基于复合结构的气体电子倍增器增益模拟和实验研究

气体电子倍增器(GEM)作为高性能的微结构气体探测器在高能物理相关领域内得到了广泛的研究和应用.其中增益是GEM探测器基本性能研究中的一个重要参数,该值的精确测量至关重要.增益的测量一般采用电流测量或者能谱测量方法,但均存在精度较低或者过程繁琐的问题,且无法精确测量低增益值.针对GEM探测器增益的精确测量,本文提出了一种由GEM探测器与微网结构气体探测器(MM)级联构成的复合结构探测器(GEM-MM).利用GEM-MM结构以相对方法实现GEM增益的精确测量.该方法既可以省去传统方法中复杂的电子学标定过程,同时不需要进行原初电离电子数的估算,保证了增益的精确测量,并且可以实现GEM低增益的测量.基于GEM-MM测量GEM增益的原理,本文首先对GEM-MM电荷输运过程进行了模拟研究,优化了合适的工作电压.比较了三种不同类型和配比工作气体下GEM增益模拟结果,并在Ar/iC_4H_(10)(95/5)气体中测量了单层GEM在3—24范围内的有效增益.不同Penning系数下GEM增益的模拟结果表明,Penning系数为0.32时GEM增益的模拟结果与实验测量结果符合得很好.由此可以确定一个大气压下的Ar/iC_4H_(10)(95/5)气体中,Penning系数为0.32±0.01.     

高增益型气体电子倍增微网结构探测器的性能研究

随着微结构气体探测器的不断发展, 不同的探测需求相继提出.为了实现气体探测器在高增益和低打火率的条件下长时间稳定工作, 结合气体电子倍增器(GEM)与微网结构气体探测器(MicroMegas)的探测优势, 成功研制出一种基于GEM作为预放大的MicroMegas探测器, 详细介绍了探测器结构和工作原理, 并利用⁵⁵Fe放射源对探测器增益、打火率、能量分辨和工作稳定性等性能进行了实验测量. 分析结果显示GEM-MicroMegas探测器可以连续工作30 h 以上, 探测器增益可以超过10⁶, 相对于无GEM膜的MicroMegas探测器, 相同增益下打火率可以降低近100倍. 关键词： 微网结构气体探测器 能量分辨率 增益 打火率     

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.     

片状放大器中片间空气间隔对小尺度自聚焦的影响

从非线性Schr?dinger方程出发,根据线性的近似分析方法,通过把介质片厚度和片间空气间隔转化为线性与非线性传输距离比讨论了系统B积分值和空气间隔对非线性增益谱的影响.着重分析了激光介质片数以及B积分值和非线性增长率之间的关系,并讨论了增长率随B积分值与片数的变化规律.其他参量不变的情况下,片间空气间隔的增大,使增益谱向长波方向移动,而介质片数则对增益谱的最高增益和谱线位置都有影响.同时,对这一现象做了无空气间隔的等效模拟.     

Near-field properties of a shell nanocylinder pair with gain materials

We study the near-field response of a shell nanocylinder pair,with its core filled by gain materials,using a twodimensional finite-difference time-domain method.It is shown that the gain materials in the core of the cylinder can compensate for the intrinsic absorption of the metal shell,leading to local-field enhancement in the gap of the active pair.A linear dependence is found between the field enhancement and the gain coefficient at resonance.The detailed physics is studied by calculating the electrical-field distribution of the shell pair filled with different gain materials.The influence of the gap width and the shell thickness on the interaction of two adjacent active shell cylinders is also investigated.     

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.     

