Rm Ce Research Articles

On the electric field components in the collisionless plasmoid instability

Using two-dimensional particle-in-cell simulations of collsionless plasmoid instability, the spatial and temporal variations of electric field components are investigated. The initial magnetic field is a Harris sheet which is added by a non-uniform perpendicular magnetic field (guide field). The effects of weak and medium guide field on the evolution of plasmoid instability and associated electric field are discussed with the input parameters of the solar corona with the condition $\omega _{{\rm pe}}/\omega _{{\rm ce}}>1$ . As the current sheet elongates, magnetic reconnection in an X-point transits into the plasmoid instability, in which secondary X-points are formed and the consequent magnetic islands coalesce and form larger islands. During the instability, electric field components show two types of disturbances. (1) Transient waves, being excited very early, propagate mainly perpendicular to the current sheet and become damped as the instability proceeds to the nonlinear stage. Fourier analysis reveals that electromagnetic right- and left-hand polarized modes parallel to the initial magnetic field and also the extraordinary mode perpendicular to the current sheet are excited. Additionally, electron Langmuir and slow magnetosonic waves are observed in both directions. (2) Inside the current sheet, an electric field is generated by the plasmoid-dominated reconnection and grows in amplitude as the plasmoid instability proceeds. Moreover, in our study, the effects of amplitude-varying guide field on the spatial structure of electric field components outside and inside the current sheet are discussed. This study is valuable because understanding the spatial and temporal variation of the electric field is an essential prerequisite for the issue of particle acceleration in plasmoid-dominated magnetic reconnection.

Suppression of antiferromagnetic order in the electron-doped cuprate T′−La2−xCexCuO4±δ

We performed systematic angle-resolved photoemission spectroscopy measurements $in$-$situ$ on $T'$-${\rm La}_{2-x}{\rm Ce}_x\rm {CuO}_{4\pm\delta}$ (LCCO) thin films over the extended doping range prepared by the refined ozone/vacuum annealing method. Electron doping level ($n$), estimated from the measured Fermi surface volume, varies from 0.05 to 0.23, which covers the whole superconducting dome. We observed an absence of the insulating behavior around $n \sim$ 0.05 and the Fermi surface reconstruction shifted to $n \sim$ 0.11 in LCCO compared to that of other electron-doped cuprates at around 0.15, suggesting that antiferromagnetism is strongly suppressed in this material. The possible explanation may lie in the enhanced -$t'$ /$t$ in LCCO for the largest $\rm{La^{3+}}$ ionic radius among all the Lanthanide elements.

Thermal atom-ion collisions in a K- Yb+ hybrid system

We present experimental studies of atom-ion collisions using buffer-gas cooled, trapped ytterbium (Yb$^+$) ions immersed in potassium (K) vapor. The range of the collisional temperature is on the order of several hundred kelvin (thermal regime). We have determined various collisional rate coefficients of the Yb$^+$ ion per K-atom number density. We find the upper bounds of charge-exchange rate coefficients $\kappa_{\rm ce}$ to be $(12.7\pm1.6)\times10^{-14}$ cm$^3$s$^{-1}$ for K-$^{171}$Yb$^+$ and $(5.3\pm0.7)\times10^{-14}$ cm$^3$s$^{-1}$ for K-$^{172}$Yb$^+$. For both isotopes, the spin-destruction rate coefficient $\kappa_{\rm sd}$ has an upper bound at $(1.46\pm0.77)\times10^{-9}$ cm$^3$s$^{-1}$. The spin-exchange rate coefficient $\kappa_{\rm se}$ is measured to be $(1.64\pm0.51)\times10^{-9}$ cm$^3$s$^{-1}$. The relatively low charge-exchange rate reported here demonstrates the advantage of using K atoms to sympathetically cool Yb$^+$ ions, and the relatively high spin-exchange rate may benefit research work in quantum metrology and quantum information processing on an atom-ion platform using K atoms and Yb$^+$ ions.

