Turbulence-Driven Tearing Modes in Inhomogeneous Magnetized Plasma

The effects of density inhomogeneity in the nonlinear growth of tearing modes in the presence of background density, electrostatic and magnetic fluctuations are investigated. The nonlinear interaction is assumed to occur in the inner layer of the tearing mode, where the fields and their variations are greatest. Our results demonstrate that turbulence-generated dissipative effects replace the collisional resistivity as the driving force of the tearing mode. The inhomogeneity introduces a real frequency to the nonlinear tearing mode, as well as new unstable tearing-mode–related drift waves.     

射频波电流驱动抑制双撕裂模不稳定性研究

采用不可压缩磁流体模型,在圆柱位形下研究了射频波电流驱动对双撕裂模不稳定性的影响。结果表明,托卡马克装置中沉积在有理面上的同向驱动电流能有效减缓3/1双撕裂模的发展。电流驱动幅值约占等离子体电流初始值的4%、驱动电流沉积宽度约为小环半径的7%时,抑制效果较好。此外,研究表明,在双撕裂模进入快速增长阶段前加入外部驱动电流,才能有效抑制撕裂模的磁爆发。     

A Simulation Study of Hall Effect on Double Tearing Modes

A Hall magnetohydrodynamics （MHD） simulation is carried out to study the dynamic process of double tearing mode. The results indicated that the growth rates in the earlier nonlinear and transition phases agree with the previous results. With further development of reconnection, the current sheet thickness is much smaller than the ion inertia length, which leads to a strong influence of the Hall effects. As a result, the reconnection in the late nonlinear phase exhibits an explosive nature with a time scale nearly independent of resistivity. A localized and severely intensified current density is observed and the maximum kinetic energy is over one order of magnitude higher in Hall MHD than that in resistive MHD.     

Suppression of Neoclassical Tearing Modes Towards Stationary High-Beta Plasmas in JT-60U

Results from stabilization of neoclassical tearing modes （NTMs） in JT-60U are described. NTM stabilization and confinement improvement have been demonstrated by employing a real-time NTM stabilization system, where the identification of the location of an NTM and the optimization of the injection angle of the electron cyclotron wave are performed in real time. Also, a high-beta plasma with the normalized beta of 3 has been sustained by suppressing NTM by applying the electron cyclotron current drive （ECCD） before the onset （＇preemptive ECCD＇）. In addition, a simulation code for analysis of the NTM evolution has been developed by combining the modified Rutherford equation with the transport code TOPICS. It is found that the simulation well reproduces the NTM behavior in JT-60U. The simulation also shows that the ECCD width is also important for NTM stabilization, and that the EC wave power for complete stabilization can be reduced by narrowing the ECCD profile.     

Study on Cavity Modes for D(H) Ion Cycloton Range Frequency Heating Scenarios in EAST

For low single-pass absorption of ion cyclotron range frequency (ICRF) wave in the EAST plasma cavity modes are expected to be excited between the low field side (LFS) antenna and the hybrid cut-off layer. The toroidal spectrum for D(H) minority heating scenarios in EAST is modeled by using FELICE（Finite Elements Ion Cyclotron Emulator）, a full wave code based on plane-stratified geometry. The excitation of cavity modes is studied. The methods for suppressing cavity modes are also discussed, to increase the efficiency of minority ion heating.     

Simulations of Reversed Shear Configuration in EAST

The reversed shear （RS） mode is one of the advanced configurations being considered in EAST. Predictive simulations of EAST reversed shear configuration are carried out using an 1.5D equilibrium evolution code. In order to have the desired monotonic q-profile during a tokamak discharge, a successful preparation phase is required. In our simulation, the plasma current is ramped up from 100 kA to a fiat-top maximum of 1.0 MA for four seconds. An ICRH power of 1 MW is applied until the plasma shape is formed at the moment of 4 s, and then the power is raised to 3 MW. A LHCD power of 3.5 MW is applied from ls to optimize the plasma current density profile. A series of simulations are performed to study the influence of the time of applying the auxiliary heating on the plasma parameters. Based on these simulations, a scheme is proposed and tested for the control of the safety factor profile, which is very useful in real time profile control in tokamak experiments.     