三级GEM探测器的增益一致性实验研究

随着二维GEM气体探测器在X射线成像探测领域的应用, 三级GEM的探测结构和电场均匀性带来的增益一致性修正问题, 成为需要深入研究的课题内容。 介绍了有效探测面积为100 mm×100 mm的三级倍增GEM探测器, 共采用100路阵列读出, 每路读出Pad面积为9.5 mm×9.5 mm。 测量了55Fe放射源准直入射的全能峰谱。 实验表明, 随着时间的变化, 探测器的增益基本上保持稳定; 随气流的增大, 增益由变化明显到变化不大。 GEM探测器各个阵列单元的增益一致性良好（>80%）; 能量分辨率在0.18～0.22之间, 运用最小二乘法拟合给出增益一致性的修正结果, 修正后相差约0.1, 为GEM气体探测器的增益一致性修正方法提供了参考方案。 With the application of the two dimensional GEM gaseous detector in X ray imaging, the correction method of gain uniformity caused by triple GEM avalanche structures and electric field uniformity should be studied. The paper reported the study of the triple GEM detector with effective area 100 mm×100 mm used the Pad’s size of 9.5 mm×9.5 mm. In the test, 100 readout channels were designed. Results showed that gain remained stable over time; as air flow increases, gain from increases obviously to changes very little. Particularly, triple GEM’s gain uniformity was very good (more than 80%) and the range of energy resolution was from 0.18 to 0.22. To improve gain consistency of results, the difference value revised was obtained to be about 0.1 by the least square method. It provided a better method to improve gain uniformity of GEM detector.     

CEE-TPC中GEM读出探测器传输性能实验研究

气体电子倍增器(GEM)因其具有较好的位置分辨以及各项同性的二维结构等优点,近年来受到了广泛的关注,在HIRFL-CSR上正在建设的低温高密核物质测量谱仪(CEE)也计划使用GEM作为TPC的读出探测器。不同电场条件下GEM探测器的传输特性对探测器的有效增益及能量分辨有较大影响。文中研究了单层GEM探测器中漂移区电场及感应区电场对探测器传输特性的影响;随后研究了双层GEM探测器的电压分配及传输区电场对探测器电荷传输性能的影响。结果表明,在单层及多层GEM探测器中,漂移区电场、传输区电场及感应区电场主要通过改变电子透过率和GEM雪崩电场强度及分布影响探测器的电荷传输性能,进而影响探测器的有效增益及能量分辨。以上实验结果表明GEM探测器是CEE-TPC读出探测器的理想选择,同时测试结果也为TPC中多层级联GEM工作点的选择提供了参考依据。     

The study of geometric effects on the explosion front propagation in a horizontal channel with a layer of spherical beads

Experiments were performed in a horizontal channel partially filled with a layer of 12.7 mm ceramic-oxide beads filled with a nitrogen-diluted stoichiometric methane–oxygen mixture, i.e., CH₄ + 2(O₂ + 2/3N₂). Ionization probes and pressure transducers were used to track the explosion front velocity in the 1.22 m long, 76 mm wide and 152 mm high horizontal channel. Schlieren photography and smoked foil techniques are used to gain insight into the explosion front structure. The explosion propagation phenomenon was characterized by the combustion in the bead layer and the unobstructed gap above. It was determined that for a fixed gap height the bead layer thickness had very little effect on the explosion propagation phenomenon. However, for a fixed bead layer height the explosion propagation was strongly influenced by the gap height. The combustion products vented from the bead layer behind the flame propagating in the gap affects the structure of the shock-flame front in the gap and the maximum flame velocity achieved. The coupling between the vented products and the flame velocity in the gap was strongly influenced by the gap height. The gap height also affects the structure of the detonation wave propagating in the gap following DDT that always occurred in the gap. The DDT run-up distance was found to increase with increasing gap height and inversely with initial pressure.     

The Application of 3D Rain Scatter Model on Horizontally Polarized SHF Signal Propagation in Tropical Location

This paper presents some results of intersystem interference as a result of hydrometeor scattering on horizontally polarized SHF signal propagation in the tropical environment using the 3D rain cell model. The cumulative distribution of transmission loss has been based on the distance dependence (terrestrial station to the center of the common volume distance); frequency dependence and antenna gain dependence. Though there is a less interference (significantly higher transmission loss) at a relatively higher frequency of 20 and 34.8 GHz, the rain-scatter interference problem may not be negligible for a tropical region with high rainfall rate because, for a small percentage of time, the rain scatter power can be received even at a large distance from an interfering station.     