Ce Substitution and Reduction Annealing Effects on Electronic States in Pr2−xCexCuO4 Studied by Cu K-edge X-ray Absorption Spectroscopy

We investigated Ce-substitution and reduction annealing effects on the electronic states at copper sites by Cu ${K}$-edge x-ray absorption near-edge structure measurements in Pr$_{2-x}$Ce$_x$CuO$_{4+\alpha-\delta}$ (PCCO) with varying $x$ and $\delta$ (the amount of oxygen loss during annealing) values. Absorption near-edge spectra were modified by Ce-substitution and reduction annealing in a similar manner with increasing $x$ and $\delta$. Considering electron doping by Ce-substitution, this similarity indicates an increase of electron number at the copper sites due to annealing $n_{\rm AN}$. Thus, the total number of electrons is determined by the amount of Ce and oxygen ions. Furthermore, quantitative analyses of the spectra clarified that the number of Cu$^+$ sites, corresponding to the induced electron number by Ce-substitution $n_{\rm Ce}$ increases linearly with $x$ in the as-sintered PCCO ($\delta=0$), whereas $n_{\rm AN}$ is not exactly equal to twice of $\delta$, which is expected from charge neutrality. For each $x$-fixed sample, $n_{\rm AN}$ tends to exceed 2$\delta$ with increasing $\delta$, suggesting the emergence of two types of carrier due to annealing.

Analysis of the Results of Accelerated Aging Tests in Insulated Gate Bipolar Transistors

The introduction of fully electric vehicles (FEVs) into the mainstream has raised concerns about the reliability of their electronic components such as IGBT. The great variability in IGBT failure times caused by the very different operating conditions experienced and the stochasticity of their degradation processes suggests the adoption of condition-based maintenance approaches. Thus, the development of methods for assessing their healthy state and predicting their remaining useful life (RUL) is of key importance. In this paper, we investigate the results of performing accelerated aging tests. Our objective is to discuss the design and the results of accelerated aging tests performed on three different IGBT types within the electrical powertrain health monitoring for increased safety (HEMIS) of FEVs European Community project. During the tests, several electric signals were measured in different operating conditions. The results show that the case temperature $(T_{C})$ , the collector current $(I_{C})$ , and the collector–emitter voltage $(V_{{\rm CE}})$ are the failure precursor parameters that can be used for the development of a prognostic and health monitoring (PHM) system for FEV IGBTs and other medium-power switching supplies.

Modulated magnetism and anomalous electronic transport inCe3Cu4As4O2

The complex magnetism and transport properties of tetragonal Ce$_3$Cu$_4$As$_4$O$_2$ were examined through neutron scattering and physical properties measurements on polycrystalline samples. The lamellar structure consists of alternating layers of $\rm CeCu_4As_4$ with a single square Ce lattice and oxygen-linked Ce bi-layer $\rm Ce_2O_2$. Extending along $\bf c$, a tube-like Fermi surface from DFT calculations points to a quasi-two-dimensional electronic system. Peaks in the specific heat at the Ne\'{e}l temperature $T_{N}=24$ $\rm K$, $T_{2}~=~16 $ $\rm K$ and $T_{3}~=~1.9$ $ \rm K$ indicate three magnetic phase transitions or distinct cross-over phenomena. For $T<T_{N}$ neutron diffraction indicates the development of ferromagnetic ab sheets for both Ce sites, with alternating polarization along $\bf{c}$, a wave vector ${\bf k}_{1}={\bf c}^*$. For $T<T_{2}$, quasi-two-dimensional low-energy spin fluctuations with ${\bf k}_{2}=\frac{1}{2}{\bf a}^*$ and polarized perpendicular to ${\bf k}_{2}$ are suppressed. The data are consistent with quasi-two-dimensional antiferromagnetic order in the $\rm CeCu_4As_4$ planes polarized along the ${\bf k}_{2}$ wave vector. $T_{3}$ marks a spin-flop transition where the ${\bf k}_{1}$ staggered magnetization switches to in-plane polarization. While the narrow 4f bands lie deep below the Fermi surface, there are significant transport anomalies associated with the transitions; in particular a substantial reduction in resistivity for $T<T_{N}$. At $T=100$ $ \rm mK$ the ${\bf k}_1$ modulated staggered moment is $0.85~\mu_B$, which matches the $0.8~\mu_B$ saturation magnetization achieved for H $~=~7$ $ \rm T$ at $T~=~2$ $ \rm K$. From low T Lorentzian fits the correlation length is in excess of 75 \AA. We argue the unusual sequence of magnetic transitions results from competing interactions and anisotropies for the two Ce sites.

