Physical Regimes of Electrostatic Wave-Wave nonlinear interactions generated by an Electron Beam Propagation in Background Plasma

Electron-beam plasma interaction has long been a topic of great interest. The validities of Quasi-Linear (QL) theory and Weak Turbulence (WT) theory are limited by the requirement of sufficiently dense mode spectrum and small wave amplitude. In this paper, by performing a large number of high resolution two-dimensional (2D) particle-in-cell (PIC) simulations and using analytical theories, we extensively studied the collective processes of a mono-energetic electron beam emitted from a thermionic cathode propagating through a cold plasma. We show that initial two-stream instability between the beam and background cold electrons is saturated by wave trapping rather than QL theory. Further evolution occurs due to strong wave-wave nonlinear processes. We show that the beam-plasma interaction can be classified into four different physical regimes in the parameter space for the plasma and beam parameters. The differences between the different regimes are analyzed in detail. For the first time, we identified a new regime in strong Langmuir turbulence featured by what we call Electron Modulational Instability (EMI) that creates a local Langmuir wave packet faster than ion frequency ({\omega}_pi) and ions initially do not respond to EMI in the initial growing stage. On a longer timescale, the action of the ponderomotive force produces very strong ion density perturbations so that the beam-plasma wave interaction stops being resonant. Consequently, in this EMI regime beam-plasma interaction is a periodic burst (intermittent) process. The beams are strongly scattered, and the Langmuir wave spectrum is significantly broadened, which gives rise to the strong heating of bulk electrons. Some interesting phenomena in the strong turbulent regime are also discussedComment: 65 pages, 19 figure

Electron Modulation Instability in the Strong Turbulent Regime for Electron Beam Propagation in Background Plasma

We study collective processes for an electron beam propagating through a background plasma using simulations and analytical theory. A new regime where the instability of a Langmuir wave packet can grow locally much faster than ion frequency ({\omega}_pi) is clearly identified. The key feature of this new regime is an Electron Modulational Instability that rapidly creates a local Langmuir wave packet, which in its turn produces local charge separation and strong ion density perturbations because of the action of the ponderomotive force, such that the beam-plasma wave interaction stops being resonant. Three evolution stages of the process and observed periodic burst features are discussed. Different physical regimes in the plasma and beam parameter space are clearly demonstrated for the first time.Comment: 19 pages, 3 figure

Fluidisable mesoporous silica composites for thermochemical energy storage

Salt hydrate based thermochemical energy storage has been widely recognised as a promising long-duration storage technology to decarbonize heating/cooling in buildings.However, currently there are few salt hydrate-based energy storage materials capable to fulfil the requirements for energy density, efficiency, scalability and stability due to inappropriate particle size of the material. In this study, a commercially available mesoporous silica with large pore volume and good fluidisability was used as the porous matrix to prepare salt composites containing different salts (CaBr2, MgBr2, MgSO4, CaCl2, and Al(NH4)(SO4)2) via a facile incipient wetness impregnation method. A variety of techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), nitrogen physisorption measurements and thermogravimetric analysis (TGA) were used to characterize the physicochemical properties and water hydration/dehydration performance of mesoporous silica-based salt composites. The results showed that both salt loading level and salt type play critical roles in determining the water adsorption performance of salt composites. Tested under hydration conditions of 30°C and vapour pressure of 25mbar, the CaCl2 based salt composites exhibited the highest water adsorption capacity, which reached 109 wt% at the CaCl2 loading level of 50wt%, while the MgBr2 based salt composites had faster water adsorption rates than other salt composites. Most of the salt composites were capable of desorbing 70–80% of the adsorbed water at temperatures below 90°C, highlighting their great potential to store low-grade heat such as industrial waste heat or solar thermal energy. Advanced characterization demonstrated that the large pore volume and pore size improved the salt molecules' accessibility and water diffusivity inside the pores, leading to high water adsorption capacity and fast hydration/dehydration rate. In the aspects of particle size for future upscaling, this work presents an all new scalable and fluidisable salt composite material that opens up the potential to develop low-temperature fluidised bed based thermal energy storage systems for the first time

Direct Implicit and Explicit Energy-Conserving Particle-in-Cell Methods for Modeling of Capacitively-Coupled Plasma Devices

Achieving entire large scale kinetic modelling is a crucial task for the development and optimization of modern plasma devices. With the trend of decreasing pressure in applications such as plasma etching, kinetic simulations are necessary to self-consistently capture the particle dynamics. The standard, explicit, electrostatic, momentum-conserving Particle-In-Cell method suffers from tight stability constraints to resolve the electron plasma length (i.e. Debye length) and time scales (i.e. plasma period). This results in very high computational cost, making this technique generally prohibitive for the large volume entire device modeling (EDM). We explore the Direct Implicit algorithm and the explicit Energy Conserving algorithm as alternatives to the standard approach, which can reduce computational cost with minimal (or controllable) impact on results. These algorithms are implemented into the well-tested EDIPIC-2D and LTP-PIC codes, and their performance is evaluated by testing on a 2D capacitively coupled plasma discharge scenario. The investigation revels that both approaches enable the utilization of cell sizes larger than the Debye length, resulting in reduced runtime, while incurring only a minor compromise in accuracy. The methods also allow for time steps larger than the electron plasma period, however this can lead to numerical heating or cooling. The study further demonstrates that by appropriately adjusting the ratio of cell size to time step, it is possible to mitigate this effect to acceptable level

Analysis of Flavor Characteristics and Characteristic Components of White Tea Made from Oolong Tea Cultivars

In order to investigate the differences in flavor quality between white tea made from Oolong tea cultivars and traditional white tea, white teas made from eight Oolong tea cultivars such as Zimeigui and Fuding Dahao white tea as a control were analyzed by sensory evaluation, biochemical assays and multivariate statistical analysis. The results showed that the appearance and infusion color of Oolong white tea were darker, while the taste and aroma were better than those of traditional white tea. The biochemical analysis revealed that the differences in conductivity, pH, and the contents of soluble sugars, free amino acids, gallocatechin gallate (GCG) and epigallocatechin gallate (EGCG) were important factors causing the differences in taste between traditional white tea and white tea made from Oolong tea cultivars. Volatile composition analysis showed that trans-2-nonenal, cis-3-nonen-1-ol, methyl palmitate, linalool, methyl linoleate, cedrol, geranyl formate, phenethyl alcohol, nerolidol, methyl salicylate, dibutyl phthalate and phytone were the key differential aroma components contributing to the difference in aroma between Oolong and traditional white tea. Findings from this study will provide a theoretical reference for flavor diversification of white tea

大口径正方形管内の鉛直上昇気液2相乱流流動特性に関する研究

京都大学0048新制・課程博士博士(工学)甲第18272号工博第3864号新制||工||1593(附属図書館)31130京都大学大学院工学研究科原子核工学専攻(主査)教授 功刀 資彰, 教授 中部 主敬, 准教授 横峯 健彦学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDGA