Density disturbance of small-scale field- aligned irregularities in the ionosphere heating experiments

A theoretical model which describes the small-scale irregularities excited by powerful high frequency (3–30 MHz) electromagnetic wave in ionosphere heating is investigated quantitatively in this paper. The model is based on the transport equation in magnetic plasma and mode conversion from electromagnetic wave to electrostatic wave in ionospheric modification. Threshold electric field for exciting small-scale (meter scale) irregularities and spatial spectra of irregularities are analytically calculated by this model. The results indicate that background electron density and geomagnetic field play an important role for the threshold electric field and the spatial scale of the electron density irregularities. The results demonstrate that the electric field threshold increases with the decrease of the spatial scale of the irregularities. For exciting meter scale irregularities, the threshold electric field is about tens of mV m^-1 . The theoretical results are consistent with those of the experiments.     

电离层对核电磁脉冲传播特性影响的分析

引入傅立叶变换,对高空核爆激励的瞬态电磁脉冲信号通过电离层向同步卫星轨道传播后的波形进行了分析。由于电离层的色散特性,使原来的瞬态电磁场不同频率的成分相互分离,频率高的相速度快,频率低的相速度慢,使到达卫星轨道的波形成为一衰减振荡,且波形持续时间拉大。考虑电离层的衰减,对20～lOOkm爆高的核电磁脉冲传播至卫星轨道后的电场仍是可以监测到的。     

Investigation of Total Absorption of Radio Waves in High Latitude Ionosphere

Using the digisonde data observed at ionospheric station Norilsk （Dip lat. 60~N） in 2006, a statistical study on the characteristics of the ionospheric plasma total absorption of radio waves （IPTAR） was performed. In the winter and some months of equinox, the IPTAR mainly occurred in the nighttime and the highest occurrence rate could be up to 90%. In the summer, the occurrence was relatively low and the differences between nighttime and daytime occurrence reduced. The total duration of IPTAR seemed longer around the winter than that around the summer. The occurrence of IPTAR events ascended as the Kp index increased. The frequent precipitation of energetic particles into the ionospheric plasma in the auroral belt may be the main cause of the IPTAR events.     

The Electrostatic Cylindrical Sheath in a Plasma

The electrostatic sheath with a cylindrical geometry in an ion-electron plasma is investigated. Assuming a Boltzmann response to electrons and cold ions with bulk flow, it is shown that the radius of the cylindrical geometry do not affect the sheath potential significantly. We also found that the sheath potential profile is steeper in the cylindrical sheath compared to the slab sheath. The distinct feature of the cylindrical sheath is that the ion density distribution is not monotonous. The sheath region can be divided into three regions, two ascendant regions and one descendant region.     

脉冲堆辐照腔内绝对中子通量及相对分布测量

本文介绍了绝对中子通量测量方法,给出了各辐照腔典型位置上的绝对中子通量及其与全堆平均中子通量的比值。还给出了各辐照腔中相对中子通量轴向分布和旋转样品槽内相对中子通量周向分布的测量结果。     

静电收集法在测氡中的应用与研究

介绍了测量空气中氡常用的方法之一--静电收集法,并对静电收集装置中探测器的选择做了简单的说明,还指出收集室体积与形状、收集电压、温度、湿度、气压等对探测效率的影响.最后对于测量中普遍存在的问题如本底影响修正和取样时间的影响两个方面做了简要的说明.     

小型单极静电加速器自动控制系统研制

本文研制了针对大气污染物PM2.5分析的小型单极静电加速器的自动控制系统。基于TCP/IP协议建立了分布式控制系统,数据传输采用了多种协议和总线技术,采用面向虚拟仪器的图形化编程方法进行了软件开发。系统在软件和硬件两方面采取了一系列抗干扰措施,极大地减少了高压打火等因素对测控系统的干扰。该控制系统工作稳定、抗干扰能力强,满足了加速器长时间运行的要求。     

高能重离子碰撞中能量密度和粒子密度数值分析

分别用无穷级数展开方法和数值积分计算中的高斯-拉盖尔求积法对高能重离子碰撞中能量密度和粒子密度数值进行计算，并对结果及级数展开中的高次项和一次项的大小进行了比较。结果表明：高斯-拉盖尔方法可以作为一种实用的算法应用在高能重离子碰撞的计算中。     

