A low-noise X-band microwave source with digital automatic frequency control for electron paramagnetic resonance spectroscopy

We report a new design of microwave source for X-band electron paramagnetic resonance spectrometer.The microwave source is equipped with a digital automatic frequency control circuit.The parameters of the digital automatic frequency control circuit can be flexibly configured for different experimental conditions,such as the input powers or the quality factors of the resonator.The configurability makes the microwave source universally compatible and greatly extends its application.To demonstrate the ability of adapting to various experimental conditions,the microwave source is tested by varying the input powers and the quality factors of the resonator.A satisfactory phase noise as low as-135 d Bc/Hz at 100-k Hz offset from the center frequency is achieved,due to the use of a phase-locked dielectric resonator oscillator and a direct digital synthesizer.Continuous-wave electron paramagnetic resonance experiments are conducted to examine the performance of the microwave source.The outstanding performance shows a prospect of wide applications of the microwave source in numerous fields of science.

Progress in Microwave Technology Applied to the Recovery of Precious Metals from the Secondary Resources

The recovery of precious metals from the secondary resources by microwave technology has emerged in recent years. Microwave technology as a new method for the recovery of precious metals has shown significant advantages against the conventional recovery procedures. This paper presents a review of the advances in microwave technology applied to the recovery of precious metals from the secondary resources. Many different applications are considered, including microwave-assisted leaching, microwave augmented ashing and microwave pyrolysis. In general, microwave enhanced recovery of precious metals from secondary resources.

Research progresses on Cherenkov and transit-time high-power microwave sources at NUDT

Research progresses on Cherenkov and transit-time high-power microwave(HPM)sources in National University of Defense Technology(NUDT)of China are presented.The research issues are focused on the following aspects.The pulse-shortening phenomenon in O-type Cerenkov HPM devices is suppressed.The compact coaxial relativistic backward-wave oscillators(RBWOs)at low bands are developed.The power efficiency in M-Type HPM tubes without guiding magnetic field increased.The power capacities and power efficiencies in the triaxial klystron amplifier(TKA)and relativistic transit-time oscillator(TTO)at higher frequencies increased.In experiments,some exciting results were obtained.The X-band source generated 2 GW microwave power with a pulse duration of 110 ns in 30 Hz repetition mode.Both L-and P-band compact RBWOs generated over 2 GW microwave power with a power efficiency of over 30%.There is approximately a 75% decline of the volume compared with that of conventional RBWO under the same power capacity conditions.A 1.755 GHz MILO produced 3.1 GW microwave power with power efficiency of 10.4%.A 9.37 GHz TKA produced the 240 MW microwave power with the gain of 34 dB.A 14.3 GHz TTO produced 1 GW microwave power with power efficiency of 20%.

Spatial-temporal variations in near-surface soil freeze-thaw cycles in the source region of the Yellow River during the period 2002–2011 based on the Advanced Microwave Scanning Radiometer for the Earth Observing System(AMSR-E) data

Detecting near-surface soil freeze-thaw cycles in high-altitude cold regions is important for understanding the Earth＇s surface system, but such studies are rare. In this study, we detected the spatial-temporal variations in near-surface soil freeze-thaw cycles in the source region of the Yellow River（SRYR） during the period 2002–2011 based on data from the Advanced Microwave Scanning Radiometer for the Earth Observing System（AMSR-E）. Moreover, the trends of onset dates and durations of the soil freeze-thaw cycles under different stages were also analyzed. Results showed that the thresholds of daytime and nighttime brightness temperatures of the freeze-thaw algorithm for the SRYR were 257.59 and 261.28 K, respectively. At the spatial scale, the daily frozen surface（DFS） area and the daily surface freeze-thaw cycle surface（DFTS） area decreased by 0.08% and 0.25%, respectively, and the daily thawed surface（DTS） area increased by 0.36%. At the temporal scale, the dates of the onset of thawing and complete thawing advanced by 3.10（±1.4） and 2.46（±1.4） days, respectively; and the dates of the onset of freezing and complete freezing were delayed by 0.9（±1.4） and 1.6（±1.1） days, respectively. The duration of thawing increased by 0.72（±0.21） day/a and the duration of freezing decreased by 0.52（±0.26） day/a. In conclusion, increases in the annual minimum temperature and winter air temperature are the main factors for the advanced thawing and delayed freezing and for the increase in the duration of thawing and the decrease in the duration of freezing in the SRYR.

