ISSN 0253-2778

CN 34-1054/N

2020 Vol. 50, No. 9

Display Method:
Review Article
Brief review to the interactions into plasma and walls in magnetic controlled fusion devices
HU Jiansheng, ZUO Guizhong, WANG Liang, DING Rui, YU Yaowei, ZHANG Yang, XU Wei
2020, 50(9): 1193-1217. doi: 10.3969/j.issn.0253-2778.2020.09.001
Controllable fusion energy, with its advantages of safety, cleanness and abundant fuel source, is considered one of the main alternatives for humans to solve the energy problem in the future. In a magnetic confinement fusion device, the high heat and particle flux released from high temperature plasma would strongly interact with the plasma facing components (PFCs). The interaction would damage the PFCs and produce impurities that degrade plasma confinement. Meanwhile, the increased recycling of the particles trapped on the walls would affect the control of plasma density. The control of the interaction between the plasma and walls is of vital importance to the achievement of long pulse plasmas with high parameters. The research efforts in this area have mainly focused on the choice of suitable plasma facing materials, effective treatment of PFCs surface, reduction of particles and high heat flux released from plasma, and increasing heat exhaust with the help of developing efficient cooling structures of PFCs. After decades of research, especially in EAST superconducting tokamak in China, a series of great advances have been made. The advantages of wall materials, such as graphite, tungsten, beryllium and molybdenum, have been realized; a few effective methods for wall surface cleaning and coating have been developed; a variety of advanced methods to reduce the heat flux released from plasma have been successfully explored; various structures of PFCs to increase heat exhaust have been designed and tested. The results of these investigations have been successfully explored in EAST, effectively promoting the achievement of the world record of high confinement mode plasma with long durations, more than 100s. The control of the interaction between plasma and walls is still facing big challenges for the future fusion reactors with a high energy neutron irradiation, a much higher heat load and much longer plasma pulse than that in the present tokamaks.
Magnetic islands in collisionless magnetic reconnection
LU Quanming, WANG Rongsheng, HUANG Kai, WANG Shui
2020, 50(9): 1218-1228. doi: 10.3969/j.issn.0253-2778.2020.09.002
The roles of magnetic islands were reviewed in two essential aspects of collisionless magnetic reconnection: are rapid dissipation from magnetic energy to plasma kinetic energy and generation of energetic electrons. The current sheet around the X line may be extended and unstable to the tearing mode instability. Secondary magnetic islands are generated and then consequentially interact each other in the extended current sheet. Such a nonstationary magnetic reconnection can maintain a large reconnection rate for a long time and efficiently dissipate magnetic energy. Electrons can be accelerated inside magnetic islands by Fermi and betatron mechanisms, as well as by reconnection electric field in the vicinity of the X line. The interaction of magnetic islands can result in further electron acceleration. These acceleration processes can make energetic electrons possess a power-law spectrum.
Chromium element and isotope geochemistry in high temperature systems
SHEN Ji, YANG Bing, XIA Jiuxing
2020, 50(9): 1229-1248. doi: 10.3969/j.issn.0253-2778.2020.09.003
In the past two decades, research on stable Cr isotopes, especially the low-temperature redox processes on the earth’s surface, has been greatly developed. However, in the same period, Cr isotope fractionations induced by high temperature systems had been poorly constrained, especially before 2010. With the improvement of mass spectrometry technology and the wide application of the double-spike method, smaller isotope fractionations in high temperature processes can be accurately identified. This review will give a detailed introduction to the distribution behavior of Cr element and Cr isotope fractionation behavior in high temperature processes achieved in recent years, and potential applications, aiming to provide feasible directions for future researches of Cr element and isotope system.
Research Article
A new generation mechanism of three-band chorus waves in the Earth’s magnetosphere
CHEN Rui, GAO Xinliang, CHEN Huayue, WANG Shui
2020, 50(9): 1249-1257. doi: 10.3969/j.issn.0253-2778.2020.09.004
A new generation mechanism of three-band chorus waves in the Earth’s magnetosphere was proposed with Van Allen Probes data, where two obvious power gaps can be observed in the spectrograms. The satellite observations reveal that there usually exist two separated electron beams in the direction opposite wave propagation along with three-band chorus waves. The linear theoretical results confirm that the existence of electron beams can indeed cause two minima of growth rates of chorus waves propagating in the opposite direction of electron beams. Therefore, the two power gaps should be formed due to the severe damping of chorus waves at gap frequencies resulting from the two electron beams.This study not only gives a new mechanism to explain the formation of three-band chorus event, but also provides new insights into understanding the well-known power gap at half electron gyrofrequency.
Spontaneous symmetric breaking in two-lane totally asymmetric simple exclusion process with narrow entrances
TIAN Bo, CHEN Denggen, GUO Shuyong, XIA Ping
2020, 50(9): 1258-1265. doi: 10.3969/j.issn.0253-2778.2020.09.005
Two-lane totally asymmetric simple exclusion process (TASEP) with narrow entrances was studied. The N-cluster mean field analysis was carried out for spontaneous symmetric breaking, in which correlation of 2N sites was considered. The analysis indicates that asymmetric LD/LD(low density/low density) phase does not exist. With increase of N, the analytical results are getting closer to the Monte Carlo simulation ones. In addition, it was found that the boundaries between the phases all exhibit exponential change, which enables us to predict the boundaries in the exact solution, and it was shown that the predicted results are in good agreement with the large size simulation ones. The spontaneous symmetric breaking exists when interaction between particles represented by parameter p is strong enough. It was found that the maximum values of entrance rate of asymmetric HD/LD(high density/low density) phase obey exponential decay with increase of p, and the critical value beyond which the asymmetric HD/LD phase disappears can be obtained in every cluster mean field analysis. What’s more, the critical values exhibit exponential increase with increase of N, and the exact solution of the critical value was also predicted. It was shown that the predicted critical value is also in good agreement with that obtained from simulations.
A Cholesky factor model in correlation modeling for discrete longitudinal data
LI Yezhen, ZHANG Weiping
2020, 50(9): 1266-1276. doi: 10.3969/j.issn.0253-2778.2020.09.006
A joint mean-correlation regression model framework was proposed for a family of generic discrete responses either balanced or unbalanced, and a Cholesky decomposition method was used for statistically meaningful reparameterization of correlation structures. To overcome computational intractability in maximizing the full likelihood function of the model, a computationally efficient Monte Carlo expectation maximization (MCEM) approach was proposed. Theoretical properties were also established for the resulting estimators. Simulation studies and a real data analysis show that the proposed approach yields highly efficient estimators for the parameters.