Preliminary Research for Mutual Dose Perturbation Influence of 125I Brachytherapy Source

For two arrangement modes of two ¹²⁵I brachytheray sources, a homo-longitudinal axis and a homotransverse axis, the sum of dose distributions caused by each single source and actual dose distribution of the two coexisting sources are calculated separately in a clinically interested area by Monte Carlo simulation. Comparisons between them are used to evaluate the mutual dose perturbation influence. The result shows, for the homo-longitudinal axis arrangement, obvious perturbation can be observed along the longitudinal direction when the distances between sources' centers, L, are 0.5 cm and 1.0 cm, up to 11:7 ± 0:4% and 4:8 ± 0:2%, respectively, but, can be negligible for the distance exceeding 2.0 cm. For the homo- transverse axis arrangement, the range of dose perturbation depends on the source length and distances between sources' centers, and an influence extent is greater than the former, e.g., 27:2 ± 1:1%, 15:4 ± 0:6%, and 7:0 ± 0:3% maximum for L = 0:5 cm, 1.0 cm, and 2.0 cm, respectively. As for dose perturbation induced by the source leaning which happened in actual implant sometimes, the result indicates a dose fluctuation became more acute with obliquity increasing. The maximum dose increasing, 54:5 ± 2:1% and 199:7 ± 7:8%, and the maximum dose decreasing, 42:6 ± 1:7% and 64:9 ± 2:6%, could be observed for 10° and 30° obliquity with L = 1:0 cm for the two arrangement modes respectively.     

热中子照相装置屏蔽的蒙特卡罗模拟

中子照相装置的屏蔽对降低反应堆大厅本底及提高中子照相质量具有重要意义。使用蒙特卡罗模拟方法,对热中子照相装置各组成部分的屏蔽进行模拟计算。结果表明：在照相装置的准直器部分使用厚130cm、密度4.6t/m3的重混凝土,飞行管部分使用厚75cm、密度3.6t/m3的重混凝土可保证屏蔽外的辐射当量剂量达到反应堆大厅的监督区要求。     

CMOS器件单粒子效应电路级建模与仿真

单粒子效应电路级建模与仿真是近年来的热点问题。为实现更高的准确度和更精细的机制分析,研究了单粒子瞬态受重离子入射位置的影响并解析建模,基于纳米尺度测试芯片的辐照试验结果验证了仿真方法的准确性。以此为基础开发了瞬时辐射效应仿真软件TREES,其输入文件为GDSII格式的版图,软件中通过解析版图提取所有有源区的形状、尺寸信息。软件还包括其他用户自定义选项,包括重离子LET值、待分析区域、激励设置等。输出文件包括对应单次入射的波性文件、单粒子效应敏感区热点图、单粒子效应截面数据等。软件第1版实现了与商用设计流程相集成,可作为Cadence工具栏中的嵌入式软件。软件第2版为不依赖于上下游商业软件的独立软件。本工作可用于评价单元电路或中小规模单粒子效应敏感性,对于熟悉电路级仿真的设计人员,可用于在设计阶段快速评价集成电路的抗辐射加固性能。     

Effects of m=0 Harmonics on Quasi-Linear Stage of m=1 Double Tearing Mode

Effects of tearing modes are inves shows that the effect of the m = 0 harmonics on the early quasi-linear stage of m = 1 double tigated. The numerical calculation with the harmonics m = 0 included the m = 0 harmonics on the mode is negligible in the linear stage. As the mode begins to grow nonlinearly, both the current and flow profiles are pinched due to the m = 0 harmonics. To make a comparison we also carry out the calculation with m = 0 harmonics turned off. The profiles of the total current, poloidal magnetic field, and poloidal shear velocity in the cases with or without the m = 0 harmonics are compared and discussed. In addition, the formation of a poloidal velocity shear is found and its mechanism is investigated.     

Dynamics of Secondary Large-Scale Structures in ETG Turbulence Simulations

The dynamics of secondary large-scale structures in electron-temperature-gradient （ETG） turbulence is investigated based on gyrofluid simulations in sheared slab geometry. It is found that structural bifurcation to zonal flow dominated or streamer-like states depends on the spectral anisotropy of turbulent ETG fluctuation, which is governed by the magnetic shear. The turbulent electron transport is suppressed by enhanced zonal flows. However, it is still low even if the streamer is formed in ETG turbulence with strong shears. It is shown that the low transport may be related to the secondary excitation of poloidal long-wavelength mode due to the beat wave of the most unstable components or a modulation instability. This large-scale structure with a low frequency and a long wavelength may saturate, or at least contribute to the saturation of ETG fluctuations through a poloidal mode coupling. The result suggests a low fluctuation level in ETG turbulence.     