System design and measurements of flux concentrator and its solid-state modulator for CEPC positron source

Positron sources are one of the most important components of the injector of a circular electron positron collector(CEPC).The CEPC is designed as an e^(+)e^(−)collider for a Higgs factory.Its accelerator system is composed of 100-km-long storage rings and an injector.The design goal of the positron source is to obtain positron beams with a bunch charge of 3 nC.The flux concentrator(FC)is one of the cores of the positron source.This paper reports the design,development,and measurements of an FC prototype system.The prototype includes an FC and an all-solid-state high-current pulse modulator.Preliminary tests show that the peak current on the FC can reach 15.5 kA,and the peak magnetic field can reach 6.2 T.The test results are consistent with the theoretical simulation.The FC system fulfills the requirements of the CEPC positron source as well as provides a reference for the development of similar devices both domestically and abroad.

Comparison of different plasma chambers in microwave ion source for the intense neutron tube

The microwave absorption efficiency, which is relevant to magnet field and its distribution, is a major parameter of the microwave ion source (MWIS) for the intense neutron tube. Based on previous work, the relations between microwave absorption efficiency and plasma chamber structure and thickness of the microwave introduction window are studied. The microwave absorption efficiency reaches to 100% when plasma chamber is 100mm long and the window thickness is 30mm. The microwave absorption efficiency as a function of pressure is also presented.

Preparation of poly(amino-quinone) by microwave-assisted solid-state polymerization

Microwave irradiation was employed to assist the synthesis of poly（amino-quinone） （PAQ） from p-benzoquinone and diamines in solid state. The effects of power, time, and pattern （continuously or intermittently） of microwave irradiation on yield and intrinsic viscosity of PAQs were studied. It is shown that the continuous microwave irradiation at a high power leads to rapid increase of yield and a sudden halt in polymerization afterwards, due to the subsequent loss of volatile reactants at a high reaction temperature. Alternatively, the high-power microwave irradiation is applicable to raising the yield if used intermittently. In contras4 the low-power microwave irradiation favours the way of continuous exposure to ensure sufficient heat for polymerization. In both cases of high and low power, the yield and intrinsic viscosity can be further promoted by prolonging the exposure time. It is found that under a preliminarily optimized condition of intermittent irradiation at 490 W with six sequences of 5 min irradiation followed by 5 rain interval, the yield and intrinsic viscosity of PAQ from p-benzoquinone and p-phenylene diamine can reach as high as 83% and 41.9 mL/g, respectively.

An investigation on improving the homogeneity of plasma generated by linear microwave plasma source with a length of 1550 mm

To develop a larger in-line plasma enhanced chemical vapor deposition(PECVD)device,the length of the linear microwave plasma source needs to be increased to 1550 mm.This paper proposes a solution to the problem of plasma inhomogeneity caused by increasing device length.Based on the COMSOL Multiphysics,a multi-physics field coupling model for in-line PECVD device is developed and validated.The effects of microwave power,chamber pressure,and magnetic flux density on the plasma distribution are investigated,respectively,and their corresponding optimized values are obtained.This paper also presents a new strategy to optimize the wafer position to achieve the balance between deposition rate and film quality.Numerical results have indicated that increasing microwave power and magnetic flux density or decreasing chamber pressure all play positive roles in improving plasma homogeneity,and among them,the microwave power is the most decisive influencing factor.It is found that the plasma homogeneity is optimal under the condition of microwave power at 2000 W,chamber pressure at 15 Pa,and magnetic field strength at 45 mT.The relative deviation is within−3.7%to 3.9%,which fully satisfies the process requirements of the equipment.The best position for the wafer is 88 mm from the copper antenna.The results are very valuable for improving the quality of the in-line PECVD device.

The microwave absorption of ceramic-cup microwave ion source

An experiment system of ceramic-cup microwave ion source has been built here. Its microwave absorption efficiency as a function of the magnetic field and the pressure is presented. When the microwave incident power is 300-500W the microwave absorption efficiencies are more than 90% if the system is optimized and the magnetic field at the microwave window is 0.095T.

PHASE AND FREQUENCY LOCKING OF MICROWAVE AND MILLIMETER WAVE POWER COMBINING

The phase and frequency locking of microwave, millimeter wave power combining were analysed and summarized in an all-round way. The master/slave phase locking of cavity oscillators, the peer phase locking of mutually coupled oscillators, and the peer phase locking of ring-connected multiple oscillators were investigated. The results of numerical calculations, and the relations of phase to phase locking model and oscillator parameters were given. And the cavity and space power combining aspects for microwave and millimeter wave were presented.

