Excitation of ion acoustic waves at the difference frequency of two microwave beams in a semiconductor

This letter presents an investigation of the resonant excitation of the electrostatic ion acoustic wave at the difference frequency of two microwave beams in a semiconductor, viz., n-type InSb. The ponderomotive force at the difference frequency on electrons drives the ion acoustic wave at the difference frequency. The resonance conditions are satisfied over a wide range of semiconductor parameters. For typical plasma parameters of n-InSb and microwave beams of power densities 1 MW cm^?2, the power density of the excited ion acoustic wave is ≈ 1.76 kW cm^?2.     

基于临界电子密度的多载波微放电全局阈值分析

多载波微放电即发生在宽带、大功率真空无源微波部件中的二次电子倍增放电现象, 是影响空间和加速器应用中无源微波部件长期可靠性的主要隐患. 多载波微放电全局阈值功率的预测对于工作在真空环境中的微波部件至关重要, 但迄今尚无有效方法进行上述阈值的准确分析. 本文将微放电发生过程中二次电子分布区域等效为等离子体, 通过在理论上建立微波部件的电磁特性和电子密度间的对应关系, 提出了一种基于测试系统可检测水平的多载波微放电全局阈值功率分析方法. 为了能够通过蒙特卡罗优化方法得到全局阈值, 进一步基于电子加速的类半正弦等效, 提出了微放电演化过程中电子数涨落的快速计算方法. 基于以上两种方法得到的针对实际微波部件的全局阈值分析结果与实验结果相符合. 不同于传统基于多载波信号功率分析的经验方法, 本文基于临界电子密度判断依据和电子数涨落快速计算, 为多载波微放电全局阈值的准确预测提供了一种高效的分析方法.     

微波磁场和斜入射对介质表面次级电子倍增的影响

分别研究了微波磁场和斜入射微波电场对介质表面次级电子倍增的影响.利用particle-in-cell/Monte Carlo方法,获得了微波磁场和斜入射微波电场条件下电子数量、介质表面直流场、电子平均能量和介质表面吸收功率的时间变化图像.模拟结果表明,斜入射和微波磁场虽然会显著影响电子的平均能量,但对电子数量和介质表面吸收功率的影响并不大,因此不会对微波介质表面击穿产生太大作用.     

介质窗横向电磁场分布下的次级电子倍增效应

本文利用自编P3D3V PIC程序, 数值研究了BJ32矩波导传输TE₁₀模式高功率微波在介质窗内、 外表面引发的次级电子倍增过程, 给出了次级电子3维空间位置分布特征、介质窗表面法向静电场分布规律以及电子数密度分布特性. 模拟结果表明: 对于介质窗内侧, 微波强场区域率先进入次级电子倍增过程; 而对于介质窗外侧, 则是微波弱场区域优先进入次级电子倍增过程. 形成机理可以解释为: 微波坡印廷矢量方向与介质窗外表面法向相同而与内表面法向相反, 内侧漂移运动导致强场区域电子易于被推回表面, 有利于次级电子倍增优先形成; 外侧漂移运动导致强场区域电子易于被推离表面, 不利于次级电子倍增形成. 准3维模型相对1维模型: 介质窗内侧次级电子倍增过程中, 次级电子倍增进入饱和时间长、饱和次级电子数目少、平均电子能量高、 入射微波功率低、沉积功率低; 介质窗外侧次级电子倍增过程中, 次级电子倍增进入饱和时间短、饱和次级电子数目少、平均电子能量低、 入射微波功率低、沉积功率低. 沉积功率与入射微波功率比值与微波模式、强度及介质窗内外侧表面关系不大, 准3维和1维模型计算结果均在1%–2%左右水平. 关键词： 高功率微波 介质表面次级电子倍增 粒子模拟 横向电磁场分布     

Microwave-resonance-induced resistivity: evidence of ultrahot surface-state electrons on liquid 3He

Measurements of the dc resistivity of surface-state electrons on liquid helium exposed to microwave radiation are reported. It is shown that the resonant microwave excitation of surface-state electrons is accompanied by a strong increase in their resistivity, which is opposite to the result expected from the previously used two-level model. We show that even a very small fraction of electrons excited to the first excited state and decaying back due to vapor-atom scattering strongly heat the electron system, causing a population of higher subbands. The calculated resistivity change is in good agreement with the observed data.     

