Conceptual design and the simulation of final cooling section for a muon collider

The scheme of final cooling for muon beams, based on using current-carrying liquid-lithium rods, is discussed. The dynamics of particles in the course of cooling taking into account the non-paraxial motion has been studied with the help of computer simulation. It is suggested to minimize the effective increase of the longitudinal emittance caused by fluctuations of ionization losses and large angular spread, by the rotation of the longitudinal phase-space portrait for arranging self-action. We have considered the non-dissipative multiple successive full emittance redistribution from the longitudinal dimension to transverse one, necessary for cooling of all degrees of freedom. This redistribution is based on special rotations of the particle six-dimensional phase space by the beam division in several streams and their consequent merging with the minimum increment of full emittance and minimal beam losses taking into account their local phase-space density. Some of the basic technical parameters of the cooling system elements have been estimated.     

Prospects for laser wakefield accelerators and colliders using CO2 laser drivers

Energy directly acquired by an electron from the laser electromagnetic field is quadratically proportional to the laser wavelength. Exploiting this feature, the emerging terawatt picosecond (TWps) CO₂ lasers, having an order of magnitude longer wavelength than the well-known table-top terawatt (T³) picosecond solid state lasers, offer new opportunities for strong-field physics research. Laser accelerators serve as an example where application of the new class of lasers will result in enhancement in gas ionization, plasma wave excitation, and relativistic self-focusing. Ponderomotively strong CO₂ laser permits a 100 times reduction in the plasma density without impeding the acceleration. The improved performance of the low-pressure laser wakefield accelerators (LWFA) is potentially due to higher electric charge per accelerated bunch and better monochromaticity. The multi-kilowatt average power, high repetition rate capability of the TWps-CO₂ laser technology opens new opportunities in development of compact, 1 m long, GeV accelerators and < 1 km long high-luminosity multi-stage LWFA colliders of the TeV scale. The first TWps-CO₂ laser is under construction at the BNL Accelerator Test Facility (ATF).     

Laser cooling of solids containing local centers with electric dipole allowed transitions: a feasibility study

Various insulating materials containing local centers with electric dipole allowed transitions were studied under excitation in the long-wavelength tail of the absorption spectrum (“laser cooling regime”). Though no actual cooling was detected, spectra with a strong anti-Stokes component were observed which demonstrate the possibility to employ electron–phonon bands of electric dipole allowed transitions for optical refrigeration. The mechanisms responsible for the absence of observable optical refrigeration are discussed.     

Anti-Stokes laser-induced cooling in rare-earth doped low phonon materials

In this work we discuss the anti-Stokes laser-induced cooling of two matrices doped with Yb³⁺ and Er³⁺: a low phonon KPb₂Cl₅ crystal and a fluorochloride glass. In order to assess the presence of internal cooling in these systems we used photothermal deflection and conventional excitation spectroscopic techniques, whereas the bulk cooling in the Er³⁺-doped materials was detected by means of a calibrated thermal sensitive camera. Furthermore, we also consider some of our findings on cooling processes occurring in Yb³⁺-doped low phonon materials from a theoretical perspective. The experimental results are in good agreement with the predictions of a model based on the presence of a second order process in the cooling mechanism. The fluorescence excess shown by the excitation spectra of Yb³⁺-doped sample obtained at high fluences, by pumping at wavelengths in the cooling region, has been explained in the framework of the configurational coordinate model by considering that the frequencies of the vibrational modes in the ground and excited states change at high pumping intensities (quadratic coupling mode). In the case of Er³⁺ ion, it is worthwhile to mention that the cooling was observed in the spectral region where some upconversion processes that initiate at the pumped ⁴I_9/2 level occur. Together with the spectroscopic characterization, a short discussion on the experimental and theoretical background of the cooling process including the possible influence of upconversion processes is presented.     

压电陶瓷/聚合物基新型阻尼复合材料的研究进展

压电陶瓷/聚合物基复合材料兼具了聚合物和压电陶瓷两相的优点,是新型的智能阻尼材料.叙述了压电陶瓷/聚合物基复合材料的阻尼性能表征、阻尼原理以及影响阻尼性能的主要因素,并展望了研究前景.指出从压电阻尼材料的基础理论、制备工艺和性能表征、结构与性能关系上寻找突破,可以获得可控的高阻尼压电复合材料.     

Analysis of surface quality of multi-film cooling holes in nickel-based single crystal superalloy

The effect of the surface quality of multi-film cooling holes processed by laser drilling (LD) and electrical discharge machining (EDM) on the mechanical properties of blades have been studied. The physical features of the cooling holes, including the diameter, conicity and shape of the holes, are measured by optical microscopy, demonstrating that the EDM process is not as accurate as the LD process. Meanwhile, metallurgical characteristics, including the recast layer, heat affected zone and micro-cracking within the surface layer, are analysed by scanning electron microscopy, demonstrating that the radial crack generated in the LD process is more dangerous than the circumferential cracks generated in the EDM process. Using finite element analysis (FEA), the single crystal superalloy specimens with multi-film holes are simulated based on the crystal plasticity theory, showing that a significant increase of the stress gradient is observed in a real hole model than in an ideal circular hole model, which means that a shape simplification in the blade design will reduce the reliability of the blade. Based on the findings above, the influence of the surface quality of holes is investigated to obtain the possible damages to nickel single crystal turbine blades.     