可控中子源密度测井仪的密度响应特性与算法研究

在可控中子源密度测井中,脉冲中子源的中子产额存在波动,采用探测器绝对计数的密度算法受地层环境、测量条件的影响较大,因此会导致密度算法的精度较差。为提高密度测量的稳定性和精确性,本文针对可控中子源一体化测井仪的研发需要,建立了适合所研发仪器的密度算法：首先,结合蒙特卡罗数值模拟软件MCNP对新型一体化测井仪及地层进行了建模;然后,利用所建模型,模拟了在不同岩性、孔隙度条件下可控中子源发射的快中子与地层物质的相互作用过程,并通过记录γ探测器的近、远非弹性散射γ计数和俘获γ计数,中子探测器的近热中子及近超热中子计数信息,获得了一体化测井仪探测器计数与地层密度之间的响应关系,并对影响密度算法的主要因素进行了分析;最后,在密度响应特性分析的基础上,提出了使用近超热中子与近热中子计数比、近远非弹γ计数比来提高稳定性和精确性的可控中子源密度测井新算法。采用新密度算法对所建模型进行计算,结果表明,砂岩、灰岩、白云岩3种岩性下计算的密度与真密度非常接近,其相对误差小于6%。与哈里伯顿和斯伦贝谢算法的计算结果相比,本文方法显示了更好的效果：公式参数少、没有探测器的绝对计数、精确度高。     

基于静电分析器的全自动高精度能谱测量系统

本文实现了一种基于静电分析器的全自动高精度能谱测量系统,并成功用于微团簇离子束同石墨烯薄膜相互作用的实验研究。基于该高精度能谱测量系统,研究了1.8 MeV的H⁺₂微团簇同4层石墨烯薄膜的相互作用过程,测量了库仑爆炸后的质子能谱和透射的H⁺₂能谱,实现了全自动的能谱采集,极大提高了数据获取速度,降低了实验误差。测量结果表明,该系统在H⁺₂的入射能量1.8 MeV处的能量分辨约为0.6 keV,对于下一步开展基于加速器的高精度能谱测量研究具有重要意义。     

Automatic Control System of Ion Electrostatic Accelerator and Anti-Interference Measures

An automatic control system for the electrostatic accelerator has been developed by adopting the PLC （Programmable Logic Controller） control technique, infrared and optical-fibre transmission technique and network communication with the purpose to improve the intelligence level of the accelerator and to enhance the ability of monitoring, collecting and recording parameters. In view of the control system＇ structure, some anti-interference measures have been adopted after analyzing the interference sources. The measures in hardware include controlling the position of the corona needle, using surge arresters, shielding, ground connection and stabilizing the voltage. The measures in terms of software involve inter-blocking protection, soft-spacing, time delay, and diagnostic and protective programs. The electromagnetic compatible ability of the control system has thus been effectively improved.     

Power Consumption in Positive Ion Beam Converter with Electrostatic Electron Suppressor

The power recovery characteristics of an in-line direct beam converter provided with electrostatic electron suppressor were studied numerically by tracing the orbits of fast primary ions and secondary charged particles generated along their beam path by collision with background gas molecules. It is shown that, in reference to the electrostatic field potential at the point of impact, the energy distribution of secondary ions impinging on the suppressor has two peaks—one corresponding to a zone of high positive potential surrounding the collector and the other to one of slightly negative potential around the electron suppressor. Secondary electron emission from the suppressor is ascribed mainly to the latter peak, associated with impingement of slower secondary ions. Far much power consumed in secondary particle acceleration is spent for emitting electrons from the suppressor than for secondary ions generated by beam-gas collision. The upper limit of background pressure is discussed on the basis of criteria prescribed for restricting the power consumed in this secondary particle acceleration, as for practical convenience of electrode cooling. Numerical examples are given of calculations based on particle trajectory analysis of both primary ions and secondary particles, for the case of a 100 keV-proton sheet beam 10 cm thick of 35mA/cm² current density.     