CMOS器件60Co γ射线、电子和质子电离辐射损伤比较

利用TRIM95蒙特卡罗软件计算了质子在二氧化硅中的质量阻止本领和能量沉积，比较了质子在二氧化硅中的电离阻止本领与核阻止本领，分析了质子在材料的表面吸收剂量与灵敏区实际吸收剂量的关系.利用⁶⁰Co γ射线、1MeV电子和2—9 MeV质子对CC4007RH和CC4011器件进行辐照实验，比较⁶⁰Co γ射线和带电粒子的电离辐射损伤情况.实验结果表明，⁶⁰Co γ射线、1MeV 电子和2—7MeV质子辐照损伤效应中，在0V栅压下可以相互等效； 关键词： γ射线 电子 质子 辐射损伤     

高功率微波及材料特性参数对沿面击穿的影响

为研究高功率微波及材料特性参数对介质沿面闪络击穿过程的影响,采用自编的1D3V PIC-MCC程序,通过粒子模拟手段,得到了电子与离子数目、电子及离子密度分布、空间电荷场时空分布、电子平均能量、放电功率、表面沉积功率、激发电离损耗功率、电离频率等重要物理量。结果表明:电离频率随场强增加而增加,达到饱和后缓慢下降,强场诱发的二次电子数目更多导致本底沉积功率增高;电离频率随频率减小而增加,达到饱和后缓慢下降,频率太高会抑制次级电子倍增;因此,低频强场下击穿压力较大;反射引发表面电场下降及磁场增加效应,降低表面场强虽使表面击穿压力下降,但磁场的增加会导致二次电子倍增起振时间缩短,且会增加器件内部击穿风险;圆极化相对线极化诱导二次电子数目更多、本底沉积功率更高,击穿风险增加;短脉冲产生电子、离子总数少,平均能量低,沉积功率低,击穿风险低于长脉冲;脉冲上升时间的缩短和延长,只会提前或推后击穿时间,并不会改善击穿压力;材料二次电子发射率的增加会给击穿造成巨大压力,表面光滑度对击穿过程影响不大;电离频率和电子平均能量随释气压强增加均先增加后减小,低气压二次电子倍增占优,高气压碰撞电离占优。     

任意时间分布电子束与单间隙微波腔的非线性自洽过程研究

将电子束作为激励源，根据Maxwell方程和电子受到的洛伦兹力，给出了描述工作模式在电 子束作用下的激励方程和电子束电子在工作模式作用下的运动方程（即微波谐振腔中电子束 与微波场相互作用的自洽方程组）.根据该自洽方程组，进一步研究了任意时间分布电子束 与单间隙微波腔的相互作用.通过分析微波腔中电子束与微波作用的线性和非线性过程，给 出了电子束调制深度、微波腔作用间隙对微波输出功率的影响.最后从理论上给出了影响微 波输出功率的综合物理参量. 关键词： 微波腔 模式 自洽方程 单间隙微波腔     

Generation of powerful subnanosecond microwave pulses by intense electron bunches moving in a periodic backward wave structure in the superradiative regime

Experimental results of the observation of coherent stimulated radiation from subnanosecond electron bunches moving through a periodic waveguide and interacting with a backward propagating wave are presented. The subnanosecond microwave pulses in Ka and W bands were generated with repetition frequencies of up to 25 Hz. The mechanism of microwave pulse generation was associated with self-bunching, and the mutual influence of different parts of the electron pulse due to slippage of the wave with respect to the electrons; this can be interpreted as superradiance. The illumination of a panel of neon bulbs resulted in a finely structured pattern corresponding to the excitation of the TM01 mode. Observation of rf breakdown of ambient air, as well as direct measurements by hot-carrier germanium detectors, leads to an estimate of the absolute peak power as high as 60 MW for the 300-ps pulses at 38 GHz. These results are compared with numerical simulations. The initial observation of 75-GHz, 10-15-MW radiation pulses with a duration of less than 150 ps is also reported.     