Radiation Response of Ce-Codoped Germanosilicate and Phosphosilicate Optical Fibers

We report an experimental investigation on the effects of Ce-codoping in determining the radiation response of germanosilicate and phosphosilicate Optical Fibers (OFs) in the UV-Visible domain and up to doses of $1~\hbox{MGy}({\rm SiO}_{2})$ . We show that the addition of Ce strongly impacts the Radiation Induced Attenuation (RIA) of both types of fibers. In the first case the radiation induced losses increase, whereas in the second one decrease. By combining the online RIA measurements with the Electron Paramagnetic Resonance (EPR) ones, we are able to infer the basic microscopic mechanisms taking place under irradiation, which involve the cerium codopant and some of the known Ge-related or P-related defects. More precisely, we found that part of the Ce atoms are incorporated in the glass matrix as ${\rm Ce}^{3 + }$ ions by the production process and act as electron donor centers under irradiation. Consequently, the concentrations of radiation induced hole centers of Ge and P are drastically reduced. The reported results give an insight into possible ways of exploiting Ce codoping to control the radiation sensitivity of the OFs. Moreover, the OFs doped with cerium and phosphorous show a strongly reduced saturation effect at high radiation doses that make them a potential candidate for RIA-based dosimetry applications in a wide range of radiation doses.

Common envelope events with low-mass giants: understanding the energy budget

Common envelope events are important interactions between two binary stars that lead to the formation of close binary systems. We present here a systematic three-dimensional study in which we model common envelope events with low-mass giant donors. The results allow us to revise the energy formalism that is usually used to determine common envelope event outcomes. We show that the energy budget for this type of system should include the recombination energy, and that it also must take into account that a significant fraction of the released orbital energy is taken away by the ejecta. We provide three ways in which our results can be used by binary population synthesis studies: a relation that links the observed post-common envelope binary with the initial binary parameters, a fitting formula for the $\alpha_{\rm ce}\lambda$ parameter of the standard energy formalism, and a revised energy formalism that takes into account both the recombination energy and the energy that is taken away by the ejecta.

The Stable Center: A New Tool to Optimize Ce-Doped Oxide Scintillators

The role and effect of stable ${\rm Ce}^{4+}$ centers in Ce-doped LuAG single crystal scintillator is further studied by means of measurements of several optical, luminescence and scintillation characteristics. Two LuAG:Ce single crystal samples are compared: in one of them the dominating ${\rm Ce}^{4 +}$ center is stabilized by high concentration ${\rm Mg}^{2+}$ codoping while the other one shows only the presence of stable ${\rm Ce}^{3 + }$ center. Tailored (Eu, Mg)–doped LuAG single crystal is also prepared to test the presence and thermal stability of hole traps in the host which affect the timing characteristics of ${\rm Ce}^{4+}$ scintillation cycle, namely its restoration back to 4+ charge state in last step of the cycle. EPR experiment was also employed at Mg- and (Eu, Mg) doped LuAG samples and the signature of the ${\rm O}^ - $ hole center stabilized by ${\rm Mg}^{2 +}$ ion was clearly obtained.

