Sawtooth-like oscillations and steady states caused by the m/n=2/1 double tearing mode

Author(s):  
Wei Zhang ◽  
Zhiwei Ma ◽  
Haowei Zhang ◽  
Xin Wang

Abstract The sawtooth-like oscillations resulting from the m/n=2/1 double tearing mode (DTM) are numerically investigated through the three-dimensional, toroidal, nonlinear resistive-MHD code (CLT). We find that the nonlinear evolution of the m/n=2/1 DTM can lead to sawtooth-like oscillations, which are similar to those driven by the kink mode. The perpendicular thermal conductivity and the external heating rate can significantly alter the behaviors of the DTM driven sawtooth-like oscillations. With a high perpendicular thermal conductivity, the system quickly evolves into a steady state with m/n=2/1 magnetic islands and helical flow. However, with a low perpendicular thermal conductivity, the system tends to exhibit sawtooth-like oscillations. With a sufficiently high or low heating rate, the system exhibits sawtooth-like oscillations, while with an intermediate heating rate, the system quickly evolves into a steady state. At the steady state, there exist the non-axisymmetric magnetic field and strong radial flow, and both are with helicity of m/n=2/1. Like the steady state with m/n=1/1 radial flow, which is beneficial for preventing the Helium ash accumulation in the core, the steady state with m/n=2/1 radial flow might also be a good candidate for the advanced steady-state operations in future fusion reactors. We also find that the behaviors of the sawtooth-like oscillations are almost independent of Tokamak geometry, which implies that the steady state with saturated m/n=2/1 islands might exist in different Tokamaks.

2000 ◽  
Vol 122 (3) ◽  
pp. 450-459 ◽  
Author(s):  
T. J. Martin ◽  
G. S. Dulikravich

An inverse computational method has been developed for the nonintrusive and nondestructive evaluation of the temperature-dependence of thermal conductivity. The methodology is based on an inverse computational procedure that can be used in conjunction with an experiment. Given steady-state heat flux measurements or convection heat transfer coefficients on the surface of the specimen, in addition to a finite number of steady-state surface temperature measurements, the algorithm can predict the variation of thermal conductivity over the entire range of measured temperatures. Thus, this method requires only one temperature probe and one heat flux probe. The thermal conductivity dependence on temperature (k-T curve) can be completely arbitrary, although a priori knowledge of the general form of the k-T curve substantially improves the accuracy of the algorithm. The influence of errors of measured surface temperatures and heat fluxes on the predicted thermal conductivity has been evaluated. It was found that measurement errors of temperature up to five percent standard deviation were not magnified by this inverse procedure, while the effect of errors in measured heat fluxes were even lower. The method is applicable to two-dimensional and three-dimensional solids of arbitrary shape and size. [S0022-1481(00)01703-5]


2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Masoumeh Sadat Latifi ◽  
Saeed Setayeshi ◽  
Giuseppe Starace ◽  
Maria Fiorentino

The thermal–hydraulic phenomena in a pebble bed modular reactor (PBMR) core have been simulated under steady-state and transient conditions. The PBMR core is basically a long right circular cylinder with a fuel effective height of 11 m and a diameter of 3.7 m. It contains approximately 452,000 fuel pebbles. A three-dimensional computational fluid dynamic (CFD) model of the PBMR core has been developed to study the influence of porosity on the core performance after reactor shutdown. The developed model was carried out on a personal computer using ANSYS fluent 14.5. Several important heat transfer and fluid flow parameters have been examined under steady-state and transient conditions, including the coolant temperature, effective thermal conductivity of the pebble bed, and the decay heat. Porosity was found to have a significant influence on the coolant temperature, on the effective thermal conductivity of the pebble bed, on the decay heat, and on the required time for heat removal.


2000 ◽  
Vol 626 ◽  
Author(s):  
Antje Mrotzek ◽  
Kyoung-Shin Choi ◽  
Duck-Young Chung ◽  
Melissa A. Lane ◽  
John R. Ireland ◽  
...  

ABSTRACTWe present the structure and thermoelectric properties of the new quaternary selenides K1+xM4–2xBi7+xSe15 (M = Sn, Pb) and K1-xSn5-xBi11+xSe22. The compounds K1+xM4-2xBi7+xSe15 (M= Sn, Pb) crystallize isostructural to A1+xPb4-2xSb7+xSe15 with A = K, Rb, while K1-xSn5-xBi11+xSe22 reveals a new structure type. In both structure types fragments of the Bi2Te3-type and the NaCl-type are connected to a three-dimensional anionic framework with K+ ions filled tunnels. The two structures vary by the size of the NaCl-type rods and are closely related to β-K2Bi8Se13 and K2.5Bi8.5Se14. The thermoelectric properties of K1+xM4-2xBi7+xSe15 (M = Sn, Pb) and K1-xSn5-xBi11+xSe22 were explored on single crystal and ingot samples. These compounds are narrow gap semiconductors and show n-type behavior with moderate Seebeck coefficients. They have very low thermal conductivity due to an extensive disorder of the metal atoms and possible “rattling” K+ ions.


2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Minjun J. Choi ◽  
Lāszlo Bardōczi ◽  
Jae-Min Kwon ◽  
T. S. Hahm ◽  
Hyeon K. Park ◽  
...  

AbstractMagnetic islands (MIs), resulting from a magnetic field reconnection, are ubiquitous structures in magnetized plasmas. In tokamak plasmas, recent researches suggested that the interaction between an MI and ambient turbulence can be important for the nonlinear MI evolution, but a lack of detailed experimental observations and analyses has prevented further understanding. Here, we provide comprehensive observations such as turbulence spreading into an MI and turbulence enhancement at the reconnection site, elucidating intricate effects of plasma turbulence on the nonlinear MI evolution.


2012 ◽  
Author(s):  
I. Ďuran ◽  
J. Sentkerestiová ◽  
K. Kovařík ◽  
L. Viererbl

Open Ceramics ◽  
2021 ◽  
pp. 100118
Author(s):  
Diana Vitiello ◽  
Benoit Nait-Ali ◽  
Nicolas Tessier-Doyen ◽  
Thorsten Tonnesen ◽  
Luís Laím ◽  
...  

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chanho Moon ◽  
Kotaro Yamasaki ◽  
Yoshihiko Nagashima ◽  
Shigeru Inagaki ◽  
Takeshi Ido ◽  
...  

AbstractA tomography system is installed as one of the diagnostics of new age to examine the three-dimensional characteristics of structure and dynamics including fluctuations of a linear magnetized helicon plasma. The system is composed of three sets of tomography components located at different axial positions. Each tomography component can measure the two-dimensional emission profile over the entire cross-section of plasma at different axial positions in a sufficient temporal scale to detect the fluctuations. The four-dimensional measurement including time and space successfully obtains the following three results that have never been found without three-dimensional measurement: (1) in the production phase, the plasma front propagates from the antenna toward the end plate with an ion acoustic velocity. (2) In the steady state, the plasma emission profile is inhomogeneous, and decreases along the axial direction in the presence of the azimuthal asymmetry. Furthermore, (3) in the steady state, the fluctuations should originate from a particular axial position located downward from the helicon antenna.


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