Cross-Correlation Detection of Point Sources in the WMAP First Year Data

We apply a Cross-Correlation （CC） method developed previously for detecting gamma-ray point sources to the WMAP first year data by using the Point-Spread Function of WMAP and obtain a full sky CC coefficient map. We find that the CC method is a powerful tool to examine the WMAP foreground residuals which can be further cleaned accord- ingly. Evident foreground signals are found in the WMAP foreground cleaned maps and the Tegmark cleaned map. In this process 101 point sources are detected, and 26 of them are new sources additional to the originally listed WMAP 208 sources. We estimate the flux of these new sources and verify them by another method. As a result, a revised mask file based on the WMAP first year data is produced by including these new sources.

Microwave Assisted Peptide Synthesis as a New Gold Standard in Solid Phase Peptide Synthesis: Phospholamban as an Example

In this study, we report the microwave assisted synthesis of Phospholamban protein (WT-PLB) as a new gold standard in solid phase peptide synthesis. Microwave energy offers benefits for both the coupling and deprotection reactions during peptide synthesis. The use of microwave energy for both the coupling and deprotection steps makes the microwave peptide synthesizers the most versatile and powerful systems available. It produces high yield and fast synthesis when compared to conventional peptide synthesizers.

Frequency-tunable microwave quantum light source based on superconducting quantum circuits

A non-classical light source is essential for implementing a wide range of quantum information processing protocols,including quantum computing,networking,communication and metrology.In the microwave regime,propagating photonic qubits,which transfer quantum information between multiple superconducting quantum chips,serve as building blocks for large-scale quantum computers.In this context,spectral control of propagating single photons is crucial for interfacing different quantum nodes with varied frequencies and bandwidths.Here a deterministic microwave quantum light source was demonstrated based on superconducting quantum circuits that can generate propagating single photons,time-bin encoded photonic qubits and qudits.In particular,the frequency of the emitted photons can be tuned in situ as large as 200 MHz.Even though the internal quantum efficiency of the light source is sensitive to the working fre-quency,it is shown that the fidelity of the propagating photonic qubit can be well preserved with the time-bin encoding scheme.This work thus demonstrates a versatile approach to realizing a practical quantum light source for future distributed quantum computing.

一种高功率微波发射阵列天线设计和试验

设计了一种用于高功率微波发射的S波段波导缝隙阵列天线。采用耦合波导和馈电波导同层排布的方式减小了天线的剖面高度,通过耦合缝隙同向偏置,辐射缝隙按照一定规律排布补偿相位,实现了缝隙单元方向图同相叠加,对缝隙参数、功分器形式与功率容量的关系进行了仿真分析,并在天线内部充入0.1 MPa SF6气体,提高了天线的功率容量。仿真和试验结果表明,在6.7%带宽内,天线电压驻波比小于1.5,增益达到27 dBi,采用窄谱高功率微波源激励天线并进行了高功率微波发射试验,天线的发射波形与微波源的输出波形具有良好一致性,测试的微波源输出功率为2.67 MW。

ATOVS卫星资料同化对三江源暴雨预报影响的试验研究

选取3个三江源的典型降水个例(2018年6月30日、7月5日、8月24日),利用NCEP FNL再分析数据,并加入ATOVS湿度探测器MHS资料同化,基于WRF模式及其三维变分同化系统对三江源区域3次降水过程进行循环同化试验,分析3次事件的模拟状况,并定量分析降水结果。结果表明,3次降水事件在加入MHS资料同化后,1)模拟的水汽增大,在中层体现最明显且更符合实际情况,高空水汽和风模拟较好,地面温度预报欠佳;2)MHS资料对降水预报的影响主要体现在降水区面积和降水量的增大,提高了降水预报水平,但也带来较多空报区域;3)从TS、ETS、POD评分结果来看,有两个降水试验的提升较为明显,其中“0630”试验TS评分结果在0.5~10 mm之间提升了0.05~0.1,ETS在5 mm提升超过0.08,在10~20 mm之间也有少量提升,POD检验在0.5~20 mm之间均有提升,在0.5~10 mm之间提升最为明显,提升了0.1~0.25,“0824”试验TS与ETS在10~20 mm之间提升超过0.1,POD检验在6~20 mm之间提升了0.1~0.4,同化后降水预报有所改善,且在大阈值降水尤为明显;4)MHS资料同化对“0705”试验降水预报改善不明显,说明同化并不是每次都能给结果带来正效应,因此在使用MHS资料时不能过于信赖它,但总体上,同化MHS资料能够提升预报质量。