阶梯阴极型L波段MILO的实验研究

 对阶梯阴极型L波段磁绝缘线振荡器（MILO）进行了实验研究。介绍了测试方法与测试系统;开展了阴极电子发射实验,发现阴极电子发射不均匀是对称结构MILO产生非对称微波模式的最关键的因素之一;并对二极管屏蔽环尺寸、扼流片半径、提取间隙等进行了研究。在电子束电压约420 kV、电流33 kA的条件下,得到了阶梯阴极型L波段MILO的高功率微波辐射功率为1.22~1.47 GW,脉宽大于20 ns,频率为1.21 GHz,束波转换效率约为10%,器件产生微波模式为TM01模,经过模式转换器后的辐射模式为TE11模。     

高功率微波沿面闪络击穿机制粒子模拟

针对高功率微波介质沿面闪络击穿物理过程,首先建立了理论模型,包括:动力学方程、粒子模拟算法、二次电子发射, 以及电子与气体分子蒙特卡罗碰撞模型、电子碰撞介质表面退吸附气体分子机制;其次,基于理论模型,编制了1D3V PIC-MCC程序,分别针对真空二次电子倍增、高气压体电离击穿和低气压面电离击穿过程,运用该程序仔细研究了电子和离子随时间演化关系、电子运动轨迹、电子及离子密度分布、空间电荷场时空分布、电子平均能量、碰撞电子平均能量、碰撞电子数目随时间演化关系、电子能量分布函数、平均二次电子发射率以及能量转换关系。研究结果表明:真空二次电子倍增引发的介质表面沉积功率只能达到入射微波功率1%左右的水平,不足以击穿;气体碰撞电离主导的高气压体电离击穿,是由低能电子（eV量级）数目指数增长到一定程度导致的,形成位置远离介质表面,形成时间为s量级;低气压下的介质沿面闪络击穿,是在二次电子倍增和气体碰撞电离共同作用下,由于数目持续增长的高能电子（keV量级）碰撞介质沿面导致沉积功率激增而引发的,形成位置贴近介质沿面,形成时间在ns量级。     

Electrothermal automodulation in incipient ferroelectric whispering-gallery microwave resonators at 4.2 K

Threshold conditions for electrothermal automodulation instability in high-Q ferroelectric microwave cryogenic resonators operating in the two-mode regime are investigated. The dependence of the electrothermal automodulation frequency on the numbers of interacting modes for different combinations of thermal modes and surface electromagnetic whispering-gallery modes is presented. The threshold power exciting the electrothermal automodulation of the oscillation of the partial mode electromagnetic amplitudes is compared with the threshold power of strictional parametric excitation of acoustic oscillations in the resonator. It is shown that the electrothermal automodulation in the two-mode regime may take place at an excitation power from 10 to 120 μW depending on the combination of interacting thermal and electromagnetic surface modes. Calculated threshold powers are low, which makes it possible to apply the electrothermal automodulation for improving the sensitivity of resonance bolometers and distributed microwave antennas with basic elements built around nonlinear microwave resonators. In addition, the electrothermal automodulation could be applied in developing novel microwave metamaterials. Nonlinear microwave whispering-gallery cryogenic resonators can be used as elements increasing the sensitivity of EPR spectroscopy methods.     

Pointlike gamma ray sources as signatures of distant accelerators of ultrahigh energy cosmic rays

We discuss the possibility of observing distant accelerators of ultrahigh energy cosmic rays in synchrotron gamma rays. Protons propagating away from their acceleration sites produce extremely energetic electrons during photopion interactions with cosmic microwave background photons. If the accelerator is embedded in a magnetized region, these electrons will emit high energy synchrotron radiation. The resulting synchrotron source is expected to be pointlike, steady, and detectable in the GeV-TeV energy range if the magnetic field is at the nanoGauss level.     

Microwave electromagnetic pulse from asymmetrical nonstationary gamma source

The coherent microwave radiation emitted in air by a low-intensity asymmetrical nonstationary gamma source is examined. A dependence of the spectral power of the microwave radiation on the frequency and characteristics of the gamma source is obtained.     

Numerical investigation of the plasma processes for propellant heating in electrothermal plasma thruster for nanosatellites

Numerical investigation of the plasma processes in a cylindrical chamber with small dimensions of a novel microwave electrothermal plasma thruster for nanosatellites has been conducted. The absorbed microwave power from the electrons in the plasma column of the surface wave discharge is included in the computational model as a heat source with Gaussian distribution. The computational model takes into account the elastic and inelastic collisions of the electrons with the atoms in the ground state and two excited states (−s, −p) and the processes of recombination and deactivation of the plasma species in the volume and on the walls of the chamber. The computational model includes the flow of neutral gas and the processes in the plasma for effective heating of neutral particles by collisions not only with electrons but also with ions. Selected combinations of input power and propellant mass flow rates are used as initial parameters for the numerical investigation. The results show that at higher mass flow rates the heating of the neutral gas is more effective and at power levels of 4 W and propellant mass flow rate of 3 mg/s the electrothermal plasma thruster demonstrates effective performance and thrust levels in the order of 1 mN.     