Propagation distances of surface electromagnetic waves on Ni,Pd, Pt,and W metal surfaces

The propagation distances, L_x, of surface electromagnetic waves (SEW) on Ni, Pd, Pt, and W were measured using the two-prism coupling technique at wavelengths from 9.3 to 10.6 microm. Metal samples consisted of films, deposited on glass substrates by electron beam deposition, and metal foils. The measured L_x values for the Pd and Pt firms and Pt foil agree to within 20% of the calculated values from the two-media dispersion relation. The measured values of the propagation distance for the Ni film and foil and the W foil agree to within 50% of the calculated L_x. Scanning electron microscope (SEM) photographs and Auger analysis indicate that film imperfections and foil surface roughness contributed to the lower propagation distances observed for Pt and Pd while imperfections, roughness, and oxidation contributed to the disagreement between measured and calculated propagation distance for Ni and W.     

Instability-free ion acceleration by two laser pulses

We demonstrate the instability-free ion acceleration regime by introducing laser control with two parallel circularly polarized laser pulses at an intensity of I = 6.8 × 10²¹?W/cm², normally incident on a hydrogen foil. The special structure of the equivalent wave front of those two pulses, which contains Gaussian peaks in both sides and a concavity in the centre (2D), can suppress the transverse instabilities and hole boring effects to constrain a high density ion clump in the centre of the foil, leading to an acceleration over a long distance and gain above 1GeV/u for the ion bunches.     

Dispersion relations for optical waves in amplifying periodic structures

The characteristics of optical waves in amplifying dielectric periodic nanostructures are studied. The formula for the dependence of the wave number on frequency, which comprises a photonic band gap and is valid for structures possessing a complex dielectric function, is obtained. It is shown that the gain is anomalously high at frequencies residing in the photonic band gap.     

Electron transmission ef f iciency of gating-GEM foil for TPC

In a TPC, ion feedback from the readout detector can cause a space-charge effect and distort the electrical field in the drift region. Gating is one of the effective methods to solve this problem, which can block ions at the expense of losing a certain amount of primary electrons. Compared with the traditional design with a wire structure, gating based on GEM foil is more attractive because of its simplicity. In this paper, the factors in uencing the electron transmission e ciency are studied with simulations and experiments. After optimizing all these parameters, an electron transmission e ciency over 80% is obtained.     

高通量下GEM探测器高压供电模式研究

GEM探测器的供电一般采用电阻链分压供电模式和多路分立供电模式,在低通量X射线下测量时区别不大,但是在高通量X射线时,电阻链分压供电模式会带来饱和效应引起工作电压的变化,造成探测器工作不稳定。本研究在高通量X 射线照射下,研究了有效面积为100 mm100 mm三层级联GEM探测器的有效增益(稳定性) 与不同高压供电模式的关系。通过测量不同分压电阻值(1, 2, 5 到30 MΩ)的实验研究,发现随着X 射线通量的增加,在电阻链分压供电模式下,出现了GEM探测器感应电极的读出电流饱和趋势,分析了可能导致饱和效应出现的原因。结果表明,当入射X射线在探测器上的有效吸收剂量不断增加时,电阻链供电模式需要调整分压单元电阻值,或者采用多路分立供电模式,从而避免因饱和效应引起的GEM探测器有效增益的变化,实现探测器稳定的工作状态。There are two methods of the HV power supply for the GEM detector. One is a HV channel divided by the resistive chain and the other is the several separate HV channels. In the smaller dose rate of X-ray, all of the methods are similar. When the dose rate increases, the resistive chain-dividing mode has more obvious saturation effect and the working voltage of the GEM detector is unstable. In the paper, a GEM detector with an effective area of 100 mm100 mm has been studied in the high dose rate using X-tube. The unit values in the divider resistance chain are set to 1, 2, 5 and 30 MΩ respectively in the test. With the resistive chain-dividing mode, the readout current of the GEM detector’s anode tends to saturate when the dose rate of X-ray increases,and the reasons of the saturation effect are analyzed. The results indicate that the effective absorbed dose of X-ray by the triple GEMs detector reaches to the pecific value and the divider resistance needs to re-select, even the several separate HV channels mode should be considered. It will keep the constant of the working voltage of the GEM detector without the saturation effect and gain variation and the performance of GEM detector is stable.     