Large Size Czochralski Growth and Scintillation Properties of

The 3 inch size Mg co-doped ${\rm Ce}:{\rm Gd}_{3} {\rm Al}_{2}{\rm Ga}_{3} {\rm O}_{12}$ single crystals were prepared by the Czochralski (Cz) method. Absorption and luminescence spectra were measured together with several other scintillation characteristics, namely the scintillation decay and light yield to reveal the effect of Mg co-doping. The timing resolution measurement for a pair of $3 \times 3 \times 3\;\hbox{mm}^3$ size GAGG:Ce.Mg scintillator crystals was performed using Si-PMs.

Scintillating Screens Based on the Single Crystalline Films of Multicomponent Garnets: New Achievements and Possibilities

The paper is dedicated to development of the novel scintillating screens based on single crystalline films (SCF) of Ce doped ${{\rm Lu}_{3 - {\rm x}}}{{\rm Tb}_{\rm x}}{{\rm Al}_{5 - {\rm y}}}{{\rm Ga}_{\rm y}}{{\rm O}_{12}}$ multicomponent garnets at ${\rm x} = 2 - 3$ and ${\rm y} = 0 - 2.5$ onto ${{\rm Y}_3}{{\rm Al}_5}{{\rm O}_{12}}$ (YAG) and ${{\rm Gd}_3}{{\rm Al}_{2.5}}{{\rm Ga}_{2.5}}{{\rm O}_{12}}$ (GAGG) substrates using the liquid phase epitaxy (LPE) method. We report the optimized content and high scintillation figure of merit of SCF of these garnets grown by the LPE method with using PbO based flux. Namely, the ${{\rm Tb}_3}{{\rm Al}_{2.5}}{{\rm Ga}_{2.5}}{{\rm O}_{12}}:{\rm Ce}$ SCFs possess the highest values of light yield (LY) compared to all earlier investigated SCF samples, with their LY exceeding by 2.35 and 1.15 times the LY values for YAG:Ce and LuAG:Ce SCF scintillators, respectively. The SCFs of the mentioned compounds show very lower thermoluminescence in the above room temperature range and relatively fast scintillation decay.

Energy Resolution and Temperature Dependence of Ce:GAGG Coupled to Silicon Photomultipliers

Scintillators are a critical component of sensor systems for the detection of ionizing radiation. Such systems have a diverse portfolio of applications from medical imaging, well logging in oil exploration, and detection systems for the prevention of the illicit movement of nuclear materials. The rare earth element cerium is an ideal dopant for a variety of host scintillating materials due to the fast $5{{\rm d}_1} \rightarrow {4} {\rm f}$ radiative transition of ${{\rm Ce}^{3 + }}$ . Cerium-doped gadolinium aluminium gallium garnet (Ce:GAGG) is a relatively new single crystal scintillator with several interesting properties. These include high light yield, an emission peak well-matched to silicon sensors, and low intrinsic energy resolution. Moreover, the material has high density and is nonhygroscopic. In this paper, we review the properties of cerium-doped GAGG and report energy-resolution (ER) measurements over the temperature range $- {\hbox {10}}^\circ\text{C}$ to $+ {\hbox {50}}^\circ \text{C}$ for ${\hbox \times {\hbox \times {\hbox {30}} \hbox{mm}^{3}$ Ce:GAGG crystals optically coupled to a silicon photomultipler (SiPM) sensor with a ${\hbox {3}} \hbox{mm} \times {\hbox {3}} \hbox{mm}$ active area. In addition, the linearity of the scintillator-SiPM response as a function of gamma energy is reported.

Advanced Accelerated Power Cycling Test for Reliability Investigation of Power Device Modules

This paper presents an apparatus and methodology for an advanced accelerated power cycling test of insulated-gate bipolar transistor (IGBT) modules. In this test, the accelerated power cycling test can be performed under more realistic electrical operating conditions with online wear-out monitoring of tested power IGBT module. The various realistic electrical operating conditions close to real three-phase converter applications can be achieved by the simple control method. Further, by the proposed concept of applying the temperature stress, it is possible to apply various magnitudes of temperature swing in a short cycle period and to change the temperature cycle period easily. Thanks to a short temperature cycle period, test results can be obtained in a reasonable test time. A detailed explanation of apparatus such as configuration and control methods for the different functions of accelerated power cycling test setup is given. Then, an improved in situ junction temperature estimation method using on-state collector–emitter voltage $V_{{\rm CE}\_{\rm ON}}$ and load current is proposed. In addition, a procedure of advanced accelerated power cycling test and test results with 600 V, 30 A transfer molded IGBT modules are presented in order to verify the validity and effectiveness of the proposed apparatus and methodology. Finally, physics-of-failure analysis of tested IGBT modules is provided.