Electron acceleration and capture in impulsive and gradual bursts: Results of analysis of microwave and hard x-ray emissions

A dynamic model is proposed that explains the relationship between microwave and hard x-ray (hx) emissions in impulsive and prolonged events (variation of intensity ratio, delay of maxima) without assuming additional shock-wave electron acceleration in prolonged bursts. According to this model, energetic electrons enter the burst arch for the entire duration of an hx flare. X-rays are generated chiefly as a thick target is approached, and, therefore, the duration is not a function of the background-plasma density and is determined only by the power of the particle source. On the other hand, microwave generation has a gyrosynchrotron mechanism, and, therefore, its intensity is determined by the instantaneous number of high-energy electrons accumulated in the trap. For the same maximum source power, the maximum number of accumulated electrons at the moment of maximum onset must be directly related to the duration of electron injection and the lifetime of electrons in the trap. The results of this model are confirmed by new empirical regularities: the intensity ratio and delay of the maxima of the microwave and hx flares are increased monotonically with an increase in flare duration, and the nature of these relationships remains unchanged with transition from impulsive to prolonged flares.Scientific-Research Radio-Physics Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 7, pp. 856–873, July, 1994.     

真空中微波等离子体喷流电子数密度分布规律实验研究

为了准确诊断真空中微波等离子体喷流的电子数密度，利用统一的发射和单郎缪尔探针测量等离子体的空间电位，再测量等离子体的电流-电压特性曲线.根据空间电位测量结果，在等离子体的电流-电压特性曲线上能准确地获取饱和电流，从而处理出电子数密度.最后的诊断实验表明，当真空环境压强为2—6 Pa、等离子体发生器以60 W以下的微波功率击穿流量范围是42—106 mg/s的氩气时，所产生的微波等离子体喷流中电子数密度分布在1×10¹⁶—7.2×10¹⁶/m³范围内.     

双频磁绝缘线振荡器微波产生特性的数值研究

 利用数值模拟的方法,研究了角向分区比例分别为1∶1,1∶2,1∶3,2∶1和2∶2的双频磁绝缘线振荡器（MILO）的微波产生特性,得到了“热腔”条件下的微波电场分布,电子的相空间图,输出微波的总功率,以及微波频率随角向的分布变化等特性。为了比较,还给出了对应于双频MILO的谐振腔深度的两种常规的角向均匀的单频MILO的模拟结果。研究揭示了双频MILO内束 波互作用分区分别工作的规律,提高了对双频MILO产生双频率高功率微波的机理的认识,为双频MILO的双频辐射技术和双频微波测试技术提供了依据。     

低引导磁场下相对论亚纳秒电子束毫米波返波振荡器的粒子模拟

提出了一种Ka波段的相对论亚纳秒电子束毫米波慢波结构,在较低引导磁场情况下,运用粒子模拟(PIC)方法成功地模拟出器件中波束互作用的非线性物理演化过程,得到了一种超辐射状态下的微波辐射,它的产生与波相对于电子束滑移引起的电子束内电子间相互作用有关,辐射微波的峰值功率与电子束总电荷的平方成正比.粒子模拟有利于对超辐射这种束波互作用非线性物理现象的理解,并且对器件的设计有一定的参考价值.     

基于混合大气传输模型的单脉冲高功率微波大气击穿理论与实验研究

综合考虑高功率微波强电场作用下的热致快速电子效应、碰撞频率、电离频率等充分体现高功率微波特性的参量模型,基于高功率微波混合大气传输模型,提出了单脉冲高功率微波混合大气统一非线性击穿模型,定义了单脉冲高功率微波击穿阈值.理论研究结果表明:考虑中性气体分子极化作用以及电子的碰撞热效应后,大气击穿时对应的等离子体频率明显变大;大气击穿阈值随高度的增加先逐渐减小然后增大,在30-60 km区域存在一个极小值.开展了X波段窄带高功率微波单脉冲大气击穿实验研究,得到了典型条件下的高功率微波击穿现象、波形和阈值,且与理论结果一致性较好.