3D simulation of micromegas detector performance

Micromegas (MICRO MEsh GAseous Structure) is a position-sensitive gaseous detector. It is widely used in particle physics. We present the results of full 3D Monte Carlo simulations of Micromegas performance, taking into account all the processes from the primary ionization, the elctron collection efficiency,and the gain to the signal formation. The simulation results are in good agreement with experimental data.     

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial resolution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.     

Study of a bulk-Micromegas with a resistive anode

The design and performance of a Micromegas with a resistive anode are presented in this paper. A thin resistive sheet with volume resistivity of 10¹² Ω·m cm is glued onto the readout electrode surface and its performance is investigated by using a ⁵⁵Fe X-ray radioactive source in the operation gas of argon and isobutene mixtures (Ar/Iso=95/5). The gas gain at different mesh high voltage, counting rate and working time are given. Energy spectra at different working voltages are measured and the results are discussed. We have oberved that a Micromegas with a resistive anode can be operated at higer gain than a standard Micromegas without sparks.     

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial reso-lution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.     

Micromegas chambers for the experiment ATLAS at the LHC (A Brief Overview)

The increase in luminosity and energy of the Large hadron collider (LHC) in the next upgrade (Phase-1) in 2018–2019 will lead to a significant increase in radiation load on the ATLAS detector, primarily in the areas close to the interaction point of the LHC proton beams. One of these regions is the Small Wheel of the ATLAS Muon Spectrometer. It is planned to be replaced with the New Small Wheel that will have Micromegas chambers as main coordinate detectors. The paper gives an overview of all existing types of Micromegas detectors with special focus on the Micromegas chambers for the ATLAS detector upgrade.     

A hybrid structure gaseous detector for ion backflow suppression

A new concept for a hybrid structure gaseous detector module with ion backflow suppression for the time projection chamber in a future circular collider is presented.It is a hybrid structure cascaded Gas Electron Multiplier(GEM) with a Micromegas detector.Both Micromegas and GEM have the capability to naturally reduce most of the ions produced in the amplification region.The GEM also acts as the preamplifer device and increases gas gain together with the Micromegas.Feasibility tests of the hybrid detector are performed using an ~(55)Fe X-ray source.The energy resolution is better than 27% for 5.9 keV X-rays.It is demonstrated that a backflow ratio better than 0.2% can be reached in the hybrid readout structure at a gain of 5000.     

Investigation of GEM-Micromegas detector on X-ray beam of synchrotron radiation

To reduce the discharge of the standard bulk Micromegas and GEM detectors, a GEM-Micromegas detector was developed at the Institute of High Energy Physics. Taking into account the advantages of the two detectors, one GEM foil was set as a preamplifier on the mesh of Micromegas in the structure and the GEM preamplification decreased the working voltage of Micromegas to significantly reduce the effect of the discharge. At the same gain, the spark probability of the GEM-Micromegas detector can be reduced to a factor 0.01 compared to the standard Micromegas detector, and an even higher gain could be obtained. This paper describes the performance of the X-ray beam detector that was studied at 1W2B Laboratory of Beijing Synchrotron Radiation Facility. Finally, the result of the energy resolution under various X-ray energies was given in different working gases. This indicates that the GEM-Micromegas detector has an energy response capability in an energy range from 6 keV to 20 keV and it could work better than the standard bulk-Micromegas.     

利用Garfield程序模拟Micromegas探测器增益和位置分辨特性

利用Garfield气体探测器模拟程序模拟了不同条件下Micromegas探测器的增益和位置分辨特性. 通过对模拟结果的分析, 得出提高探测器位置分辨和增益的有效途径. 该工作不仅可以优化气体探测器结构设计, 缩短实验周期, 而且还能极大程度的节约经费.     

Micromegas prototypes with thermo-bond film separators

In this paper we report the results of Micromegas prototypes constructed by attaching micromesh to an anode using thermo-bond films. The excellent metal attaching ability and good dielectical property of this kind of film make it a promising material to be used as avalanche gap spacers. Several prototypes are successfully made. The electron transmission properties are first studied and then the gas gain is measured in argon-isobutane mixtures. The maximum gain of more than 10⁴ is easily obtained. The energy resolutions for ⁵⁵Fe 5.9 keV K_α ray can be better than 20% over one magnitude in gain for different operational gas mixtures and the best energy resolution of 13.7% (FWHM) can be achieved with the gas mixture of 94% argon concentration. The preliminary test results of the prototypes with sensitive area of 45 mm×45 mm without internal support show good uniformity across the sensitive area.     