A Dual-Ended Readout Detector Using a Meantime Method for SiPM TOF-DOI PET

We have investigated a dual-ended readout detector based on two silicon photo-multipliers (SiPMs) using a 30 mm long cerium-doped lutetium-yttrium oxyorthosilicate ( ${\rm Lu}_{0.5}{{\rm Y}_{1.4}}{\rm Si}_{0.5}:{\rm Ce}$ , LYSO) crystal to study the feasibility of a time-of-flight (TOF) and depth-of-interaction (DOI) positron emission tomography (PET). To improve the timing resolution in the dual-ended readout detector, a novel meantime measurement was employed. The meantime was obtained by averaging two signal arrival times at two SiPMs, each of which was attached to both ends of the LYSO crystal. The meantime method minimizes the arrival time difference along the crystal. Both timing and DOI resolutions using the meantime method were better than those of a single-ended readout detector.

Amplification of filamentation instability by negative hydrogen ions stream driven by a magnetized counterstreaming e–H− plasmas

AbstractThe main purpose of this theory is to present a simple picture of magnetic field generation by a relativistic equilibrium counterstreaming electron–negative hydrogen ion (e–H−) plasmas propagating parallel to an ambient external magnetic field. The existence of such kind of plasma flows can be imagined during the negative hydrogen ion propagation through neutralizing plasma, in order to generate an energetic neutral hydrogen beam. The produced magnetic field deflects the electron and negative hydrogen ion flows and reduces the efficiency of hydrogen neutral beam generation. We focused our analysis on the influences of the negative hydrogen ion contribution, the particles thermal velocity and the external magnetic field on the growth rate of generated sheared magnetic field. The dispersion relation is obtained using a relativistic two-fluid model and Maxwell equations. The analytical and numerical solutions admit generation of a purely growing transverse electromagnetic field across the ambient external magnetic field. It is shown that H− current filaments are responsible for deep penetration of the sheared magnetic fields into plasma, however, applying a weak magnetic field ${\rm \omega} _{{\rm ce}}^2 {\rm \ll} {\rm \omega} _{{\rm pe}}^2 $ suppresses magnetic field generation for a counterstreaming e–H− plasma in the absence of H− ions dynamics. On the other hand, a magnetic field exists with a small growth rate for strongly magnetized (${\rm \omega} _{{\rm ce}}^2 \;{\rm \gg}\; {\rm \omega} _{{\rm pe}}^2 $) e–H− plasma when the influence of H− ions is included. Although the growth rate is small, we expect that magnetic field generation is further amplified and the penetration depth is increased owing to H− ions stream, on a time scale much longer than the plasma period $t\;{\rm \gg}\; {\rm \omega} _{{\rm pe}}^{ - 1} $.

Theoretical uncertainties of the Type Ia supernova rate

It is thought that type Ia supernovae (SNe Ia) are explosions of carbon-oxygen white dwarfs (CO WDs). Two main evolutionary channels are proposed for the WD to reach the critical density required for a thermonuclear explosion: the single degenerate scenario (SD), in which a CO WD accretes from a non-degenerate companion, and the double degenerate scenario (DD), in which two CO WDs merge. However, it remains difficult to reproduce the observed SN Ia rate with these two scenarios. With a binary population synthesis code we study the main evolutionary channels that lead to SNe Ia and we calculate the SN Ia rates and the associated delay time distributions. We find that the DD channel is the dominant formation channel for the longest delay times. The SD channel with helium-rich donors is the dominant channel at the shortest delay times. Our standard model rate is a factor five lower than the observed rate in galaxy clusters. We investigate the influence of ill-constrained aspects of single- and binary-star evolution and uncertain initial binary distributions on the rate of type Ia SNe. These distributions, as well as uncertainties in both helium star evolution and common envelope evolution, have the greatest influence on our calculated rates. Inefficient common envelope evolution increases the relative number of SD explosions such that for $\alpha_{\rm ce} = 0.2$ they dominate the SN Ia rate. Our highest rate is a factor three less than the galaxy-cluster SN Ia rate, but compatible with the rate determined in a field-galaxy dominated sample. If we assume unlimited accretion onto WDs, to maximize the number of SD explosions, our rate is compatible with the observed galaxy-cluster rate.