A technique for the absolute measurement of the W-value for X-rays in counting gases

A technique was developed for the absolute measurement of the W-value (the mean energy for the production of an electron-ion pair) for low-energy X-rays in a wide range of gases at atmospheric pressures, with a standard uncertainty better than 1%. This technique is based on the absolute measurement of the primary ionization charge produced by X-ray photons from a constant intensity monoenergetic X-ray source, e.g. a long lifetime radioactive source. The ionization charge is calibrated by the number of X-ray photons absorbed in the gas, counted with a photon detector. For this purpose, a hybrid detector system was tested and its use in W-value measurements was investigated. The technique was applied to pure xenon at 825 Torr with 5.9 keV X-rays and a W-value of 21.61_−0.10^+0.14 eV was obtained for a 68% confidence level. The required corrections and the different factors contributing to the accuracy of the results are discussed. The advantages and limitations of this technique are explored and future developments are discussed.     

Observation of glass transition upon cooling in Pd40Ni10Cu30P20 alloy by DSC

Two-stage cooling experiments were carried out in a differential scanning calorimeter for an untreated bulk amorphous alloy Pd₄₀Ni₁₀Cu₃₀P₂₀. The results showed that the critical cooling rate for glass formation for the alloy was about 50 K/min. The continuous cooling transformation (CCT) curve was constructed based on the cooling experimental results and the critical cooling rate for glass formation subsequently calculated is in excellent agreement. The present results are compared with previous reported results and effects on the critical cooling rate for glass formation are discussed.     

Low energy electron induced characteristic losses in the Fe73.6Cu1Nb2.4Si15.8B7.2 (FINEMET) alloy surface

Electron Energy Loss Spectroscopy has been employed for investigation of the electronic states of amorphous and crystalline Fe_73.6Cu₁Nb_2.4Si_15.8B_7.2 (FINEMET) alloy surface and alloy components. Electron energy losses have been measured for primary electron beam energies E₀ from 150 to 650 eV. The characteristic energy loss spectra were composed of main peaks which we have interpreted due to surface and bulk plasmons, a combination of surface and bulk losses, high harmonics of plasma losses, inter-band transitions and ionization of core levels. The measured energies for the plasmon excitations were found not to agree with calculated values according to the classical theory for the collective oscillations in solids. Changes in the intensity lines of the surface and bulk plasmons were observed for all specimens depending on primary electron energy E₀. The present results are compared with characteristic energy loss data reported in the literature.     

冷却速率对Mg68Zn28Y4自生复合材料I相形成的影响

采用两种不同冷却方式的普通铸造技术在Mg68Zn28Y4合金中制备了镁合金稳定态二十面体准晶相,分析了冷却速率对准晶相形成、分布、数量和晶粒尺寸的影响.通过扫描电镜、能谱分析仪和透射电子显微分析技术,确定了合金的组织、相成分及准晶相结构.结果表明:Mg68Zn28Y4三元合金在室温冷却过程中,准晶相直接从液相形核、长大;在铸铁模型腔内冷却时,铸件断面的温度梯度小,温度场较为平坦,沿铸型纵横截面准晶相分布均匀、晶粒尺寸约为10～15μm;在铸铁板表面冷却时,铸件断面的温度梯度较大,导致冷却速率显著影响准晶相的分布、数量及形貌.准晶相的晶粒尺寸为10～60μm不等,分布由均匀弥散到不均匀散布再到均匀.     

不同冷却润滑方式对切削SiCP/Al复合材料刀具磨损的影响

为探究不同冷却润滑方式对切削SiC_P/Al复合材料刀具磨损的影响,进行了干切削（Dry）、微量润滑（MQL）、液氮（LN₂）、切削油（Oil）和乳化液（Emulsion）共五种冷却润滑条件下的车削实验,分析了冷却润滑方式对刀具边界磨损、刀具破损和后刀面磨损的影响。结果表明:MQL和LN₂有更佳的流体冲刷效果,可以将脱落的SiC颗粒及时带离切削区,减少边界磨损; Oil和Emulsion冲刷效果较差,会加剧边界磨损。LN₂的使用会增加刀具受到的热应力和机械冲击,积屑瘤发生完全脱落,造成切削过程不平稳,当切削距离达到1 100 m时,刀具发生破损; Oil切削时,严重的边界磨损导致刀尖部位尺寸减小,强度降低,当切削距离达到825 m时发生了刀具破损。MQL良好的润滑渗透性和LN₂有效的冷却效果可以减少后刀面磨损。因此,MQL兼具冷却、润滑和流体冲刷效果,更加适合作为切削SiC_P/Al复合材料的冷却润滑方式。      

