Observation of quantum interference conductance fluctuations in metal rings with strong spin-orbit coupling

Ramos, R.*; Makiuchi, Takahiko*; Kikkawa, Takashi*; Daimon, Shunsuke*; Oyanagi, Koichi*; Saito, Eiji

Applied Physics Letters, 117(24), p.242402_1 - 242402_5, 2020/12

https://doi.org/10.1063/5.0031708

Superconductivity in the orbital degenerate model for heavy fermion systems

Takimoto, Tetsuya; Hotta, Takashi; Ueda, Kazuo*

Journal of Physics; Condensed Matter, 15(28), p.S2087 - S2093, 2003/07

https://doi.org/10.1088/0953-8984/15/28/329

Rich physics is expected to appear due to the coupling between orbital and spin degrees of freedom in strongly correlated electron system with orbital degeneracy. Especially, it is considered that the superconducting transition in orbital degenerate system is one of the most interesting phenomena. For instance, triplet superconductivity occurs in SrRuO where three cylindrical Fermi surfaces are observed. Also, heavy fermion superconductors are considered to have potentially orbital degree of freedom due to large degeneracy of -electron states. We discuss the effect of orbital fluctuations on superconductivity by using random phase approximation and fluctuation exchange (FLEX) approximation. It is also expected that the FLEX approximation is useful to study the correlation between spin and orbital fluctuations for the orbital degenerate system.

Spin fluctuation-induced superconductivity controlled by orbital fluctuation

Takimoto, Tetsuya; Hotta, Takashi; Maehira, Takahiro; Ueda, Kazuo*

Journal of Physics; Condensed Matter, 14(21), p.L369 - L375, 2002/06

https://doi.org/10.1088/0953-8984/14/21/101

A microscopic Hamiltonian of the orbitally-degenerated Hubbard model reflecting correct symmetry of -orbitals is proposed to discuss superconductivity in -electron systems. In the degenerated region, cancellation among spin and orbital fluctuations basically destabilizes singlet superconductivity, while -wave superconductivity mediated by spin fluctuations emerges out of the suppression of orbital fluctuations due to the lift of orbital degeneracy. We argue that the present scenario can be applied to recently discovered Ce-based heavy-fermion superconductor.

Current status and future plan for thermaI striping investigations at JNC

; kasahara, Naoto; ; ; Kamide, Hideki

JNC TN9400 2000-010, 168 Pages, 2000/02

JNC-TN9400-2000-010.pdf:8.78MB

Thermal striping is significant issue of the structural integrity, where the hot and cold fluids give high cycle fatigue to the structure through the thermal stress resulted from the time change of temperatur distibution in the structure. In the sodium cooled fast reactor, temperature change in fluid easily transfers to the structure because of the high thermal conductivity of the sodium. It means that we have to take care of thermal striping, The thermal striping is complex phenomena between the fluid and structure engineering fields. The investigations of thermal striping are not enough to evaluate the integrity directly. That is the fluctuation intensity at the structure surface is assumed to be temperature difference between source fluids (upstream to the mixing region) as the maximum value in the design. 0therwise, the design conditions are defined by using a mockup experiment and large margin of temperature fluctuation intensity. Furthermore, such evaluation manners have not yet been considered as a design rule. Transfer mechanism of temperature fluctuation from fluid to structure has been investigated by the authors on the view points of the fluid and structure. Attenuation of temperature fluctuation was recognized as a dominant factor of thermal fatigue. We have devdoped a numerical analysis system which can evaluate thermal fatigue and crack growth with consideration of the attenuation of temperature fluctuation in fluid, heat transfer, and structure. This system was applied to a real reactor and the applicability was confirmed. Further verification is planned to generalize the system. For the higher cost performance of the fast reactor, an evaluation rule is needed, which can estimate thermal loading with attenuation and can be applied to the design. An idea of the rule is proposed here. Two methods should be prepared; one is a precise evaluation method where mechanism of attenuation is modeled, and the other is simple evaluation method where ...

Numerical investigation on thermal striping conditions for a tee junction of LMFBR coolant pipes (II); Investigation for the MONJU EVST tee junction

PNC TN9410 98-044, 47 Pages, 1998/06

PNC-TN9410-98-044.pdf:6.69MB

Thermal striping phenomena characterized by stationary random temperature fluctuations are observed in the region immediately above the core exit of liquid-metal-cooled fast breeder reactors (LMFBRs) due to the interactions of cold sodium flowing out of a control rod (C/R) assembly and hot sodium flowing out of adjacent fuel assemblies (F/As). Therefore the in-vessel components located in the core outlet region, such as upper core structure (UCS), flow guide tube, C/R upper guide tube, etc., must be protected against the stationary random thermal process which might induce high-cycle fatigue. In this study, thermal striping conditions at the tee junction in the MONJU EVST system (maximum temperature difference : 110 C, Velocity ratio between main and branch pipes : 0.25) were investigated numerically by the use of computer programs. From the investigations, the following results have been obtained: (1) Effects of the secondaly flows generated by the existence of 90 elbow located at upstream position of the tee junction were negligeble, because the flow velocity in the main pipe is 0.25 of the flow velocity in the branch pipe. (2) A ration between maximum and effective amplitudes of the temperature fluctuations calculated by the DINUS-3 code was 3.18. It was concluded that the value 6.0 as the ratio used in the integrity evaluation of the EVST system is a coservative side. (3) There was a limit in ability of a time-averaged multi-dimensional code AQUA, in the evaluation of thermal striping phenomena with recirculation flows. One of the reasons was considered that the local equilibrium of turbulence flows was not established in this tee junction problem.

