当基于微通道板(MCP)的光电探测器受到强辐射干扰时, MCP的饱和将导致探测器的时间分辨率和空间分辨率发生改变.本文建立了饱和工作状态下MCP电子云运动仿真模型, 与常规的线性工作状态的不同之处在于, 该模型考虑了MCP通道壁上累积的正电荷对通道内电子云运动特性的影响.仿真结果表明, 当MCP工作在线性状态, 电极浸入深度的不同对通道电子云能量分布有很大差异, 而工作在饱和状态, 通道电子云能量分布趋于一致.电子能量分布曲线与相关文献的实验数据拟合良好, 验证了模型的正确性.

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%.

A recently proposed analytical hemodynamic model1 [S. Fantini, NeuroImage 85, 202–221 (2014)] is able to predict the changes of oxy, deoxy, and total hemoglobin concentrations (model outputs) given arbitrary changes in blood flow, blood volume, and rate of oxygen consumption (model inputs). One assumption of this model is that the capillary compartment is characterized by a single blood transit time. In this work, we have extended the original model by considering a distribution of capillary transit times and we have compared the outputs of both models (original and extended) for the case of sinusoidal input signals at different frequencies, which realizes the new technique of coherent hemodynamics spectroscopy (CHS). For the calculations with the original model, we have used the mean value of the distribution of capillary transit times considered in the extended model. We have found that, for distributions of capillary transit times having mean values around 1 s and a standard deviation less than about 45% of the mean value, the original and extended models yield the same CHS spectra (i.e., model outputs versus frequency of oscillation) within typical experimental errors. For wider capillary transit time distributions, the two models yield different CHS spectra. By assuming that Poiseuille's law is valid in the capillary compartment, we have related the distribution of capillary transit times to the distributions of capillary lengths and capillary speed of blood flow to calculate the average capillary and venous saturations. We have found that, for standard deviations of the capillary transit time distribution that are less than about 80% of the mean value, the average capillary saturation is always larger than the venous saturation. By contrast, the average capillary saturation may be less than the venous saturation for wider distributions of the capillary transit times.

在CST Particle Studio环境下建立了长径比为40的铅玻璃MCP的三维结构，将有限积分法与蒙特卡罗方法相结合，模拟了直流和高斯脉冲偏置下微通道内二次电子倍增过程，得到了通道轴向二次电子云密度的动态分布曲线。结果显示，二次电子云在通道轴向成高斯分布；在直流偏置下电子云在漂移过程中密度逐渐增大，分布逐渐变得集中，当电子云漂移至靠近输出电极位置时密度达到最大；在高斯偏置下，脉宽对电子倍增过程有决定性影响，当脉宽大于二次电子平均渡越时间时，倍增过程与直流偏置相似。

考虑外场和镜像电荷的影响, 对F-N公式进行了改进, 利用改进的势垒穿透公式对阴极阵列场致发射太赫兹源的物理机制进行了分析, 利用渡越时间效应导出了束波相互作用的能量交换, 并在此基础上讨论了电子注能量增量、电子注功率、负载电导和束波转换效率等。

当传统高功率微波器件向高频段拓展时，器件尺寸的缩小将造成空间极限电流及功率容量的减小。基于此提出一种Ku波段同轴结构的渡越辐射振荡器。通过引入同轴结构，器件内部的空间极限电流及功率容量得到了有效提升。调制腔采用三谐振腔结构，与两腔结构相比，调制电子束的能力明显增强。采用高频场软件对调制腔和输出腔进行了冷腔分析。利用2.5维粒子模拟软件对Ku波段同轴渡越辐射振荡器进行了数值模拟，在导引磁场0.6 T、二极管电压392 kV、电流15.2 kA的条件下，在中心频率为14.184 GHz处获得1.2 GW的高功率微波输出，功率转换效率达20%。

研究了同轴边加载三腔谐振腔的高频特性，从圆柱坐标系下的Borgnis位函数出发求解各个区域的场表达式，利用边界条件和相邻区域公共界面上的匹配条件，导出同轴边加载三腔谐振腔内角向均匀的TM模式的色散关系和各个区域场分布的解析表达式。将求得的谐振频率和数值模拟所得到的谐振频率进行了对比验证，求解所得谐振模式的频率和场分布与数值模拟的结果基本一致。

描述了小空间尺度下一种硅外延平面二极管过流时的实验现象, 以电压调控开关的模型解释这种现象。通过电压调控开关模型的二极管间隙间电势变化过程的定性分析可知, 由于空间电荷效应, 超过或临界空间电荷时, 二极管电流有可能呈现振荡特性。通过无限大空间内薄束漂移的时间行为证明了这种振荡存在的可能性。用非线性方程的数学模型对这种现象做了仿真, 仿真结果与实验现象相吻合。