基于全永磁微波离子源钛自成靶的D-D中子源设计研究

介绍了一种基于全永磁微波离子源钛自成靶技术的紧凑型氘氘(D-D)中子源,其设计中子产额为1×10^(9)s^(-1)。该D-D中子源已经进行了800 h以上的测试,系统可重复稳定运行。早期测试结果显示,系统打火频率高、中子产额低,长时间放电后反向电子会烧蚀Al2O3陶瓷窗,导致微波耦合困难,氘等离子体无法点亮。通过在等离子体腔室中添加氮化硼(BN)保护片以及在钛靶与高压电极之间增加电子抑制电阻,有效抑制了Al2O3陶瓷窗的损伤。通过对等离子体电极孔径的优化和降低腔室压力,降低了打火频率,提高了中子的产额。系统优化后,氘离子能量为70 keV、束流强度为5 mA时,中子产额达到了2.0×10^(8)s^(-1)。在氘离子能量为97 keV、束流强度为6.6 mA时,系统中子产额达到5.2×10^(8)s^(-1)。

基于T形四周期谐振慢波结构的X波段高功率微波产生技术的理论与仿真

优化设计了T形四周期谐振慢波结构,并进行了高频理论分析.利用镜像法将T形波导单元进行脊波导化等效设计,并通过等效电路分析了等效脊波导的高频特性,由此进行T形波导的谐振频率与结构解析理论分析.在此基础上构造了T形四周期谐振慢波结构,对该结构进行色散特性分析,确定谐振模式和频率,得到了模式同步电压范围.最后基于提出的T形周期谐振慢波结构进行对应的相对论扩展互作用辐射源的仿真验证.通过三维粒子仿真模拟分析及优化设计,在448 kV注电压、400 A注电流和0.4 T的均匀轴向磁场条件下,得到了频率为9.8 GHz、平均输出功率71.4 MW的高功率微波,对应电子效率为39.8%.本文提出的以T形波导为单元的新型谐振慢波结构有效地利用较少周期实现高效率、高功率微波产生,为高功率微波科学提供了有效的高频结构的紧凑化方案.

复合负反馈技术在宽带有源微波冷噪声源中的应用

针对C波段宽带有源微波冷噪声源设计中输出低温噪声性能与工作带宽的矛盾,文中选用Avago公司的ATF38143型GaAs基赝掺杂高电子迁移率晶体管(pHEMT)设计了一款C波段宽带有源微波冷噪声源。采用串、并联负反馈电路拓扑结构,在保证低温噪声输出性能的同时提升了工作带宽,其中心频点为6.95 GHz,工作带宽为1.3 GHz,相对带宽为18.7%,常温条件下带内输出最低噪声温度为141.62 K,工作频段可覆盖C波段微波辐射计中心频点为6.60 GHz、6.93 GHz、7.30 GHz的三个通道。

微波毫米波与太赫兹噪声源发展现状

微波毫米波与太赫兹噪声源主要用于产生噪声信号,是噪声系数测试系统的核心组成部分。本文对近年来国内外噪声源的发展情况进行总结,将现有的噪声源归纳为基于数字和模拟电路技术、基于固态二极管技术、基于场效应管技术、基于黑体和热电阻技术、基于光电融合技术共5类噪声源,并对这5类噪声源的主要技术特点进行了分析,同时对各类型噪声源的国内外研究现状进行了对比,并对其应用前景和发展趋势进行了展望。

土壤水分多源卫星遥感联合反演研究进展

土壤水分与全球气候变化、碳循环、水循环等过程,以及农业生产、生态保护修复等环节密切相关。土壤水分的探测经历了从地面测量到遥感探测的发展过程,实现了全球及区域尺度的调查监测。由于数据谱段不一、辐射传输机制不同、反演算法多样,需从算法机理、优势、局限等角度进行全面分析,为精度提升、算法改进提供基础。为此,该文从光学遥感、微波遥感、光学微波协同3个方面,系统梳理了光学遥感温度-植被指数空间特征、温度-地表短波净辐射时间特征反演土壤水分,被动、主动微波反演和主、被动微波遥感联合反演,以及基于精度改善和时空尺度转化的光学微波协同反演等技术方法的特点、存在的问题。目前,多源遥感数据联合反演土壤水分主要存在如下问题:①数据存在缺失及时空尺度不匹配问题;②不同数据源对地表穿透性不一致;③联合反演模型依赖于经验参数和大量辅助参数。随着卫星监测网络的完善、数据源对地表探测深度研究的深入,以及联合反演物理机理的明确、辅助参数时空连续数据集的建立,上述问题会得到有效解决。