Development of analytical model for evaluating temperature fluctuation in coolant (XII); Investigation of stationary random temperature fluctuation characteristics in frequency domain

PNC TN9410 98-013, 48 Pages, 1998/03

PNC-TN9410-98-013.pdf:1.51MB

Thermal striping phenomena characterized by stationary random temperature fluctuation are observed in the region immediately above the core exit of liquid-metal-cooled fast breeder reactors (LMFBRs) due to the interactions of cold sodium flowing out of a control rod (C/R) assembly and hot sodium flowing out of adjacent fuel assemblies (F/As). Therefore the in-vessel components located in the core outlet region, such as upper core structure (UCS), flow guide tube, C/R upper guide tube, etc., must be protected against the stationary random thermal process which might induce high-cycle fatigue. In this study, frequency characteristics of stationary random temperature fluctuations were investigated by the use of the time-series data from parallel impinging jet experiments, TIFFSS-I. From the investigations, the following results have been obtained; [Auto-Power Spectral Density Functions] (1)Higher frequency componets were decreased drastically with the close to the test piece surface, due to the presence of filtering effect by the laminar sub-layer and heat tansfer to the surface from coolant. (2)Dependence to the nozzle velocities was observed at the outside and inside positions of the laminar sub-layer region. It was due to the increasing of turbulent intensities with increase of the nozzle velocities. [Coherence Functions] (1)Coherency between outer temperatures of the laminar sub-layer was very small. 0ne of the main reasons is that the outer temperatures of the laminar sub-1ayer were dominated by the stationary random phenomena of turbulence flows. (2)It was confirmed that the coherency between immediate positions of different thermocouples had relatively higher values. [Transfer Functions] (1)The dominant frequency band of the gain was about 3 - 10 Hz for the transfer functions of the outer position to the inner position of the laminar sub-layer, and of the inner position of the laminar sub-layer to the test piece surface. (2)There wasno dependence of ...

Development of analytical model for evaluating temperature fluctuation in coolant(XI); Validation of the evaluation model for thermally fluid-structure interaction phenomena

PNC TN9410 97-039, 187 Pages, 1997/05

PNC-TN9410-97-039.pdf:11.45MB

A numerical evaluation system, which is consisted of four codes, AQUA, DINUS-3, THEMIS and BEMSET has been developed for thermal striping phenomena. To validate the system for the phenomena, thermally fluid - structure interaction analysis was carried out using a existing sodium experiment of parallel impinging jet simulating the outlet region of an LMFBR core. Calculational results on the RMS values of temperature fluctuation, the histograms of temperature amplitudes and frequencies, the auto-power spectral density distributions of temperature fluctuations and the damping characteristics of temperature fluctuations showed good agreement with the measured values under the test conditions of various flow velocity. From the comparisons with the experimental data, it was concluded that the numerical evaluation system is applicable to the evaluation of thermally fluid - structure interaction phenomena related to the thermal striping.

Development of analytical model for evaluating temperature fluctuation in coolant (X); Investigation of thermally response characteristics of in-vessel structures using the BEMSET code

PNC TN9410 96-136, 92 Pages, 1996/05

PNC-TN9410-96-136.pdf:2.53MB

Thermal striping phenomena characterized by stationary random temperature fluctuations are observed in the region immediately above the core exit of liquid-metal-cooled fast breeder reactors (LMFBRs) due to the interactions of cold sodium flowing out of a control rod (C/R) assembly and hot sodium flowing out of adjacent fuel assemblies (F/As). Therefore the in-vessel components located in the core outlet region, such as upper core structure (UCS), flow guide tube, C/R upper guide tube, etc, must be protected against the stationary random thermal process which might induce high-cycle fatigue. In this study, thermally response characteristics of the flow guide tube made by SUS 316 stainless steels were investigated using a boundary element method code BEMSET under the temperature transient conditions of Sine wave, quasi-random wave, and Sine wave with quasi-random components. From the numerical investigations, it was concluded that the detailed handling on turbulence phenomena in coolant is very important in the evaluation of actual LMFBRs, because of the thermally response of the structures are influenced significantly on random fluctuating components.

None

PNC TJ1632 95-001, 107 Pages, 1995/03

PNC-TJ1632-95-001.pdf:2.58MB

no abstracts in English

Development of analytical model for temperature fluctuationin in coolant (VI); Investigation of sodium temperature fluctuation by the DINUS-3 code

PNC TN9410 94-182, 29 Pages, 1994/06

PNC-TN9410-94-182.pdf:0.93MB

A three-dimensional temperature fluctuation analysis was carried out using a general-purpose multi-dimensional thermohydraulics direct numerical simulation code DINUS-3 for parallel impinging jet experiments in sodium and water simulating thermal striping phenomena. The code utilized a third-order upwind scheme and an adaptive control system based on the Fuzzy theory to control time step sizes. The calculated results in both the cases showed evident differences mainly attributed to fluid properties such as heat conductivity, molecular viscosity, etc.. From the analysis, the following conclusions were obtained. (1)The amount of the temperature fluctuation damping by fluid mixing in sodium flow shows approximately two times larger than in water flow. While the damping amounts due to the laminar sub-layer in sodium flow is approximately 1/3 of that in water flow, (2)The variance of the probabilily density function for the calculated sodium temperature fluctuations is two times of the calculated water temperature fluctuations, and (3)The histogram of the normalized amplitude for calculated water temperature fluctuations can be fitted by a Layleigh distribution. By contrast, in the sodium case, the profile is very much like a exponential distribution. The results obtained in this work are very encouraging; the DINUS-3 code is one of the efficient measures to evaluate thermal striping phenomena in sodium, a low Prandtl number fluid, when one wishes to perform thermal striping evaluation in Liquid Metal Fast Breeder Reactors.