等离子体微波辐射简介和研究进展

近年来,等离子体微波辐射作为新兴高功率微波源,因其具有频带宽、相干和可调谐等优点,因而受到国际上的广泛关注.本文着重介绍了几种典型的等离子体微波辐射理论和实验研究现状,包括电子束与等离子体互作用、等离子体局部扰动、三波互作用等.     

Microwave nonlinearity measurements of epitaxial YBa2Cu3O7−x thin film by bridged resonator

A simple bridged resonator method is presented for microwave nonlinearity measurement of epitaxial superconductor thin film. By this method, microwave current is concentrated in local bridged part on the resonator, and local inductive and resistive nonlinearity in this part are measured. At the same time, undesired nonlinearity are eliminated from the tested results by the special current distribution of the resonator, which enhances the accuracy of the measured nonlinearity.     

A 100 kW, 140 GHz pulsed gyrotron

The design and operation of a 100 kW, 140 GHz pulsed gyrotron are reported. To our knowledge, this is the highest frequency at which high gyrotron output power (>-100 kW) has been achieved. Results are presented for gyrotron operation in the range of magnetic field from 4 to 7 T, voltage from 23 to 80 kV and current up to 7.5 A. Near a value of magnetic field of 5.4 T, and output power of 100 kW was obtained at 140.4 GHz in single mode operation in the TE₀₃₁ resonator mode.     

The Design of the Microwave Exciter for Klystron

To carry out lower hybrid wave heating and current drive plasma experiment on tokamak, we need mega-watt order of microwave power generated by the parallel-running klystrons. Those klystrons must be driven by the microwave exciter. Now our microwave exciter is used for many years and its performance is decreased very much. It can not satisfy any more the hybrid wave heating and current drive plasma experiment. So we set out to design a new microwave exciter that is consist of the microwave solid components, amplitudestabilization control, modularization design with multitude-outputs, microwave phase control in order to satisfy the demand of the different work in the hybrid wave heating and current drive plasma experiment.     

延长速调管使用寿命的方法

描述了一种延长EPR波谱仪中速调管使用寿命的方法.根据这种方法,只要正确地调谐微波桥的工作状态和适当地调整功率电平器的功率校正电平.即使对于已经严重老化的速调管仍然可以继续使用一段时间,维持仪器的正常运行.     

Non-resonant microwave absorption studies of superconducting MgB2 and MgB2 + MgO

Non-resonant microwave absorption (NRMA) studies of superconducting MgB₂ and a sample containing ∼10% by weight of MgO in MgB₂ are reported. The NRMA results indicate near absence of intergranular weak links in the pure MgB₂ sample. A linear temperature dependence of the lower critical field H _c1 is observed indicating a non-s wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d wave symmetry is also not observed. In the MgB₂ + MgO sample, much larger low field dependent absorption is observed indicating the presence of intergranular weak links. The hysteretic behavior of NRMA is compared and contrasted in the two samples. In the pure MgB₂ sample, a large hysteresis is observed between the forward and the reverse scans of the magnetic field indicating strong pinning of flux lines. This hysteresis saturates a few degrees below T _c while in the MgB₂ + MgO sample, a much slower increase of hysteresis with decreasing temperature is observed, a signature of weaker pinning.     

Millimeter wave spectrum of glycine

We present new investigations of the millimeter wave spectra of the two lowest-energy conformers of glycine (NH₂CH₂COOH). Measurements of these spectra have been carried out between 75 and 260 GHz using the millimeter-wave spectrometer in Kharkov. The new data set involves rotational transitions with J up to 44 and K_a up to 15 for conformer I and transitions with J up to 43 and K_a up to 14 for conformer II. This represents a more than twofold expansion both in the frequency range and J quantum-number range in comparison with previous investigations. The improved sets of spectroscopic parameters obtained for both conformers provide accurate transition frequencies for the key lines necessary for radio astronomy searches for interstellar glycine.     

Magnetoresistance oscillations due to Zener tunneling and microwave radiation in a 2D electron gas in GaAs quantum well with AlAs/GaAs superlattices barriers

The effect of microwave radiation in the frequency range from 1.2 to 10 GHz on the magnetoresistance of a high-mobility two-dimensional electron gas has been studied in a GaAs quantum well with AlAs/GaAs superlattice barriers. It has been found that the microwave field induces magnetoresistance oscillations periodic in the reciprocal magnetic field (1/B). It has been shown that the period of these oscillations in the covered frequency range depends on the microwave radiation power.     

Photonic instantaneous measurement of microwave frequency using fiber Bragg grating

A photonic approach to realizing instantaneous measurement of microwave frequency based on optical monitoring using a fiber Bragg grating (FBG) is proposed and demonstrated. In the approach, a frequency-unknown microwave signal is modulated on an optical carrier in a Mach-Zehnder modulator biased at the minimum transmission point. After detecting the transmission and reflection optical powers at the output of the FBG, the microwave frequency can be determined according to the value of transmission-to-reflection power ratio, due to the fixed relationship between the microwave frequency and the power ratio. A proof-of-concept experiment has been performed, which demonstrates that a measurement resolution of ±0.08 GHz over a 10 GHz measurement bandwidth is achieved. The measurement performance in terms of resolution is better than previously reported results.     

Antennas for Short Distance Communications in Cryogenic Environment

Sets of bow-tie antennas, used in a single emitter-receiver near-field configuration and in array configuration, have been studied to be used as wireless means to transmit 8–12 GHz microwave signals from the cold stage of a cryogenic system to a room-temperature processing unit. Indeed, the absence of heat conduction allows increasing the performance of cryogenic systems and open the way to multichannel microwave systems that are necessary for imagers. Transmission loss has been found to be lower than 3 dB over a 1.5 GHz bandwidth while crosstalk in the array configuration is kept below −20 dB when antennas are located at around 90 mm transversally from each other.     

微波沥青路面除冰斜角辐射喇叭天线设计

 为拓展微波加热的应用领域，对微波路面除冰进行了研究。为使辐射天线与沥青负载近距离达到较好匹配，改善加热区域，减少波导阵列的加热盲区，设计了矩形口径喇叭。在此基础上，还设计了带有不同倾斜角的斜角喇叭，测试了斜角喇叭天线在沥青混合料为加热负载时的驻波比，做了实际的加热对比实验。对实验结果进行了分析，得到不同斜角喇叭在沥青料加热中的性能和使用高度,发现15°斜角喇叭符合微波除冰等近距离加热要求。