Reversed rotation of limit cycle oscillation and dynamics of low-intermediate-high confinement transition

The dynamics of the confinement transition from L mode to H mode(LH) is investigated in detail theoretically via the extended three-wave coupling model describing the interaction of turbulence and zonal flow(ZF) for the first time.Thereinto, turbulence is divided into a positive-frequency(PF) wave and a negative-frequency(NF) one, and the gradient of pressure is added as the auxiliary energy for the system. The LH confinement transition is observed for a sufficiently high input energy. Moreover, it is found that the rotation direction of the limit cycle oscillation(LCO) of PF wave and pressure gradient is reversed during the transition. The mechanism is illustrated by exploring the wave phases. The results presented here provide a new insight into the analysis of the LH transition, which is helpful for the experiments on the fusion devices.     

沉痛悼念黄祖洽先生

<正>中国科学院院士,著名理论物理学家、核物理学家、教育家,我国氢弹研制的探路先锋和我国核武器物理问题研究的主要负责人之一,北京师范大学教授黄祖洽先生因病医治无效,于2014年9月7日在北京逝世,享年90岁。黄祖洽1924年10月2日出生于湖南省长沙市,1944年考入西南联大学习物理,1950年清华大学研究生毕业后到中国科学院近代物理研     

Enhanced electron positron pair creation by the frequency chirped laser pulse

Based on the quantum Vlasov equation, the effect of frequency chirp on electron-positron pair production is investigated. The cycle parameter, which characterizes the laser field cycle degree within the pulse, is also considered. In both supercycle and subcycle laser pulses the frequency chirp can greatly enhance the momentum distribution function of created pairs and the pair number density. The pair number density created by a supercycle laser pulse is larger than that by a subcycle pulse under the same laser frequency and chirping. There exists an optimal cycle parameter corresponding to the maximum value of the created pair number density for different chirp rates. It is found that the pair number density is sensitive/insensitive to chirping rate when the cycle parameter lies below/above the optimal one.     

Electronic transport of Lorentz plasma with collision and magnetic field effects

The electronic transverse transport of Lorentz plasma with collision and magnetic field effects is studied by solving the Boltzmann equation for different electron density distributions. For the Maxwellian distribution, it is shown that transport coefficients decrease as ? increases, ? is the ratio of an electron's magneto-cyclotron frequency to plasma collision frequency. It means that the electrons are possible to be highly collimated by a strong magnetic field. For the quasimonoenergetic distribution with different widths, it is found that the transport coefficients decrease greatly as εˉ decreases.In particular when the width approaches to zero the transverse transport coefficients are hardly affected by the magnetic field and the minimal one is obtained. Results imply that the strong magnetic field and quasi-monoenergetic distribution are both beneficial to reduce the electronic transverse transport. This study is also helpful to understand the relevant problems of plasma transport in the background of the inertial confinement fusion.     

FRACTAL PATTERN GROWTH OF METAL ATOM CLUSTERS IN ION IMPLANTED POLYMERS

The fractal and multi-fractal patterns of metal atoms are observed in the surface layer and cross section of a metal ion implanted polymer using TEM and SEM for the first time. The surface structure in the metal ion implanted polyethylene terephthalane (PET) is the random fractal. Certain average quantities of the random geometric patterns contain self-similarity. Some growth origins appeared in the fractal pattern which has a dimension of 1.67. The network structure of the fractal patterns is formed in cross section, having a fractal dimension of 1.87. So it can be seen that the fractal pattern is three-dimensional space fractal. We also find the collision cascade fractal in the cross section of implanted nylon, which is similar to the collision cascade pattern in transverse view calculated by the TRIM computer program. Finally, the mechanism for the formation and growth of the fractal patterns during ion implantation is discussed.     

Spatial Characteristics of Thomson Scattering Spectra in Laser and Magnetic Fields

Spatial characteristics of Thomson scattering spectra are studied for an electron moving in the circularly polarized laser field in the presence of a strong uniform magnetic field. The results show that the angular distributions of the spectra with respect to the azimuthal and polar angles exhibit different symmetries, respectively, which depend on the fields and electron parameters sensitively and significantly. Moreover, for relatively large parameters such as high laser intensity, high magnetic resonance parameter as well as large initial momentum of electron, the two lobes in spectra tend to the laser-propagating direction so that the radiation can be collimated in the forward direction. Furthermore, an important finding is that by choosing the appropriate fields and initial momentum of electron, the high frequency part of the Thomson scattering spectra can reach the frequency range of soft x-ray,in which a high radiation power per solid angle as ～10~(11) a.u. can be obtained.     

深情寄木铎——追忆黄祖洽先生

<正>曾经,北京师范大学的讲台上有这样一位师者,他虽已年届九旬,却仍然坚守在本科教学的讲台上;他虽已重病住院,却仍然从医院请假回来给学生上课.他就是敬爱的黄祖洽先生.黄祖洽先生是为我国原子能事业和战略核武器设计立下不朽功勋的理论物理学家,是为我国物理学基础教学和研究殚思极虑,锐意开拓,广育人才,无私奉献的教育家.1980年黄祖洽先生调入北京师范大学任教.近十几年来,耄耋之年的黄祖洽先生一     

Phase Synchronization as a Mechanism of Controlling Spatiotemporal Chaos via External Periodic Signal

We find that phase synchronization (PS) is a mechanism in which the spatiotemporal chaos (STC) can be suppressed to a spatially regular (SR) state by applying an external periodic signal in a one-dimensional driven drift-wave system.In the driving wave coordinate,the nonlinear system can be transformed to a set of coupled oscillators moving in a periodic potential.In this multi-dimensional system,the internal modes are slaved one by one through PS by the control signal.Two types of responses of the internal modes to the external periodic signal are observed.For some modes,the stabilization is through frequency-locking;while for the other modes,a special kind of PS without frequency-locking,namely multi-looping PS,is developed.     

电子、正电子、离子等离子体尾场中被加速正电子的研究

为了研究在激光驱动的等离子体尾场中被加速正电子的动力学,使用了由电子、正电子、离子组成的等离子体,通过采用数值模拟方法得到了非对称脉冲驱动的尾波场中被加速的正电子的运动相图、动能变化,势能。数据结果表明：非对称激光脉冲驱动尾场中正电子得到很高的能量。提高等离子体中的正电子比例会使电子和正电子的加速效果减弱。在非对称激光脉冲驱动的激光尾场中,为了有效地加速正电子,要选择恰当的上升激光脉冲长度和下降激光脉冲长度。