Micromegas探测器计数曲线、增益以及能量分辨特性的研究

介绍了自行研制的Micromegas探测器的基本结构和工作原理. 在不同工作气体(Ar和CO₂)配比条件下,利用⁵⁵Fe放射源对该探测器的能量分辨、计数曲线和气体增益等特性进行了较为详尽的测试. 对相关结果进行了讨论. 关键词： Micromegas探测器 计数曲线 能量分辨率 增益     

A new gaseous detector- micro mesh gaseous structure

The structure and working principle of Micromegas (MICRO Mesh Gaseous Structure) is discussed. Some radiation sources of a and X rays are used to test this detector. The optimized electric-field intensity of the conversion gap is obtained. The transmission of electrons and the uniformity of the amplification gap are also presented. The energy resolution of the 5.9 keV peak is better than 27%.     

Micromegas中子探测器位置分辨特性的Monte-Carlo研究(英文)

利用GEANT4和Garfield气体探测器模拟程序模拟了Micromegas中子探测器位置特性。 在漂移极上加一层聚乙烯薄膜作为转换材料, 通过反冲质子法测量中子的位置。 提出了一套通过设定探测器上层结构的方案来得到探测器的位置分辨特性。 通过对模拟结果的分析与比较, 得到一种易于测定探测器位置分辨特性的方法。 该工作不仅可以优化气体探测器结构设计, 缩短实验周期, 而且还能极大程度地节约经费。 In the present work, the spatial resolution of Micromegas as a neutron detector was simulated with GEANT4 and Garfield program. The polyethylene foil was used as neutron converter. A new method based on structural setting on the top layer of the detector was adopted to obtain spatial resolution. According to our simulation, it turned out to be a better spatial resolution, and this method was easily realized in experiment.     

Micromegas prototypes with thermo-bond film separators

In this paper we report the results of Micromegas prototypes constructed by attaching micromesh to an anode using thermo-bond films. The excellent metal attaching ability and good dielectical property of this kind of film make it a promising material to be used as avalanche gap spacers. Several prototypes are successfully made. The electron transmission properties are first studied and then the gas gain is measured in argon-isobutane mixtures. The maximum gain of more than 104 is easily obtained. The energy resolutions for 55Fe 5.9 keV Kα ray can be better than 20% over one magnitude in gain for different operational gas mixtures and the best energy resolution of 13.7% (FWHM) can be achieved with the gas mixture of 94% argon concentration. The preliminary test results of the prototypes with sensitive area of 45 mm×45 mm without internal support show good uniformity across the sensitive area.     

激光辐照下PV型HgCdTe探测器反常响应机理

 利用PV型探测器开路电压的表达式,并考虑探测器的温度变化建立模型,对激光辐照下PV型HgCdTe探测器开路电压的变化进行了理论计算。当激光较弱时,计算结果与实验结果符合得很好。当激光较强时,对于辐照过程当中探测器输出变化的一般性趋势以及激光完全停照后的热弛豫过程,该模型也能给出较好的解释;但对于激光开始辐照时输出下跳和激光停止辐照时输出上跳的反常现象,该模型不能给出合理的解释。分析认为,该模型较好地描述了晶格温升对探测器输出的影响,但是它没有考虑热载流子效应;当激光较强时,热载流子效应不可忽略,特别是激光开始辐照和激光停止辐照时,载流子与晶格的温度差有比较明显的快速变化,从而导致了探测器的反常响应。     

旁路耦合电弧焊温度场模拟及验证

针对旁路耦合电弧焊的特点, 建立了一种适于用旁路耦合电弧焊的复合热源模型. 利用该热源模型对不同焊接参数下的旁路耦合电弧焊温度场进行了数值分析, 得到了总电流相同时不同旁路电流下的焊缝熔深、母材温度和特征点焊接热循环曲线的模拟结果, 分析了旁路耦合电弧焊焊接参数对母材热输入的影响, 并将特征点热循环曲线的模拟结果与相同条件下的试验结果进行了比较. 结果表明, 焊接总电流相同时母材热输入随着旁路电流的增加而降低, 且越靠近焊缝母材热输入的降幅越大, 特征点焊接热循环曲线的模拟结果与试验结果基本一致, 旁路耦合电弧焊温度场模型是合理的, 所建立的热源模型能够正确反映焊接参数与母材热输入之间的关系.     