Simulations of cascades in pure and alumina doped magnesia

Atomic scale molecular dynamics simulations of displacement cascades are carried out in an initially defect-free MgO lattice and in a lattice where 0.2% of the Mg²⁺ ions have been replaced by Al³⁺ ions, charge compensated by magnesium vacancies. Results show that the properties of the cascade in the perfect lattice exhibit considerable anisotropy with respect to the direction of the incident primary knock-on atom (PKA). We find that a different anisotropy of equivalent magnitude occurs as a consequence of the (random) distribution of defects in the vicinity of the cascade. This suggests that the details of damage production during a cascade event can depend sensitively on the distribution of dopants and impurity atoms around the PKA.     

离子束辐照对玉米诱变效应的初步研究

利用兰州重离子加速器提供的12C6+和36Ar18+离子束对玉米自交系郑58、鲁9801、金象4C-1、CSR24001、308和478进行辐照诱变育种试验,探讨了重离子辐照对玉米的诱变效应。结果显示,重离子辐照后种子出苗率和成苗率根据材料不同表现不一,浸泡后种子对辐照敏感性增加。辐照后M1代叶型变异较大;M2代植株经济性状发生变异较多,产生了许多有益的突变性状;M3代部分突变性状能够稳定遗传。由此可见,重离子束辐照育种有利于品种改良和种质创新,是玉米遗传改良的一种有效手段。     

多孔材料填充方式对通道传热效果影响的数值研究

基于结构/非结构同位网格的SIMPLE算法,编写了多孔材料内部流动和传热计算程序.程序中多孔区域动量方程采用Brinkman-Forchheimer拓展Darcy模型,能量方程采用局部热平衡模型.对恒热流边界条件下平行通道沿中心及壁面区域填充多孔材料时的流动和传热特性进行数值分析.分析结果表明,与不填充多孔材料相比,填...     

聚变裂变混合乏燃料焚烧堆FDS-SFB燃料循环方案设计与分析

针对聚变裂变混合乏燃料焚烧堆FDS-SFB(Spent Fuel Burner),基于湿法和干法两种后处理技术途径提出了不同的燃料循环方案。并分别对FDS-SFB燃料循环所需的初装资源量、燃料制备和乏燃料后处理能力进行初步质量流分析和可行性初步评估。基于较好嬗变和增殖性能的FDS-SFB典型中子学方案的质量流初步分析表明:两种方案燃料循环其所需的初装资源量、燃料制备、乏燃料后处理能力具有初步的可行性。     

CARR保护系统可靠性分析

保护系统是保证中国先进研究堆（CARR）安全的重要系统之一,它的高可靠性是保证其完成预期功能的重要条件。本工作以保护系统为研究对象,利用故障模式及影响分析和故障树等可靠性分析方法,建立相应模型,对保护系统进行了定性和定量的分析,得到了保护系统发生故障的概率和最小割集,其可靠性水平达到了CARR工程的设计要求,验证了设计,为CARR其他系统分析和验证奠定了基础。     

Simulations of mass attenuation coefficients for shielding materials using the MCNP-X code

In this paper,mass attenuation coefficients of concrete,bricks and cement plaster,as shielding materials,are calculated at 59.5,356,662,1173,1274 and 1333 keV by using the MCNP-X (version 2.4.0) code.The numerical simulation results are compared with previous Monte Carlo studies,experimental results and XCOM data.The effects of barite on mass attenuation coefficients are investigated.The mass attenuation coefficients increase with the barite content.Thus,our results agree well with experimental studies on gamma ray shielding of barite.It is flexible for the MN method to change the barite rates in material by small increments,which is experimentally difficult.Also,modeled geometry can be used for future approaches such as new designs and new structures especially in investigating new barite-containing materials to build nuclear reactors or high-energy radiation therapy facilities.     

弥散颗粒对中子学计算影响的初步分析

弥散颗粒燃料是一种先进的燃料元件形式,双重非均匀性是它的固有特性。本文基于弥散型燃料,使用MCNP程序对不同燃料颗粒直径、燃料富集度、燃料相体积、可燃毒物颗粒直径和可燃毒物类型的板栅元进行了分析,研究了双重非均匀性对中子学计算的影响,指出双重非均匀性在一定的尺寸下,对于纯燃料芯体板栅元影响较小,对含有弥散可燃毒物的板栅元影响较大,在反应性计算、临界安全分析时必须加以考虑。     

电离辐射诱发的非靶效应及其生物学意义

辐射诱发的非靶效应包括基因组不稳定性、旁效应、断裂因子以及亲代受照射后的遗传效应。非靶效应在辐射致癌、辐射防护、放射治疗、辐射危险评估以及细胞衰老等方面有重要的生物学意义。本文主要从辐射诱发的基因组不稳定性和旁效应两方面介绍辐射诱发的非靶效应及其生物学意义。