to conclude that the phenomenon is a multiparticle tunneling process.     

Photon energy dependence of spatial non-uniformity in super-conducting tunnel junction detectors between 200 ev and 10 keV

It has been demonstrated by Low-Temperature Scanning Synchrotron Microscope that the spatial profiles of Nb/Al/AlO_x/Al/Nb detectors are abnormally large in an energy range between 2 and 10 keV, and thus the detectors produce no clear total absorption peaks. Below 2 keV, on the other hand, full illumination experiments have afforded the evidence that the spatial uniformity is significantly improved, for example, an 100 μm square junction has an intrinsic energy resolution of 5.4 eV at 200 eV. These results reconfirm that carefully designed junction detectors with a reasonable size are ideal for energy-dispersive spectroscopy in a soft X-ray range.     

城市公路隧道峒口污染物扩散的数值模拟与分析

根据大气扩散方程建立公路隧道峒口污染物扩散的物理数学模型,并对某城市隧道峒口在冬、夏两季主导风向情况下CO扩散情况、浓度分布进行了数值模拟。数值计算结果表明,在距地面1.5m的标高上CO集中隧道引道坡附近,对人行道附近人员影响较小;在横向风向下,局部地区CO浓度超标。     

精细化管理在隧洞光面爆破施工中的作用

在乌干达卡鲁玛水电站尾水隧洞14.584km的主洞开挖施工中,为了取得良好的光面爆破效果,减少爆破对围岩的扰动,在做好光面爆破设计、选用合理的参数、严格实施钻孔爆破工艺的同时,采取了针对钻爆作业人员和每个开挖作业面的精细化管理,对出现的问题及时沟通,反复培训,指导改进钻爆工艺。隧洞开挖施工的全过程贯穿着"服务、指导、监督"的管理理念,最终尾水隧洞开挖取得了较好的光面爆破效果,光面爆破半孔率达90%以上。实践表明:对于隧洞开挖光面爆破,除了合理的设计装药结构、线装药密度外,做好员工培训、测量放线、钻孔、装药、联网爆破的每一个环节,才能取得令人满意的光爆效果。     

地铁隧道电子与非电子雷管爆破振动信号的HHT对比分析

运用HHT分析方法对深圳地铁7号线及北京地铁16号线的实测爆破振动信号进行分析,对比普通毫秒延时雷管和电子雷管在爆破振动强度、延时时间、时频特性和能量分布特征等方面的不同。结果表明:电子雷管应用于单孔连续起爆技术,能量利用率高,可以有效的减小爆破振动强度和振动持续时间,在降低了单段装药量的同时增加了循环进尺深度。普通毫秒雷管爆破产生的瞬时能量较大,在频带范围内的分布相对较广;电子雷管的瞬时能量相对较小,且在频带上分布多集中在中低频部分。利用HHT瞬时能量法可以有效识别普通毫秒雷管的实际延时时间,而电子雷管相邻段位间的延时间隔时间很小,爆炸应力波发生了复杂的叠加和干扰,识别出的突变峰值明显小于普通毫秒雷管的爆破。     

地铁隧道电子与非电子雷管爆破振动信号的HHT对比分析

运用HHT分析方法对深圳地铁7号线及北京地铁16号线的实测爆破振动信号进行分析,对比普通毫秒延时雷管和电子雷管在爆破振动强度、延时时间、时频特性和能量分布特征等方面的不同。结果表明:电子雷管应用于单孔连续起爆技术,能量利用率高,可以有效的减小爆破振动强度和振动持续时间,在降低了单段装药量的同时增加了循环进尺深度。普通毫秒雷管爆破产生的瞬时能量较大,在频带范围内的分布相对较广;电子雷管的瞬时能量相对较小,且在频带上分布多集中在中低频部分。利用HHT瞬时能量法可以有效识别普通毫秒雷管的实际延时时间,而电子雷管相邻段位间的延时间隔时间很小,爆炸应力波发生了复杂的叠加和干扰,识别出的突变峰值明显小于普通毫秒雷管的爆破。     

力学因素对钢中氢扩散行为的影响

采用阴极电解渗氢法和气相色谱测氢法研究了塑性变形和负载应力对氢在钢中的溶解和逸出的影响,认为:随塑性变形和负载应力的增加氢的溶解度和溶解时的扩散系数增大,溶解扩散激活能减小;氢逸出时的扩散系数减小逸出扩散激活能增大;电解渗入的氢有一部分不能扩散逸出,这部分残留下来的氢随溶解氢量的提高而增加;溶解扩散系数比逸出扩散系数大一个数量级。     

Experimental investigation of extinction properties and thermal conductivity of metal-coated dielectric fibers in vacuum

This paper describes first experimental steps of an attempt to replace evacuated multifoils by metal-coated dielectric fibers as a new superisolation. Calculations of the Rosseland mean of spectral extinction coefficients for thin highly relective fibers show that radiation transport can be reduced to the same extent that is achievable with multifoils. Experimental results of extinction coefficients and thermal conductivity of Al-coated glass fibers are reported. Apparently, the metal coating does not increase seriously the small solid thermal conductivity of pure glass fibers. The procedure for optimizing this insulation is thus reduced to an optimization of its extinction properties.     

Chemical vapor deposition growth of Fe3O4 thin films and Fe/Fe3O4 bi-layers for their integration in magnetic tunnel junctions

A possible route for the synthesis of Fe₃O₄, Fe, and Fe/Fe₃O₄ bi-layers with chemical vapor deposition by employing the same Fe₃(CO)₁₂ carbonyl precursor is presented. The comprehensive structural, chemical, and morphological investigation of the as-deposited thin single films and bi-layers is performed by X-ray diffraction, X-ray reflectivity, Raman spectroscopy, and time-of-flight secondary ion mass spectrometry depth profiling. We present the possibility of performing the deposition of pure metallic Fe and Fe₃O₄/γ-Fe₂O₃ by adjusting the deposition pressure from 10^- 3/^- 4 Pa to 1 Pa, respectively. The integration of Fe₃O₄ thin films in a magnetic tunnel junction stack fully synthesized by in situ atomic layer and chemical vapor deposition processes is also presented, showing good stack stability and marginal interdiffusion.     

The effect of diffusion processes on the interaction in multicomponent silicate systems

The results of studying diffusion processes in silicate multicomponent systems, which are widely used as binders in variously purposed composite materials, have been generalized and described. It has been shown that the effective diffusion coefficients of alkali and alkaline-earth cations in a diffusion pair are not a single-valued function of the ion radius of the cation but depend on structural factors and on the energy of the cation bonding with other ions of the melt.     

浅析工业生产中采暖伴热与节能减排

工业生产过程中,正确使用和控制采暖伴热,通过技术改造和有序控制来实现采暖伴热的低碳、环保,并依据影响采暖伴热的各种因素来调整工业采暖,确保工业生产中生产过程的连续性和能源利用的合理性,达到既充分利用资源,又促进节能减排的最佳状态.