新型顶部加载单极天线

提出了一种新型顶部加U型负载的单极天线结构,给出了设计思想和结构模型,该天线采用同轴馈电,辐射轴向笔状波束且线极化特性良好的波,在理论分析的基础上具体对其进行了仿真,并依照仿真的尺寸结果,加工实物进行了实验研究。仿真结果表明:该天线实现了同轴馈电单极天线的轴向辐射,当工作频率在4.0 GHz时,天线轴向增益为8.33 dBi,轴向轴比为-69.64 dB,反射系数为0.034;在3.83~4.5 GHz的频率范围内反射系数小于0.1。实验结果表明:该天线在中心频率时测量增益为8.116 dBi,驻波比为1.098,并且在3.75~4.50 GHz的范围内驻波比都小于1.2,可以看出仿真结果与实验结果基本一致,互相进行了验证。     

Relativistic motion of a free particle in a uniform gravitational field

The problem of the motion of a free particle in a uniform gravitational field is considered. A relativistic solution based on the assumption that the motion is a consequence of the curvature of spacetime is obtained. The results are compared with various results based on the assumption that spacetime is flat in a region in which the gravitational field is uniform. In the curved spacetime approach, if a particle is projected from a point in a uniform gravitational field, the vertical distance covered by the particle in infinite coordinate time is infinite, but the horizontal distance covered and the elapsed proper time of the particle are finite. If spacetime is assumed to be flat and the gravitational motion of a particle a consequence of a relativistic force proportional to the relative mass of the particle, then the results obtained for the motion of a particle in a uniform gravitational field are close to the curved spacetime results. All other assumptions, including the assumption that the motion of a particle in a uniform gravitational field is equivalent to the motion of a particle in a uniformly accelerating frame of reference, lead to results in serious disagreement with the curved spacetime results.     

显微栅线投影法用于微镜转角测量

采用显微栅线投影法结合相移技术测量了微镜在不同驱动电压下的转角,并同理论值进行了比较,平均误差为4.5%,结果表明:测量值和理论值比较吻合.     

光脉冲传输模拟的快速数值差分递推算法及其应用研究

利用零邻域的马克劳林展开对归一化非线性薛定谔方程的频域差分形式进行分析，得出一个能够同时考虑光学媒质的色散作用以及非线性克尔作用的时域快速数值差分递推公式.选取若干算例，将运用该公式的数值计算结果与已知的解析结果和传统分步傅里叶方法所得的计算结果做了相应的比较，结果表明这种快速数值差分递推公式不但拥有相当快的计算速度，也有很高的计算精度，而且在物理上符合光脉冲在光学媒质中传输时色散和非线性作用同时施加影响的客观实际，这说明它是研究非线性光学媒质中光脉冲传输的一种科学、合理而快速有效的数值计算方法. 关键词： 快速数值差分递推公式 零邻域马克劳林展开 非线性薛定谔方程 光脉冲传输     

耦合带状线定向耦合器大功率合成器的设计

介绍了直线加速器高频全固态功率源中大功率合成器件-3 dB定向耦合器的理论计算和工程设计过程, 该合成器工作频率80.5 MHz, 输出连续波功率大于20 kW。 分析了合成器的功率容量, 并对相应的理论计算结果、 CST (Computer Simulation Technology)软件模拟计算结果和实际功率合成器件测量结果进行了比较。 通过比较得出, CST仿真结果与测试结果基本一致, 隔离度和电压驻波比等实测指标优于设计指标, 只有耦合度与设计指标有些偏差, 总体上达到了预期的设计要求。 在输出功率20 kW时, 取样波形无失真, 合成器无明显温升, 满足固态功率源大功率稳定运行的要求。 The principle of design and calculation of the power synthesis in the solid state amplifier are described in this paper. The working frequency of the synthesizer is 80.5 MHz. The output continuous wave power is more than 20 kW; The synthesizer power capacity is analyzed. The theoretical calculation results, Computer Simulation Technology (CST) simulated results are compared with the measured results of the actual 3 dB couplers. The analysis of the measured results and CST calculated results shows that the simulation is in agreement with the measurement results which meet the design requirements of the solid state amplifier. Except the coupling coefficient, the isolation, the VSWR and other parameters are better than the design target. When the output power is 20 kW, the sampling waveform has no deform and the temperature of the synthesizer is stable.