Heating/cooling channels design for an automotive interior part and its evaluation in rapid heat cycle molding

Rapid heat cycle molding (RHCM) is a recently developed innovative injection molding technology. Rapid heating and cooling of the injection mold is the most crucial technique in RHCM because it not only has a significant effect on part quality but also has direct influence on productivity and cost-efficiency. Accordingly, Heating and cooling system design plays a very important role in RHCM mold design. This study focuses on the heating/cooling system design for a three-dimensional complex-shaped automotive interior part. Heat transfer simulation based on finite element analysis (FEA) was conducted to evaluate the thermal response of the injection mold and thereby improve heating/cooling channels design. Baffles were introduced for heating/cooling channels to improve heating/cooling efficiency and uniformity of the mold. A series of thermal response experiments based on full factorial experimental design were conducted to verify the effectiveness of the improved heating/cooling channels design with baffles. A mathematical model was developed by regression analysis to predict the thermal response of the injection mold. The effects of the cavity surface temperature on weld mark and surface gloss of the part were investigated by experiments. The results show that the developed baffle-based heating/cooling channels can greatly improve thermal response efficiency and uniformity of the mold. The developed mathematical model supplies an efficient approach for precise predication of mold thermal response. As the cavity surface temperature raises to a high enough level, automotive interior parts with high gloss and non-weld mark surface can be obtained.     

Reaction processes in a ZnO + 1%Gd2O3 powder mixture during mechanical and laser processing

X-ray diffraction, electron paramagnetic resonance, Fourier transform infrared spectroscopy and scanning electron microscopy were used to study the defect formation and reaction processes in a ZnO + 1%Gd₂O₃ powder mixture during its mechanical and laser processing. Mechanical treatment of the ZnO + 1%Gd₂O₃ powder mixture leads to a grinding of initial ZnO particles and formation of three types of superficial paramagnetic donor defect centers. The rise of the sample temperature with increasing processing time promotes a successive annealing of ZnO defects with small activation energies and of superficial defects in Gd₂O₃. The formation of a ZnO:Gd³⁺ solid solution in the used mechanical processing regimes has not been observed. Laser surface melting of the ZnO + 1%Gd₂O₃ pellets provokes formation of a surface layer exhibiting a texture. The crystallization directions in the superficial layers of different specimens have a random character. In the superficial layers and deep sub-surface layers, processes of solid-state interactions (formation of an inhomogeneous ZnO:Gd³⁺ solid solution) take place. The surplus charges of the Gd³⁺ ions are compensated by the formation of Zn vacancies or interstitial oxygen ions which in the laser-surface-melted layers are located closer to the Gd³⁺ ions than in the case of single-crystalline samples.     

A simple method for prediction of heating and cooling cooling in solids of various shapesUne méthode simple de prévision du taux de réchauffage et de refroidissement dans des solides de diverses formes

Methods for prediction of temperature-time profiles in solids undergoing heating or cooling are examined. Because physical data are often uncertain a prediction method that is accurate to ±10% is adequate in many situations. A procedure is proposed that meets this criterion, is simple to use, and is applicable to a wide range of regular and irregular shapes. The method introduces a concept of the number of equivalent heat transfer dimensions to take account of the solid's geometry. Alignment charts can then be used to find the centre temperature of a body as a function of time and the external heat transfer conditions.     

Impact of fin spacing on temperature distribution in adsorption cooling system for vehicle A/C applications

Effects of fin spacing on the temperature distribution in a finned tube adsorber bed are studied to decrease the temperature gradient inside the adsorber bed and minimize the adsorber bed to adsorbent mass ratio (AAMR) for vehicle air conditioning applications. Finned tube adsorber beds have shown higher specific cooling power and coefficient of performance, and low AAMR among the existing adsorber beds. A single-adsorber bed ACS with interchangeable heat exchangers is built and equipped with hermetic type T thermocouples. Two copper heat exchangers with 6.35 mm (1/4″) and 9.5 mm (3/8″) fin spacing are custom-built and packed with 2–4 mm silica gel beads. The experimental results show that by decreasing the fin spacing from 9.5 mm to 6.35 mm, the temperature difference between the fin and adsorbent reduces by 4.6 °C under the cycle time of 600 s and an adsorption to desorption time ratio (ADTR) of one. A greater reduction in the temperature gradient inside the adsorber bed with smaller fin spacing is observed for short cycle time operation, e.g. 600 s, compared to long cycle time operation, e.g. 1400 s. Finally, simultaneous comparison of the temperature gradient between the fins and AAMR against fin spacing indicates that the optimum fin spacing for a finned tube heat exchanger packed with 2–4 mm silica gel beads is about 6 mm.