改进型混合表面等离子体微腔激光器的研究

设计了一种拥有增益介质脊和空气间隙的改进型混合表面等离子体微腔激光器,并在微腔的两端面镀一层50 nm厚的银反射镜,有效地提高了纳米激光器的性能.基于COMSOL Multiphysics软件分别构建二维截面和三维立体模型,在1550 nm的工作波长下对该改进型结构的传输性能以及微腔性能进行分析.结果表明:该激光器具有显著的亚波长限制能力和很大的传输距离,最长距离可以达到1.29 mm.测试该激光器的微腔性能时,通过调整结构参数获得了高质量因子、低增益阈值以及深亚波长下的超小有效模式体积0.001092μm~3和超高的Purcell因子8.29×10~5.与先前结构对比,在结构参数统一时,所设计的结构具有更低的激光激射阈值和更强的微腔局域能力.所设计的改进型混合表面等离子体微腔激光器可以作为各种光子器件的基本构建模块,并可应用于传感、纳米聚焦和纳米激光等领域.     

基于GEM探测器的时间投影室TPC的讨论

自20世纪90年代以来, GEM探测器以其高电子倍增、高空间分辨和高计数率等优势在粒子物理和辐射成像等领域得到了广泛和深入的研究, 具有广阔的应用前景. 如果将GEM作为读出探测器应用在时间投影室TPC系统上, 和传统的读出方式比较起来, 既有许多优点也有许多挑战. 目前世界上有许多机构正在研究将此方案用于将来的大型正负电子对撞机ILC. 本文论述了这些研究课题的概况, 讨论了TPC的各项关键性能指标与GEM探测器的关系及存在的问题.     

Electron transmission efficiency of gating-GEM foil for TPC

In a TPC, ion feedback from the readout detector can cause a space-charge effect and distort the electrical field in the drift region. Gating is one of the effective methods to solve this problem, which can block ions at the expense of losing a certain amount of primary electrons. Compared with the traditional design with a wire structure, gating based on GEM foil is more attractive because of its simplicity. In this paper, the factors in uencing the electron transmission e ciency are studied with simulations and experiments. After optimizing all these parameters, an electron transmission e ciency over 80% is obtained.     

Reentrant semiconducting behavior of zigzag carbon nanotubes at substitutional doping by oxygen dimers

The electronic structures of carbon nanotubes doped with oxygen dimers are studied using the ab initio pseudopotential density functional method. The fundamental energy gap of zigzag semiconducting nanotubes exhibits a strong dependence on both the concentration and configuration of oxygen-dimer defects that substitute for carbon atoms in the tubes and on the tube chiral index. For a certain type of zigzag nanotube when doped with oxygen dimers, the energy gap is closed and the tube becomes semimetallic. At higher oxygen-dimer concentrations the gap reopens, and the tube exhibits semiconducting behavior again. The change of the band gap of the zigzag tube is understood in terms of their response to the strains caused by the dimer substitutional doping.     

Effect of gas pressure on amplitude and duration of electron beam current in a gas-filled diode

The parameters of an electron beam generated in helium in the pressure range p = 10⁻⁴−12 atm are studied. Nanosecond high-voltage pulses are applied to a gap between a tubular cathode and planar anode, which is made of 45-μm-thick AlBe foil. Behind the anode, an electron beam is detected at a helium pressure of 12 atm. The pressure dependence of the beam current amplitude shows three peaks at p ≈ 0.01, ≈ 0.07, and ≈ 3 atm. The beam-induced glow of a luminescent film placed behind the foil and the discharge glow at different helium pressures in the gas-filled diode are photographed.