Evaluation of $V_{\rm ce}$ Monitoring as a Real-Time Method to Estimate Aging of Bond Wire-IGBT Modules Stressed by Power Cycling

The supervision of semiconductor power devices in operation demonstrates an obvious interest to improve the operating safety of electronic power converters used in critical applications. Unfortunately, this is a significant challenge due to the variability of stress conditions on the one hand and to the difficulty to implement accurate measurement systems in power stages on the other. Using VCE measurement as a real-time supervision method is evaluated here by using aging test results obtained on insulated gate bipolar transistor (IGBT) modules stressed by power cycling. These results are related to the aging of bond wires and metallization, on the top part of the module. Results were obtained in original test benches whose characteristics are overviewed briefly in the first part of this paper, along with a description of test conditions. The second part presents selected results extracted from a larger work and focusing on the VCE evolution with respect to degradations of the module's top part. Their analysis highlights the potential of VCE measurement. The last part proposes the principle of a specific system able to achieve real-time VCE supervision in the test benches in operation.

Evolution from a magnetically correlated state to a single impurity state in heavy fermion system Ce3−xLaxCo4Sn13

AbstractCe3Co4Sn13 crystallizes in the cubic Yb3Rh4Sn13 structure, which is closely related to the one of scutterudites, well known thermoelectric materials. Ce3Co4Sn13 exhibits novel physical properties, a large increase in Cmag/T was recently observed at low temperatures with a maximum value of about 4 J K−2 ${\rm mol}_{{\rm Ce}}^{- 1} $. The specific heat data suggested that Ce3Co4Sn13 is likely near a magnetic quantum critical point (QCP). In this report we investigate the low‐temperature specific heat of Ce3−xLaxCo4Sn13 in order to study the proximity of Ce3Co4Sn13 to the possible magnetic QCP. We found the critical concentration xc ≈ 0.6 which separates the magnetically correlated state with a maximum in C(T)/T at ∼0.7 K for x &lt; xc, and a single impurity state for x &gt; xc in heavy fermion (HF) system Ce3−xLaxCo4Sn13. However, for xc the low‐temperature C(T)/T behaviour is not characteristic of the QCP.

Effect of Pump-Probe Polarization and Crystal Orientation on Propagation of Flat Top Pulse in ${\rm Ce{:}BaTiO}_{3}$ via Degenerate Two-Wave Mixing

The propagation of flat top pulse is studied inside the crystal via degenerate two-wave mixing as a function of various polarization states of a pump-probe beam. Subluminal as well as superluminal pulse propagation is observed by tuning the crystal orientation for S-S and P-S polarization states of a pump-probe laser beam.

Influence of ${\rm Ce}^{3+}$ Codoping on the Photoluminescence Excitation Channels of Phosphosilicate Yb/Er-Doped Glasses

The luminescence properties of the Yb/Er-doped phosphosilicate preforms used for the design of active optical fibers were investigated under a tunable laser excitation from ultraviolet to infrared domain. We demonstrated that codoping the glass matrix with Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions strongly influences the infrared emission associated with Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions, it enhances the energy transfer from Yb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> to Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions, and it provides an additional ultraviolet excitation channel for the emission of both Yb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> and Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. The excitation/emission pathways are discussed on the basis of models proposed in literature for other systems.