基于静电收集型固体核径迹氡探测器尺寸的蒙特卡罗方法优化

设计了一种新型的基于静电收集的固体核径迹探测器,并利用蒙特卡罗方法对其尺寸进行优化模拟,确定最优尺寸使装置达到效能最大化,结果表明转换系数作为优化对象随着探测器直径的增大而近似线性增加,当管子半径增大到2 cm后曲线逐渐变缓,而后在约等于3 cm处转换系数基本不再增加甚至有下降的趋势,由此可得出结论探测器半径取3 cm...     

J-2.5MV静电加速器加速管的研制

介绍了为２．５ＭＶ静电加速器研制的加速管的结构特点和性能测试结果。该加速管已成功地用于国产Ｊ－２．５ＭＶ质子静电加速器上,性能稳定可靠。     

过电离层核爆电磁脉冲信号模拟源的实现

设计一种数字式核爆电磁脉冲信号源模拟装置。大气层核爆电磁脉冲纵向传输经过电离层后的信号属于瞬态脉冲信号,频率范围为30 MHz～300 MHz,因为电离层对电磁脉冲信号的色散特性,脉冲信号高频部分出现的时刻早于低频部分出现的时刻。基于DSP+DDS数字电路实现了30 MHz～300 MHz频率色散瞬态脉冲信号的输出,其输出频率的最小控制周期为4 ns,幅值可调、波形规则、可靠性高、调试方便,实验证明模拟信号反映了大气层核爆电磁脉冲信号过电离层后的主要特征。     

Density Enhancement of Polyethylene Solidified Wastes

To overcome the impediment against practical utilization of the technically already available process of solidifying low- and intermediate-level radioactive wastes for disposal in ocean bottom, arising from the regulatory minimum density of 1.2 prescribed for such solidified wastes, a method is proposed of thickening the polyethylene with 36~38w/o sodium sulfate anhydride to raise the density above 1.2. The resulting thickened polyethylene loaded with simulated radioactive waste showed a monoaxial compressive strength far exceeding 150 kg/cm², and proved to possess good stability in deionized water in immersion tests lasting 400 days. Polyethylene was also found to provide a volume reduction factor far higher than obtained with cement or asphalt solidification.     

北京大学4.5 MV静电加速器核反应分析系统

为满足对聚变堆面向等离子体材料中氘氚滞留问题的研究,北京大学4.5 MV静电加速器在原束线基础上新增核反应分析系统,该系统使用能量0.8～3.6 MeV的H⁺、D⁺、³He⁺和⁴He⁺粒子束流,可对核反应微分截面和样品中元素浓度的深度分布进行测量分析。本文对核反应分析原理、核反应分析系统的设备布局和实验方法进行了讨论,并以D(³He,p)⁴He核反应为例,分析了微分截面计算和样品中氘元素浓度深度分布的数据结果,其深度分辨小于1.5 μm,实验误差约为7.5%。     

静电加速器中输电带张力与转速的最佳关系

采用输电带的静电加速器运行时,一般通过调节输电带张力来减小输电带的抖动。本工作采用一个简化的计算模型,导出输电带在运行过程中发生抖动的基本规律。结果表明：输电带张力、输电带所带电荷密度和输电带的转速间存在一使输电带抖动最小的最佳关系。     

Density fluctuations in baryon-rich quark matter

At finite baryon chemical potential,the density of a quark matter develops large fluctuations when it undergoes a first-order phase transition.Based on the transport equation derived from the Nambu–Jona-Lasinio(NJL) model,we have studied the density fluctuations in a baryon-rich quark matter that is confined in a finite volume.Allowing the expansion of the quark matter using initial conditions from either a blast wave model or a multiphase transport(AMPT) model,we have further studied the survivability of the density fluctuations as the density and temperature of the quark matter decrease.Possible experimental signatures of the density fluctuations are suggested.     

静电收集法测量氡浓度的两种技术路线比较

基于静电收集法的连续测氡仪得到了广泛应用,但静电场对带正电的氡子体的收集效率受空气湿度的影响较大,因此该方法需要进行除湿或湿度修正。对这两种技术路线进行分析后发现：使用干燥管除湿可以很好的解决这一问题,且测量精度高,但是在相同的泵流率下干燥管的空隙体积增加了测量延迟效应;使用温、湿度曲线修正,会由于温、湿度的测量而导致附加的测量误差,但延迟效应较小,且有不需要更换干燥剂的优点,特别适合于无人值守时对氡浓度的长期连续测量。